Raman investigation of the ageing of Ni-BaTiO<Subscript>3</Subscript> multilayer ceramic capacitors

Ni-BaTiO₃ multilayer ceramic capacitors (MLCC) have been aged at 121 °C and 100% Relative Humidity for 2,600 h. Raman and energy dispersive spectral measurements have been made on both aged and unaged samples. Raman spectra indicate the presence of a coating of substoichiometric SnO _x (1 < x < 2) in the aged samples. Morphological and elemental changes occurring in the MLCC were examined by Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). Preliminary, frequency dependent dielectric measurements indicate that ageing causes a substantial decrease (about 50%) of the capacitance, even if only surfaces are affected by the ageing phenomenon.     

MEMS_DSC: a new device for microcalorimetric analysis in the biological field

The metabolism of cells is studied by scientists using a number of cells high enough to have a signal in the regular differential scanning calorimetry (DSC). Currently the number of cells necessary for thermal analysis is on the order of hundreds of thousands. The cell metabolism researchers have been trying to reduce this number with an eye on the final prize of sample size of one. In this paper, we report a novel MEMS_DSC (Micro Electro Mechanical System-Differential Scanning Calorimetry), which reduces the number of cells needed for analysis by about two orders of magnitude. It uses the Seebeck effect generated by a polysilicon n-gold junction to convert the temperature measured from cells directly into a voltage signal. To characterize the device a laser was used to heat the sensor; a lock-in amplifier, coupled with an optical chopper, allowed us to measure a very low heat power (25.5 nW).     

Wear mechanisms and residual stresses in alumina-based laminated cutting tools

The outstanding performances of the Al₂O₃ cutting tools in terms of potential cutting speed can lead to substantial economies in the machining of metallic materials.Nevertheless, their widespread use is limited by some drawbacks such as the tendency to edge chipping and to the propagation of microcracks, which can lead to premature failures.These shortcomings are due to the intrinsic low toughness of the ceramic material, which is in turn related to its characteristics non-metallic bonds.A well-recognised method of increasing the toughness of brittle materials is the introduction of surface compressive stresses, which can be obtained through a suitable lamination geometry of the tools as consequence of the different coefficients of thermal expansion (CTE) of the constituent layers.The performances of an alumina/zirconia laminated cutting tool used for machining steel have been investigated and compared to those of a non-laminated commercial alumina/zirconia cutting tool. The different wear mechanisms are explained on the basis of the different microstructures and chemical compositions. We have shown that residual compressive stresses, measured by Piezo-Spectroscopy, are effective in avoiding the microchipping on the flank zone but cannot avoid larger fractures caused by the residual porosity.     

Design and testing of a 5-degrees-of-freedom,large working range micropositioning stage

This paper discloses the design principles of a compact 5-degrees of freedom piezoelectric micropositioning stage. The presented system exhibits the capability of generating large displacements, while maintaining a simple and modular structure. Due to a double-stage mechanical amplification strategy of the displacements generated by the piezoelectric actuators, the driving voltages can be kept low while reaching the desired performances in terms of amplitude of the working volume, thus allowing for the use of low-cost electronics. Experiments conducted to assess the static performances of a prototype device are in good agreement with the theoretical models.Possible applications include micromachining, micromanipulation and other positioning tasks in scientific instrumentation.     

Thermal gelation modeling of a pluronic-alginate blend following coronary angioplasty

To overcome the complications connected to the treatment of coronary atherosclerosis by means of percutaneous transluminal angioplasty followed by stent implantation, the in situ release of antiproliferative nucleic acid based drugs (NABD) seems a promising approach. For their fragile nature, NABD cannot be released from drug eluting stents but they need to be embedded in a soft gel coating the coronary wall (endoluminal gel paving). This article deals with the thermal fate, once in the catheter, of a polymer blend composed by pluronic, giving rise to a soft gel in water upon temperature rise, and alginate, a natural polysaccharide giving origin to a strong gel in the presence of divalent cations. Simulations reveal that while the formation of a pregel is rapidly achieved, the formation of a mature gel takes a much longer time with respect to the residence time of the polymer blend inside the catheter. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48539.     

Delayed-reference control (DRC) applied to machining operations

This paper deals with a non-time based control for machining operations. Such a control can be implemented in most of the CNC centers in a practical way. Basically, in this control, which belongs to the category of non-time based controllers, the desired input reference is a function of the time and of a variable which plays the role of a time delay: x_d(t−T). Indeed, the proposed controller is called delayed-reference control (DRC). It is recalled that in a time-based control, the desired input reference is described as a function of time only, which is referred to as reference time: x_d(t). The calculation of this function is usually implemented off-line by means of the so called path-planning process. According to this traditional approach, during the task execution, at each instant, the control module is required to track an input reference. What is relevant is that such a reference can never be modified by any event or circumstance. The DRC control differs from time-based controllers in the sense that time delay is properly calculated on-line according to the measured force signals in such a way to improve the interaction during the cutting process. In fact, the DRC consists in an outer force feedback loop around an inner position feedback loop. The effectiveness of the controller has been proven by means of its implementation on a three axes CNC center for wood machining. Eventually, experimental results are presented.