5,931 research outputs found
Multiscale modelling of the influence of convection on dendrite formation and freckle initiation during vacuum arc remelting
Vacuum Arc Remelting (VAR) is employed to produce homogeneous ingots with a
controlled, fine, microstructure. It is applied to reactive and segregation prone alloys
where convection can influence microstructure and defect formation. In this study, a
microscopic solidification model was extended to incorporate both forced and natural
convection. The Navier-Stokes equations were solved for liquid and mushy zones using a
modified projection method. The energy conservation and solute diffusion equations
were solved via a combined stochastic nucleation approach along with a finite difference
solution to simulate dendritic growth. This microscopic model was coupled to a 3D
transient VAR model which was developed by using a multi-physics modelling software
package, PHYSICA. The multiscale model enables simulations covering the range from
dendrites (in microns) to the complete process (in meters). These numerical models were
used to investigate: (i) the formation of dendritic microstructures under natural and forced
convections; (ii) initiation of solute channels (freckles) in directional solidification in
terms of interdendritic thermosolutal convection; and (iii) the macroscopic physical
dynamics in VAR and their influence on freckle formation.
2D and 3D dendritic microstructure were simulated by taking into account both solutal
and thermal diffusion for both constrained and unconstrained growth using the
solidification model. For unconstrained equiaxed dendritic growth, forced convection
was found to enhance dendritic growth in the upstream region while retarding
downstream growth. In terms of dimensionality, dendritic growth in 3D is faster than 2D
and convection promotes the coarsening of perpendicular arms and side branching in 3D.
For constrained columnar dendritic growth, downward interdendritic convection is
stopped by primary dendritic arms in 2D; this was not the case in 3D. Consequently, 3D
simulations must be used when studying thermosolutal convection during solidification,
since 2D simulations lead to inappropriate results. The microscopic model was also used
to study the initiation of freckles for Pb-Sn alloys, predicting solute channel formation
during directional solidification at a microstructural level for the first time. These
simulations show that the local remelting due to high solute concentrations and
continuous upward convection of segregated liquid result in the formation of sustained
open solute channels. High initial Sn compositions, low casting speeds and low
temperature gradients, all promote the initiation of these solute channels and hence
freckles.
to study the initiation of freckles for Pb-Sn alloys, predicting solute channel formation
during directional solidification at a microstructural level for the first time. These
simulations show that the local remelting due to high solute concentrations and
continuous upward convection of segregated liquid result in the formation of sustained
open solute channels. High initial Sn compositions, low casting speeds and low
temperature gradients, all promote the initiation of these solute channels and hence
freckles
Detecting the position of non-linear component in periodic structures from the system responses to dual sinusoidal excitations
Based on the Nonlinear Output Frequency Response Functions (NOFRFs), a novel method is developed to detect the position of nonlinear components in periodic structures. The detection procedure requires exciting the nonlinear systems twice using two sinusoidal inputs separately. The frequencies of the two inputs are different; one frequency is twice as high as the other one. The validity of this method is demonstrated by numerical studies. Since the position of a nonlinear component often corresponds to the location of defect in periodic structures, this new method is of great practical significance in fault diagnosis for mechanical and structural systems
Non-Fermi liquid states in the pressurized system: two critical points
In the archetypal strongly correlated electron superconductor CeCuSi
and its Ge-substituted alloys CeCu(SiGe) two quantum
phase transitions -- one magnetic and one of so far unknown origin -- can be
crossed as a function of pressure \cite{Yuan 2003a}. We examine the associated
anomalous normal state by detailed measurements of the low temperature
resistivity () power law exponent . At the lower critical point
(at , ) depends strongly on Ge
concentration and thereby on disorder level, consistent with a
Hlubina-Rice-Rosch scenario of critical scattering off antiferromagnetic
fluctuations. By contrast, is independent of at the upper quantum
phase transition (at , ), suggesting critical
scattering from local or Q=0 modes, in agreement with a density/valence
fluctuation approach.Comment: 4 pages, including 4 figures. New results added. Significant changes
on the text and Fig.
CLEC14A was up-regulated in hepatocellular carcinoma and may function as a potential diagnostic biomarker
Objective: The current work aimed to investigate the expression and potential clinical significance of C-type Lectin domain family 14 (CLEC14A) in hepatocellular carcinoma.
Methods: The relative expressions of CLEC14A in the Hepatocellular Carcinoma (HCC) tissue and adjacent normal tissue of 105 HCC patients were examined using RT-qPCR methods. Furthermore, Receiver Operating Characteristic (ROC) curve was drawn for exploring the diagnostic value of CLEC14A. Next, the expressions of CLEC14A in HCC cell lines and normal liver epithelial cells were compared, and the effects of knockdown of CLEC14A on the growth and apoptosis of HCC cells were examined.
Results: The authors found that the expression of CLEC14A was markedly increased in hepatocellular carcinoma tumors in comparison with the adjacent tissue, and the expression level of CLEC14A was positively correlated with the size and differentiation of the tumor. Moreover, results of ROC analysis showed CLEC14A might function as a sensitive diagnostic biomarker for HCC. Furthermore, CLEC14A was up-regulated in HCC cell lines, and transient over-expression of CLEC14A decreased the proliferation and increased the apoptosis of HCC cells in vitro.
Conclusions: Our results suggested that CLEC14A was up-regulated in HCC and might function as a potential diagnostic marker
Mechanism of Polarization Fatigue in BiFeO3: the Role of Schottky Barrier
By using piezoelectric force microscopy and scanning Kelvin probe microscopy,
we have investigated the domain evolution and space charge distribution in
planar BiFeO3 capacitors with different electrodes. It is observed that charge
injection at the film/electrode interface leads to domain pinning and
polarization fatigue in BiFeO3. Furthermore, the Schottky barrier at the
interface is crucial for the charge injection process. Lowering the Schottky
barrier by using low work function metals as the electrodes can also improve
the fatigue property of the device, similar to what oxide electrodes can
achieve
Dynamics of Threshold Voltage Shifts in Organic and Amorphous Silicon Field-Effect Transistors
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