1,721,108 research outputs found
Room temperature aging of Laminate Composites of Alumina/3-mol%-Yttria-Stabilized Tetragonal Zirconia Polycrystals
No full textThe stresses of laminate structures obtained by joining single layers of pure alumina (A), pure yttria-stabilized tetragonal zirconia, 3Y-TZP (Z), and an intimate mixture of alumina and zirconia (AZ) have been determined by fluorescence (in alumina) and Raman (in zirconia) piezospectroscopy. Three symmetrical stacking sequences were examined, namely, A/Z/A, A/AZ/A, and AZ/Z/AZ, with the aim of designing structures where the higher coefficient of thermal expansion (CTE) of zirconia could be used to induce compressive stress in the external layers (and ensuing tensile stress in the central layer). Two experimental sessions, 6 years apart, were conducted on the same samples, also taking care to record the spectra from the same locations; during the time elapsed between the two sessions, the samples were kept at room temperature and humidity. The stress values in alumina obtained during the more recent session were markedly different from those observed in the first session
Effects of sample orientation in Raman microspectroscopy of collagen fibers and their impact on the interpretation of the amide III band
No full textIn most tissues, collagen is present in the form of fibrils, large supramolecular assemblies of fundamental
structural units of polypeptide chains. In this contribution we report a clear correlation between the
intensity profile of the Raman spectrum of collagen and the orientation of a collagen fiber, depending on
the laser polarization. More specifically, fiber orientation is shown to affect the relative intensity ratio
between the bands at 1245 and 1268cm−1 (amide III doublet). In view of this finding based on the analysis
of a collagen fiber, the customary use of this parameter as an exclusive marker for collagen secondary structure in tissues has to be reconsidered, taking into account fibrils orientation. Moreover, in Raman microspectroscopy of tissues this effect could be exploited to yield information, which could be relevant for diagnostic purposes or fundamental research, about the orientation of collagen fibrils
Low temperature degradation -aging- of zirconia: a critical review of the relevant aspects in dentistry
No full textThis review present a survey of all experimental data about the low temperature degradation of zirconia (often referred to as “aging”) due to the tetragonal-to-monoclinic transformation, which have been collected at temperatures of interest for dental application (room temperature to about 100°). It is shown that the main factors affecting the aging phenomenon are the stabilizers type and content, the residual stress and the grain size. It is also shown that extrapolating the low temperature degradation rate from accelerated aging tests can lead to unacceptable conclusions about the lifetime of the zirconia-based components. Finally, based on the experimental evidence, a set of engineering guidelines for the use of zirconia in restorative and prosthetic dentistry is proposed
Deformation bands in ceria-stabilized tetragonal zirconia/alumina: II, stress-induced aging at room temperature
No full textA stress-induced aging phenomenon was observed to occur at room temperature in deformation bands introduced into a 8.5 mol% ceria-stabilized tetragonal zirconia/alumina composite by flexural loading. Over a period of 100 days, the concentration of monoclinic zirconia within a deformation band increases and, in addition, the wedge-shaped deformation band grows with time. Accompanying these two changes are an increase in the tensile stress in the remaining tetragonal zirconia within the deformation band and a consequential increase in the overall compressive stress within the band. The average value of the monoclinic concentration within the deformation band was found to increase parabolically with time, suggesting the mechanism responsible for the observed aging is diffusion limited. Away from the deformation bands, no aging was observed to occur suggesting aging is stress dependent
Piezo-Spectroscopic Behavior of the emission bands of alfa-alumina in the 13900-14250 cm-1 spectral range
No full textSurface-enhanced Raman spectroscopy for therapeutic drug monitoring in oncology: a study on sample preparation
No full textReproducible quantification of drugs using surface-enhanced Raman spectroscopy (SERS) is
currently drawing considerable attention in the research field of therapeutic drug monitoring
(TDM) for cancer therapy, due to the possibility to provide analyses of drugs in body fluids within few minutes, with comparable or smaller errors with respect
to routine TDM methods.
However, clinical samples are complex mixtures containing lipids and proteins that can bind the drug of interest; thus only a fraction of the drug molecules will be free to interact to the metal surface, and, hence, to benefit from the signal enhancement. Sample preparation methods and experimental conditions must be carefully evaluated to obtain interpretable and
comparable results.
Here we report the development of a standardized preanalytical method for two
chemotherapeutic drugs, imatinib and irinotecan, both exhibiting strong affinity to plasma proteins.
To find the most efficient method for sample preparation, we analyzed different protein precipitation methods as well as ultrafiltration, for both reproducibility and reduction of matrix effect
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