205 research outputs found
Pollen and seed desiccation tolerance in relation to degree of developmental arrest, dispersal, and survival
No full textIn most species, arrest of growth and a decrease in water content occur in seeds and pollen before they are dispersed. However, in a few cases, pollen and seeds may continue to develop (germinate). Examples are cleistogamy and vivipary. In all other cases, seeds and pollen are dispersed with a variable water content (2-70%), and consequently they respond differently to environmental relative humidity that affects dispersal and maintenance of viability in time. Seeds with low moisture content shed by the parent plant after maturation drying can generally desiccate further to moisture contents in the range of 1-5% without damage and have been termed 'orthodox'. Pollen that can withstand dehydration also was recently termed orthodox. Seeds and pollen that do not undergo maturation drying and are shed at relatively high moisture contents (30-70%) are termed 'recalcitrant'. Since recalcitrant seeds and pollen are highly susceptible to desiccation damage, they cannot be stored under conditions suitable for orthodox seeds and pollen. Hence, there are four types of plants with regard to tolerance of pollen and seeds to desiccation. Orthodoxy allows for dispersal over greater distances, longer survival, and greater resistance to low relative humidity. The advantage of recalcitrance is fast germination. Orthodoxy and recalcitrance are often related to environment rather than to systematics. It has been postulated that certain types of genes are involved during presentation and dispersal of pollen and seeds, since molecules (sucrose, polyalcohols, late embryogenic abundant proteins, antioxidants, etc.) that protect different cell compartments during biologically programmed drying have been detected in both. © 2011 The Author
Convergence of the Neumann Laplacian on Open Book Structures
No full textWe consider a compact C ���-stratified 2D variety M in R^3 and its ��-neighborhood Mv�� , which we call a ���fattened open book structure.��� Assuming absence of zero-dimensional strata, i.e. ���corners,��� we show that the (discrete) spectrum of the Neumann Laplacian in M, converges when ����� 0 to the spectrum of a differential operator on M.
Similar results have been obtained before for the case of fattened graphs, i.e. M being one-dimensional. In the case of a 2D smooth submanifold M, the problem has been studied well. However, having singularities along strata of lower dimensions significantly complicates considerations. As in the quantum graph case, such considerations are triggered by various applications such as micro-electronics, photonic devices, and dynamical systems with two ���slow��� and one ���fast��� degrees of freedom. The results are obtained under two restrictions: 1) there are no zero dimensional strata (corners); 2) the pages are transverse at the bindings (no cusps). We begin with the ���uniformly fattened case:��� width of the fattened domain shrinks with the same speed around ���pages��� and ���bindings.��� Next we consider more general fattened open book structures with a finite number of parameters which control the size of the fattened neighborhood around each point. In particular we consider �� -sized neighborhoods around the bindings and ��-sized neighborhood around the pages. By properly tuning these parameters, we demonstrate three classes of limit operators on M. We show that there is a relative length scale (controlled by ��) between the ���fattened pages��� and ���fattened binding��� which causes the system to undergo phase transitions. Two such phases have novel boundary currents along the bindings
Need for endoscopic removal of oesophageal coins in children was similar for strategies of immediate removal and watchful waiting
No full textThe author provides a brief commentary on the research reported in Waltzman ML, Baskin M, Wypij D, et al. A randomized clinical trial of the management of esophageal coins in children. Pediatrics 2005;116:614–9
IMAGING PHOSPHOLIPASE D ACTIVITIES IN LIVE CELLS WITH A REAL-TIME, BIOORTHOGONAL APPROACH AND ITS APPLICATIONS TO UNDERSTAND CELL SIGNALING AND PHOSPHOLIPID TRAFFICKING
No full text226 pagesLocalized production of signaling agents is an essential feature for living cells. Many of these signaling molecules are lipid entities. However, due to their hydrophobic nature and highly diverse cellular functions, certain potent, low-abundance lipids that act as signaling agents remain understudied with traditional biochemical techniques. Thus, the advancement of modern chemical biology tools represents a promising perspective to tackle these complex biological problems. Chapter 1 summarizes the challenges and recent advancement to study phospholipid signaling and discusses its relevance towards cell signaling and lipid trafficking. In Chapter 2, the author discusses the design, synthesis and characterization of a novel, bioorthogonal chemistry-based strategy, termed RT-IMPACT, to image the biosynthesis of a specific signaling lipid called phosphatidic acid (PA). With fast chemical kinetics and optimal enzyme specificity, PA produced by phospholipase D (PLD) enzyme activity can be visualized in living cells in real-time. The author further demonstrates that RT-IMPACT is capable of accurately reporting subcellular locations of PA production in response to different upstream stimuli. In Chapter 3, the author applies RT-IMPACT tools to investigate PTHR signaling that are previously underexplored. The author shows that PLD activation is specifically downstream of PTHR-Gq protein signaling. Moreover, the Gq signaling pathway, in stark contrast to the Gs pathway, is transient and localized on the plasma membrane as revealed by time-resolved imaging of PLD activities. Lastly, through inhibition of endocytic pathways, a competitive relationship between the Gq and Gs pathway is revealed. In Chapter 4, the author characterizes a family of lipid transfer proteins—ESyts—that are responsible for trafficking of unnatural fluorescent lipids from PM to ER. A positive correlation between the expression levels of ESyts and trafficking rates from PM to ER is established. Next, through protein engineering, lipid transfer activities of ESyts are shown to be directly responsible for removal of unnatural fluorescent lipids from the PM. In the final chapter, the author summarizes the major findings and significance of this work towards understanding of physiologically relevant pathways. Several potential future directions, including screening for potential upstream stimuli and identifying other lipid transfer proteins, are briefly described
The Surfaces of Contemporary Capitalism
No full textThis is the author accepted manuscript. the final version is available from Johns Hopkins University Press via the link in this recor
Lead Us Not Into Translation: Notes Toward a Theoretical Foundation for Asian Studies
No full textI begin this work with a simple question. Why is it impossible to imagine, much less write, a work like Michel Foucault's Discipline and Punish within Asian area studies? The impossibility I am referring to is not of content but of form. It is not just about writing such a text but about having it read as something more than a description; having it read for its theoretical significance more generally. That is to say, it is about the impossibility of writing a work that is principally of a theoretical nature but that is empirically and geographically grounded in Asia rather than in Europe or America. Why is it that, when it comes to Asian area studies, whenever “theory” is invoked, it is invariably understood to mean “applied theory” and assumed to be of value only insofar as it helps tell the story of the “real” in a more compelling way?
To some extent, what follows is an attempt to explain historically how Western area studies on Asia came to appreciate theory in this limited and limiting way. At the same time, as I began to investigate the history and prehistory of this diaphanous field, I began to recognize the possibilities of a very different form of area studies that could have emerged had different sets of pressures pushed it in a slightly different direction. This essay is therefore an attempt to recuperate these now forgotten possibilities and to build on them in order to produce a different way of seeing, writing, and theorizing Asian area studies
Plant Canopy May Promote Seed Dispersal by Wind
No full textSeed dispersal has received much research attention. The plant canopy can intercept diaspores, but the effect of the plant canopy (the aboveground portion of a plant consisting of branches and leaves) on dispersal distance has not been explored empirically. To determine the effect of plant canopy on seed dispersal distance, a comparison of diaspores falling through open air and through plant canopy was made in a wind tunnel using three wind speeds and diaspores with various traits. Compared with diaspores falling through open air, the dispersal distance of diaspores falling through plant canopy was decreased or increased, depending on wind speed and diaspore traits. When falling through a plant canopy, dispersal distance of diaspores with thorns or those without appendages was promoted at low wind speed (2 m s−1), while that of diaspores with low wing loading (0.5 mg mm−2) and terminal velocity (2.5 m s−1) was promoted by relatively high (6 m s−1) wind speed. A plant canopy could increase seed dispersal distance, which may be due to the complicated updraft generated by canopy. The effect of maternal plants on seed dispersal regulates the distribution pattern and the species composition of the community
IDENTIFICATION OF SMALL MOLECULES THAT REGULATE NEMATODE – ENVIRONMENT INTERACTIONS
No full text173 pagesSupplemental file(s) description: Supplementary File 1.One of the central channels of nematode-environment interactions is through small molecules (non-polymeric chemical entities with a molecular mass <1000 Daltons). Nematodes release an abundance of small molecules which affect their environment, such as the ascarosides, di-deoxy sugar lipids which control the development and behavior of nematodes and other members of their environment. Through the advancement of high-resolution mass spectrometry and analysis software, we now find a wealth of other small molecules produced by nematodes which play key roles in their environmental interactions. Herein the author describes the integrated use of 2D NMR and high-resolution UHPLC-MS/MS to aid metabolomics of complex natural samples to characterize small molecules that regulate interactions between nematodes and their environment. Combining these analytical techniques with biological assay data, the author has characterized small molecules from nematodes which elicit defensive responses in other nematodes and affect microbial and nematode growth. The library of small molecules presented in this dissertation provide a new layer of structural diversity in nematodes and define a path forward in discovering other molecules of their kind. The novel small molecules shown in this thesis include - Branched chain sulfolipids (sufal/ac), molecules that cause defensive behavior in prey nematodes that appear to be linked to the development of the predator nematode’s mouth dimorphism. Cyclic sulfates (cysul), a class of metabolites unprecedented in nature, with possible epoxide precursors that suggest a straightforward biosynthetic pathway. The cyclic sulfates, unlike the branched chain sulfolipids, do not affect defensive behaviors in other nematodes, but may play a yet undiscovered role in a nematode’s interactions with its environment. Cyclopropyl lipids (cpfa), nematode derivatives of bacteriogenic metabolites which inhibit microbial growth in several species. The activity of these lipids was found to be stereochemically specific, suggesting that the effect on microbial growth may be through a signaling mechanism. Through these studies the author hopes to convey connections between small molecules created by nematodes with their environment and draw parallels with their potential effect on other organisms
Writing and the rights of reality: usurpation and potentiality in Derrida, Plato, Nietzsche, and Beckett
No full textThe thesis critically evaluates Jacques Derrida's conferral of the rights of reality on writing, focussing on his theory of an arche-text in light of the speculative nature of this theory. The theory is initially considered in the context of Derrida's elucidation of the usurpatory status of writing within the Platonic and Nietzschean texts. This consideration reveals an admission of writing's usurpatory status by both writers while at the same time demonstrating their awareness of the intrinsically speculative nature of this view, the significance of writing lying in its ability to exteriorise the radically indeterminate status of consciousness m relation to reality rather than its ability to displace consciousness or reality The analyses, therefore, not only bring the Derridean hypothesis of a repressive or phonocentric metaphysical episteme into question but also exhibit the historical and philosophical role of potentiality in relation to writing, writing's ultimate significance lying in its capacity to exteriorise our existence as a mode of potentiality. Accordingly, in the second half of the thesis the Derridean theory of writing is countered with a specifically Aristotelian theory of the text as it is exhibited in the prose of Samuel Beckett, an author whose significance lies in his close alignment with Derridean theory within contemporary criticism. It is demonstrated that this identification has obviated an awareness of the significance of potentiality within the Beckettian text, his work consequently being appraised in the previously neglected context of Aristotelian metaphysics
Dissertatio de ortu et interitu Imperii Romani : qua examinatur nobilis illa, ut eam vocat merito summus Grotius, cum apud historicos, tum etiam JCtos tractata quaestio, anea, quae olim fuerint Romani Imperii, jam sint Germanici regni, propter translationem Imperii Romani in Carolum M. factam, vel an nulla translatio ejusmodi facta, sed, populo Romano eodem hodie, qui olim fuit, penes eundem quoque imperium mansisse dicendum, tanquam penes corpus, in quo esset ac viveret /
No full textErrata, p. [28] of preliminaries.Signatures: pi² *⁴ 2*⁸ A-L¹² M⁶.Frontispiece by Jan van Vianen after Jan Goeree. Plates (unsigned) depict medals.Mode of access: Internet.Ownership inscription of Lisa & Leonard Baskin on back pastedown, with notation of bookseller Ced[ric] Rob[in]son and date 1970; Baskin's initial B written in pencil after signature letter L; his printed labels for Fort Hill and Lurley Manor on front pastedown. Signature of W.B. Goodwin on front free endpaper.Binding: vellum, tooled in blind. Author, title & date written on spine. Edges mottled blue & red
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