In this work, we examine the kink-nucleation process in BCC screw dislocations using atomistic simulation and transition pathway analysis, with a particular focus on the compact core structure. We observe the existence of a threshold stress, which results in an abrupt change in the minimum energy path of the kink-nucleation process, and hence, a discontinuity in the activation energy versus stress for the process. The magnitude of the discontinuity is found to be related to the degree of metastability of an intermediate split-core structure. This feature appears to be a direct consequence of the so-called 'camel-hump' nature of the Peierls potential, which manifests itself in the existence of a metastable, intermediate split-core structure. The effect is observed in a number of empirical EAM potentials, including Fe, Ta, V, Nb and Mo, suggesting a generality to the observations.
CB6F1 mice exhibit intermediate resistance to infection with Leishmania major compared to their highly susceptible (BALB/c) and resistant (C57BL/6) parental strains. Unlike the C57BL/6 and BALB/c strains, which rapidly develop dominant Th1-or Th2-type responses, respectively, after infection, CB6F1 mice develop responses in which both Th1-and Th2-type cytokines are elevated through at least the first month of infection before Th1 responses become dominant as cutaneous lesions gradually heal. We have examined the effects of interleukin-12 (IL-12) and/or anti-IL-4 antibody treatment on cytokine production and the course of disease in CB6F1 mice with chronic L. major infections. When administered at 1 month of infection, IL-12 treatment led to a rapid decrease in mRNA levels for IL-4 within parasitized lesions and a moderate increase in gamma interferon (IFN-␥) transcript levels in lymph nodes draining the site of infection. When IL-12 and anti-IL-4 antibody were administered together, they induced a marked decrease in IL-4 and transforming growth factor  mRNA expression within lesions and a more dramatic increase in lymph node IFN-␥ transcript levels within 4 days after treatment. In comparison, similar treatment of infected BALB/c mice led to only a moderate increase in IFN-␥ transcripts but no decrease in mRNA levels for Th2-type cytokines. Treatment of CB6F1 mice with either IL-12 or anti-IL-4 antibody had no significant effect on the subsequent course of infection, whereas combined IL-12 plus anti-IL-4 treatment resulted in a decrease in lesion size and parasite numbers and a shift towards a Th1-dominant response. These results suggest that the immediate effects of cytokine or anti-cytokine therapy may be predictive of the long-term effects on the course of infection and that down-regulation of Th-2 type cytokines may be critical to the development of a Th1-dominant response.
Lithiation/delithiation of the electrode materials in Li-ion batteries (LIBs) induces large strains in the host material leading to plasticity and fracture. Lithiation is also often accompanied by phase transformations, such as electrochemically-driven solid-state amorphization (ESA). These electrochemical reaction-induced microstructural events limit the energy capacity and cycle lifetime of LIBs. It was recently reported that lithium-ion anode materials composed of nanowires can offer improved performance and lifetime compared to those of micron-scale or larger materials. The improvements are often attributed to the nanowire's unique geometry and enhanced accommodation of the transformation strains that occur during cycling. However, the detailed mechanisms of strain-induced plasticity and strain accommodation in nanowires during electrochemical charging are largely unknown. We report the creation of a nanoscale electrochemical device inside a transmission electron microscopeconsisting of a single SnO 2 nanowire anode, an ionic liquid electrolyte and a bulk LiCoO 2 cathode -and the in-situ observation of the lithiation of the SnO 2 nanowire during electrochemical charging [1]. Upon charging, a reaction front propagated progressively along the nanowire, causing the nanowire to swell, elongate, and spiral (Fig. 1). The reaction front is a "Medusa zone" containing a high density of mobile dislocations, which are continuously nucleated and absorbed at the moving front (Fig. 2). This dislocation cloud indicates large in-plane misfit stresses and is a structural precursor to electrochemically-driven solid-state amorphization. Because lithiation induced volume expansion, plasticity and pulverization of electrode materials are the major mechanical effects that plague the performance and lifetime of high capacity anodes in lithium-ion batteries, our observations provide important mechanistic insight for the design of advanced batteries.
Purpose: To investigate the effects of miniphantom materials on output ratio in‐air Method and Materials: Output ratios in‐air were measured for beam energies of 6 MV and 15 MV, for collimator settings ranging from 3×3 to 40×40 cm2, and radiological depths between 1.83 – 36.6 g/cm2 for graphite, 1.6 – 33.6 g/cm2 for copper, and 2.28 – 21.6 g/cm2 for lead, respectively. The miniphantoms were of cylindrical shape. The lateral dimensions of the miniphantoms (> 4 g/cm2) were large enough to provide electron equilibrium and small enough to ensure coverage by the beam. Attenuation coefficients for those beam quality were measured with good geometry for the miniphantom materials. Results: At 6 MV, the maximum variations of the output ratios with the depths were −0.67%, −0.89%, and −0.66% for graphite, copper, and lead, respectively. At 15 MV, they were −1.68%, −0.84%, and −0.43%, respectively. Output ratios measured with copper and lead at the same radiological depth, e.g., 10 g/cm2, varied by −0.56% and −0.62% respectively at 6 MV, and −0.84% and −0.93% respectively at 15 MV, compared to graphite, a water equivalent material. Attenuation correction factors varied by −3.62%, −4.76%, and −4.89% at 6 MV, at the depth of 10 g/cm2, for graphite, copper, and lead, respectively. And they varied by −1.53%, −2.85%, and −2.45%, respectively at 15 MV. Mass energy transfer correction factors of copper and lead, compared to graphite, varied by 6.24% and 9.42%, respectively at 6 MV, and 6.77% and 2.76%, respectively at 15 MV. Conclusion: Output ratios measured using miniphantoms made of high Z materials showed variations from the miniphantom made of water equivalent material. For the same miniphantom, output ratio varied with its thickness. These differences can be accounted for by a collimator size dependent correction factor. We have measured various components of the correction factor.
Purpose: It is desirable to preserve mass and topology at every element during deformable image registration. We present some preliminary results using an ALE mesh for deformable image registration of head and neck tumors. Method and Materials: Arbitrary Lagrangian‐Eulerian (ALE) moving mesh is a finite‐element based technique that preserves mass and topology during deformation. The displacement of the moving boundary can propagate to the interior nodes throughout the domain. A smooth mesh deformation can be obtained by solving partial‐differential equations (PDEs) for the mesh displacements. We adopted this technique in deformable image registration. The idea of our image registration, currently contour‐based, is to generate ALE mesh in a reference image, move the external boundary (or surface) to match the boundary in a target image, and track the contours of the interior organs or tumors, which are deformed by the ALE mesh movement. The software COMSOL Multiphysics (Comsol, Inc., MA) was used. Results: The image registration was tested with two‐dimensional images, using structure contours of head and neck tumors. Two sets of CT images and structure contours taken before and after chemotherapy, respectively, were used. The external contour obtained before the chemotherapy was moved to match the external contour obtained after the chemotherapy. Displacement vectors of the domain enclosed by the external contour were derived from the moving mesh, which were then examined with the deformation of gross target volume (GTV) contour. A warped GTV contour was obtained by applying the displacement vectors to the GTV obtained before the chemotherapy. The result showed that the warped GTV nearly agreed with the GTV obtained after the chemotherapy, except a small part. Conclusion: The preliminary study shows promising application of deformed mesh in image registration. Further studies in three dimensions and comparing the agreements between our methods and elastic‐mechanical modeling will be included.
Lithium ion batteries (LIBs) are attracting attention for energy storage device for electric vehicles where high power, energy density, and cyclability are required. Nanowire (NW) electrode [1] has advantage over conventional electrodes due to its unique geometry that enhances the electron and Li + transport. In addition, NWs can accommodate large volume change during charge/discharge cycles [2], leading to the improved cyclability and stability. In this study, the lithiation processes of individual ZnO NW electrodes in a LIB configuration were observed by in-situ transmission electron microscopy (TEM) using a unique nano-battery setup inside the TEM [3] developed recently for observing the electrochemistry processes in real time.The nano-battery consisted of a single ZnO NW as an anode, an ionic-liquid electrolyte (ILE), and LiCoO 2 particles as cathode. Figure 1 shows the lithiation process of the ZnO NW. The initial NW was straight and had smooth surface (Fig. 1A). After contact with ILE, a potential of -4.0 V with respect to the LiCoO 2 counter electrode was applied to the ZnO NW (Fig.1B). The solid-state reaction front propagated along the longitudinal direction of the NW away from the ILE (Fig. 1B-K). As the reaction front propagated, the diameter and the length of the NW increased, causing the NW to bend. Figure 1L-O shows detailed view of the reaction front propagation. Interestingly, the reaction front did not move progressively along the NW. Instead, it advanced by initiating discrete cracks about 80 nm before the reaction front (Fig. 1M, red arrowheads). The lithiation then propagated laterally along its two side (Fig. 1 N-O). The cracks divided the NW into smaller segments. The new crack grew in a similar fashion to the old crack, and this process repeated until the entire nanowire was lithiated. From the above observations, the lithiation of the ZnO NW consists of three steps. 1) The Li + adsorbs on the NW surface initiating the lithiation.2) The reaction leads to crack formation in the NW making path from the surface inward the bulk. 3) Li + penetrates into the NW from the crack and reacts with the NW. The lithiation process is schematically illustrated in Fig. 2A. The crack formation during the lithiation process caused the ZnO NW to break into multiple segments (Fig. 2B).The fracture of the NW is considered to cause poor cyclability of the battery when ZnO is used as the LIB electrode. Our observations provide important insight for developing battery with higher performance and longer lifetime by providing the failure mechanism of the electrode material [4].
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