Regio- and stereoselective synthesis of carbocyclic 2'',3''-dideoxy-3''-fluoro nucleosides as potential antiviral agents

OBJECTIVE: To determine the prevalence of the symptom of urinary incontinence during athletic endeavors among a group of nulliparous, elite college varsity female athletes. METHODS: All women currently participating in varsity athletics at a large state university were asked to fill out a questionnaire about the occurrence of urinary incontinence while participating in their sport and during activities of daily life. One hundred forty-four of 156 eligible women (92%) responded. RESULTS: The mean age was 19.9 years, and all women were nulliparous. Overall, 40 athletes (28%) reported urine loss while participating in their sport. The proportions in different sports were: gymnastics 67%, basketball 66%, tennis 50%, field hockey 42%, track 29%, swimming 10%, volleyball 9%, softball 6%, and golf 0%. Two-thirds of the women who noted urine loss during athletics were incontinent more often than rarely. There were no statistically significant relations between incontinence and amenorrhea, weight, hormonal therapy, or duration of athletic activity. Activities most likely to provoke incontinence included jumping, high-impact landings, and running. Forty percent and 17% of the women first noted incontinence during their sport while in high school and junior high school, respectively. CONCLUSIONS: Incontinence during physical stresses is common in young, highly fit, nulliparous women. This suggests that there is a continence threshold which, when exceeded, can result in urine loss, even in the absence of known risk factors for incontinence.     

Modes in curved step-index optical fibres

By using parabolic, instead of circular, cylindrical co-ordinates the field distributions of the natural modes of curved step-index fibres can be described completely, yet simply. The mode caustics corresponding to the geometrical guiding limit of the equivalent rays of curved fibre can be clearly demonstrated. Near-field mode patterns and caustics obtained experimentally are in excellent agreement with the theory.     

Mechanism of feeding discrimination between matured and juvenile foliage by two species of pine sawflies

Two species of pine sawflies,Neodiprion rugifrons Midd. andN. swainei Midd., feed only on matured foliage of jack pine,Pinus banksiana Lamb., and leave juvenile or current-season foliage intact. This unique form of adaptation was studied from the viewpoint of the chemical ecology of this insect-host plant relationship. It was first determined that the differential larval feeding behavior reflects the presence of feeding deterrents. Two major biologically active substances were isolated and identified as 13-keto-8(14)-podocarpen-18-oic acid and dehydroabietic acid. These account for 63.5% and 24.6% of the total deterrency, respectively. The content of the former substance in current-year foliage decreases, as the foliage begins to mature, to the levels that become acceptable toN. swainei by August (60 days old) and to the second generationN. rugifrons by September (90 days old). The timing of their acceptance of juvenile foliage indicates the high levels of adaptation by these insects to allow oviposition for the on-coming adults and acceptable needles for the next generation of larvae. The level of dehydroabietic acid, on the other hand, does not change appreciably during the same time period: this indicates that the component does not play a significant role in the mechanism of differentiating juvenile from matured foliage by the sawfly larvae.     

Reduced pressure collapsing MCVD method for single polarization optical fibers

A simple fabrication method of single polarization optical fibers has been proposed. Core, clad, and jacket layers are deposited in a silica tube. The tube is then collapsed while the inner pressure of the tube is reduced. The core circularity and the jacket ellipticity are controlled by the careful selection of the softening points of core/clad and jacket materials, and the inner pressure. The pressure reduction and the softening points of the constituent glasses play an important role in fabricating single polarization optical fibers.     

Atomic Layer Epitaxy of Silicon

Two methods are proposed and demonstrated successfully for low temperature atomic layer epitaxy (ALE) of Si, where H atoms play essential roles. The first method is the use of H as a self-limiting factor. Trisilane (Si₃H₈) was used as source gas and the substrate temperature was modulated in order to alternate steps in an ALE cycle. When the temperature was less than 380°C in the adsorption step and more than 520°C in the desorption step, respectively, the grown layer thickness per cycle was 0.8 ML/cycle. The second method is the use of atomic H as an active reducer of a self-limiting factor. A clean surface was exposed to dichlorosilane (SiH₂Cl₂) as source gas to grow an Si monolayer covered with CI. Next, atomic H was injected to reduce CI from the surface. An ideal monolayer growth was obtained with the substrate temperature over 540°C.     

Bond strength of adhesive resin to three nickel-chromium alloys with varying chromium content

This in vitro study evaluated the influence of chromium content on bond strength and durability between nickel-chromium alloys and an adhesive resin that contained 4-methacryloxyethyl trimellitate anhydride. Three nickel-chromium alloys with different chromium content, as well as pure chromium and pure nickel metals, were bonded and tested for shear strength. After repeated thermocycling, shear bond strength decrease was lower in alloys containing high chromium content. Pure chromium metal demonstrated a 15.2% decrease, whereas pure nickel metal demonstrated the greatest (53.7%) decrease. The results suggest that nickel-chromium alloys with higher chromium content are desirable for 4-methacryloxy-ethyl trimellitate anhydride resin-bonded restorations.     

Low-temperature growth of InSb by vacuum MOCVD using TEln and SbH3

This report describes the homo-epitaxial growth of InSb by the Metal-Organic Chemical Vapor Deposition Method (MOCVD) using triethylindium (TEIn) and stibine (SbH₃) for indium and antimony sources, respectively. Single crystal InSb layers were grown at 400° C. The gas flow rate ratio (= SbH₃/TEIn) should be more than 8 in order to grow a layer with good morphology. The epitaxial layer was n-type, with a carrier density and mobility of 1.5 x 10¹⁶ cm^-3 and 7.6 x 10⁴ cm²/Vs, respectively, at 77 K. By inserting a buffer layer grown at 400° C, the single crystal InSb layer was grown even at 300° C.