High performance GaAs MESFETs with molecular implanted and optimized lowly-doped drain structure for maximized speed, gain and breakdown performance

GaAs MESFETs with novel lowly-doped drain structures have been developed utilizing molecular implants of silicon trifluoride. Short-channel effects in the 1/4 μm enhancement- and depletion-mode transistors have been suppressed with drain-induced barrier height lowering of less than 70 mV/V and pinch-off voltage shifts of less than 220 mV as the gate length was scaled from 1.0 to 1/4 μm. The 3-terminal breakdown, the transconductance to output conductance ratio, and the unity current gain, cut-off frequency were simultaneously optimized. The E-mode device possessed breakdown of >10 V, G_m · R_ds > 9.5, F_t > 55 GHz, and nominal on-resistance of 2.1 Ω mm while the D-mode device had breakdown >10 V, G_m · R_ds > 6.0, F_t > 45 GHz, and nominal on-resistance of 1.9 Ω mm. These optimized transistors enabled the realization of a variety of low-power digital and high-power mixed signal circuits, using 3-level source-coupled transistor and common-mode logic, such as laser and electro-optic drivers, highly integrated transceivers, multiplexers, demultiplexers, and clock data recover circuits.     

Suppression of tumorigenicity of rat liver epithelial tumor cell lines by a putative human 11p11.2-p12 liver tumor suppressor locus

We have previously identified and mapped a locus within human chromosome 11p11.2-p12 that suppresses the tumorigenic potential of a rat liver tumor cell line (termed GN6TF) which contains well defined chromosomal aberrations involving rat chromosomes 1, 4, 7, and 10. In the present study, we investigated the potential of this human 11p11.2-p12 liver tumor suppressor locus to suppress the tumorigenic potential of two other rat liver tumor cell lines (GN3TG and GP10TA) following microcell-mediated introduction of human chromosome 11. These tumor cell lines are aneuploid and contain chromosomal abnormalities that are similar to the GN6TF tumor line. The tumorigenic potential and other phenotypic characteristics of GN3TG-11neo and GP10TA-11neo microcell hybrid (MCH) cell lines were variable, and dependent upon the status of the introduced human chromosome 11. MCH cell lines that retained the region of 11p11. 2-p12 delineated by microsatellite markers D11S1385 and D11S903 exhibited suppression of tumorigenicity in vivo (decrease in tumorigenicity and/or elongation of latency), whereas, the tumorigenic potential of one MCH line that lacked markers in this region of human 11p11.2-p12, but retained flanking markers, was not changed from that of the parental tumor cell line. The chromosomal interval between microsatellite markers D11S1385 and D11S903 encompasses the previously localized minimal liver tumor suppressor region, suggesting that a common locus is responsible for tumor suppression among the rat liver tumor cell lines examined. The results of the present study have verified the presence of a liver tumor suppressor locus within human 11p11.2-p12, and have identified a substantial number of microsatellite markers that are closely linked to this tumor suppressor region. These chromosomal markers will facilitate positional cloning of candidate genes from this region, and may prove useful for determining the involvement of this locus in the pathogenesis of human liver cancer.     

3 μm laser performance of Ho:YAlO3 andNd,Ho:YAlO3

A study of the 3-μm laser transitions in Ho:YAlO₃ and Nd,Ho:YAlO₃ using both flashlamp and laser pumping is discussed. Fluorescence measurements for the Nd,Ho:YAlO₃ rod indicate that the neodymium is effective in quenching the lower holmium laser level and in sensitizing the upper level. Intracavity laser pumping of Ho:YAlO₃ produced laser lines at 2.92 and 2.85 μm and demonstrated high efficiency     

Progress towards the development of hydrogen sorption cryocoolers for space applications

Sorption cryocoolers utilize metal hydride sorbent beds for the closed-cycle circulation of gaseous hydrogen through heat exchangers and a Joule-Thomson (J-T) expansion valve in order to achieve cold-stage temperatures below 30 K. These devices have high potential for satellite missions that require long term reliability, minimal vibrations, and low operating power. Designs for nominal 25 K liquid and 10 K solid hydrogen refrigerators are described. Prototype hydride sorbent beds for breadboard studies of sorption cryocoolers have been fabricated and tested to simulate expected operation. The sorbents contained in the beds are VH_x, LaNi_5−ySn_yH_x, and ZrNiH_x. Some of these hydride beds have been integrated with a hydrogen J-T cold-stage. These experiments confirm that the selected metal hydrides and bed designs satisfy the constraints associated with the proposed liquid and solid hydrogen cryocoolers.     

A review of the electrofusion joining process for polyethylene pipe systems

Electrofusion joining is now an essential and widely used method to assist in the creation of polyethylene pressure pipe systems. The process of electrofusion joining is reviewed by examining the experimental and some computer simulation literature relating to the temperature and melt pressure changes during the fusion process, and on how varying fusion time and pipe/fitting gap influences the strength of electrofusion joints. From this literature review, four key stages in the joining process are identified. First, an incubation period where the joint has no strength. Second, a joint formation and consolidation stage where an increasing joint temperature aids molecular diffusion to both increase the joint strength and promote a more ductile mode of failure. A plateau region then follows where the joint strength, and ductility, remain reasonably constant despite the fusion time increasing. This plateau is thought to allow some welding variables, such as gap, to have only a small influence on joint strength (for gap maintained within reasonable limits). Finally there is a cooling stage where the joint bridging “tie molecules” become locked into either side of the joint. It is these tie molecules that give the joint its ductility and strength. The concluding section of the review notes some of the important on-site practices that, if followed, allow electrofusion joints to acquire their good strength properties, and hence give polyethylene pressure pipe systems of a high integrity.     

The differences in human cumulative irritation responses to positive and negative irritant controls from three geographical locations

A retrospective analysis was conducted to evaluate whether studies from three geographically diverse locations have similar response profiles to the positive and negative controls in a standard 14‐day cumulative irritation study. The positive irritant control (0.1% sodium lauryl sulphate) and the negative control (0.9% sodium chloride, saline) data from seventeen 14‐day cumulative irritation studies were reviewed. The studies were compiled from three locations representing dry/hot, humid/hot, and dry/cold environments (Scottsdale, Arizona; St Petersburg, Florida; and Winnipeg, Manitoba, respectively). Irritation scores were generated by trained skin graders from a total of 442 subjects studied between 1999 and 2005. Cumulative irritation scores were reviewed and compared between study locations. The irritation scores for the positive and negative controls were not significantly different between locations. Temperature and relative humidity variation did not correlate significantly with overall irritation. However, the dryer climate (i.e. negative or low dew point) had a tendency to induce a higher overall irritation level for both positive and negative controls.