Microstructure and electrical properties of (Ta, Co, Pr) doped TiO2 based electroceramics

The addition of different dopants affects the densification, mean grain size and electrical properties of TiO₂-based varistor ceramics. This paper discusses the microstructural and electrical properties of (Ta, Co, Pr) doped TiO₂ systems, demonstrating that some of these systems display electrical properties that allow for their use as low voltage varistor. Dopants such as Ta₂O₅ play a special role in the formation of barriers at the grain boundary and in the nonlinear behavior in TiO₂-based systems. The higher values of nonlinear coefficient and breakdown electric field were obtained in the system just doped with Ta₂O₅ and CoO.     

Jahn–Teller Driven Electronic Instability in Thermoelectric Tetrahedrite

Tetrahedrite, Cu₁₂Sb₄S₁₃, is an abundant mineral with excellent thermoelectric properties owing to its low thermal conductivity. The electronic and structural origin of the intriguing physical properties of tetrahedrite, including its metal‐to‐semiconductor transition (MST), remains largely unknown. This work presents the first determination of the low‐temperature structure of tetrahedrite that accounts for its unique properties. Contrary to prior conjectures, the results show that the trigonal–planar copper cations remain in planar coordination below the MST. The atomic displacement parameters of the trigonal–planar copper cations, which have been linked to low thermal conductivity, increase by 200% above the MST. The phase transition is a consequence of the orbital degeneracy of the highest occupied 3d cluster orbitals of the copper clusters found in the cubic phase. This study reveals that a Jahn–Teller electronic instability leads to the formation of “molecular‐like” Cu₅⁷⁺ clusters and suppresses copper rattling vibrations due to the strengthening of direct copper–copper interactions. First principles calculations demonstrate that the structural phase transition opens a small band gap in the electronic density of states and eliminates the unstable phonon modes. These results provide insights on the interplay between phonon transport, electronic properties, and crystal structure in mixed‐valence compounds.     

Impact of partial element accuracy on PEEC model stability

This paper details the impact of partial element accuracy on quasi-static partial element equivalent circuit (PEEC) model stability in the time domain. The potential sources of inaccurate partial element values are found to be poor geometrical meshing and the use of unsuitable partial element calculation routines. The impact on PEEC model stability of erroneous partial element values, and the coefficients of potential and partial inductances, are shown as theoretical constraints and practical results. Projection meshing, which is a discretization strategy suitable for the PEEC method, is shown to improve calculated partial element values for the same number of unknowns, thus improving model stability.     

The risk of acute leukemia in patients treated for Hodgkin's disease is significantly higher aft [see bined modality programs than after chemotherapy alone and is correlated with the extent of radiotherapy and type and duration of chemotherapy: a case-control study

BACKGROUND AND OBJECTIVE: Patients treated for Hodgkin's disease have an increased risk of developing subsequent acute leukemia. This co-operative study was conducted to assess the relative risk associated with several candidate factors including age, splenectomy, combined modality therapy and cumulative drug dose including alkylating agents and nitrosurea derivatives. DESIGN AND METHODS: This study evaluated the risk of acute leukemia according to pretreatment variables and therapy modalities among 1659 patients treated for Hodgkin's disease and followed for a median time of 10 years. Both case-control and actuarial risk studies were performed. Median age was 34 years (range: 12-83); 53% of patients were splenectomized. As to the overall therapy, 348 patients (21%) were given radiotherapy (RT) alone, 375 (23%) chemotherapy (CT) alone (including MOPP, MOPP + ABVD or MOPP + ABVD + lomustine); 936 (56%) received both CT and RT, either as primary or salvage treatment. RESULTS: The overall 15-year actuarial risk of leukemia was 4.2%; the hazard function curve showed two peaks of risk at the 3th and the 8th year from the initiation of therapy and no leukemia beyond the 12th year of follow-up. Risk of leukemia was 0.3% after RT alone, 2.8% after CT alone (2.2% after MOPP; 4.4% after MOPP + ABVD + lomustine), and 5.4% in patients given combined modality therapy (10.2% for RT + MOPP; 15.6% for RT + MOPP + lomustine). No leukemia occurred after ABVD alone and the risk was low (0.6%) when neither mechlorethamine nor lomustine were utilized. Patients who had received extended radiotherapy including abdomen and pelvis in addition to MOPP showed a significantly higher risk of leukemia compared to those given limited RT + MOPP (P = 0.01). Case-control analysis indicated advanced stage, type and duration (> 8 months) of CT and extension of RT as significant risk factors for leukemia. Compared to RT alone, the odds ratio was 5.9 after MOPP + extended RT, and 8 when a lomustine-containing regimen was used, as well. Neither age nor splenectomy were independent risk factors for leukemia; splenectomy was influential only when patients had been given MOPP chemotherapy, as well. INTERPRETATIONS AND CONCLUSIONS: Both case-control and actuarial analyses indicated that: a) combined modality therapy with MOPP and extensive RT (including abdomen and pelvis), and the use of lomustine added to the leukemogenic risk of MOPP alone; b) programs without mechlorethamine, procarbazine and lomustine were almost devoid of leukemogenic risk.     

Ceramic support for cell cultures

Research was carried out on the use of ceramics as supports to host mammalian cells. The research was part of a programme whose priority was to study the possibility of using ceramics in the non-traditional sector of the biomedical field. The aim of the study was also to verify the suitability of particular types of ceramics dealt with in the literature for these applications. Among the different samples tested the cordieritic one proved to be very interesting, at least in relation to the cellular cultures considered. The chemical composition of the material is not, however, the only important aspect, since other parameters concur to make the hosting of cells highly acceptable. Of particular importance is the rugosity and porosity of the surface and its flaking, not only externally, but also in the pores.This paper was originally accpeted after the 1993 Conference of the European Society for Biomaterials.     

Flexible composite via rapid titania coating by microwave-assisted hydrothermal synthesis

The aim of this work was to prepare a flexible nanocomposite from ultra-fine titanium oxide (\(\hbox {TiO}_{2}\)) growth on carbon fibre via microwave-assisted hydrothermal synthesis (MHS) and to evaluate its photocatalytic properties. The \(\hbox {TiO}_{2}\) nanoparticles were directly grown on the carbon fibre (CF). Thus, a study comparing the conventional titania coating vs. the MHS were performed. The significant layer interaction as a function of the coating method on the visible and dark dye photodegradation performance was observed. Techniques such as X-ray diffraction, electron microscopy (field-emission scanning electron microscope (FESEM)), Raman spectroscopy, among others were used aiming to characterize the different route samples. This study reports a reproducible and single method to manufacture of nanocomposites through the growth of \(\hbox {TiO}_{2}\) nanoparticle on CF by MHS that allow controlling the thickness layer. Similar procedure of synthesized nanocomposite could be applied in different chemical compositions to advanced applications, based on the electrochemical nanostructure.     

Offset Difference Measure Enhancement for the Feature-Selective Validation Method

The feature-selective validation (FSV) method is proving itself to be a robust and helpful technique to quantify visually complex measurement sets, such as those resulting from computational electromagnetic validation exercises or experimental repeatability studies. This paper reports on an enhancement to this technique that includes data related to the level of dc difference (i.e., offset) between two sets of results, hitherto disregarded within the method. This offset difference measure (ODM) contributes to the amplitude difference measure (ADM) and ensures that the ADM and global difference measure values reflect the level of disagreement between the two traces even if this is the only difference between the two. The paper describes the background to this development and provides details of the selection and implementation of the ODM measure.     

Wide-band Lorentzian media in the FDTD algorithm

This paper considers the case of a wide-band Lorentzian (WBL) algorithm in the finite-difference time-domain (FDTD) modeling of dispersive media. It is shown herein that the WBL model is a physically meaningful and practically useful case of the frequency behavior of materials along with the Debye and narrow-band Lorentzian (NBL). The recursive convolution algorithms for the finite-difference time-domain technique for NBL and WBL models differ. The Debye model, which is suitable for comparatively low-frequency dispersive materials, may not have sufficient number of parameters for describing the wide-band material, especially if this material exhibits pronounced absorption at higher frequencies. It is shown that the Debye model can be used, if the Q-factor of the linear circuit analog corresponding to the Lorentzian model of the material is less than approximately 0.8. If the quality factor is in the limits of about 0.81, the NBL model must be applied. The NBL model is suitable for dielectrics exhibiting resonance effects in the microwave frequency range. The WBL model is typical for composites filled with conducting fibers.