The role of sublimation as a driver of climate signals in the water isotope content of surface snow: Laboratory and field experimental results

Ice core water isotope records from Greenland and Antarctica are a valuable proxy for paleoclimate reconstruction, yet the processes influencing the climate signal stored in the isotopic composition of the snow are being challenged and revisited. Apart from precipitation input, post-depositional processes such as wind-driven redistribution and vapor–snow exchange processes at and below the surface are hypothesized to contribute to the isotope climate signal subsequently stored in the ice. Recent field studies have shown that surface snow isotopes vary between precipitation events and co-vary with vapor isotopes, which demonstrates that vapor–snow exchange is an important driving mechanism. Here we investigate how vapor–snow exchange processes influence the isotopic composition of the snowpack. Controlled laboratory experiments under forced sublimation show an increase in snow isotopic composition of up to 8 ‰ δ18O in the uppermost layer due to sublimation, with an attenuated signal down to 3 cm snow depth over the course of 4–6 d. This enrichment is accompanied by a decrease in the second-order parameter d-excess, indicating kinetic fractionation processes. Our observations confirm that sublimation alone can lead to a strong enrichment of stable water isotopes in surface snow and subsequent enrichment in the layers below. To compare laboratory experiments with realistic polar conditions, we completed four 2–3 d field experiments at the East Greenland Ice Core Project site (northeast Greenland) in summer 2019. High-resolution temporal sampling of both natural and isolated snow was conducted under clear-sky conditions and demonstrated that the snow isotopic composition changes on hourly timescales. A change of snow isotope content associated with sublimation is currently not implemented in isotope-enabled climate models and is not taken into account when interpreting ice core isotopic records. However, our results demonstrate that post-depositional processes such as sublimation contribute to the climate signal recorded in the water isotopes in surface snow, in both laboratory and field settings. This suggests that the ice core water isotope signal may effectively integrate across multiple parameters, and the ice core climate record should be interpreted as such, particularly in regions of low accumulation.publishedVersio

Structure and Electrochemical Properties of LiMn2O4 Thin Films

The structure and electrochemical properties of LiMn{sub 2}O{sub 4} films depend upon the deposition and annealing conditions. Films which were deposited by rf magnetron sputtering of LiMn{sub 2}O{sub 4} in Ar + N{sub 2} gas mixtures and annealed in O{sub 2} at temperatures between 400 to 1000{degrees}C had the cubic spinel structure with an a-axis length that increased linearly from 8.13 to 8.25 {Angstrom} with increasing anneal temperature. Thin-film lithium cells with cathodes of different a-axis lengths exhibited marked differences in their voltage profiles. In particular, the ratio of the capacities at 4 V and 3 V increased with the a-axis length. A defect model of LiMn{sub 2}O{sub 4} which is consistent with the structural and electrochemical data is represented by [Li{sub 1-y+z}Mn{sup 2+}{sub y-z}]{sub 8a}[Mn{sup 2+}{sub z}]{sub 16c}[Li{sub x}Mn{sub 2-x}]{sub 16d}O{sub 4}. Based on this model and the results of in-situ XRD measurements, it is proposed that Mn ions migrate from 8(a) tetrahedral sites to 16(c) octahedral sites on charging the cells in the 5V plateau

Effects of neutral-beam injection and gas puffing on deuterium and impurity levels in the scrapeoff layer of ISX-B

Plasma-material interactions in the scrapeoff region of a tokamak have important effects on the overall performance of the machine. In order to prudently select the most-appropriate materials for walls, limiters, and armor plate, it is necessary to characterize the plasma that interacts with these surfaces and to understand what effect different modes of operation of the tokamak have on plasma characteristics. We have made a series of measurements on the ISX tokamak using deposition-probe techniques to identify and quantify the impurities (Z greater than or equal to 8) in the limiter shadow, and to determine the temporal behavior of both impurity and plasma particles in this region. These measurements have been made under a variety of tokamak operating conditions, including both ohmic and neutral-beam heated discharges. The results are interpreted in terms of edge conditions, impurity introduction, gas puffing, and the relative importance of wall and limiter contributions

Formation of oriented particles in an amorphous host: ZnS nanocrystals in silicon

Processes for incorporating randomly oriented crystalline precipitates in an amorphous host can be traced back to the 17th century when Cassius produced “gold ruby” glass. In this glass, octahedral colloidal precipitates of gold scatter light by the Mie process to produce a deep red color. In contrast to gold ruby glass, we describe a type of material in which the crystalline precipitates are crystallographically aligned in a coherent manner—even though they are dispersed in an amorphous matrix. Ion implantation and thermal processing are first used to form zinc sulfide nanocrystals that are coherently oriented with respect to a crystalline Si host. The Si is then amorphized by ion irradiation leaving the highly radiation-resistant ZnS precipitates in an aligned crystalline state. The process is anticipated to find applications in the creation of surfaces with unique optoelectronic properties. © 1999 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69678/2/APPLAB-74-5-697-1.pd

Optical properties of multicomponent cadmium-silver nanocluster composites formed in silica by sequential ion implantation

Formation and optical properties of nanometer dimension metal colloid composites formed by sequential implantation of Cd then Ag and by single element implantations of Cd and Ag in silica were characterized by TEM and optical spectroscopy. A nominal dose of 6x10{sup 16} ions/cm{sup 2} as determined by current integration was used for both ion species. Doses used for the sequential implantations were a 1 to 1 ratio of Cd to Ag. Sequential implantations of Cd and Ag led to formation of both multi-component metal nanoclusters and elemental nanoclusters. Electron diffraction indicated that the polycrystalline particles of Ag{sub 5}Cd{sub 8} and elemental Ag were formed. The optical response was consistent with results expected from effective medium theory

Weight change measurements of erosion/deposition at beryllium limiter tiles in ISX-B

The weight changes of Be tiles which functioned as a rail limiter in ISX-B for more than 3500 beam-heated discharges have been determined. The net weight loss for the limiter was 2.0 g, with the central tiles losing a total of 3.2 g and inboard tiles gaining 1.2 g. The weight loss is attributed primarily to the release of Be droplets as a result of limiter surface melting. The weight gains resulted from an inward flow of molten material along the limiter surface. The results indicate high erosion (melt loss) with incomplete and nonuniform redeposition (melt flow) of limiter material during periods of limiter melting

Efficacy of tunnel technique in the treatment of localized and multiple gingival recessions: A systematic review and metaâ analysis

BackgroundTunnel technique (TUN) has recently gained popularity among clinicians for its promising clinical and esthetic results in treating gingival recession (GR) defects. However, evidence regarding the efficacy of the TUN is not yet conclusive. Therefore, the aim of the present systematic review and metaâ analysis was to investigate the predictability of TUN and its comparison to the coronally advanced flap (CAF) procedure.MethodsA literature search on PubMed, Cochrane libraries, EMBASE, and handâ searched journals through November 2017 was conducted to identify clinical studies investigating TUN for root coverage procedures. Only randomized controlled trials (RCTs) were considered for the metaâ analysis comparing TUN to CAF.ResultsA total of 20 articles were included in the systematic review and six in the metaâ analysis. The overall calculated mean root coverage (mRC) of TUN for localized and multiple GR defects was 82.75 ± 19.7% and 87.87 ± 16.45%, respectively. Superior results were found in maxillary and in Miller Class I and II GR defects. TUN outcomes may have been enhanced by splitâ thickness flap preparation and microsurgical approach. TUN and CAF had comparable mRC, complete root coverage (CRC), keratinized tissue gain, and root coverage esthetic score when varying combinations of graft material were evaluated. However, CAF demonstrated superior outcomes to TUN when the same graft (connective tissue or acellular dermal matrix) was used in both techniques.ConclusionsTUN is an effective procedure in treating localized and multiple GR defects. Limited evidence is available comparing TUN to CAF; however, CAF seemed to be associated with higher percentage of CRC than was TUN when the same grafts (connective tissue or acellular dermal matrix) were used in both techniques.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/145520/1/jper10154.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/145520/2/jper10154_am.pd

Subwavelength Structured Narrow-Band Integrated Optical Grating Filters

A unique type of narrow band integrated optical filter is investigated based on embedding a subwavelength resonant grating structure within a planar waveguide. Current integrated narrow-band optical filters are limited by their size, density of devices that can be produced, overall performance, and ability to be actively altered for tuning and modulation purposes. In contrast, the integrated optical filters described in this work can have extremely narrow bandwidths--on the order of a few angstroms. Also, their compact size enables multiple filters to be integrated in a single high density device for signal routing or wavelength discrimination. Manipulating any of the resonant structure`s parameters will tune the output response of the filter, which can be used for modulation or switching applications