High voltage characterization of tin oxide varistors

High current characterization of SnO₂-based varistors have been carried out and the results obtained have been compared with those ZnO-based commercial surge arresters. It is shown that for a high temperature sintering (1350 °C), the leakage current, breakdown voltage and the saturation at high current density are similar between both types of surge arresters. The paper shows, for the first time, that the high breakdown voltage observed with tin dioxide cannot be easily maintained since the saturation of the ceramics is reached for current densities of several amperes per square centimetre.     

Two-Dimensional Visualization of Fluorescence Lifetimes by use of a Picosecond Laser and a Streak Camera

Two-dimensional distributions of the effective lifetime of the fluorescence emission induced by short-pulsed laser radiation are obtained from two-dimensional images recorded with a streak camera and a charge-coupled device by means of a separation algorithm method (SAM). In theory, the best response with respect to noise is obtained for lifetimes corresponding to a range of pixels of 5-50 in the CCD, that is, 5-50 ps at the fastest streak speed. In experiments the SAM is compared with pure time-resolved measurements, and it is used for two-dimensional lifetime evaluation. The laser-pulse duration is 25 ps, and the lower limit of the lifetime resolution as used in the experiments is estimated to be 200-250 ps. The results demonstrate the possibility of performing pattern recognition independently of the relative distribution of emission intensity between regions of different fluorescence lifetimes. The technique is demonstrated for static objects but can in principle be extended to nonstationary objects if two detectors are used.     

Adolescents and sexuality in family practice. A pilot study

It is well established that teenagers are generally dissatisfied with the sexual education they receive from school and parents. While several alternative sources of sex counselling have been suggested (i.e. an anonymous and semi-official telephone hot-line), the role of the general practitioner in sexual guidance of youngsters is only poorly evaluated. One hundred and sixty-eight teenage callers of "The Adolescent Sexuality Hot-line" were asked about their experience with sexual counselling by their family doctor. One third had actually discussed such topics with their g.p., and a total of 44.6% (significantly more girls than boys) regarded their g.p. as a desirable interlocutor on these issues. The reasons for having approached a g.p. for counselling differed according to gender, as did the causes for not wanting to involve a g.p. in sexual matters: boys tended to state shyness and lack of anonymity as main causes, whereas girls more often pointed to personal aspects of the doctor.     

The continuing road toward Internet media

Internet and IP telephony is rapidly capturing mindshare across the telecommunications world. Every major US telephone company and many cable TV companies are already offering services, or at least experimenting with them, and the number of independent service providers who aren't associated with ISPs continues to grow. Most of the Fortune 500 enterprises are considering enterprise-level deployment of IP telephony, driven, at least in part, by the fact that almost no research or development work is being done on non-IP-based telephony. Equipment vendors have overwhelmingly bet their R&D dollars on the IP telephony horse.     

A Tunable,Stable, and Bioactive MOF Catalyst for Generating a Localized Therapeutic from Endogenous Sources

The versatile chemical and physical properties of metal organic frameworks (MOFs) have made them unique platforms for the design of biomimetic catalysts, but with only limited success to date due to instability of the MOFs employed in physiological environments. Herein, the use of Cu(II)1,3,5‐Benzene‐tris‐triazole (CuBTTri) is demonstrated for the catalytic generation of the bioactive agent nitric oxide (NO) from endogenous sources, S‐nitrosothiols (RSNOs). CuBTTri exhibits structural integrity in aqueous environments, including phosphate buffered saline (76 h, pH 7.4, 37 °C), cell media used for in vitro testing (76 h, pH 7.4, 37 °C), and fresh citrated whole blood (30 min, pH 7.4, 37 °C). The application of CuBTTri for use in polymeric medical devices is explored through the formation of a composite CuBTTri‐poly by blending CuBTTri into biomedical grade polyurethane matrices. Once prepared, the CuBTTri‐poly material retains the catalytic function towards the generation of NO with tunable release kinetics proportional to the total content of CuBTTri embedded into the polymeric material with a surface flux corresponding to the therapeutic range of 1–100 nm cm^?2 min^?1, which is maintained even following exposure to blood.     

New method of analysing static converter behaviour using global analogue simulation

The use of analogue models for semi-conductors enables classical simulation methods to be extended to the global simulation of static converters. The inherent disadvantages of classical analogue simulation are eliminated by the design of specific electronic circuits to make the analogue models into floating devices. These devices enable the analogue simulator to be wired in exactly the same way as the actual converter. Example of the simulation method applied to force commutated converter is presented.     

Phase equilibria for iron-rich Fe−Cu−C alloys: 1500 to 950°C

Isothermal sections for the iron rich corner of the Fe−Cu−C system have been constructed at 1500, 1450, 1200, 1172, 1150, 1000, and 950°C. A ternary invariant point exists at 1172°C where an iron rich liquid, a copper rich liquid, austenite, and graphite coexist. The iron rich liquid contains 3.7 wt pct Cu and 4.0 wt pct C. The austenite contains 7.3 pct Cu and 1.6 pct C. The copper rich liquid contains 2.4 pct Fe, and apparently very little carbon. The diagrams are used to explain the phenomena of “inverse segregation” that occurs during the solidification of iron rich Fe−Cu−C alloys. KRISHNA PARAMESWARAN, formerly Metallurgy Graduate Student, University of Missouri-Rolla KENNETH METZ, formerly Metallurgy Graduate Student, University of Missouri-Rolla     

Stimulation level preferences of autistic children.

Ten autistic, 10 schizophrenic, and 10 outstandingly successful children operated a lever controlling the volume of tape-recorded sound, in a laboratory study designed to follow up clinical reports of abnormal responsiveness to auditory stimulation in autistic children. Results indicated (p