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Li, Jingbo

Publications and source records attributed to Li, Jingbo.

At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

The role of eukaryotic translation initiation factor 5A-1 (eIF5A-1) gene in HPV 16 E6 induces cell growth in human cervical squamous carcinoma cells

Highlights: • HPV 16 E6 and eIF5A-1 gene were highly expressed in the vast majority of cervical tumor tissues. • HPV 16 E6 gene could increase the expression of eIF5A-1 and induce the apoptosis of C33a and SiHa cells. • eIF5A-1 gene could effectively increase viability, migrated and cell proliferation of cervical squamous carcinoma cell line (C33a and SiHa). • Silencing the eIF5A-1 gene or blocking the DOHH could induce the apoptosis of HPV 16 E6-infected cervical carcinoma cells. Human Papillomavirus (HPV) is considered as the major risk factor for the development and progression of cervical cancer. The high expression of HPV 16 E6 may be the causative factor for induction and maintenance of the transformed phenotype. These oncoproteins would interact with several intracellular proteins, such as eukaryotic translation initiation factor 5A-1 (eIF5A-1) that is essential for proliferation of eukaryotic cells. Our study explored the expression level of HPV 16 E6 and eIF5A-1 in human cervical squamous carcinoma samples and the adjacent non-cancerous cervix samples. Both C33a cells and SiHa cells transfected with a vector encoding HPV 16 E6 resulted in increase of eIF5A-1 expression level and enhancement of viability, migration and proliferation of these cells, furthermore, these effects in both C33a cells and SiHa cells could be abrogated by treatment with eIF5A-1 small-interfering RNA (siRNA) or the specific inhibitors ciclopirox (CPX) that was used to inhibit the function of eIF5A-1 via blocking the main enzymes deoxyhypusine hydroxylase (DOHH). Our results support that the silencing the eIF5A-1 gene or blocking the DOHH could induce the apoptosis of HPV 16 E6-infected cervical carcinoma cells. Thus might provide a new approach to preventing and treating cervical cancer.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2017

Curved-line search algorithm for ab initio atomic structure relaxation

Ab initio atomic relaxations often take large numbers of steps and long times to converge, especially when the initial atomic configurations are far from the local minimum or there are curved and narrow valleys in the multidimensional potentials. An atomic relaxation method based on on-the-flight force learning and a corresponding curved-line search algorithm is presented to accelerate this process. In this work, results demonstrate the superior performance of this method for metal and magnetic clusters when compared with the conventional conjugate-gradient method.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Glass-like energy and property landscape of Pt nanoclusters

Pt nanoclusters play an important role in catalysis-related applications. Essential to their activities are their geometries and energy landscapes. In this work, we studied the energy landscapes of Pt clusters using a parallel differential evolution optimization algorithm and an accelerated ab initio atomic relaxation method, which allowed us to explore unprecedentedly large numbers of geometry local minima at ab initio level. We found many lower-energy isomers with low symmetry in their geometry. The energy landscapes were demonstrated to be glass-like with a large number of local minimum structures close to the global minimum. The electronic and magnetic properties of most glass-like local minima were dramatically different from the global minimum, and they should be observed in the experimental measurements. The connections between these local minima were further analyzed using data mining techniques.

Chen, Zhanghui↗
DOE OSTI2016

Structural anisotropy results in strain-tunable electronic and optical properties in monolayer GeX and SnX (X = S, Se, Te)

Using first-principles calculations, the structural and electronic properties of group-IV monochalcogenide monolayers are investigated. It is demonstrated that all the monolayers employed here possess moderate indirect bandgaps. In-plane elastic stiffness calculation demonstrates the structural anisotropy in these materials, further resulting in anisotropic response to in-plane strains in their electronic properties and anisotropic optical properties. The bandgaps of GeX and SnX monolayers can be linearly reduced by applied in-plane compressive strains and the semiconductor-to-metal transition can be realized under large compressive strains; while tensile strains exert less influence on the electronic properties in comparison to compressive strains. Some monolayers will experience indirect-to-direct bandgap transition when subjected to proper strains. A further insight into the variation of bandgaps of these monolayers can be obtained from the changing band edges.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Anisotropic in-plane thermal conductivity of black phosphorus nanoribbons at temperatures higher than 100 K

Black phosphorus attracts enormous attention as a promising layered material for electronic, optoelectronic and thermoelectric applications. Here we report large anisotropy in in-plane thermal conductivity of single-crystal black phosphorus nanoribbons along the zigzag and armchair lattice directions at variable temperatures. Thermal conductivity measurements were carried out under the condition of steady-state longitudinal heat flow using suspended-pad micro-devices. We discovered increasing thermal conductivity anisotropy, up to a factor of two, with temperatures above 100 K. A size effect in thermal conductivity was also observed in which thinner nanoribbons show lower thermal conductivity. Analysed with the relaxation time approximation model using phonon dispersions obtained based on density function perturbation theory, the high anisotropy is attributed mainly to direction-dependent phonon dispersion and partially to phonon–phonon scattering. Lastly, our results revealing the intrinsic, orientation-dependent thermal conductivity of black phosphorus are useful for designing devices, as well as understanding fundamental physical properties of layered materials.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Modulation of the electronic property of phosphorene by wrinkle and vertical electric field

The electronic properties of wrinkled phosphorene and its response to charge injection and external vertical electric field have been studied using first-principles calculations. It is found that small-size wrinkle systems have lower energy than wrinkle-free monolayer, suggesting that free-standing phosphorene spontaneously forms small protrusion on its nanosheet. The ratio of wrinkle height to curvature radius increases with enlarging height, indicating a promotion of field enhancement factor. Furthermore, the injected charges mostly distribute at peak and valley. Direct-to-indirect band-gap transition has been found for zigzag wrinkle with height of 14.81 Å. The band gaps of wrinkled nanosheets decrease almost linearly with increasing field, which is caused by charge separation of valence band maximum and conduction band minimum.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Tunable Polarity Behavior and Self-Driven Photoswitching in p-WSe 2 /n-WS 2 Heterojunctions

In Van der Waals (vdW) p–n heterojunctions consisting of various 2D layer compounds are fascinating new artificial materials that can possess novel physics and functionalities enabling the next-generation of electronics and optoelectronics devices. Here, it is reported that the WSe 2 /WS 2 p–n heterojunctions perform novel electrical transport properties such as distinct rectifying, ambipolar, and hysteresis characteristics. Intriguingly, the novel tunable polarity transition along a route of n-“anti-bipolar”–p-ambipolar is observed in the WSe 2 /WS 2 heterojunctions owing to the successive work of conducting channels of junctions, p-WSe 2 and n-WS 2 on the electrical transport of the whole systems. Moreover, the type-II band alignment we obtained from first principle calculations and built-in potential in this vdW heterojunction can also facilitate the efficient electron–hole separation, thus enabling the significant photovoltaic effect and a much enhanced self-driven photoswitching response in this system.

14 SOLAR ENERGY↗
DOE OSTI2014

Edge-states ferromagnetism of WS{sub 2} nanosheets

The multilayer WS{sub 2} nanosheets prepared from WO{sub 3} nanowires exhibit strong ferromagnetic behavior with saturation magnetization (M{sub S}) of 0.0058 emu/g and coercive field (H{sub C}) of 92 Oe at room temperature. By decreasing the temperature down to 3 K the H{sub c} is increased up to 1115 Oe, revealing the existence of long-range magnetic ordering. Density functional theory spin-polarized calculations predict that strong ferromagnetic moments in WS{sub 2} nanosheets are attributed to the zigzag edge sulphur S and tungsten W atoms. Our findings also suggest that the WS{sub 2} nanosheets with a high density of edge spins could be used to fabricate spintronics devices, which are circuits utilizing the spin of the electron to process and store information.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2014

Approximate Hessian for accelerating ab initio structure relaxation by force fitting

We present a method to approximate the Hessian matrix of the Born-Oppenheimer energy landscape by using a simple force field model whose parameters are fitted to on-the-flight ab initio results. The inversed Hessian matrix is used as the preconditioner of conjugate gradient algorithms to speed up the atomic structure relaxation, resulting in a speedup factor of 2 to 5 on systems of bulk, slab, sheets, and atomic clusters. Because the force field model employed is simple and general, the parameter fitting is straightforward; the method is applicable to a variety of complicated systems for minimum structure relaxation. In the metal cluster new structure search, the new method yields better structures than the one obtained before with conventional algorithms.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Insight into the photoelectron angular dependent energy distribution of negative-electron-affinity InP photocathodes

Energy distribution and angular distribution of the photoelectrons from InP photocathodes are investigated using a precise Monte Carlo model. It is found that Γ-valley electrons contribute to the first peak of the energy distribution curve, but the second peak is contributed by both Γ-valley and L-valley electrons rather than only L-valley electrons. L valley electrons are shown to have a smaller angular spread than Γ-valley electrons, which is attributed to the much higher potential energy of L-valley minimum. The further simulation indicates that the performance of InP photocathodes can be improved by increasing the hole concentration or decreasing the temperature, but the activation layer thickness variation only has very slight influence on either energy or angular distribution.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Enhancing structural transition by carrier and quantum confinement: Stabilization of cubic InN quantum dots by Mn incorporation

We demonstrate in this work controllable synthesis of cubic InN nanocrystals through Mn doping. We show that the pristine nanocrystal has the wurtzite structure, but can be converted into the zinc-blende (ZB) structure when it is doped with Mn. Our first-principles calculations show that the phase transition is caused by the stronger p-d coupling between the host p valence state and the impurity d level in the ZB structure, which makes the hole generation in the ZB structure easier. Quantum confinement in the nanocrystals further enhanced this effect. This observation lays an important foundation for defects control of crystal phases.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2013

Metal to semiconductor transition in metallic transition metal dichalcogenides

We report on tuning the electronic and magnetic properties of metallic transition metal dichalcogenides (mTMDCs) by 2D to 1D size confinement. The stability of the mTMDC monolayers and nanoribbons is demonstrated by the larger binding energy compared to the experimentally available semiconducting TMDCs. The 2D MX{sub 2} (M = Nb, Ta; X = S, Se) monolayers are non-ferromagnetic metals and mechanically softer compared to their semiconducting TMDCs counterparts. Interestingly, mTMDCs undergo metal-to-semiconductor transition when the ribbon width approaches to ∼13 Å and ∼7 Å for zigzag and armchair edge terminations, respectively; then these ribbons convert back to metal when the ribbon widths further decrease. Zigzag terminated nanoribbons are ferromagnetic semiconductors, and their magnetic properties can also be tuned by hydrogen edge passivation, whereas the armchair nanoribbons are non-ferromagnetic semiconductors. Our results display that the mTMDCs offer a broad range of physical properties spanning from metallic to semiconducting and non-ferromagnetic to ferromagnetic that is ideal for applications where stable narrow bandgap semiconductors with different magnetic properties are desired.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Defects activated photoluminescence in two-dimensional semiconductors: interplay between bound, charged and free excitons

Point defects in semiconductors can trap free charge carriers and localize excitons. The interaction between these defects and charge carriers becomes stronger at reduced dimensionalities, and is expected to greatly influence physical properties of the hosting material. We investigated effects of anion vacancies in monolayer transition metal dichalcogenides as two-dimensional (2D) semiconductors where the vacancies density is controlled by a-particle irradiation or thermal-annealing. We found a new, sub-bandgap emission peak as well as increase in overall photoluminescence intensity as a result of the vacancy generation. Interestingly, these effects are absent when measured in vacuum. We conclude that in opposite to conventional wisdom, optical quality at room temperature cannot be used as criteria to assess crystal quality of the 2D semiconductors. Our results not only shed light on defect and exciton physics of 2D semiconductors, but also offer a new route toward tailoring optical properties of 2D semiconductors by defect engineering.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS2012

Coincident Observation of Lightning using Spaceborne Spectrophotometer and Ground-Level Electromagnetic Sensors

The present study aims at assessing a possible new way to reveal the properties of lightning flash, using spectrophotometric data obtained by FORMOSAT-2/ISUAL which is the first spaceborne multicolor lightning detector. The ISUAL data was analyzed in conjunction with ground ]based electromagnetic data obtained by Duke magnetic field sensors, NLDN, North Alabama Lightning Mapping Array (LMA), and Kennedy Space Center (KSC) electric field antennas. We first classified the observed events into cloud ]to ]ground (CG) and intra ]cloud (IC) lightning based on the Duke and NLDN measurements and analyzed ISUAL data to clarify their optical characteristics. It was found that the ISUAL optical waveform of CG lightning was strongly correlated with the current moment waveform, suggesting that it is possible to evaluate the electrical properties of lightning from satellite optical measurement to some extent. The ISUAL data also indicated that the color of CG lightning turned to red at the time of return stroke while the color of IC pulses remained unchanged. Furthermore, in one CG event which was simultaneously detected by ISUAL and LMA, the observed optical emissions slowly turned red as the altitude of optical source gradually decreased. All of these results indicate that the color of lightning flash depends on the source altitude and suggest that spaceborne optical measurement could be a new tool to discriminate CG and IC lightning. In the presentation, we will also show results on the comparison between the ISUAL and KSC electric field data to clarify characteristics of each lightning process such as preliminary breakdown, return stroke, and subsequent upward illumination.

Adachi, Toru↗