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Notes: Abstract. We extend the concept of the polygon visible from a source point S in a simple polygon by considering visibility with two types of reflection, specular and diffuse. In specular reflection a light ray reflects from an edge of the polygon according to the rule: the angle of incidence equals the angle of reflection. In diffuse reflection a light ray reflects from an edge of the polygon in all inward directions. Several geometric and combinatorial properties of visibility polygons under these two types of reflection are described, when at most one reflection is permitted. We show that the visibility polygon Vs(S) under specular reflection may be nonsimple, while the visibility polygon Vd(S) under diffuse reflection is always simple. We present a Θ(n 2 ) worst-case bound on the combinatorial complexity of both Vs(S) and Vd(S) and describe simple O(n 2 log 2 n) time algorithms for constructing the sets.

Notes: Summary ¶ A retrospective analysis of a consecutive series of 12 patients with 15 intracranial hemangiopericytomas treated at the University of Virginia using Gamma surgery is presented. Clinical and radiographic follow up of 3 to 56 months is available for 10 patients with 12 tumors. There was one tumor present at the time of initial Gamma surgery in each patient. Two new tumors occurred in patients previously treated. Nine of the tumors decreased in volume and three remained stable. Four of the nine tumors that shrank later progressed at an average of 22 months after treatment. Of the tumors that decreased in volume and have not progressed, the response has been for an average of 11 months. The follow-up for two tumors that remained unchanged was 10 and 34 months (average 22 months). A third tumor was unchanged at 42 months but the patient died of new disease adjacent to the treated area in the anterior skull base. There were no complications and the quality of life following the procedure was maintained or improved in every case. Gamma surgery is effective in palliating the patients by decreasing tumor volume and delaying recurrence.

Notes: Abstract The characteristics of VHF radiowave scintillations at 244 MHz (FLEETSAT) during a complete solar cycle (1983–93) at a low-latitude station, Waltair (17.7°N, 83.3°E), are presented. The occurrence of night-time scintillations shows equinoctial maxima and summer minima in all the epochs of solar activity, and follows the solar activity. The daytime scintillation occurrence is negatively correlated with the solar activity and shows maximum occurrence during the summer months in a period of low solar activity. The occurrence of night-time scintillations is inhibited during disturbed days of high solar activity and enhanced during low solar activity.

Notes: Summary We present our results of Gamma Knife surgery for craniopharyngioma in nine patients. The current status of surgery, radiation therapy, intracavitary instillation of radionucleides and Gamma Knife surgery in the management of craniopharyngiomas is discussed.

Notes: Summary Three patients with pituitary adenomas (ACTH-secreting, non-secretory, and multi-secretory) with unfavorable course, in spite of repeated microsurgery, drag therapy, as well as radiotherapy and radiosurgery, are presented. Each case was re-evaluated for possible flaws in management. Two of the invasive tumors continued to grow, in spite of correct management. The third patient with a pituitary adenoma underwent microsurgical resection, and later following a false positive finding of recurrence, received radiotherapy and underwent radiosurgery. The lesion actually was chronic inflammatory tissue.

Notes: The control of weeds and nematodes by solar heating of the soil using transparent polyethylene (PE) sheets was studied in the field during the summer of 1990. PE mulching for 32 days decreased the emergence from seed of the dominant weeds Dactyloctenium aegyptium (L.) P. Beauv., Acrachne racemosa (Roem. & Schult.) Ohwi, Trianthema monogyna L. and Cyperus rotundus L. by over 90%. Emergence of C. rotundus from tubers was increased by the mulching treatments. Mulching for 16 days also decreased weed emergence but to a lesser extent than the 32-day treatment. The main solarization effect was restricted to the 0–5 cm layer of soil.Solarization reduced the population of plant-parasitic nematodes (Tylenchus, Heterodera, Xiphinema, Hoplolaimus, Pratylenchus and Ro-tylenchus spp.) by about 90% and of saprophytic nematodes by about 60% but, after 70 days, the nematode levels had largely recovered. The mean maximum soil temperatures recorded at 5 cm were higher when mulching followed irrigation. Data are given on the soil temperatures recorded over the 32-day period. The growth of soybean was improved and seed yield increased by up to 78% following solarization. Effet de la solarisation du sol sur les mauvaises herbes et les nematodes en conditions tropicales indiennes La lutte contre les mauvaises herbes et les nématodes par solarisation du sol à l'aide de films de polyéthylène transparent (PE) a étéétudiée au champ pendant l'été 1990. Trente deux jours de solarisation diminuaient de plus de 90% la levée à partir de graines des mauvaises herbes dominantes Dactyloctenium aegyptium (L.) P. Beauv., Acrachne racemosa (Roem. & Schult.) Ohwi, Trianthema monogyna L. et Cyperus rotundus L. La levée de C. rotundusà partir de tubercules était accrue par la solarisation. Seize jours de solarisation diminuaient aussi la levée des mauvaises herbes, mais dans un moindre mesure. L'effet de solarisation s'exerçait principalement dans les 5 centimètres superficiels du sol.La solarisation réduisait d'environ 90% la population de nématodes parasites des plantes (Tylenchus, Heterodera, Xiphinema, Hoplolaimus, Pratylenchus et Rotylenchus spp.) et d'environ 60% la population des nématodes saprophytes. Après 70 jours, les populations de nematodes étaient pratiquement reconstituées. Les moyennes des températures maximales du sol enregistrées à 5 cm de profondeur étaient plus élevées quand l'installation du film polyéthylène suivait une irrigation. Des données concernant la température du sol sur 32 jours sont communiques. La croissance du soja était accrue et le rendement en grains augmentait jusqu'à 78% après solarisation. Wirkung der Bodensolarisation auf Unkräuter und Nematoden unter tropischen Bedingungen Die Bekämpfung von Unkräutern und Nematoden durch Solarisation mittels farbloser Polyethylenfolia (PE) wurde im Sommer 1990 im Freiland untersucht. Nach 32tägiger Solarisation nahm die Keimung der vorherrschenden Unkräuter Dactyloctenium aegypticum (L.) P. Beauv., Acrachne racemosa (Roem. & Schult.) Ohwi, Trianthema monogyna L. und Cyperus rotundus L. um über 90% ab. Der Austrieb von Cyperus rotundus aus Knollen wurde gefördert. Eine l6tägige Solarisation war nicht so wirkungsvoll. Die Wirkung war auf die oberste Bodenschicht bis 5 cm Tiefe beschränkt. Gegen pflanzenparasitische Nematoden (Tylenchus, Heterodera, Xiphinema, Hoplolaimus, Pratylenchus und Rotylenchus spp.) betrug die Wirkung der Solarisation etwa 90%, gegen saprophytische Nematoden rund 60%, aber nach 70 Tagen hatten sich die Nematodenpopulationen wieder weitgehend erholt. Nach Bewässerung wurde in 5 cm Tiefe eine höhere Bodentemperatur erreicht. Für die 32-Tage-Periode werden die Temperaturdaten wiedergegeben. Nach der Solarisation war das Wachstum von Sojabohne verbessert, und die Erträge stiegen um bis zu 78%.

Notes: The effects of dispersion on the pulsewidth of a mode-locked fiber ring laser are examined. We have identified two different modes of operation, one where the pulsewidth is determined by the path-integrated (global) dispersion of the cavity and another novel mode where pulsewidth is not limited by the global dispersion. Experimental results show that for some configurations, the local dispersion of the cavity plays an important role in determining the pulsewidth of the laser. © 1996 American Institute of Physics.