ABSTRACT
Based on the attractive properties of phosphate glass, improved molybdenum phosphate glasses of composition 40P2O5, 20MoO3, 15MgO, (25-x)Li2O, xSrO, [x = 0, 5, 10, 15 and 20 mol %] were prepared via the melt-quench technique. They were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), UV-visible reflectance and Electron spin resonance (ESR). FTIR confirmed the existence of several structural phosphate groups other than MoO4 and MoO6 units. Optical analysis revealed the active species of molybdenum ions. SrO addition decreases the bandgap energy, converting the glass insulator features into semiconductor properties. The measured AC electrical conductivity (σac) increased within the temperature range of 298-473(K) and decreased in the frequency range of 0.042 kHz-1 MHz. The estimated DC electrical conductivity increased with temperature, suggesting the semiconducting behavior. The highest electrical conductivity was found in base and 5% SrO samples. Therefore, it appears that the prepared glasses are viable candidates for opto-electronic applications.
ABSTRACT
Cadmium lead bismuthate glasses in the system xCdO-(1-x)[0.5PbO + 0.5Bi2O3](40 mol% ≤ x ≤ 90 mol%) were successfully prepared by melt-quenching method. The structural and elastic properties have been investigated using XRD, FTIR and ultrasonic pulse-echo techniques. The XRD patterns confirmed the amorphous nature of the samples prepared. Density and ultrasonic velocity data were used to evaluate various elastic properties. Addition of CdO gave rise to decreased density and molar volume and increased elastic moduli, micro-hardness, and Debye temperature. The FTIR analysis revealed that increasing CdO content enhances the BiO6 octahedral sites at the expense of the BiO3 and PbO4 units. This results in the formation of Pb-O-Bi(6) and Bi(3)-O-Bi(6) linkages in the glass network, which stiffen the structure and improve the elastic properties. A correlation between elastic and compositional parameters was achieved on the basis of theories and approaches in the field.
ABSTRACT
Binary strontium borate host glass together with samples doped with 0.25 %WO3 and one of the rare - earth ions (0.125% Eu3+, Dy3+ or Pr3+) were prepared by conventional melting - annealing technique. DTA analysis of the host base glass was carried out to derive the proper temperatures which are necessary to convert glasses into their corresponding glass -ceramic through controlled thermal heat -treatment regime. Measurements of optical, FTIR, and PL spectra were carried out with special analysis of the spectral properties. The identity of glass - ceramic derivatives were investigated through x-ray diffraction, and TEM & SEM tools to identify their crystalline morphological features. The absorption spectrum of WO3 - doped glass refers to the existence of dominant hexavalent tungsten ions. The RE- doped glass reveal characteristic visible - NIR absorption peaks due to the respective rare earth ions. FTIR spectra show absorption bands due to both triangular and tetravalent borate groups (BO3, BO4).PL spectra reveal excitation and emission characteristic peaks due to each specific rare earth ions. XRD indicate the preference of the host glass to form strontium pyroborate (SrB4O7) crystalline phase. This facilitates the clear knowledge of the crystallization behavior and hence can justify the effect of the crystallization on the studied properties.
ABSTRACT
OBJECTIVE: Screening for keratoconus and potential risk factors in a medical student population in Lebanon using anterior topography. POPULATION AND METHODS: We randomly selected 110 medical students doing rotations in the Hôtel-Dieu de France hospital in Lebanon between November 2009 and February 2010. Ninety-two students agreed to participate in the screening protocol, which included a questionnaire and an anterior topography. The topography was performed using the placido disk Tomey(®) Topographic Modeling System TMS-4. The results were interpreted using the analysis programs supplied with the machine and by an experienced ophthalmologist. RESULTS: Ninety-two students participated in the study (83.6%): 49 males (53.2%) and 43 females (46.8%). The mean age was 23.6±1 year. Fifty-eight students were ametropic (63.1%): 44 participants were myopic (47.8%), 40 had astigmatism (43.4%), and six were hyperopic (6.5%). Three students (six eyes) were diagnosed with keratoconus. The prevalence of keratoconus was 3.3%, of which 2.2% were already known cases. The prevalence of forme frustre keratoconus was 1.1%. Eleven students (12.1%) had a family history of keratoconus, only one was diagnosed with the disease. Atopy and eye rubbing were not found significantly related to keratoconus in this population. CONCLUSION: Keratoconus is a prevalent disease among our population of Lebanese medical students, which confirms the clinical impression that keratoconus is relatively frequent in Lebanon. Further studies need to be conducted on a larger and more representative sample to assess keratoconus prevalence and risk factors in Lebanon.
