Resonance modes in the standard piezoceramic shear geometry: A discussion based on finite element analysis

El pdf del artículo es el manuscrito de autor.Several authors developed methods for the complex characterization of piezoceramics from complex impedance measurements at resonance. Alemany et al. developed an automatic iterative method, applied and reported in a first publication to four modes of resonance: (1) the length extensional mode of a thickness poled rectangular bar; (2) the length extensional mode of long rods or rectangular bars, length poled; (3) the thickness extensional mode of a thin plate and (4) the thickness shear mode of a thin plate. In a second publication it was reported the application of the method to (5) the radial mode of a thin disk, thickness poled, the most mathematically complex geometry. The (2), (3), (4) and (5) modes of resonance are sufficient for the purpose of the determination of the full set of complex elastic, dielectric and piezoelectric coefficients of piezoceramics, a 6mm symmetry material. This work presents the results of the FEA modeling of a thin plate based on the characterization of a commercial ceramic. The comparison of the experimental resonance spectra and the FEA results obtained for elastically, dielectrically and piezoelectrically homogeneous samples is presented and discussed. The complex characterization for the first time of the shear mode of a new lead-free piezoceramic is also shown.This work was carried out under the projects PIRAMID (G5RD-CT-2001-00456) of the GROWTH Program of the EC and MAT 2001-4819-E, MAT2002-00463 and the Ramon y Cajal Program, of the Spanish CICyT, and has benefited from the synergy provided by the POlar ELEtroCERamics, POLECER, (G5RT-CT2001-05024) Thematic Network of the EC.Peer reviewe

Characterization of c-kit expression in small cell lung cancer: prognostic and therapeutic implications

PURPOSE: The tyrosine-kinase receptor c-kit and its ligand stem cell factor are coexpressed in many small cell lung cancer (SCLC) cell lines, leading to the hypothesis that this coexpression constitutes an autocrine growth loop. To further evaluate the frequency and pathogenic relevance of c-kit expression, tumor tissue together with the corresponding clinical data of SCLC patients was analyzed. EXPERIMENTAL DESIGN: Tumor tissue of 102 consecutive SCLC cancer patients was analyzed immunohistochemically using an affinity-purified polyclonal c-kit antibody. Immunostaining data were correlated with survival and other relevant clinical parameters. RESULTS: A positive c-kit expression was observed in 37% of patients. c-kit expression was associated with decreased survival in the likelihood-ratio-forward selection model of the Cox regression including clinically relevant risk factors (c-kit expression, age, gender, stage, tumor stage, node stage, metastasis stage, weight loss, performance status, response to chemotherapy, lactate dehydrogenase, neuronspecific enolase, hemoglobin). Only c-kit expression [hazard ratio, 2.00; confidence interval (CI), 1.17-3.41; P = 0.012], response to chemotherapy (hazard ratio, 4.49; CI, 2.36-8.55; P < 0.001), and tumor stage (hazard ratio, 2.11; CI, 1.18-3.74; P = 0.008) were explanatory prognostic factors. These factors and all possible interactions between them were further analyzed in a second Cox regression model. As expected, response to chemotherapy had the highest impact on survival (hazard ratio, 3.06; CI, 1.69-5.54; P < 0.001). In patients with extensive disease, minor response to chemotherapy, and positive c-kit expression, the risk to die increased to 8.4 (hazard ratio, 2.74; CI, 1.52-4.91; P = 0.002). In a Kaplan-Meier analysis median survival of patients with minor response to chemotherapy and extensive stage was 288 days (CI, 255-321 days) when c-kit expression was negative compared with only 71 days (CI, 0-237 days) for c-kit-positive patients (log rank test: P = 0.003). CONCLUSIONS: c-kit represents a new prognostic factor in SCLC. c-kit expression is of particular clinical relevance in patients with advanced disease and poor response to chemotherapy. Given the very limited therapeutic options and unfavorable prognosis of these patients, clinical studies aimed at targeting c-kit (e.g., STI571) are clearly warranted

C-Kit and Its Ligand Stem Cell Factor: Potential Contribution to Prostate Cancer Bone Metastasis1

The tyrosine kinase receptor c-kit and its ligand stem cell factor (SCF) have not been explored in prostate cancer (PC) bone metastasis. Herein, we found that three human PC cell lines and bone marrow stromal cells express a membrane-bound SCF isoform and release a soluble SCF. Bone marrow stromal cells revealed strong expression of c-kit, whereas PC cells showed very low levels of the receptor or did not express it all. Using an experimental model of PC bone metastasis, we found that intraosseous bone tumors formed by otherwise c-kit-negative PC3 cells strongly expressed c-kit, as demonstrated using immunohistochemical and Western blot analyses. Subcutaneous PC3 tumors were, however, c-kit-negative. Both bone and subcutaneous PC3 tumors were positive for SCF. Immunohistochemical analysis of human specimens revealed that the expression frequency of c-kit in epithelial cells was of 5% in benign prostatic hyperplasia, 14% in primary PC, and 40% in PC bone metastases, suggesting an overall trend of increased c-kit expression in clinical PC progression. Stem cell factor expression frequency was more than 80% in all the cases. Our data suggest that the bone microenvironment up-regulates c-kit expression on PC cells, favoring their intraosseous expansion