Technological possibilities of laser cladding with the help of powerful fiber lasers

Metal Science and Heat Treatment - The results of experimental studies of the process of laser cladding with scanning with the help of a 15-kW fiber laser are presented. The surface layers are...     

Study on development of dry band on ADSS fibre optic cable

All dielectric self supporting (ADSS) fiber optic cables are suffering from damage caused by dry-band arcing. This paper investigates the formation of the dry band, which is crucial to the arcing. The formation of the dry band is the result of evaporation of water deposit some point on the cable surface. When the dry band is formed the current is interrupted. Then high voltage is applied to the small gap separated by the dry band, and may cause arcing. This paper discusses the drying process of the wet layer on the surface of the cable in detail. The differential equation of the drying rate is formulated and numerical simulation is performed. With this equation, the time-to-arcing and variation of the layer resistance can be estimated. For verification of the results, the time-to-arcing and layer resistance are measured in the laboratory. The numerical results provide guidance for design of an automatic dry-band arcing aging test system. The onset of arcing is investigated based on the results.     

The effect of felodipine on endothelin-1 levels, peripheral vasoconstriction and flap survival during microvascular breast reconstruction

OBJECTIVE: To collect questionnaire data from patients in a large clinical population that would allow for an estimate of the prevalence of self-reported symptoms of dry eyes. METHODS: A 13-point questionnaire (The Canada Dry Eye Epidemiology Study, CANDEES) was mailed to all optometric practices in Canada in October 1994, with the request that it be completed by 30 successive nonselected patients. RESULTS: Four hundred fifty sets of questionnaires (total, 13,517) were analyzed (a 15.7% return rate) from patients aged from < 10 years to > 80 years; 55% were in the 21- to 50-year age group; 60.7% were female; and 24.3% were contact lens wearers. A total of 28.7% reported dry eye symptoms, of whom 24.2% reported concurrent dry mouth, 24.5% had worse symptoms in the morning, 30.3% reported concurrent lid problems, and 35.7% reported a history of allergies. Of the 3716 patients reporting symptoms, 62 (1.6%) were in the "severe" category and 290 (7.8%) were in the "constant but moderate" category. Contact lens wear, concurrent allergies, dry mouth, lid problems, or use of medications increased the chance of a patient reporting dry eye symptoms. CONCLUSIONS: The prevalence of patients reporting any level of symptoms of dry eyes was approximately 1 in 4; severe symptoms were reported by 1 in 225 patients.     

Effect of structure modification on rheological properties of biodegradable poly(ester‐urethane)

Biodegradable lactic acid based poly(ester‐urethanes) (PEU) were polymerized and their structure and rheological properties were characterized. The polymerization process comprised two steps: lactic acid monomer was oligomerized to low molecular weight prepolymer, and this was then linked to high molecular weight PEU with chain extender, 1,6‐hexamethylene diisocyanate. The properties of PEU were modified by varying the amount of chain extender from 1.05:1 to 1.35:1 (NCO/OH ratio). The modification was mostly seen in the molecular weight distribution of the polymers, which was broadened from 2.2 to 3.5 as the amount of chain extender was increased. The telechelicity of the prepolymer was found to play an essential role in successful linking of the prepolymer units. In addition, the rheological properties of poly(ester‐urethane) were determined with capillary and dynamic rheometers. All PEU samples were pseudoplastic and broadening of their molecular weight distribution was accompanied by increased viscosity and complex viscosity at low shear rates and increased shear thinning. The temperature dependency of the measurement was pronounced. Rheological measurements also showed that PEU starts to degrade at 100°C and further rise in temperature increases the rate of degradation significantly.     

Surface reactions of bioactive glasses in buffered solutions

In vitro bioactivity of glasses is usually measured in buffered solutions whereby a formation of a hydroxyapatite layer on the surface is taken as an indication of the bioactivity. In this work we compare the layer formation on three glasses in simulated body fluid, Tris buffer solution, sodium phosphate buffered saline and osteoblast medium. Two of the glasses are known bioactive glasses, 45S5 (45 wt.% SiO₂) and S53P4 (53 wt.% SiO₂), while the third is an experimental composition with a higher silica content (68 wt.% SiO₂). Plates of the glasses were immersed in the solutions at 37 °C for different times up to two weeks. The results showed clear differences between the layer developments on the three glasses in the different solutions. The results indicated that the relative order of the reactivity depended on the solution. Thus, results gained in different solutions for different glasses cannot be directly compared.