Results 1 - 6 of 6
Results 1 - 6 of 6. Search took: 0.013 seconds
|Sort by: date | relevance|
[en] Optical nonlinearity or the nonlinear hyperpolarizability of amorphous materials (e.g., glasses) is related directly to the complex third-order susceptibility. The imaginary part of third-order susceptibility affects negatively the maximum data rate in telecommunication systems. In addition, many transition metals containing glasses have bandgaps with semiconductor-like behavior. So, due to the necessity of operation near the absorption band edge, the study of optical nonlinearity and band structure in glasses is very essential. In this work, we investigated the relationship between the imaginary third-order nonlinear susceptibility and the bandgap of some different series of prepared oxide glasses. A universal empirical formula is given to correlate the imaginary part of the third-order nonlinear susceptibility of the glasses and their optical bandgaps. The obtained nonlinearity is discussed in view of available theories and mechanisms.
[en] During radiotherapy of thoracic tumors, the heart is often included in the primary treatment volume, and chronic impairment of myocardial function occurs. The cellular biomolecules are altered directly by radiation or damaged indirectly by free radical production. The purpose of this investigation was to evaluate the biochemical and functional response of the rat heart to a single high dose of radiation. The effect of 20 Gy local X irradiation was determined in the heart of Wistar rats under general anesthesia. Mechanical performances were measured in vitro using an isolated perfused working heart model, and cardiac antioxidant defenses were also evaluated. Hearts were studied at 1 and 4 months after irradiation. This single dose of radiation induced a marked drop in the mechanical activity of the rat heart: aortic output was significantly reduced (18% less than control values) at 1 month postirradiation and remained depressed for the rest of the experimental period (21% less than control 4 months after treatment). This suggests the development of myocardial failure after irradiation. The decline of functional parameters was associated with changes in antioxidant defenses. The decrease in cardiac levels of vitamin E (-30%) was associated with an increase in the levels of Mn-SOD and glustathione peroxidase (+45.5% and +32%, respectively, at 4 months postirradiation). However, cardiac vitamin C and catalase levels remained constant. Since these antioxidant defenses were activated relatively long after irradiation, it is suggested that this was probable due to the production of free radical species associated with the development of inflammation. 49 refs., 8 figs., 1 tab
[en] The effect of gamma irradiation on the optical and sub-bandgap properties of cellulose triacetate (CTA) films is studied. Sellmeier and Wemple-DiDomenico models are used to study the optical dispersion. The refractive index is decreased with increasing irradiation dose, revealing the existence of chain scission. An increase in Urbach energy is obtained, confirming the existence of bond breaking and chain scission mechanism. Phonon assisted optical transition exists with no appreciable change in the bandgap energy values. Such behaviour indicates that the optical properties of the irradiated CTA polymer are attributable to changes in the linear electronic polarizability of the material rather than its bandgap or electronic structure. The obtained tunability in the optical properties of gamma-irradiated CTA polymer makes it of great interest in a number of optical applications.
[en] An attempt has been made to analyze the magnetic-spin quenching property of Co, as a representative of transition metals, in Co-doped single-walled carbon nanotubes (SWCNTs) as well as the binding property of CO with the side walls of the Co-doped SWCNTs by means of hybrid density functional theory (DFT) calculations. Four different types of SWCNTs are considered: semi-conducting (5,0) zigzag, metallic (5,2) and semi conducting (5,3) chirals, and metallic (5,5) armchair. The results show that while the spin states of Co in the whole of the present Co-doped SWCNTs were preserved, the combined effects of adsorbate (CO) and substrate (Co-doped SWCNT) were strong enough to favor the low-spin states, and to quench the spins in the Co-doped SWCNTs (5,0) and (5,2). The doped Co atom converts the endothermic reactions of CO molecules on the outer surfaces of the pure SWCNTs into exothermic reactions. The nature of charge transfer between the d-orbitals of Co, and the π* orbital of the nearby C of CO is clarified. Natural bond orbital (NBO) analysis reveals that the electronic configuration of the doped Co metal represents a qualitative change with respect to that of the free-metal. The binding of CO precursor is mostly dominated by the metal E(i)Co..CO pairwise additive contributions, and the role of the SWCNTs is not restricted to supporting the metal. The spin quenched SWCNTs are characterized in terms of isodensity contours of frontier orbitals. Molecular electrostatic potentials (MEPs) indicate that SWCNTs can act as effective gas sensors for nucleophiles. The results show that Co-doped SWCNTs can be useful in spintronics applications and sensor technology.
[en] An attempt has been made to analyze the spin transition energies of Cr, a representative example of transition metals, in a variety of complexes formed at regular (001) surfaces of MgO, as well as the adsorption of CO by means of hybrid density functional theory calculations and embedded cluster models. Clusters of moderate sizes are embedded in the simulated Coulomb fields that closely approximate the Madelung fields of the host surfaces. While the spin states of Cr are reduced and preserved in all complexes, be they defect-free or-defect containing, the combined effects of the adsorbate and the substrate in the defect-free OC.Cr.Mg9O13O2- complex were strong enough to favor the low-spin state and to quench the spin. The deposited Cr atoms enhance the adsorption of CO. The significant weakening of bond strength between OC and Cr in complexes supports the concept of bond order conservation. The natural bond orbital (NBO) analysis reveals that the electronic structure of the adsorbed metal represents a qualitative change with respect to that of the free metal. The effects of spin contamination on the geometry, Mulliken charges and adsorption energy are examined. The binding of CO precursor is dominated by the E (i)Cr.CO pairwise additive components, and the role of the support was not restricted to supporting the metal. Relations are established between the process of spin transition and the energy gaps between frontier orbitals. The results show that the spin state of adsorbed metal atoms on oxide supports and the role of precursor molecules in the properties of spin transition energies of Cr in complexes need to be explicitly taken into account. (paper)
[en] Following gene expression profiling which compared the two well established prognostic markers in CLL, ZAP-70 and CD 38 with un mutated and mutated IgVH, ZAP-70 has emerged as the most promising surrogate marker for the IgVH mutation status. CD38 expression has also been suggested as a surrogate marker for the IgVH mutation status. Aim: We aimed to investigate the impact of ZAP-70 and CD38 expressions as well as their combined expressions on the treatment outcome and survival of our CLL patients. Patients and Methods: This study included 50 CLL patients as well as 10 normal volunteers as a control group. All patients were subjected to complete work up and immuno phenotyping to confirm the diagnosis. ZAP-70 and CD38 expressions were studied in (CD19 +, CD5+) B cells. Results were expressed as percent expression and mean flourecent index (MFI). Results were correlated to the treatment outcome and survival as well as to other prognostic markers of CLL including TLC, Hb level, platelets count, modified Rai staging at diagnosis, P53 and BCL 2. Results: A significant association was found between ZAP-70 percent expression and the diffuse pattern of bone marrow infiltration (p<0.002) as well as the P53 percent expression (p=0.005). A Significant increase in serum levels of LDH and B2M in ZAP-70 positive as compared to negative groups was detected (p=0.049 and 0.007 respectively). A higher number of non-responding patients was reported in the ZAP70 positive as compared to ZAP70 negative group (p<0.001). ZAP-70 percent expression was significantly associated with shorter time to disease progression (TDP) and shorter overall survival (p=0.025 and 0.029 respectively). A significant increase in serum levels of B2M in CD38 percent positive as compared to negative group was en- countered (p=0.045). CD38-MFI showed a significant associations to advanced modified Rai staging at diagnosis (p=0.019) and to higher serum levels of both LDH and B2M (p=0.03 and 0.05 respectively). CD38, either expressed as a percentage or as MFI, showed a significant association with the non-responders (p=0.034 and 0.006 respectively). There was a significant inverse relation between CD38 expression and time to disease progression (p=0.033) while no significant relation was encountered with overall survival (p=0.197). Combined expression of both markers, ZAP-70+ /CD38+ was reported in 5 patients (10%) while ZAP-70- /CD38- expression was encountered in 24 patients (48%). Patients with either ZAP-70+ or CD38+ represented 42% of the cases (21 patients).There were significant differences between the three groups and the initial response to chemotherapy (p=<0.001) and the pattern of bone morrow infiltration (p=0.015), while no significant relation was found with age, sex, modified Rai staging at diagnosis or BCL2 percent expression. Patients with combined expression of ZAP-70 and CD38 had significantly shorter TDP and overall survival (p<0.001 and 0.03 respectively). Conclusion: ZAP-70 is one of the most important prognostic markers in CLL, it appears to be more predictive of disease progression and poor outcome than CD38 expression. Semi quantification of the CD38 antigen by flow cytometry greatly improves the prognostic value of its expression. The combination of ZAP-70 and CD38 increases the prognostic power of either alone