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Wang, Chenchen

Publications and source records attributed to Wang, Chenchen.

7 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

A numerical study of ignition and flame development characteristics in GCI combustion using large eddy simulations and chemical explosive mode analysis

Here, this work investigates the ignition and flame development processes of low reactivity fuel combustion under compression ignition conditions based on the large eddy simulation approach. The chemical explosive mode analysis (CEMA) is employed to characterize the local combustion features, including gas-liquid fuel zone, auto-ignition, diffusion-assisted, extinction, cool flame and post-ignition zone, among which auto-ignition and post-ignition are found to play a key role in the overall heat release process. The local flame propagation modes in gasoline compression ignition (GCI) are determined by quantifying the relative magnitude of diffusion/chemistry at a representative progress variable in the pre-ignition zone. The results show that autoignition fronts and deflagration waves exist simultaneously in the ignition and intense high temperature heat release (HTHR) stages, but autoignition fronts dominate. In addition, the chemical kinetic processes of four heat release periods are analyzed. The heat release during the ignition period is found to be dominated by the reactions CH 3 + H (+M) <=> CH 4 (+M) and CH 3 CHO + H <=> CH 2 CHO + H 2 . The reaction CH 2 OH + OH <=> CH 2 O + H 2 O always plays an important role in the heat releases during the other three combustion stages including intense HTHR, moderate HTHR and post-combustion.

33 ADVANCED PROPULSION SYSTEMS↗
DOE OSTI2021

Tuning local chemistry of P2 layered-oxide cathode for high energy and long cycles of sodium-ion battery

Layered transition-metal oxides have attracted intensive interest for cathode materials of sodium-ion batteries. However, they are hindered by the limited capacity and inferior phase transition due to the gliding of transition-metal layers upon Na + extraction and insertion in the cathode materials. Here, we report that the large-sized K + is riveted in the prismatic Na + sites of P2-Na 0.612 K 0.056 MnO 2 to enable more thermodynamically favorable Na + vacancies. The Mn-O bonds are reinforced to reduce phase transition during charge and discharge. 0.901 Na + per formula are reversibly extracted and inserted, in which only the two-phase transition of P2 ↔ P’2 occurs at low voltages. It exhibits the highest specific capacity of 240.5 mAh g -1 and energy density of 654 Wh kg -1 based on the redox of Mn 3+ /Mn 4+ , and a capacity retention of 98.2% after 100 cycles. This investigation will shed lights on the tuneable chemical environments of transition-metal oxides for advanced cathode materials and promote the development of sodium-ion batteries.

25 ENERGY STORAGE↗
DOE OSTI2015

Unraveling the luminescence signatures of chemical defects in polyethylene

Chemical defects in polyethylene (PE) can deleteriously downgrade its electrical properties and performance. Although these defects usually leave spectroscopic signatures in terms of characteristic luminescence peaks, it is nontrivial to make unambiguous assignments of the peaks to specific defect types. In this work, we go beyond traditional density functional theory calculations to determine intra-defect state transition and charge recombination process derived emission and absorption energies in PE. By calculating the total energy differences of the neutral defect at excited and ground states, the emission energies from intra-defect state transition are obtained, reasonably explaining the photoluminescence peaks in PE. In order to study the luminescence emitted in charge recombination processes, we characterize PE defect levels in terms of thermodynamic and optical charge transition levels that involve total energy calculations of neutral and charged defects. Calculations are performed at several levels of theory including those involving (semi)local and hybrid electron exchange-correlation functionals, and many-body perturbation theory. With these critical elements, the emission energies are computed and further used to clarify and confirm the origins of the observed electroluminescence and thermoluminescence peaks.

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

BTG/Tob family members Tob1 and Tob2 inhibit proliferation of mouse embryonic stem cells via Id3 mRNA degradation

The mammalian BTG/Tob family is a group of proteins with anti-proliferative ability, and there are six members including BTG1, BTG2/PC3/Tis21, BTG3/ANA, BTG4/PC3B, Tob1/Tob and Tob2. Among them, Tob subfamily members, specifically Tob1/Tob and Tob2, have the most extensive C-terminal regions. As previously reported, overexpression of BTG/Tob proteins is associated with the inhibition of G1 to S-phase cell cycle progression and decreased cell proliferation in a variety of cell types. Tob subfamily proteins have similar anti-proliferative effects on cell cycle progression in cultured tumor cells. An important unresolved question is whether or not they have function in rapidly proliferating cells, such as embryonic stem cells (ESCs). Tob1 and Tob2 were expressed ubiquitously in mouse ESCs (mESCs), suggesting a possible role in early embryonic development and mESCs. To address the above question and explore the possible functions of the Tob subfamily in ESCs, we established ESCs from different genotypic knockout inner cell mass (ICM). We found that Tob1{sup −/−}, Tob2{sup −/−}, and Tob1/2 double knockout (DKO, Tob1{sup −/−} & Tob2{sup −/−}) ESCs grew faster than wild type (WT) ESCs without losing pluripotency, and we provide a possible mechanistic explanation for these observations: Tob1 and Tob2 inhibit the cell cycle via degradation of Id3 mRNA, which is a set of directly targeted genes of BMP4 signaling in mESCs that play critical roles in the maintenance of ESC properties. Together, our data suggest that BTG/Tob family protein Tob1 and Tob2 regulation cell proliferation does not compromise the basic properties of mESCs. - Highlights: • We established mouse Tob1/2 double knockout embryonic stem cells. • Tob1 and Tob2 inhibit the proliferation of ESCs without effect on pluripotency. • Tob1 and Tob2 involved in the degradation of Id3 in mESCs.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2014

Pneumatic Microvalve-Based Hydrodynamic Sample Injection for High-Throughput, Quantitative Zone Electrophoresis in Capillaries

A hybrid microchip/capillary CE system was developed to allow unbiased and lossless sample loading and high throughput repeated injections. This new hybrid CE system consists of a polydimethylsiloxane (PDMS) microchip sample injector featuring a pneumatic microvalve that separates a sample introduction channel from a short sample loading channel and a fused silica capillary separation column that connects seamlessly to the sample loading channel. The sample introduction channel is pressurized such that when the pneumatic microvalve opens briefly, a variable-volume sample plug is introduced into the loading channel. A high voltage for CE separation is continuously applied across the loading channel and the fused silica capillary separation column. Analytes are rapidly separated in the fused silica capillary with high resolution. High sensitivity MS detection after CE separation is accomplished via a sheathless CE/ESI-MS interface. The performance evaluation of the complete CE/ESI-MS platform demonstrated that reproducible sample injection with well controlled sample plug volumes could be achieved by using the PDMS microchip injector. The absence of band broadening from microchip to capillary indicated a minimum dead volume at the junction. The capabilities of the new CE/ESI-MS platform in performing high throughput and quantitative sample analyses were demonstrated by the repeated sample injection without interrupting an ongoing separation and a good linear dependence of the total analyte ion abundance on the sample plug volume using a mixture of peptide standards. The separation efficiency of the new platform was also evaluated systematically at different sample injection times, flow rates and CE separation voltages.

Eletrophoresis↗
DOE OSTI2014

Sheathless interface for coupling capillary electrophoresis with mass spectrometry

A sheathless interface for coupling capillary electrophoresis (CE) with mass spectrometry is disclosed. The sheathless interface includes a separation capillary for performing CE separation and an emitter capillary for electrospray ionization. A portion of the emitter capillary is porous or, alternatively, is coated to form an electrically conductive surface. A section of the emitter capillary is disposed within the separation capillary, forming a joint. A metal tube, containing a conductive liquid, encloses the joint.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗