ABSTRACT
The propagation characteristics of a focused laser beam in a SBN:75 photorefractive crystal strongly depend on the signal-to-background intensity ratio (R=Is/Ib) under reverse external electric field. In the range 20>R>0.05, the laser beam shows enhanced self-defocusing behavior with increasing external electric field, while it shows self-focusing in the range 0.03>R>0.01. Spatial solitons are observed under a suitable reverse external electric field for R=0.025. A theoretical model is proposed to explain the experimental observations, which suggest a new type of soliton formation due to "enhancement" not "screening" of the external electrical field.
Subject(s)
Barium/chemistry , Crystallization , Lasers , Niobium/chemistry , Refractometry/methods , Scattering, Radiation , Strontium/chemistry , Barium/radiation effects , Materials Testing , Niobium/radiation effects , Strontium/radiation effectsABSTRACT
Resistivity ρ(T), Hall coefficient RH(T), superconducting transition temperature Tc and slopes of the upper critical field dHc2/dT were studied in (Ba1-xKx)Fe2As2 (x = 0.218, 0.356, 0.531) single crystals irradiated with fast neutrons. It is found that dTc/dρSC-the rate of decreasing Tc as a function of the ρSC (ρSC is the resistivity at T = Tc)-linearly increases with concentration x. Slow changes in the Hall coefficient RH, as well as the quadratic electronic contribution to the resistivity, show that there are no substantial changes in the topology of the Fermi surface caused by irradiation. The slopes of the upper critical field dHc2/dT in ab and c directions as a function of ρSC determined by Hall measurements show a reasonable agreement with a model that suggests constancy of the band parameters.
Subject(s)
Arsenic/chemistry , Barium/chemistry , Iron/chemistry , Models, Chemical , Potassium/chemistry , Alloys/chemistry , Alloys/radiation effects , Arsenic/radiation effects , Barium/radiation effects , Computer Simulation , Crystallization , Electric Conductivity , Electric Impedance , Iron/radiation effects , Magnetic Fields , Neutrons , Potassium/radiation effects , Radiation Dosage , Transition TemperatureABSTRACT
Terahertz time-domain spectroscopy has been used to investigate the dielectric and optical properties of ferroelectric Ba(x)Sr(1-x)TiO(3) thin films for nominal x-values of 0.4, 0.6, and 0.8 in the frequency range of 0.3 to 2.5 THz. The ferroelectric thin films were deposited at approximately 700 nm thickness on [001] MgO substrate by pulsed laser deposition. The measured complex dielectric and optical constants were compared with the Cole-Cole relaxation model. The results show that the Cole-Cole relaxation model fits well with the data throughout the frequency range and the dielectric relaxation behavior of ferroelectric Ba(x)Sr(1-x)TiO(3) thin films varies with the films compositions. Among the compositions of Ba(x)Sr(1-x)TiO(3) films with different Ba/Sr ratios, Ba(0.6)Sr(0.4)TiO(3) has the highest dielectric constants and the shortest dielectric relaxation time.
Subject(s)
Barium/chemistry , Membranes, Artificial , Strontium/chemistry , Titanium/chemistry , Barium/radiation effects , Electric Conductivity , Materials Testing , Radiation Dosage , Strontium/radiation effects , Terahertz Radiation , Titanium/radiation effectsABSTRACT
Limited cure depth is a drawback of light-activated composites. We hypothesize that curing light transmission and cure depth are influenced by monomer reactivity and filler/resin refractive index mismatch. Light transmission throughout cure was recorded for composites based on strontium (refractive index 1.51) or barium (refractive index 1.53) glass fillers. Fillers were mixed (70 wt%) with 4 bisphenol-A diglycidyl-ether-dimethacrylate (bis-GMA):triethylene glycol dimethacrylate (TEGDMA) formulations with refractive indices ranging from 1.4703 to 1.5370. Following polymerization, cure depth and pre- and post-cure translucency parameters were determined. Transmission changes and cure depths related to monomer reactivity and filler/resin refractive index mismatch with significant interaction. Composites became more opaque or translucent on curing. Optimizing filler/resin refractive index mismatch provides increased curing depth and assists shade-matching.
Subject(s)
Composite Resins/chemistry , Glass/chemistry , Barium/chemistry , Barium/radiation effects , Bisphenol A-Glycidyl Methacrylate/chemistry , Bisphenol A-Glycidyl Methacrylate/radiation effects , Color , Composite Resins/radiation effects , Glass/radiation effects , Humans , Materials Testing , Optics and Photonics , Polyethylene Glycols/chemistry , Polyethylene Glycols/radiation effects , Polymers/chemistry , Polymers/radiation effects , Polymethacrylic Acids/chemistry , Polymethacrylic Acids/radiation effects , Refractometry , Strontium/chemistry , Strontium/radiation effects , Surface Properties , TemperatureABSTRACT
Patient doses for barium meal examination performed at three general hospitals in Serbia and Montenegro were measured using a kerma-area product (KAP) meter. The results were analysed in order to obtain dose-related parameters. Although the observed doses were within the range reported in other studies, intra-hospital and inter-hospital dose variations were significant. Mean KAP values for total examination in three hospitals were 8.4, 24.4 and 13.9 Gy cm2, respectively. Contribution from fluoroscopy was greater than from radiography. Factors contributing to the increased dose delivery were determined and the recommendations on radiographic techniques were made. Changes in radiography settings allowed dose reduction up to 48% in the radiographic part of examination, that is, up to 12% in total dose without loss of image quality. In addition, fluoroscopy time was noted as the second major contributor to the dose variations. The results demonstrated the need for standardisation of practice for barium meal examination in the country.