Arctic Sea Ice Microstructure Observations Relevant to Microwave Scattering

Sea ice microstructure characteristics relevant to ice microwave scattering were studied during SIMMS'91 field experiment in Resolute Bay in May/June 1991. Thin sections of the top 300 mm layer of first-year ice (from hummocks and melt ponds) were prepared and examined. Analysis is based mostly on qualitative observations, although statistics on bubble dimensions and geometry were obtained from digital analysis of thin section photographs. First-year ice featured mostly an oriented columnar grain structure. Both spherical and needle-shaped brine pockets were observed. In multi-year ice, a variety of grain structures and inclusion patterns were observed from the same floe. Hummock and melt pond ice are different in terms of grain structure and air bubble contents. Air bubbles in hummock ice are highly random and interconnected, especially near the surface. At lower depths, they retain simpler shapes and become oriented parallel to the dominant grain growth direction. In melt pond ice, two types of air inclusions whose typical dimensions differ by an order of magnitude were observed. Significant spatial variability of multi-year microstructure within a single floe is demonstrated.Key words: sea ice, ice microstructure, ice microwave scattering, SAR ice signatures, air bubbles in sea iceAu cours de l'étude de terrain SIMMS'91 menée dans la baie Resolute en mai/juin 1991, on a étudié les caractéristiques de la microstructure de la glace de mer pertinentes à la diffusion d'hyperfréquences par la glace. On a préparé et examiné de fines coupes transversales prélevées dans les 300 mm supérieurs de la glace de l'année et de la glace pluri-annuelle (provenant de hummocks et de mares de fonte). L'analyse s'appuie principalement sur des observations qualitatives, bien que les statistiques sur les dimensions et la géométrie des bulles aient été obtenues à partir du traitement numérique de photographies représentant de fines coupes transversales. La glace de l'année affichait principalement une structure granulaire prismée. On a observé des poches de saumure sphériques ainsi qu'aciculaires. Dans la glace pluri-annuelle, on a observé dans le même floe une diversité de structures granulaires et de schémas d'inclusion. Les hummocks et la glace des mares de fonte diffèrent quant à leur structure granulaire et au contenu des bulles d'air. Dans la glace de hummock, les bulles d'air sont distribuées au hasard et reliées entre elles, surtout près de la surface. À de plus grandes profondeurs, elles conservent des formes plus simples et s'orientent parallèlement à la direction dominante de la croissance granulaire. Dans la glace des mares de fonte, on retrouve deux types d'inclusions d'air dont les dimensions typiques diffèrent d'un ordre de grandeur. On démontre qu'il existe une importante variabilité spatiale de la microstructure de la glace pluri-annuelle à l'intérieur d'un même floe.Mots clés: glace de mer, microstructure de la glace, diffusion d’hyperfréquences par la glace, signatures de la glace obtenues avec le RALS, bulles d’air dans la glace de me

A suberized exodermis is required for tomato drought tolerance.

Plant roots integrate environmental signals with development using exquisite spatiotemporal control. This is apparent in the deposition of suberin, an apoplastic diffusion barrier, which regulates flow of water, solutes and gases, and is environmentally plastic. Suberin is considered a hallmark of endodermal differentiation but is absent in the tomato endodermis. Instead, suberin is present in the exodermis, a cell type that is absent in the model organism Arabidopsis thaliana. Here we demonstrate that the suberin regulatory network has the same parts driving suberin production in the tomato exodermis and the Arabidopsis endodermis. Despite this co-option of network components, the network has undergone rewiring to drive distinct spatial expression and with distinct contributions of specific genes. Functional genetic analyses of the tomato MYB92 transcription factor and ASFT enzyme demonstrate the importance of exodermal suberin for a plant water-deficit response and that the exodermal barrier serves an equivalent function to that of the endodermis and can act in its place

Short strain relaxation/recovery tests for evaluating creep response of nickel-base superalloys like IN-738LC

NRC publication: Ye

Winter Contaminants & friction tests at K.I. Sawyer Airbase, Michigan, USA \uef\ubf\ubd February 1999

NRC publication: Ye

Constant-load tertiary creep of mickel-base single crystal superalloys: role of specimen geometry

NRC publication: Ye

Limitations of Stress Relaxation Tests for Determining Stress Dependence of Strain Rate at High Temperatures

NRC publication: Ye

A Critical Look at Experimental Data on Constant Strain-Rate Tensile Strength of Titanium Forging

NRC publication: Ye