Papers by Keyword: Concentration Gradient

Abstract: As the single molecules detection tool, nanopore is applied in more and more fields, such as medicine controlled delivery, ion conductance microscopes, nanosensors and DNA sequencing. When molecules pass through a nanopore, they will physically block the pore and produce measurable changes in ionic currents under an external electrical potential. Based on analyzing the resultant electrical signals, it is possible to detect various bio-molecules.Generally, the capturing ratio of nanopre for molecules is dependent on the intensity of electrical potential, to which the duration time of event is inversely proportional. It is difficult to analyze the too short duration time. Therefore, we investigate the study on concentration gradient of ionic solution effect on the capturing ratio of nanopore for DNA, which is in order to get the higher capturing ratio with the invariant duration time.In the experiments, we add different concentration solution in trans and cis parts of naopore separately to form the concentration gradient. We use three different types nanopore (α-hemolysin nanopore, Si3N4 membrane nanopore, glass capillary nanopore) to compare and get the similar results. The events of DNA translocating through nanopore are observed more compressed during the fixed time under the higher concentration gradient and there is no change to the duration time of DNA passing through the nanopore. It is demonstrated that concentration gradient could increase the capturing ratio of nanopore for DNA.

Abstract: The surface properties of W-implanted H13 steel are investigated using pulse multi-charged ion implantation. Computer simulations based on the binary collision approximation, TRIDYN, have been applied to calculate the concentration depth profiles of implanted tungsten ions in H13 steel. The calculated result by TRIDYN program is compared with that from experimental results. The factors affecting the surface properties of W-implanted H13 steel have been discussed. The radiation enhanced diffusion induced by spike is the main factor affecting the concentration depth profile. Compared with single energy ion implantation, the multi-charged ion implantation will make the concentration gradient become small, which is conducive to the formation of a kind of relatively uniform surface structure, and further improve the wear resistance of H13 steel.

Abstract: It is crucial to know the distribution coefficients of chemical elements in melts. This is essential for obtaining a given composition and properties of epitaxial layers grown from the liquid phase, for determining the regimes of high purification of materials obtained by zone melting, for producing the desired gradient of distribution of alloying elements throughout the layers of construction materials treated by chemical-thermal methods, etc. This paper presents the results of computing the distribution coefficient of arsenic during the growth of layers of phosphide-arsenide of gallium from the liquid phase (molten gallium), saturated with phosphorus. We also obtain the dependencies between the distribution coefficient of arsenic, the temperature and the concentration of arsenic inside the gallium melt during the growth of epitaxial layers. As well a practical application of the results with a given gradient of concentration for the gallium arsenide layer is demonstrated.

Abstract: An experimental approach employing temperature and concentration gradients is presented that is suitable for determining impurity diffusion coefficients in a single experimental cycle. The Al-Cu system is used to illustrate the feasibility of the method. In a single phase α-Al solid solution, concentration gradients are generated by exposing a cylindrical sample to steep temperature gradients and by annealing until the initially formed mushy zone is re-solidified. The annealing is performed such that a symmetric, ramp shaped profile in the form of a roof is generated. The sample is then again exposed to a temperature gradient at somewhat lower temperatures for an extended time period. The symmetric profile then becomes asymmetric due to the varying diffusion coefficient along the sample. Information on the pre-exponential factor D₀ and the activation energy for diffusion Q_D is retrieved from the asymmetry of the resulting concentration profile. The asymmetry becomes increasingly pronounced with longer diffusion times, yielding an increasing accuracy of the diffusion coefficients. The experimental approach is generally applicable to alloy systems with finite solubility.