RESUMEN
NASA's Magellan mission revealed that many Venus highlands exhibit low radar emissivity values at higher altitudes. This phenomenon is ascribed to the presence of minerals having high dielectric constants, produced or stabilized by temperature-dependent chemical weathering between the rocks and the atmosphere. Some large volcanoes on Venus have multiple reductions of radar emissivity at varying altitudes. The authors present morphological maps of major lava flow units at Maat, Ozza, and Sapas montes and compare them to radar emissivity. Sapas has a single reduction in emissivity values at 6,054.6 km, while Maat and Ozza have several reductions at altitudes of 6,052.5-6,056.7 km. Emissivity values are highly spatially correlated to individual lava flows indicating that minerals in the rocks control the emissivity signature. The emissivity patterns at these volcanoes require at least four individual ferroelectric mineral compositions in the rocks that are highly conductive at Curie temperatures of 693-731 K. These temperatures are compatible with chlorapatite and some perovskite oxides. Modeling the minimum volumes of ferroelectrics (10-100s ppm) shows the volume and type of ferroelectric may vary over the lifetime of a single volcano. The modeled volumes of ferroelectrics in Ozza and Sapas are greater than in Maat, consistent with the production of ferroelectrics via weathering over a longer period of time, and supporting the idea that Maat has younger volcanic activity. The stratigraphic relationship of Maat's youngest flows with impact craters may indicate the timeframe of the production of specific ferroelectrics via chemical weathering is over 9-60 Ma.
RESUMEN
Multiple studies reveal that most of Venus highlands exhibit anomalously high radar reflectivity and low radar emissivity relative to the lowlands. This phenomenon is thought to be the result of atmosphere-surface interactions in the highlands, due to lower temperatures. These reactions are a function of rock composition, atmospheric composition, and degree of weathering. We examine the Magellan radar emissivity, altimetry and SAR data for all major volcanoes and coronae on Venus. We characterize and classify edifices according to the pattern of the variation of radar emissivity with altitude. The volcanic highlands can be classified into 7 distinct patterns of emissivity that correspond to at least 3 discrete types of mineralogy based on the altitude (temperature) of the emissivity anomalies. The majority of emissivity anomalies support the hypothesis of a weathering phenomenon at high altitude (>6053 km), but we also find strong emissivity anomalies at lower altitudes that correspond spatially to individual lava flows, indicating variations in mineralogy within an evolving volcanic system. The emissivity signature of tallest volcanoes on Venus are consistent with the presence of ferroelectric minerals in their rocks, while volcanic edifices in western Ishtar Terra and eastern Aphrodite Terra are consistent with the presence of semiconductor minerals. Sapas Mons and Pavlova Corona are also consistent with ferroelectrics, but at a different Curie temperature than the other volcanoes in Atla Regio. The spatial distribution of radar emissivity classes correlates to different geologic settings indicating that different mantle source regions (deep/shallow plumes, and possible convergence zones) may contribute to differences in mineralogy for the studied edifices. Finally, we show that the emissivity signatures of Idunn, Maat and other volcanic edifices are consistent with relatively fresh and unweathered rocks, indicating recent or possibly current volcanism on Venus.
RESUMEN
The menstrual cycle, pregnancies, and offspring were evaluated before and after initial combined radiation (RT) and chemotherapy with thiotepa, vinblastine, vincristine, procarbazine, and prednisone (TVPP), in 34 women between the ages of 18 and 44 (median 26.5 years) treated for Stage II and Stage III Hodgkin's disease. The median range of follow-up is 83.1 months (range 40.5-140). After therapy 94.1% (32/34) continued to menstruate. Two of the four patients over the age of 35 ceased to menstruate. All patients under the age of 35 continued to menstruate (30/30). Age at the time of diagnosis was the only factor affecting change in menses with a significant probability (p = .001) that women greater than 30 years of age will experience some change in menstrual pattern. Seventeen pregnancies occurred in 12 women after therapy; 2 had 4 elective abortions; 10 delivered 12 children with normal physical development; 1 will deliver six months from now. Twelve of thirteen patients who wanted to become pregnant have conceived. The ability to become pregnant and deliver normal children after intensive treatment with combined radiation and chemotherapy (RT/TVPP) was comparable to the patients' pretreatment record.