Thermally Switchable Periodicities and Diffraction from Mesoscopically Ordered Materials     

JM Weissman  HB Sunkara  AS Tse  SA Asher 《Science (New York, N.Y.)》1996,274(5289):959-960

Two switchable, mesoscopically periodic materials were created by combining crystalline colloidal array (CCA) self-assembly with the temperature-induced volume phase transition of poly(N-isopropylacrylamide) (PNIPAM). Body-centered-cubic CCAs of hydrated, swollen PNIPAM particles Bragg-diffract infrared, visible, and ultraviolet light weakly, whereas arrays of compact shrunken particles diffract efficiently. A tunable diffracting array was also created by embedding a CCA of polystyrene spheres within a PNIPAM hydrogel that swells and contracts with temperature; thus the array lattice constant varies with temperature, and the diffracted wavelength was thermally tunable across the entire visible spectrum. These materials may find applications in many areas of optics and materials science.  相似文献   

Wild potato (Solanum sect.Petota) germplasm collecting expedition to Argentina in 1990, and status of Argentinian potato germplasm resources     

David M. Spooner  Andrea M. Clausen 《Potato Research》1993,36(1):3-12

Summary A joint Argentina/United States expedition collected wild potato (Solanum sect.Petota) germplasm in Argentina between February 4–28 and March 28–April 18, 1990. This was followed by a short expedition between February 27 and March 3, 1991. Collections were made in the Andes Mountains from southern Tucumán Province (27°20′S), south to southern Rio Negro Province (40°52′S) and comprised 88 lots of germplasm of ten species, 76 as true-seed and 12 as tubers. The most important new collections included germplasm ofS. brevidens, S. maglia, S. x rechei andS. venturii. By summarizing details of these collections with those of existing collections, we have been able to suggest future collecting in Argentina.  相似文献   

Pollen-style compatibility relations in natural populations of the wild diploid potato species Solanum spegazzinii Bitt.     

Luis Ernesto Erazzú  Elsa Lucila Camadro  Andrea Martina Clausen 《Euphytica》1999,105(3):219-227

Solanum spegazzinii Bitt., a wild diploid potato species endemic to Argentina, possesses resistance to adverse biotic and abiotic agents. Northwestern Argentinean populations grouped according to their morphological variability (G1 = localities East of the Calchaquí Valley, G2 = Calchaquí Valley and G3 = locality Belén) presented problems in seed set following controlled crosses. Thus, to evaluate if the morphological variability previously reported was sustained on a genetic basis, three introductions per group and five plants per introduction were used in controlled crosses (genotypic combinations). These were classified according to the number of seeds produced per fruit. Pollen-style compatibility relations were studied in those crosses that did not set seeds or that produced less than 30 seeds each. Within groups, G1 produced seeds normally, whereas hybridization barriers were found in 71.4% and 50.0% of the combinations within G2 and G3, respectively; on the other hand, from 46.7% to 73.3% of the combinations among groups exhibited similar barriers. Variability in the expression of the sites of pollen tube inhibition in the style was observed both within and among groups. Speculations are made on the possible hybrid origin of the populations. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

冀中南棉区棉花黄萎病发生与气象因子关系分析   总被引：8，自引：0，他引：8  

齐俊生  马存  李红梅  姚树然 《棉花学报》1998,(5)

１９８６～１９９６年在石家庄河北棉花所黄、枯萎病混生病圃,对中棉所１２每年８月２０～２５日进行黄萎病调查,并与当地６～８月每旬的平均气温、降水量、日照时数和空气相对湿度等与发生黄萎病关系进行单项和综合分析。结果表明,７月份气温２７℃是发病轻重的转折点,７月中下旬的气温是影响黄萎病发病强度的主要因素,可分为高温、低湿、少雨轻病年和低温、高湿、多雨重病年,两者出现频率接近５０％。经过对黄萎病指（Ｙ）与所有因子逐步回归分析,入选因子为７月中旬湿度（Ｘ５）、６月下旬降水量（Ｘ１２）、７月中旬降水量（Ｘ１４）、７月下旬日照时数（Ｘ２４）和６月下旬平均气温（Ｘ３０）,得出回归方程可试用于黄萎病发病的预测预报。  相似文献