Search results for " Gradient"
showing 10 items of 575 documents
Thermoelectric current and magnetic field interaction influence on the structure of directionally solidified Sn-10 wt.%Pb alloy
2013
International audience; In this experimental work Sn-10 wt.% Pb alloy is directionally solidified in Bridgman setup at various growth velocities (from 0.5 mu m/s to 20 mu m/s) under transverse 0.4 T magnetic field. Temperature gradient of 8 K/mm is maintained perpendicular to the solidification direction during experiments. Liquid phase convection and its influence on the structure and segregation of an alloy, caused by magnetic field and thermoelectric current interaction (thermoelectromagnetic convection or TEMC) is studied experimentally and estimated theoretically in this work. Detailed velocity order of magnitude estimation is carried out. Besides optical microscopy, component distribu…
Ab initio studies on the lattice thermal conductivity of silicon clathrate frameworks II and VIII
2016
The lattice thermal conductivities of silicon clathrate frameworks II and VIII are investigated by using ab initio lattice dynamics and iterative solution of the linearized Boltzmann transport equation(BTE) for phonons. Within the temperature range 100-350 K, the clathrate structures II and VIII were found to have lower lattice thermal conductivity values than silicon diamond structure (d-Si) by factors of 1/2 and 1/5, respectively. The main reason for the lower lattice thermal conductivity of the clathrate structure II in comparison to d-Si was found to be the harmonic phonon spectra, while in the case of the clathrate structure VIII, the difference is mainly due to the harmonic phonon spe…
Conoscopic Studies of Optical Homogeneity of the LiNbO3:Mg Crystals
2012
An essential modification of the method to observe large-scale conoscopic images is proposed. Divergent beam of wide-aperture radiation is formed by a diffuser placed before entrance of a lithium niobate crystal. The optical homogeneity of LiNbO3:Mg crystals is studied in a wide range of the admixture concentrations (0.01 – 5.5 mol.%). An inhomogeneous distribution of the admixture is found to increase with the admixture concentration being accompanied by growth bands, micro-defects, such as micro-domains, domain boundaries, and block structures particularly in parts of higher concentration gradients at the boundaries of the growth bands.
Magnetic Field Gradiometer with Sub-Micron Spatial Resolution Based on Caesium Vapour in an Extremely Thin Cell
2015
Abstract In this paper we present a device for measuring the magnetic field and its gradient with a spatial resolution of several hundred nanometres. This device is based on caesium metal vapour confined to an extremely thin cell (ETC). To measure magnetic signals, we use absorption and very low laser powers, which might be appealing for modern fabrication techniques. A portable, fully automated device was constructed.
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…
A plasticity model for predicting the rheological behavior of paperboard
2017
The sorption of water into the paperboard exposes a container to reversible and irreversible deformations under relative humidity variations. In this study, an elasto-plastic material model is used to demonstrate how through-thickness dry solids content gradients can generate permanent in-plane strains in paperboard. The measurements presented in this paper indicate that in consecutive loading-unloading cycles, the yield stress either remains roughly constant or decreases, and an additional permanent set of strain is obtained even when the maximum tension of repetitions stays constant. Two modified approaches concerning elasto-plastic hardening behavior based on the measurements of this wor…
Direct Numerical Methods for Optimal Control Problems
2003
Development of interior point methods for linear and quadratic programming problems occurred during the 1990’s. Because of their simplicity and their convergence properties, interior point methods are attractive solvers for such problems. Moreover, extensions have been made to more general convex programming problems.
Least-Norm Regularization For Weak Two-Level Optimization Problems
1992
In this paper, we consider a regularization for weak two-level optimization problems by adaptation of the method presented by Solohovic (1970). Existence and approximation results are given in the case in which the constraints to the lower level problems are described by a multifunction. Convergence results for the least-norm regularization under perturbations are also presented.
Higher integrability and stability of (p,q)-quasiminimizers
2023
Using purely variational methods, we prove local and global higher integrability results for upper gradients of quasiminimizers of a $(p,q)$-Dirichlet integral with fixed boundary data, assuming it belongs to a slightly better Newtonian space. We also obtain a stability property with respect to the varying exponents $p$ and $q$. The setting is a doubling metric measure space supporting a Poincar\'e inequality.