Engineering topics
Chen, Jun
Publications and source records attributed to Chen, Jun.
Discovery of a Potent and Selective BCL-X L Inhibitor with in Vivo Activity
Abstract not provided
Atomistic modeling and HAADF investigations of misfit and threading dislocations in GaSb/GaAs hetero-structures for applications in high electron mobility transistors
A detailed investigation on the misfit and threading dislocations at GaSb/GaAs interface has been carried out using molecular dynamics simulation and quantitative electron microscopy techniques. The sources and propagation of misfit dislocations have been elucidated. The nature and formation mechanisms of the misfit dislocations as well as the role of Sb on the stability of the Lomer configuration have been explained.
Activation of RAS/ERK alone is insufficient to inhibit RXRα function and deplete retinoic acid in hepatocytes
Highlights: • The activation of RAS/ERK is insufficient to inhibit RXRα function and deplete RA. • The retinoid metabolism-related genes are down-regulated by ras oncogene. • The atRA has no effect on preventing hepatic tumorigenesis or curing the developed hepatic nodules. - Abstract: Activation of RAS/ERK signaling pathway, depletion of retinoid, and phosphorylation of retinoid X receptor alpha (RXRα) are frequent events found in liver tumors and thought to play important roles in hepatic tumorigenesis. However, the relationships among them still remained to be elucidated. By exploring the transgenic mouse model of hepatic tumorigenesis induced by liver-specific expression of H-ras12V oncogene, the activation of RAS/ERK, the mRNA expression levels of retinoid metabolism-related genes, the contents of retinoid metabolites, and phosphorylation of RXRα were determined. RAS/ERK signaling pathway was gradually and significantly activated in hepatic tumor adjacent normal liver tissues (P) and hepatic tumor tissues (T) of H-ras12V transgenic mice compared with normal liver tissues (Wt) of wild type mice. On the contrary, the mRNA expression levels of retinoid metabolism-related genes were significantly reduced in P and T compared with Wt. Interestingly, the retinoid metabolites 9-cis-retinoic acid (9cRA) and all-trans-retinoic acid (atRA), the well known ligands for nuclear transcription factor RXR and retinoic acid receptor (RAR), were significantly decreased only in T compared with Wt and P, although the oxidized polar metabolite of atRA, 4-keto-all-trans-retinoic-acid (4-keto-RA) was significantly decreased in both P and T compared with Wt. To our surprise, the functions of RXRα were significantly blocked only in T compared with Wt and P. Namely, the total protein levels of RXRα were significantly reduced and the phosphorylation levels of RXRα were significantly increased only in T compared with Wt and P. Treatment of H-ras12V transgenic mice at 5-week-old or 5-month-old with atRA had no effect on the prevention of tumorigenesis or cure of developed nodules in liver. These events imply that the depletion of 9cRA and atRA and the inhibition of RXRα function in hepatic tumors involve more complex mechanisms besides the activation of RAS/ERK pathway.
Zero Thermal Expansion and Ferromagnetism in Cubic Sc 1-x M x F 3 (M = Ga, Fe) over a Wide Temperature Range
The rare physical property of zero thermal expansion (ZTE) is intriguing because neither expansion nor contraction occurs with temperature fluctuations. Most ZTE, however, occurs below room temperature. It is a great challenge to achieve isotropic ZTE at high temperatures. Here we report the unconventional isotropic ZTE in the cubic (Sc 1-x M x )F 3 (M = Ga, Fe) over a wide temperature range (linear coefficient of thermal expansion (CTE), α l = 2.34 × 10 -7 K -1 , 300-900 K). Such a broad temperature range with a considerably negligible CTE has rarely been documented. The present ZTE property has been designed using the introduction of local distortions in the macroscopic cubic lattice by heterogeneous cation substitution for the Sc site. Even though the macroscopic crystallographic structure of (Sc 0.85 Ga 0.05 Fe 0.1 )F 3 adheres to the cubic system (Pm3 - m) according to the results of Xray diffraction, the local structure exhibits a slight rhombohedral distortion. This is confirmed by pair distribution function analysis of synchrotron radiation Xray total scattering. This local distortion may weaken the contribution from the transverse thermal vibration of fluorine atoms to negative thermal expansion, and thus may presumably be responsible for the ZTE. In addition, the present ZTE compounds of (Sc 1-x M x )F 3 can be functionalized to exhibit high-T c ferromagnetism and a narrow-gap semiconductor feature. The present study shows the possibility of obtaining ZTE materials with multifunctionality in future work.
Structure and ferroelectricity of nonstoichiometric (Na[subscript 0.5]Bi[subscript 0.5])TiO[subscript 3]
Abstract not provided
In situ monitoring of stacking fault formation and its carrier lifetime mediation in p-type 4H-SiC
Using the fine control of an electron beam (e-beam) in scanning electron microscopy with the capabilities of both electrical and optical imaging, the stacking fault (SF) formation together with its tuning of carrier lifetime was in situ monitored and investigated in p-type 4H-SiC homoepitaxial films. The SFs were formed through engineering basal plane dislocations with the energy supplied by the e-beam. The e-beam intensity required for the SF formation in the p-type films was ∼100 times higher than that in the n-type ones. The SFs reduced the minority-carrier lifetime in the p-type films, which was opposite to that observed in the n-type case. The reason for the peculiar SF behavior in the p-type 4H-SiC is discussed with the cathodoluminescence results.
High piezoelectric performance and temperature dependence of ferroelectric and piezoelectric properties of Bi(Mg 0.5 Zr 0.5 )O 3 –PbTiO 3 near morphotropic phase boundary
According to consideration on the average radius of B-site cation of BiMeO 3 , we reported that the Bi(Mg 0.5 Zr 0.5 )O 3 –xPbTiO 3 compound at the morphotropic phase boundary (MPB) of x=0.58 possesses a piezoelectric coefficient d33 as high as 306 pC/N. The optimal piezoelectric and ferroelectric properties near the MPB might be attributed to its lower lattice distortion, as described by change of FWHM value for {1 1 1}PC peaks. Furthermore, Bi(Mg 0.5 Zr 0.5 )O 3 –xPbTiO 3 displayed stable ferroelectric and piezoelectric properties over a temperature range from ambient temperature to above 160 °C, as exhibited by temperature dependence polarization and strain versus electric field curves and thermal depoling process.
Bi-O covalency in PbTiO{sub 3}-BiInO{sub 3} with enhanced ferroelectric properties: Synchrotron radiation diffraction and first-principles study
High-T{sub C} ferroelectric (1 − x)PbTiO{sub 3}-xBiInO{sub 3} shows a sustainable spontaneous polarization in tetragonal phase by amount of BiInO{sub 3} augmented. It is rare and interesting that weak ferroelectric In{sup 3+} substitution does not reduce ferroelectricity as most of BiMeO{sub 3} materials. To understand this abnormality behavior, the structure and the cation displacements are studied by means of synchrotron radiation diffraction. The cation displacements of A-site atoms and B-site atoms exhibit a coupling property. Their sustainedly increasing trend is quantitatively associated with spontaneous polarization. Moreover, the structure, the valence electron density distributions, electron localization function, and Bader analysis have been researched on the chemical bond in (1 − x)PbTiO{sub 3}-xBiInO{sub 3} through first-principles calculations here. Although In atoms substitution reduces the covalency degree, this loss is offset by enhanced covalency between Bi-O bonds. The crucial role of Bi atom substitution not only contributes to enhance the covalency but also promotes the polarization.
Accuracy of the centrifugal sudden approximation in the H + CHD{sub 3} → H{sub 2} + CD{sub 3} reaction
The initial state selected time-dependent wave packet method has been extended to calculate the coupled-channel reaction probabilities with total angular momentum J{sub tot} > 0 for the title reaction with seven degrees of freedom included. Fully converged integral cross sections were obtained for the ground and a number of vibrational excited initial states on a new potential energy surface recently constructed by this group using neural network fitting. As found from a previous study with the centrifugal sudden (CS) approximation, all these initial vibrational excitations investigated in this study enhance the reactivity considerably at a given collision energy, in particular the CH stretch excited state. The energy initially deposited in CH stretch motion is more effective than translational energy on promoting the reaction in the entire energy region, while for CH bending or CD{sub 3} umbrella excitations only at the high collision energy the vibrational energy becomes more effective. Our calculations also revealed that the accuracy of the CS approximation considerably deteriorates with the increase of J{sub tot}, in particular on the threshold energy. The CS approximation underestimates the integral cross sections for all these initial states, albeit not very severely. In general, it works better at high collision energies and for vibrationally excited initial states, with the increase of integral cross section.
Molecular dynamics simulation of shock induced ejection on fused silica surface
Shock response and surface ejection behaviors of fused silica are studied by using non-equilibrium molecular dynamics combining with the Tersoff potential. First, bulk structure and Hugoniot curves of fused silica are calculated and compared with experimental results. Then, the dynamical process of surface ejection behavior is simulated under different loading velocities ranging from 3.5 to 5.0 km∕s, corresponding to shock wave velocities from 7.1 to 8.8 km∕s. The local atomistic shear strain parameter is used to describe the local plastic deformation under conditions of shock compression or releasing. Our result shows that the shear strain is localized in the bottom area of groove under the shock compression. Surface ejection is observed when the loading velocity exceeds 4.0 km∕s. Meanwhile, the temperature of the micro-jet is ∼5574.7 K, which is close to experiment measurement. Several kinds of structural defects including non-bridging oxygen are found in the bulk area of the sample after ejection.
Refinement of particle detection by the hybrid method in digital in-line holography.
Abstract not provided.
Characterization of Aerodynamic Fragmentation of a Drop by Cross-beam Two-view Digital In-line Holography.
Abstract not provided.
Liquid film thickness measurement by two-line TDLAS
A fiber-based two-line tunable diode-laser absorption sensor with two near-infrared (NIR) distributed-feedback (DFB) diode lasers at ∼1.4 μm was used for non-intrusive time-resolved liquid water film thickness measurement. When probing the liquid film at two different wavelengths with significantly different absorption cross-sections, the additional signal losses due to surface fowling, reflection and beam steering can be eliminated. In this work, the evaporation process of a liquid film on transparent quartz plate was tracked and large fluctuations of film thickness were found at the end of the evaporation.
Large-Scale Synthesis of Isotropic Single-Crystalline ScF 3 Cubes by Hydrothermal Method
Abstract not provided
Extensive domain wall motion and deaging resistance in morphotropic 0.55Bi(Ni{sub 1/2}Ti{sub 1/2})O{sub 3}–0.45PbTiO{sub 3} polycrystalline ferroelectrics
Domain wall motion is known as a major source of extrinsic contributions to the dielectric and piezoelectric properties of ferroelectric materials. In the present work, we report the extent of non-180° domain wall motion during strong and weak electric field amplitudes in situ using time-resolved, high-energy X-ray diffraction in the ferroelectric morphotropic phase boundary composition 0.55Bi(Ni{sub 1/2}Ti{sub 1/2})O{sub 3}–0.45PbTiO{sub 3} (BNT-45PT). After application of strong electric fields, two phases are shown to coexist. In the tetragonal phase of this material, the extent of 90° domain wall motion is significant and the domain alignment is nearly saturated. Weak (subswitching) cyclic electric fields are then also shown to induce domain wall motion. Deaging, or the progressive loss of preferred domain orientation during sequentially increasing field amplitudes, is notably low in these materials, showing that the initial domain alignment is strongly stabilized. Overall, the in situ measurements reveal that domain wall motion significantly impacts the structure and properties of BNT-45PT and reinforces the importance of understanding domain wall motion contributions to the physical properties of ferroelectrics.