scholarly journals Transverse Aeolian Ridge Growth Mechanisms and Pattern Evolution in Scandia Cavi, Mars

2021 ◽  
Vol 8 ◽  
Author(s):  
Lori K. Fenton ◽  
Simone Silvestro ◽  
Gary Kocurek
Keyword(s):  
Defect Density ◽  
Coarse Grained ◽  
Growth Dynamic ◽  
Growth Mechanisms ◽  
Dune Field ◽  
Migration Rates ◽  
The Past ◽  
Pattern Development ◽  
Dune Migration ◽  
Lateral Linking

In Scandia Cavi on Mars, barchans migrating over a field of transverse aeolian ridges (TARs) leave behind distinctive trails (“wakes”) comprising both TARs undergoing exhumation and coarse-grained ripples being shed from the barchans. With distance upwind from the barchans, the combined pattern of these bedforms coarsens and defect density decreases, thus appearing to mature with exposure time. We present results of morphological analyses of the wake bedform crestlines using HiRISE images, seeking to determine how the wake pattern reflects TAR growth and pattern development. TARs interact with each other, exhibiting defect repulsions and possible lobe extensions, indicating that these bedforms have migrated in the past, despite the lack of identifiable change in overlapping images spanning 9.5 years. Mapping one wake in detail, we found that the TAR pattern is not affected by superposing ripples. However, the ripples undergo many interactions, first with one another, and later (with distance upwind) with the underlying TARs. Near the dune, many ripples laterally link, growing in length, and they preferentially form along TAR crests, resulting in small bedform repulsions and longer superposing ripples. Most of these ripples will be consumed by the TARs, an as-yet unreported growth dynamic for TARs that is consistent with the work of others, who have found a continuum between TARs and the meter-scale ripples that form on dunes. Constructing a DTM, orthorectifying HiRISE images, and measuring dune migration rates places the timescale of ripple absorption by TARs in a wake at several thousand years, with the first ∼1,000 years dominated by lateral linking of ripples. Assuming that TAR growth is accomplished entirely through dune burial and subsequent ripple consumption, we estimate a lower limit age of the TARs, and by extension, the dune field, to be ∼270 kyr.

scholarly journals The perigranitic W-Au Salau deposit (Pyrenees, France): polyphase genesis of a late Variscan intrusion related deposit

2021 ◽  
Vol 192 ◽  
pp. 22
Author(s):  
Thomas Poitrenaud ◽  
Éric Marcoux ◽  
Romain Augier ◽  
Marc Poujol
Keyword(s):  
3D Modeling ◽  
Main Part ◽  
Isotopic Analysis ◽  
Shear Zones ◽  
Coarse Grained ◽  
Axial Zone ◽  
The Past ◽  
Regional Deformation ◽  
Deposit Type ◽  
Ore Types

A field study combined with a laboratory study and 3D modeling have been performed in order to decipher the genesis of the Salau deposit W-Au mineralization (Pyrenees, France), one of the most important for tungsten in Europe. Results show the existence of two superimposed ore types, emplaced ca. 10 km depth and within decreasing temperature conditions: a calcic silicates skarn with rare scheelite and disseminated sulphides followed by a mineralized breccia with massive sulphides (pyrrhotite and chalcopyrite dominant), coarse-grained scheelite and gold, representing the main part of the ore mined in the past. This breccia is localized in ductile-brittle shear-zones which crosscut the granodiorite. U/Pb dating on zircon, apatite and scheelite, previously realized, confirmed this polyphase evolution. These two types of mineralization, linked to the emplacement of two successive intrusions as confirmed by sulphur isotopic analysis, granodioritic then leucogranitic, can be classified as belonging to the Intrusion-Related Gold Deposit type (IRGD). The emplacement of the high-grade gold and scheelite breccia was initiated by the progressive localization of the regional deformation in the Axial Zone of the Pyrenees during the Permian within E-W dextral-reverse faults.

scholarly journals Towards Repeatable, Scalable Graphene Integrated Micro-Nano Electromechanical Systems (MEMS/NEMS)

Micromachines ◽  
2021 ◽  
Vol 13 (1) ◽  
pp. 27
Author(s):  
Joon Hyong Cho ◽  
David Cayll ◽  
Dipankar Behera ◽  
Michael Cullinan
Keyword(s):  
Mass Production ◽  
Large Scale ◽  
Basic Research ◽  
Growth Mechanisms ◽  
Electromechanical Systems ◽  
Major Barrier ◽  
The Past ◽  
Integrated Devices ◽  
Graphene Devices ◽  
High Repeatability

The demand for graphene-based devices is rapidly growing but there are significant challenges for developing scalable and repeatable processes for the manufacturing of graphene devices. Basic research on understanding and controlling growth mechanisms have recently enabled various mass production approaches over the past decade. However, the integration of graphene with Micro-Nano Electromechanical Systems (MEMS/NEMS) has been especially challenging due to performance sensitivities of these systems to the production process. Therefore, ability to produce graphene-based devices on a large scale with high repeatability is still a major barrier to the commercialization of graphene. In this review article, we discuss the merits of integrating graphene into Micro-Nano Electromechanical Systems, current approaches for the mass production of graphene integrated devices, and propose solutions to overcome current manufacturing limits for the scalable and repeatable production of integrated graphene-based devices.

Gate Oxide Integrity as Affected by Hf Last Wafer Treatments and Passivating Techniques

1993 ◽  
Vol 303 ◽  
Author(s):  
R.C. Hawthorne ◽  
R.P.S. Thakur ◽  
K. Morinville ◽  
R. Kauffman
Keyword(s):  
Defect Density ◽  
Gate Oxide ◽  
Device Performance ◽  
Primary Process ◽  
Chemical Treatments ◽  
The Past ◽  
Performance Requirements ◽  
Wafer Cleaning ◽  
Processing Data ◽  
Wafer Surfaces

ABSTRACTAs device performance requirements increase, device features become smaller and films become thinner. The resultant sensitivity to defect density is such that controlling the condition of wafer surfaces prior to primary process steps becomes more and more critical. Wafer cleaning technologies of the past may not be optimum in providing needed device characteristics and reliability of tomorrow's semiconductors. In this paper, we compare the currently used RCA wafer clean chemistries to newer HF last, vapor dry technologies which use direct displacement of liquids to minimize contaminants. Subsequent passivation of these hydrophobic wafer surfaces is accomplished by various methods of oxidation including chemical treatments and RTP processing. Data collected from I-V, SIMS and DEFECT DENSITY testing will be included in the presentation.

scholarly journals Measuring Sand Dune Migration Rates with COSI-Corr and Landsat: Opportunities and Challenges

2019 ◽  
Vol 11 (20) ◽  
pp. 2423 ◽  
Author(s):  
Thomas Baird ◽  
Charlie Bristow ◽  
Pieter Vermeesch
Keyword(s):  
Sand Dune ◽  
Control Points ◽  
Migration Rates ◽  
Ground Control Points ◽  
Two Factors ◽  
Dune Migration ◽  
Level 1 ◽  
Bodele Depression ◽  
Processing Steps ◽  
Calculated Average

It has been over a decade since COSI-Corr, the Co-Registration of Optically Sensed Images and Correlation, was first used to produce a raster map of sand dune movement, however, no studies have yet applied it to the full Landsat archive. The orthorectified and geolocated Landsat Level-1 Precision Terrain (L1TP) products offer the opportunity to simplify the COSI-Corr pre-processing steps, allowing an automated workflow to be devised. In the Bodélé Depression, Chad, this automated workflow has calculated average dune speeds of 15.83 m/year and an increase in dune movement of 2.56 m/year ±12.58 m/year from 1987 to 2009. However, this increase does not stem from a systematic increase in dune mobility. The fastest 25% of dunes from 1987 to 1998 reduced their speed by 18.16%. The overall increase stems from the acceleration of features previously moving under 13.30 m/year. While successfully applied to the Bodélé Depression, the automated workflow produces highly variable outputs when applied to the Grand Erg Oriental, Algeria. Variations within path/row scene pairings are caused by the use of mobile features, such as dune crests, as ground control points (GCPs). This has the potential to warp Landsat scenes during the L1TP processing, potentially obfuscating dune migration. Two factors appear to be crucial in determining whether a Landsat scene is suitable for COSI-Corr analysis. Firstly, dune mobility must exceed the misregistration criteria. Secondly, GPCs should be located on static features such as bedrock outcrops.

scholarly journals Modelling desert dune fields based on discrete dynamics

2002 ◽  
Vol 7 (1) ◽  
pp. 7-17 ◽  
Author(s):  
Steven R. Bishop ◽  
Hiroshi Momiji ◽  
Ricardo Carretero-González ◽  
Andrew Warren
Keyword(s):  
Spatial Patterns ◽  
Lattice Dynamics ◽  
Sand Dunes ◽  
Mathematical Formulation ◽  
Discrete Dynamics ◽  
Physical Processes ◽  
Dune Field ◽  
Proposed Model ◽  
Dune Migration ◽  
Physical Features

A mathematical formulation is developed to model the dynamics of sand dunes. The physical processes display strong non-linearity that has been taken into account in the model. When assessing the success of such a model in capturing physical features we monitor morphology, dune growth, dune migration and spatial patterns within a dune field. Following recent advances, the proposed model is based on a discrete lattice dynamics approach with new features taken into account which reflect physically observed mechanisms.

MINERALOGY AS AN INDICATOR OF LONG-TERM CURRENT FLUCTUATIONS IN BAFFIN BAY

1966 ◽  
Vol 3 (2) ◽  
pp. 191-201 ◽  
Author(s):  
J. I. Marlowe
Keyword(s):  
Size Range ◽  
Coarse Sand ◽  
Coarse Grained ◽  
Current Fluctuations ◽  
Baffin Bay ◽  
Core Samples ◽  
The Past

A study of core samples from Baffin Bay indicates that gravel and coarse sand occur in all parts of the bay. Fragments in this size range are considered to have been transported into the area by floating ice. This coarse-grained sediment is rich in granitic detritus, but samples from an area within approximately 200 km of the Canadian coast also contain limestone fragments. The distribution of limestone fragments on the bottom coincides closely with the track of the Baffin Land current, in which icebergs originating in areas of limestone outcrop move southward through the bay. The distribution of limestone detritus in subbottom samples, however, suggests that the Baffin Land current has in the past flowed over a wider area than it does at present.

Late Holocene Varve Chronology and High-Resolution Records of Precipitation in the Central Tibetan Plateau

2020 ◽  
Author(s):  
Kejia Ji ◽  
Erlei Zhu ◽  
Guoqiang Chu ◽  
Juzhi Hou
Keyword(s):  
Tibetan Plateau ◽  
Lake Sediment ◽  
Sediment Cores ◽  
Coarse Grained ◽  
The Tibetan Plateau ◽  
Past Climate ◽  
Environment Changes ◽  
The Past ◽  
Varve Chronology ◽  
Past 2000 Years

<p>Precise age controls are fundamental prerequisites for reconstructing past climate and environment changes. Lakes on the Tibetan Plateau are one of the important archives for studying past climate and environment changes. However, radiocarbon ages for lake sediment core are subject to old radiocarbon reservoir effects, which caused severe problems in constructing age controls for lake sediment cores, especially on the Tibetan Plateau (TP). Here we present a varve chronology over the past 2000 years at Jiang Co on the central TP. The clastic-biogenic varves comprise of a coarse-grained layer and a fine-grained layer observed by petrographic microscope and Electron Probe Micro Analyzer. Varve chronology is supported by measurements of <sup>210</sup>Pb and <sup>137</sup>Cs, which is further used to determine the radiocarbon reservoir ages in the past ~2000 years. The percentage of coarse-grain layer thickness within single varves was considered as proxy for precipitation as the coarse grains were mainly transported by runoff, which is highly correlated with local meteorological observation. During the past 2000 years, the precipitation records show centennial-scale fluctuations that are consistent with regional records. The varve chronology at Jiang Co provides a valuable opportunity to examine variation in reservoir ages on the TP and a robust chronology for reconstructing paleoclimate.</p>

The Influence of Plastic Deformation on Lattice Defect Structure and Mechanical Properties of 316L Austenitic Stainless Steel

2017 ◽  
Vol 885 ◽  
pp. 13-18 ◽  
Author(s):  
Moustafa El-Tahawy ◽  
Jenő Gubicza ◽  
Yi Huang ◽  
Hye Lim Choi ◽  
Hee Man Choe ◽  
...  
Keyword(s):  
Plastic Deformation ◽  
Stainless Steel ◽  
Dislocation Density ◽  
Defect Structure ◽  
High Pressure Torsion ◽  
Defect Density ◽  
Lattice Defect ◽  
Coarse Grained ◽  
316L Austenitic Stainless Steel ◽  
Processed Sample

The effect of different plastic deformation methods on the phase composition, lattice defect structure and hardness in 316L stainless steel was studied. The initial coarse-grained γ-austenite was deformed by cold rolling (CR) or high-pressure torsion (HPT). It was found that the two methods yielded very different phase compositions and microstructures. Martensitic phase transformation was not observed during CR with a thickness reduction of 20%. In γ-austenite phase in addition to the high dislocation density (~10 × 1014 m-2) a significant amount of twin-faults was detected due to the low stacking fault energy. On the other hand, γ-austenite was gradually transformed into ε and α’-martensites with transformation sequences γ→ε→α’ during HPT deformation. A large dislocation density (~133 × 1014 m-2) was detected in the main phase (α’-martensite) at the periphery of the disk after 10 turns of HPT. The high defect density is accompanied by a very small grain size of ~45 nm in the HPT-processed sample, resulting in an very large hardness of 6130 MPa.

Sign in / Sign up

Export Citation Format

Share Document