Search results for "temperature gradient"
showing 10 items of 73 documents
Interferometric Z-scan method for thermo-optical effect studies
2021
We demonstrated a new approach to measuring third-order nonlinear optical effects using an experimental setup incorporating both Z-scan and Mach-Zehnder interferometer methods. This method could be especially purposive for thermo-optical effect studies as it can simultaneously probe thermal gradient profile as well as absolute temperature changes induced by an optical beam. The experimental setup was tested using chloroform. Experimental measurements were carried out using 1064 nm Nd:YAG laser with 8 ns pulse width and 40 kHz pulse repetition rate. The measured nonlinear refractive index of chloroform was mainly induced by the thermo-optical effect. As thermo-optical response depends on bea…
Spark Plasma Sintering tool design for preparing alumina-based Functionally Graded Materials
2016
Abstract A way to produce Functionally Graded Materials (FGM) is by means of Spark Plasma Sintering (SPS) and specifically designated tools. These new tools permit a current density modulation and therefore a temperature variation along the z-axis. The key feature relies on a varying die section. FEM modelling has given the suitable range of die dimensions between the top and the bottom to obtain a given temperature gradient (around 300 °C) out of roughly a 15 mm height. Experiments conducted in different configurations (with or without samples) and the measurement of the associated thermal gradient led to improvements of the mould (in particular the introduction of a counter-piston). By th…
Solidification microstructure during selective laser melting of Ni based superalloy: experiment and mesoscopic modelling
2019
International audience; A set of single track laser melting experiments was performed in a selective laser melting (SLM). The tracks were done on an Inconel 718 plate with various laser scan velocities at a constant laser power of 150 W. The geometries of the molten pool (MP), as well as the solidified dendrite structures, i.e., primary and secondary dendrite arm spacing (PDAS and SDAS), in the cross sections of the molten path were characterized to evaluate the effect of the laser scan velocity during SLM. Moreover, the local solidification thermal conditions (cooling rate R*, tip growth velocity V* and temperature gradient G*) at the MP bottom were deduced from the SDAS and the geometries…
Changes in chemical and biological soil properties as induced by anthropogenic disturbance: A case study of an agricultural soil under recurrent floo…
2006
Abstract Monitoring the environmental impact of anthropogenic disturbance on soil ecosystem is of great importance for optimizing strategies for soil use, conservation and remediation. The aim of this study was to assess whether and to what extent a long-term, human-induced disturbance could have affected main chemical and biological properties in an agricultural soil. The study site was a hazel (Corylus avellana L.) orchard located in the area surrounding the volcanic apparatus of Somma-Vesuvius (Southern Italy). For the last two decades, the site has been repeatedly subjected to floodings by wastewaters containing not only alluvial sediments but also potentially hazardous compounds from i…
Bridgman growth of paratellurite single crystals
2004
Abstract The growth of paratellurite single crystals by the vertical-gradient freezing technique is reported for the first time. Boules of 120 mm long and 25 mm in diameter were obtained under a temperature gradient of 10°C cm −1 and translation rates lower than 0.6 mm h −1 . The spatial distribution of defects along the growth axis reveals a continuous evolution of the free convective fluid-flow regime as growth proceeds. Gas bubbles and dark inclusions rejected to the periphery in the upper part of the crystal are observed to lay preferentially in (1 0 0), (0 0 1), ( 1 1 ¯ 0 ) and (1 1 2) crystallographic planes. Among them, SEM and microprobe analyses evidenced the presence of metallic p…
Transport properties of 2F = F2 in a temperature gradient as studied by molecular dynamics simulations
2007
International audience; We calculate transport properties of a reacting mixture of F and F2 from results of nonequilibrium molecular dynamics simulations. The reaction investigated is controlled by thermal diffusion and is close to local chemical equilibrium. The simulations show that a formulation of the transport problem in terms of classical non-equilibrium thermodynamics theory is sound. The chemical reaction has a large effect on the magnitude and temperature dependence of the thermal conductivity and the interdiffusion coefficient. The increase in the thermal conductivity in the presence of the chemical reaction, can be understood as a response to an imposed temperature gradient, whic…
Isolation and Characterization of Novosphingobium sp. Strain MT1, a Dominant Polychlorophenol-Degrading Strain in a Groundwater Bioremediation System
2002
ABSTRACT A high-rate fluidized-bed bioreactor has been treating polychlorophenol-contaminated groundwater in southern Finland at 5 to 8°C for over 6 years. We examined the microbial diversity of the bioreactor using three 16S ribosomal DNA (rDNA)-based methods: denaturing gradient gel electrophoresis, length heterogeneity-PCR analysis, and restriction fragment length polymorphism analysis. The molecular study revealed that the process was dependent on a stable bacterial community with low species diversity. The dominant organism, Novosphingobium sp. strain MT1, was isolated and characterized. Novosphingobium sp. strain MT1 degraded the main contaminants of the groundwater, 2,4,6-trichloroph…
The Root Mycobiota of Betula aetnensis Raf., an Endemic Tree Species Colonizing the Lavas of Mt. Etna (Italy)
2021
Betula aetnensis is an endemic tree of high conservation value, which thrives on the nutrient-poor volcanic soils of Mount Etna. Since plant–microbe interactions could play a crucial role in plant growth, resource uptake, and resistance to abiotic stresses, we aimed to characterize the root and rhizosphere microbial communities. Individuals from natural habitat (NAT) and forest nursery (NURS) were surveyed through microscopy observations and molecular tools: bacterial and fungal automated ribosomal intergenic spacer analysis (ARISA), fungal denaturing gradient gel electrophoresis (DGGE). B. aetnensis was found to be simultaneously colonized by arbuscular (AM), ectomycorrhizal (ECM), ericoid…
Transitions in a stratified Kolmogorov flow
2016
We study the Kolmogorov flow with weak stratification. We consider a stabilizing uniform temperature gradient and examine the transitions leading the flow to chaotic states. By solving the equations numerically we construct the bifurcation diagram describing how the Kolmogorov flow, through a sequence of transitions, passes from its laminar solution toward weakly chaotic states. We consider the case when the Richardson number (measure of the intensity of the temperature gradient) is $$Ri=10^{-5}$$ , and restrict our analysis to the range $$0<Re<30$$ . The effect of the stabilizing temperature is to shift bifurcation points and to reduce the region of existence of stable drifting states. The…
Lokalisatorischer Nachweis von Thermorezeptoren beiDorcus parallelepipedus L. undPyrrhocoris apterus L.
1951
A temperature gradient is described in which the temperature of the air is measured. The “avoiding reaction” of normal and partially amputated insects is established, and a comparison of the results shows that inDorcus parallelpipedus L. (Coleoptera) the 3 distal segments of the antennae and the maxillar palps are sensitive to temperature. Of great importance is the last segment of the antennae inPyrrhocoris apterus L. (Heteropterae), because after its removal, the “avoiding reaction” suddenly increases at 4° C. Probably the trichoid sensillae are specialized receptors for temperature; their number seems to be important for the sensitivity to temperature.