Search results for "MATTER"
showing 10 items of 16762 documents
Grain boundary ridges slow dawn grain boundary motion: In-situ observation
2014
Abstract The impact of grain boundary (GB) ridge on motion of high-angle GB in Zn was studied. The steady-state motion of faceted GB half-loop with [ 10 1 ¯ 0 ] tilt GB and GB ridge was recorded in-situ. The temperatures of faceting–roughening transition were experimentally defined for three GB half-loops. Above the transition temperature GB half-loops had GB “rough-to-rough” ridge with continuously curved GB segments. Below the transition temperature a facet appeared and coexisted with two “facet-to-rough” ridges. For the first time we could extract mobility of “rough-to-rough” and “rough-to-facet” ridges and bring out clearly that GB ridge slows down GB motion. Present removes contradicti…
The effect of plasticity in crumpling of thin sheets
2008
Bridging the gap between theoretical and experimental work to understand the effect of plasticity on the crumpling of thin sheets into a small volume has proved difficult. A realistic numerical model now makes a distinction between elastic and elasto-plastic behaviour. Crumpling a thin sheet of material into a small volume requires energy for creating a network of deformations such as vertices and ridges1,2. Scaling properties of a single elastic vertex3,4,5 or ridge have been analysed theoretically6,7,8, and crumpling of a sheet by numerical simulations1,9,10. Real materials are however elasto-plastic11,12,13,14,15 and large local strains induce irreversible plastic deformations. Hence, a …
Acoustic spectroscopy of aerogel precursors
2007
We investigate the acoustical properties of silica gels, which are precursors in the aerogel production process. These gels exhibit a strong “ringing gel” behavior, that is they emit a characteristic sound if one knocks against the container. We study this sound emission with a very simple spectroscopic technique and observe resonances which are characteristic for natural frequencies of a cylindrical body. From a fit of the experimental frequency positions to calculated values, we determine a sound velocity of c T = 4 m/s for a gel sample with porosity φ = 97.5%. This low sound velocity can only be interpreted as the transverse sound mode predicted by Biot’s theory for sound propagation in …
Numerical study of silicon crystal ridge growth
2014
Abstract The size of the ridge-like protrusions appearing on the external surface of dislocation-free 〈 100 〉 silicon crystals grown from a melt was studied theoretically. According to existing models the growth of the ridges is caused by the presence of { 111 } crystal planes at the crystal–melt interface. They affect the height of triple phase line, free surface orientation and the crystal growth angle. A numerical 2-dimensional model was proposed for the calculation of the size of the crystal ridges. The model included the effect of the undercooling of the crystal–melt interface on the crystal growth angle. The numerical model estimated the effect of the ridge size on the free surface at…
Precipitation Pulses and Soil CO2 Emission in Desert Shrubland of Artemisia ordosica on the Ordos Plateau of Inner Mongolia, China
2009
National Natural Science Foundation of China [40730105, 40501072, 40673067]; National Key Basic Research Program (973 Program) of China [2002CB412503]; Chinese Academy of Sciences [KZCX2-YW-149]
Deterministic folding in stiff elastic membranes.
2008
Crumpled membranes have been found to be characterized by complex patterns of spatially seemingly random facets separated by narrow ridges of high elastic energy. We demonstrate by numerical simulations that compression of stiff elastic membranes with small randomness in their initial configurations leads to either random ridge configurations (high entropy) or nearly deterministic folds (low elastic energy). For folding with symmetric ridge configurations to appear in part of the crumpling processes, the crumpling rate must be slow enough. Folding stops when the thickness of the folded structure becomes important, and crumpling continues thereafter as a random process.
The effect of the pore structure and zeta potential of porous polymer monoliths on separation performance in ion-exchange mode.
2007
Most often, in bioseparations involving charged macromolecules, the chromatographic systems have low Reynolds and high Peclet numbers. For such systems, an expression is developed and presented in this work for evaluating the throughput in polymeric monoliths where ion-exchange adsorption occurs, as a function of (i) the pressure drop along the length of the monolith, (ii) the functional form and width of the throughpore-size distribution of the monolith, and (iii) the magnitude of the zeta potential on the surface of the throughpores of the monolith. Gaussian and log-normal throughpore-size distributions whose mean throughpore-size and standard deviation values are based on experimentally …
Drained organic soils under agriculture — The more degraded the soil the higher the specific basal respiration
2019
Abstract Drained peatlands are hotspots of carbon dioxide (CO2) emissions from agricultural soils. As a consequence of both drainage-induced mineralisation and anthropogenic mixing with mineral soils, large areas of former peatlands under agricultural use underwent a secondary transformation of the peat (e.g. formation of aggregates). These soils show contents of soil organic carbon (SOC) at the boundary between mineral and organic soils. However, the carbon (C) dynamics of such soils have rarely been studied so far. The aim of the present study was to evaluate the vulnerability of soil organic matter (SOM) to decomposition over the whole range of peat-derived soils under agriculture includ…
A pedotransfer function for estimating the soil erodibility factor in Sicily
2009
The soil erodibility factor, K, of the Universal Soil Loss Equation (USLE) is a simple descriptor of the soil susceptibility to rill and interrill erosion. The original procedure for determining K needs a knowledge of soil particle size distribution (PSD), soil organic matter, OM, content, and soil structure and permeability characteristics. However, OM data are often missing and soil structure and permeability are not easily evaluated in regional analyses. The objective of this investigation was to develop a pedotransfer function (PTF) for estimating the K factor of the USLE in Sicily (south Italy) using only soil textural data. The nomograph soil erodibility factor and its associated firs…
Politiskā līdzdalība, Latvijas gadījums, starptautiskie protesti
2021
Pētnieciskā darba nosaukums ir: “Politiskā līdzdalība, Latvijas gadījums, starptautiskie protesti”. Pētījuma ietvaros izvirzītais mērķis ir sekojošs - izprast galvenos iemeslus, kāpēc cilvēki piedalās vai nepiedalās protestos. Darba izpētes jautājums tiek izvirzīts- kāpēc Latvijas iedzīvotāju līdzdalība starptautiskos protestos ir tik zema un kāpēc protesti uzrunā/neuzrunā iedzīvotājus. Bakalaura darba teorētiskās daļas pirmajā apakšnodaļā tika aplūkota protesta kā jēdziena definēšana un tā nozīme politikā, tostarp, kas veicina līdzdalību protestos un protestu ietekme. Pētnieciskā darba teorētiskās daļas otrajā apakšnodaļā tika apskatīti iemesli, kāpēc cilvēki nepiedalās protestos. Teorētis…