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ResumenPresentamos una actividad alternativa a una práctica de laboratorio habitual en la enseñanza universitaria. Su intención es acercar a los estudiantes a la metodología científica mediante el planteamiento de preguntas relevantes.

A magnetic refrigerator device based on adiabatic magnetic refrigeration is described. The magnetic material is cyclically magnetized and demagnetized by permanent magnets in an adiabatic process. A temperature difference of 1.6 K between the hot and cold regions was obtained under a low magnetic field (0.3 T). Gadolinium was the magnetic material used in experiments at room temperature. The range of working temperatures is between 70 and 300 K for a variety of active magnetic materials. The optimized experimental setup increased the device efficiency by achieving a temperature difference between hot and cold sources up to 5 K. Index Terms--Magnetic refrigerator, magnetocaloric effect.

This paper discusses a device that detects bubbles in glue depositions on a windshield glass, which may cause water leakages inside the cockpit. This device is inexpensive, more reliable than other existing solutions, and implements a specific signal treatment and a bubble size calculation model. The device is based on microwave radiation system in the X-band and has been developed and implemented in real production in the final assembly area of the automotive industry [ABSTRACT FROM PUBLISHER]

Magnetic properties of the nonstoichiometric phases with the fluorite-type "defect" structure Na[sub 0.4]R[sub 0.6]F[sub 2.2] (R = Ho, Er, Tm, Yb) and Na[sub 0.35]D[sub 0.56]F[sub 2.3] have been studied as well as some ordered phases with different distortions of the initial fluorite lattice (NaHo[sub 2]F[sub 7], Na[sub 7]Tm[sub 13]F[sub 46], NaYb[sub 2]F[sub 7], and Na[sub 7]Yb[sub 13]F[sub 46]) and Na[sub 1.5]Dy[sub 1.5]F[sub 6] with the gagarinite-type structure (NaCaYF[sub 6]). Magnetic susceptibility Z was measured with the aid of the Faraday balance in the temperature range from 20 to 300 K. The crystals with R = Dy, Ho, Er, Tm are paramagnetic; their temperature dependence Z is described by the Curie-Weiss law. It is shown that in the temperature range studied, magnetic susceptibility does not depend on the degree of order of Dy, Ho, Er, and Tm ions in the structure. Below 80 K, the temperature dependence of magnetic susceptibility of the the Yb[sup 3+]- containing phases differs from the analogous dependence Z of an ideal paramagnetic crystal, which is assumed to be caused by the interaction of the crystalline field with Yb[sup 3+] ions. [ABSTRACT FROM AUTHOR]

The dependence of magnetization on the applied magnetic field and temperature was measured carefully near their Curie temperatures for two perovskite manganite samples: La0.67Ca0.33MnOδ and La0.60Y0.07Ca0.33MnOδ. It is suggested by the results that these materials can be utilized as both the thermal storage (passive regeneration) and as the working material (active regeneration) in an active magnetic regenerative refrigerator with very large temperature span, for their significant entropy change upon the application of a magnetic field and the easily tuned Curie temperatures. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]