University of Massachusetts Boston

About: University of Massachusetts Boston is a education organization based out in Boston, Massachusetts, United States. It is known for research contribution in the topics: Population & Health care. The organization has 6541 authors who have published 12918 publications receiving 411731 citations. The organization is also known as: UMass Boston.

Self-incompatibility systems in the rubiaceae of a tropical lowland wet forest

Abstract: A program of experimental field pollinations was carried out on 14 species of woody Rubiaceae in a Costa Rican wet forest in order to test for the presence of self-incompatibility systems. Species of Cephaelis, Coussarea, Fara mea, Ha melia, Posoqueria, Psychotria, R udgea, and WarszewiczEa were investigated in the study. Ten of the species are distylous, and of these, nine were found to be self-incompatible. The site of the incompatibility barrier varied between and within species. Short style plants always had stigmatic inhibition of pollen tubes following self and intraform pollinations, but the site of the rejection response in long style plants was quite variable. In several species, pollen tubes, resulting from incompatible pollinations of the long style flowers, penetrated to the base of the style. Fruit set was followed in two of these species, and despite deep penetration of self and intraform pollen tubes in the long style morph, only interform pollinations resulted in fruit set. Four of the species tested are florally monomorphic and each was found to be self-incompatible on the basis of fruit set patterns. Pollen tubes in the styles of self-pollinated flowers of two of the monomorphic species, penetrated to the ovary, but no fruits resulted from selfpollinations. A LARGE PROPORTION of the hermaphroditic tree species tested in neotropical forests have been shown to be self-incompatible (Bawa, 1974,1979; Ruiz and Arroyo, 1978). The existence of self-incompatibility in those species has been inferred on the basis of diffierences in fruit set between selfand cross-pollinated flowers. This study examines the nature of pollen tube-pistil interactions and patterns of fruit set in 14 species of neotropical Rubiaceae. The objectives of the study were: 1) to estimate the proportion of self-compatible and self-incompatible species in a sample of Rubiaceae from one community, and 2) to determine the site in the pistil at which self-pollen is inhibited in the self-incompatible species. The Rubiaceae were chosen because the family shows a diversity of sexual systems. Both florally monomorphic and heteromorphic species exist, and sporophytic and gametophytic selfincompatibility systems have been reported as well (Bir Bahadur, 1968). The investigation was conducted at the La ' Received for publication 15 September 1982; revision accepted 8 June 1983. The authors would like to acknowledge the staS of the Organization for Tropical Studies for much administrative and logistic support of the research. B. E. Hammel, J. D. Dwyer, R. B. Foster, and G. S. FIartshorn kindly assisted with floristic information and species determinations. S. C. H. Harrett, M. H. Grayum, D. L. Mulcahy, G. B. Mulcahy and K. Searcy donated valuable advice-and criticism on earlier drafts of the manuscript. The work was supported by NSF Grants DEB 75-2 1018 and DEB 77-25558 to K. S. Bawa and DEB 79-21485 to D. L. Mulcahy. Selva Field Station of the Organization for Tropical Studies, located at the confluence of the Rio Sarapiqui and Rio Puerto Viejo, in Heredia Province, Costa Rica. The vegetation of La Selva is considered transitional between Tropical Wet Forest and Premontane Wet Forest Life Zones in the Holdridge System (Tosi, 1969) and has been described in detail by Holdridgeetal. (1971). The breeding systems ofthe following species were examined: Cephaelis elata $wartz, Coussarea sp. (voucher Beach 1424), Coussarea sp. (Beach 1467)7 Faramea sp. (Beach 1477)) F. suerrensis Donn. Smith, Hamelia patens Jacq., H. xerocarpa Kuntze, Posoqueria grandiflora Standley, Psychotria acuminata Benth., P. chiapensis Standley, P. ofDicinalis (Aubl.) Sandw., P. suerrensis Donn. Smith, Rudgea cornifolia (Humb. & Bonpl.) Standley, and Warszewiczia coccinea (Vahl) Klotzsch. Information on the ecological features of these species is provided in Table 1. Members of the Rubiaceae at La Selva occur predominantly in the understory and in light gaps of varying age as shrubs and small trees, although about 30 species are herbs, vines, or epiphytes. Our sample of 14 woody species constitutes 23% of the 60 species of trees and shrubs in the family known to occur at La Selva (B. E. Hammel, unpubl.). METHODS-Experimental pollinations were undertaken to determine if species were selfcompatible or self-incompatible. Controlled

Closing the Gap: Addressing the Vocabulary Needs of English-Language Learners in Bilingual and Mainstream Classrooms:

Abstract: Gaps in reading performance between Anglo and Latino children are associated with gaps in vocabulary knowledge. An intervention was designed to enhance fifth graders' academic vocabulary. The meanings of academically useful words were taught together with strategies for using information from context, from morphology, from knowledge about multiple meanings, and from cognates to infer word meaning. Among the principles underlying the intervention were that new words should be encountered in meaningful text, that native Spanish speakers should have access to the text's meaning through Spanish, that words should be encountered in varying contexts, and that word knowledge involves spelling, pronunciation, morphology, and syntax as well as depth of meaning. Fifth graders in the intervention group showed greater growth than the comparison group on knowledge of the words taught, on depth of vocabulary knowledge, on understanding multiple meanings, and on reading comprehension. The intervention effects were as la...

Metalenses: Advances and Applications

Abstract: DOI: 10.1002/adom.201800554 and optoelectronics. Metasurfaces as 2D artificial photonic structures are composed of subwavelength resonators (often referred to as meta-atoms).[1–8] The optical responses/functionalities of metasurfaces can be tailored by choosing the proper geometrical parameters of these metaatoms.[9–14] They have been applied to realize ultrathin invisible cloaking,[15] metahologram,[16–20] surface plasmon launchers,[21–23] compact nonlinear devices,[24–28] nanolasers,[29–34] and many novel compact photonic devices.[11,35–57] Among all the promising applications of metasurfaces, planar metalenses with superior performance and functionalities over their conventional counterparts are definitely one of the most exciting and important research areas. This is because metasurface lenses (metalenses) can not only show better optical functionalities but also allow for much more compact device design than the conventional high-end objective lenses. In this article, we will review the progress in the development of metalenses. This article is organized into three major parts. First, the working mechanisms of chromatic and achromatic metalenses will be introduced. The design principle of integrated-resonant units for correcting chromatic aberration of a metalens will be discussed. Second, novel applications of metalenses mentioned in the first part for full color imaging, sensing, and spectroscopy will be reviewed. After the discussion of the passive metalenses, the emerging tunable metalenses and their applications will be surveyed, followed by concluding remarks on future prospects.

Design of a Si-based lattice-matched room-temperature GeSn/GeSiSn multi-quantum-well mid-infrared laser diode.

Abstract: This paper presents modeling and simulation of a silicon-based group IV semiconductor injection laser diode in which the active region has a multiple quantum well structure formed with Ge(0.9)Sn(0.1) quantum wells separated by Ge(0.75)Si(0.1)Sn(0.15) barriers. These alloy compositions were chosen to satisfy three conditions simultaneously: a direct band gap for Ge(0.9)Sn(0.1), type-I band alignment between Ge(0.9)Sn(0.1) and Ge(0.75)Si(0.1)Sn(0.15,) and a lattice match between wells and barriers. This match ensures that the entire structure can be grown strain free upon a relaxed Ge(0.75)Si(0.1)Sn(0.15) buffer on a silicon substrate - a CMOS compatible process. Detailed analysis is performed for the type I band offsets, carrier lifetime, optical confinement, and modal gain. The carrier lifetime is found to be dominated by the spontaneous radiative process rather than the Auger process. The modal gain has a rather sensitive dependence on the number of quantum wells in the active region. The proposed laser is predicted to operate at 2.3 μm in the mid infrared at room temperature.