9,481 research outputs found
Application of Image Analysis for the Identification of Prehistoric Ceramic Production Technologies in the North Caucasus (Russia, Bronze/Iron Age)
The recent advances in microscopy and scanning techniques enabled the image analysis of archaeological objects in a high resolution. From the direct measurements in images, shapes and related parameters of the structural elements of interest can be derived. In this study, image analysis in 2D/3D is applied to archaeological ceramics, in order to obtain clues about the ceramic pastes, firing and shaping techniques. Images were acquired by the polarized light microscope, scanning electron microscopy (SEM) and 3D micro X-ray computed tomography (µ-CT) and segmented using Matlab. 70 ceramic sherds excavated at Ransyrt 1 (Middle-Late Bronze Age) and Kabardinka 2 (late Bronze–early Iron Age), located in in the North Caucasian mountains, Russia, were investigated. The size distribution, circularity and sphericity of sand grains in the ceramics show site specific difference as well as variations within a site. The sphericity, surface area, volume and Euler characteristic of pores show the existence of various pyrometamorphic states between the ceramics and within a ceramic. Using alignments of pores and grains, similar pottery shaping techniques are identified for both sites. These results show that the image analysis of archaeological ceramics can provide detailed information about the prehistoric ceramic production technologies with fast data availability
Gas transport in partially-saturated sand packs
Understanding gas transport in porous media and its mechanism has broad
applications in various research areas, such as carbon sequestration in deep
saline aquifers and gas explorations in reservoir rocks. Gas transport is
mainly controlled by pore space geometrical and morphological characteristics.
In this study, we apply a physically-based model developed using concepts from
percolation theory (PT) and the effective-medium approximation (EMA) to better
understand diffusion and permeability of gas in packings of angular and rounded
sand grains as well as glass beads. Two average sizes of grain i.e., 0.3 and
0.5 mm were used to pack sands in a column of 6 cm height and 4.9 cm diameter
so that the total porosity of all packs was near 0.4. Water content, gas-filled
porosity (also known as gas content), gas diffusion, and gas permeability were
measured at different capillary pressures. The X-ray computed tomography method
and the 3DMA-Rock software package were applied to determine the average pore
coordination number z. Results showed that both saturation-dependent diffusion
and permeability of gas showed almost linear behavior at higher gas-filled
porosities, while deviated substantially from linear scaling at lower gas
saturations. Comparing the theory with the diffusion and permeability
experiments showed that the determined value of z ranged between 2.8 and 5.3,
not greatly different from X-ray computed tomography results. The obtained
results clearly indicate that the effect of the pore-throat size distribution
on gas diffusion and permeability was minimal in these sand and glass bead
packs
Observations of Backscatter from Sand and Gravel Seafloors Between 170-250 kHz
Interpreting observations of frequency-dependence in backscatter from the seafloor offers many challenges, either because multiple frequencies are used for different observations that will later be merged or simply because seafloor scattering models are not well-understood above 100 kHz. Hindering the understanding of these observations is the paucity of reported, calibratedacoustic measurements above 100 kHz. This manuscript seeks to help elucidate the linkages between seafloor properties and frequency-dependent seafloor backscatter by describing observations of backscatter collected from sand, gravel, and bedrock seafloors at frequencies between 170 and 250 kHz and at a grazing angle of 45°. Overall, the frequency dependence appeared weak for all seafloor types, with a slight increase in seafloor scattering strength with increasing frequency for an area with unimodal, very poorly to moderately well sorted, slightly granular to granular medium sand with significant amounts of shell debris and a slight decrease in all other locations
Effect of impurities on morphology and growth mode of (111) and (001) epitaxial-like ScN films
ScN material is an emerging semiconductor with an indirect bandgap. It has
attracted attention for its thermoelectric properties, use as seed layers, and
for alloys for piezoelectric application. ScN or other transition metal nitride
semiconductors used for their interesting electrical properties are sensitive
to contaminants, such as oxygen or fluorine. In this present article, the
influence of depositions conditions on the amount of oxygen contaminants
incorporated in ScN films were investigated and their effects on the electrical
properties (electrical resistivity and Seebeck coefficient) were studied. The
epitaxial-like films of thickness 125 +-5 nm to 155 +-5 nm were deposited by
D.C.-magnetron sputtering on c-plane Al2O3, MgO(111) and r-plane Al2O3 at a
substrate temperature ranging from 700 to 950 degree C. The amount of oxygen
contaminants presents in the film, dissolved into ScN or as an oxide, was
related to the adatom mobility during growth, which is affected by the
deposition temperature and the presence of twin domain growth. The lowest
values of electrical resistivity of 50 micro-ohm cm were obtained on
ScN(111)/MgO(111) and on ScN(001)/r-plane Al2O3 grown at 950 degree C with no
twin domains and the lowest amount of oxygen contaminant. At the best, the
films exhibited an electrical resistivity of 50 micro-ohm cm with Seebeck
coefficient values maintained at -40 microV K-1, thus a power factor estimated
at 3.2 10-3 W m-1 K-2 (at room temperature)
Use of visible, near-infrared, and thermal infrared remote sensing to study soil moisture
Two methods are described which are used to estimate soil moisture remotely using the 0.4- to 14.0 micron wavelength region: (1) measurement of spectral reflectance, and (2) measurement of soil temperature. The reflectance method is based on observations which show that directional reflectance decreases as soil moisture increases for a given material. The soil temperature method is based on observations which show that differences between daytime and nighttime soil temperatures decrease as moisture content increases for a given material. In some circumstances, separate reflectance or temperature measurements yield ambiguous data, in which case these two methods may be combined to obtain a valid soil moisture determination. In this combined approach, reflectance is used to estimate low moisture levels; and thermal inertia (or thermal diffusivity) is used to estimate higher levels. The reflectance method appears promising for surface estimates of soil moisture, whereas the temperature method appears promising for estimates of near-subsurface (0 to 10 cm)
Revolving rivers in sandpiles: from continuous to intermittent flows
In a previous paper [Phys. Rev. Lett. 91, 014501 (2003)], the mechanism of
"revolving rivers" for sandpile formation is reported: as a steady stream of
dry sand is poured onto a horizontal surface, a pile forms which has a river of
sand on one side owing from the apex of the pile to the edge of the base. For
small piles the river is steady, or continuous. For larger piles, it becomes
intermittent. In this paper we establish experimentally the "dynamical phase
diagram" of the continuous and intermittent regimes, and give further details
of the piles topography, improving the previous kinematic model to describe it
and shedding further light on the mechanisms of river formation. Based on
experiments in Hele-Shaw cells, we also propose that a simple dimensionality
reduction argument can explain the transition between the continuous and
intermittent dynamics.Comment: 8 pages, 11 figures, submitted to Phys Rev
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