scholarly journals The near-surface evening transition

2017 ◽  
Vol 143 (708) ◽  
pp. 2940-2948 ◽  
Author(s):  
L. Mahrt
Keyword(s):  
Near Surface ◽  
Evening Transition

An Analysis of the Processes Affecting Rapid Near-Surface Water Vapor Increases during the Afternoon to Evening Transition in Oklahoma

2019 ◽  
Vol 58 (10) ◽  
pp. 2217-2234 ◽  
Author(s):  
W. G. Blumberg ◽  
D. D. Turner ◽  
S. M. Cavallo ◽  
Jidong Gao ◽  
J. Basara ◽  
...  
Keyword(s):  
Water Vapor ◽  
Surface Water ◽  
Surface Cooling ◽  
Near Surface ◽  
Evening Transition ◽  
Relative Contribution ◽  
Oklahoma Mesonet ◽  
Conditional Instability ◽  
Water Vapor Mixing Ratio ◽  
Spring Harvest

AbstractThis study used 20 years of Oklahoma Mesonet data to investigate the changes of near-surface water vapor mixing ratio qυ during the afternoon to evening transition (AET). Similar to past studies, increases in qυ are found to occur near sunset. However, the location, magnitude, and timing of the qυ maximum occurring during the AET are shown to be dependent on the seasonal growth and harvest of vegetation across Oklahoma in the spring and summer months. Particularly, the late spring harvest of winter wheat grown in Oklahoma appears to modify the relative contribution of local and nonlocal processes on qυ. By analyzing time series of qυ during the AET, it is found that the likelihood of a presunset qυ maximum is strongly dependent upon vegetation, soil moisture, wind speed, and cloud cover. Analysis also reveals that the increase in qυ during the AET can increase the parcel conditional instability despite the surface cooling produced by loss of insolation. Next to known changes in low-level wind shear, these changes in instability and moisture demonstrate new ways the AET can modify the presence of the key ingredients relevant to explaining the climatological increase in severe convective storm hazards around sunset.

Benthic foraminiferal zonation in deep-water carbonate platform margin environments, northern Little Bahama Bank

1988 ◽  
Vol 62 (01) ◽  
pp. 1-8 ◽  
Author(s):  
Ronald E. Martin
Keyword(s):  
Deep Water ◽  
Benthic Foraminifera ◽  
Carbonate Platform ◽  
Sedimentary Facies ◽  
Depositional Environments ◽  
Near Surface ◽  
Sediment Gravity Flows ◽  
Gravity Flows ◽  
Platform Margin ◽  
Water Carbonate

The utility of benthic foraminifera in bathymetric interpretation of clastic depositional environments is well established. In contrast, bathymetric distribution of benthic foraminifera in deep-water carbonate environments has been largely neglected. Approximately 260 species and morphotypes of benthic foraminifera were identified from 12 piston core tops and grab samples collected along two traverses 25 km apart across the northern windward margin of Little Bahama Bank at depths of 275-1,135 m. Certain species and operational taxonomic groups of benthic foraminifera correspond to major near-surface sedimentary facies of the windward margin of Little Bahama Bank and serve as reliable depth indicators. Globocassidulina subglobosa, Cibicides rugosus, and Cibicides wuellerstorfi are all reliable depth indicators, being most abundant at depths >1,000 m, and are found in lower slope periplatform aprons, which are primarily comprised of sediment gravity flows. Reef-dwelling peneroplids and soritids (suborder Miliolina) and rotaliines (suborder Rotaliina) are most abundant at depths <300 m, reflecting downslope bottom transport in proximity to bank-margin reefs. Small miliolines, rosalinids, and discorbids are abundant in periplatform ooze at depths <300 m and are winnowed from the carbonate platform. Increased variation in assemblage diversity below 900 m reflects mixing of shallow- and deep-water species by sediment gravity flows.

Analysis of 2D and 3D defects associated with precipitation of Cu in silicon

1991 ◽  
Vol 49 ◽  
pp. 870-871
Author(s):  
P.M. Rice ◽  
MJ. Kim ◽  
R.W. Carpenter
Keyword(s):  
Colony Growth ◽  
Dark Field ◽  
Dark Side ◽  
Silicide Phase ◽  
Strain Fields ◽  
Near Surface ◽  
Unknown Composition ◽  
Secondary Precipitates ◽  
20 Nm ◽  
2D And 3D

Extrinsic gettering of Cu on near-surface dislocations in Si has been the topic of recent investigation. It was shown that the Cu precipitated hetergeneously on dislocations as Cu silicide along with voids, and also with a secondary planar precipitate of unknown composition. Here we report the results of investigations of the sense of the strain fields about the large (~100 nm) silicide precipitates, and further analysis of the small (~10-20 nm) planar precipitates.Numerous dark field images were analyzed in accordance with Ashby and Brown's criteria for determining the sense of the strain fields about precipitates. While the situation is complicated by the presence of dislocations and secondary precipitates, micrographs like those shown in Fig. 1(a) and 1(b) tend to show anomalously wide strain fields with the dark side on the side of negative g, indicating the strain fields about the silicide precipitates are vacancy in nature. This is in conflict with information reported on the η'' phase (the Cu silicide phase presumed to precipitate within the bulk) whose interstitial strain field is considered responsible for the interstitial Si atoms which cause the bounding dislocation to expand during star colony growth.

Shock consolidation of Ni-Ti alloy powder

1986 ◽  
Vol 44 ◽  
pp. 430-431
Author(s):  
Naresh N. Thadhani ◽  
Thad Vreeland ◽  
Thomas J. Ahrens
Keyword(s):  
Alloy Powder ◽  
Amorphous Material ◽  
Ti Alloy ◽  
Two Phase ◽  
Near Surface ◽  
Optical Micrograph ◽  
Shock Compaction ◽  
Powder Particles ◽  
Ti Powder ◽  
Rapidly Solidified

A spherically-shaped, microcrystalline Ni-Ti alloy powder having fairly nonhomogeneous particle size distribution and chemical composition was consolidated with shock input energy of 316 kJ/kg. In the process of consolidation, shock energy is preferentially input at particle surfaces, resulting in melting of near-surface material and interparticle welding. The Ni-Ti powder particles were 2-60 μm in diameter (Fig. 1). About 30-40% of the powder particles were Ni-65wt% and balance were Ni-45wt%Ti (estimated by EMPA).Upon shock compaction, the two phase Ni-Ti powder particles were bonded together by the interparticle melt which rapidly solidified, usually to amorphous material. Fig. 2 is an optical micrograph (in plane of shock) of the consolidated Ni-Ti alloy powder, showing the particles with different etching contrast.

Preparation of cross-sectional samples for near-surface TEM studies

1987 ◽  
Vol 45 ◽  
pp. 380-381
Author(s):  
R.C. Dickenson ◽  
K.R. Lawless
Keyword(s):  
Standard Sample ◽  
Surface Region ◽  
Specimen Preparation ◽  
Thick Sheet ◽  
Drill Bit ◽  
Sample Holder ◽  
Metal Interface ◽  
Cross Sectional ◽  
Near Surface ◽  
Cold Worked

In thermal oxidation studies, the structure of the oxide-metal interface and the near-surface region is of great importance. A technique has been developed for constructing cross-sectional samples of oxidized aluminum alloys, which reveal these regions. The specimen preparation procedure is as follows: An ultra-sonic drill is used to cut a 3mm diameter disc from a 1.0mm thick sheet of the material. The disc is mounted on a brass block with low-melting wax, and a 1.0mm hole is drilled in the disc using a #60 drill bit. The drill is positioned so that the edge of the hole is tangent to the center of the disc (Fig. 1) . The disc is removed from the mount and cleaned with acetone to remove any traces of wax. To remove the cold-worked layer from the surface of the hole, the disc is placed in a standard sample holder for a Tenupol electropolisher so that the hole is in the center of the area to be polished.

Near-Surface Aggregation of Sn In Heavily Sn-Doped GaAs Films Grown By Molecular Beam Epitaxy

1985 ◽  
Vol 43 ◽  
pp. 368-369
Author(s):  
S. H. Chen
Keyword(s):  
Molecular Beam Epitaxy ◽  
Cross Section ◽  
Electron Spectroscopy ◽  
Molecular Beam ◽  
Surface Segregation ◽  
Secondary Ion Mass Spectrometry ◽  
Specimen Preparation ◽  
Near Surface ◽  
Gaas Films ◽  
Secondary Ion

Sn has been used extensively as an n-type dopant in GaAs grown by molecular-beam epitaxy (MBE). The surface accumulation of Sn during the growth of Sn-doped GaAs has been observed by several investigators. It is still not clear whether the accumulation of Sn is a kinetically hindered process, as proposed first by Wood and Joyce, or surface segregation due to thermodynamic factors. The proposed donor-incorporation mechanisms were based on experimental results from such techniques as secondary ion mass spectrometry, Auger electron spectroscopy, and C-V measurements. In the present study, electron microscopy was used in combination with cross-section specimen preparation. The information on the morphology and microstructure of the surface accumulation can be obtained in a fine scale and may confirm several suggestions from indirect experimental evidence in the previous studies.

Specimen Preparation of Near Surface Ion Irradiated Samples

1985 ◽  
Vol 43 ◽  
pp. 170-171
Author(s):  
K. F. Russell ◽  
L. L. Horton
Keyword(s):  
Radiation Damage ◽  
Heavy Ions ◽  
Target Material ◽  
Metal Alloys ◽  
Specimen Surface ◽  
Specimen Preparation ◽  
Particle Accelerators ◽  
Near Surface ◽  
Graaff Accelerator ◽  
Van De Graaff

Beams of heavy ions from particle accelerators are used to produce radiation damage in metal alloys. The damaged layer extends several microns below the surface of the specimen with the maximum damage and depth dependent upon the energy of the ions, type of ions, and target material. Using 4 MeV heavy ions from a Van de Graaff accelerator causes peak damage approximately 1 μm below the specimen surface. To study this area, it is necessary to remove a thickness of approximately 1 μm of damaged metal from the surface (referred to as “sectioning“) and to electropolish this region to electron transparency from the unirradiated surface (referred to as “backthinning“). We have developed electropolishing techniques to obtain electron transparent regions at any depth below the surface of a standard TEM disk. These techniques may be applied wherever TEM information is needed at a specific subsurface position.

Comparison of Ion-Milling Techniques For Cross-Sectional TEM of Semiconductors

1985 ◽  
Vol 43 ◽  
pp. 166-167
Author(s):  
Julia T. Luck ◽  
C. W. Boggs ◽  
S. J. Pennycook
Keyword(s):  
Analytical Techniques ◽  
Sample Surface ◽  
Ion Milling ◽  
Cross Sectional ◽  
Reliable Technique ◽  
Near Surface ◽  
Transmission Electron ◽  
Thin Region ◽  
Transient Thermal

The use of cross-sectional Transmission Electron Microscopy (TEM) has become invaluable for the characterization of the near-surface regions of semiconductors following ion-implantation and/or transient thermal processing. A fast and reliable technique is required which produces a large thin region while preserving the original sample surface. New analytical techniques, particularly the direct imaging of dopant distributions, also require good thickness uniformity. Two methods of ion milling are commonly used, and are compared below. The older method involves milling with a single gun from each side in turn, whereas a newer method uses two guns to mill from both sides simultaneously.

Preparation of Backthinned Ceramic Specimens

1985 ◽  
Vol 43 ◽  
pp. 182-183
Author(s):  
A. T. Fisher ◽  
P. Angelini
Keyword(s):  
Electron Microscopy ◽  
Analytical Electron Microscopy ◽  
Vacuum System ◽  
Back Surface ◽  
Surface Microstructure ◽  
Ion Milling ◽  
Near Surface ◽  
Depth Profiles ◽  
Analytical Electron ◽  
Ion Implanted

Analytical electron microscopy (AEM) of the near surface microstructure of ion implanted ceramics can provide much information about these materials. Backthinning of specimens results in relatively large thin areas for analysis of precipitates, voids, dislocations, depth profiles of implanted species and other features. One of the most critical stages in the backthinning process is the ion milling procedure. Material sputtered during ion milling can redeposit on the back surface thereby contaminating the specimen with impurities such as Fe, Cr, Ni, Mo, Si, etc. These impurities may originate from the specimen, specimen platform and clamping plates, vacuum system, and other components. The contamination may take the form of discrete particles or continuous films [Fig. 1] and compromises many of the compositional and microstructural analyses. A method is being developed to protect the implanted surface by coating it with NaCl prior to backthinning. Impurities which deposit on the continuous NaCl film during ion milling are removed by immersing the specimen in water and floating the contaminants from the specimen as the salt dissolves.

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