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Wang, Cong

Publications and source records attributed to Wang, Cong.

At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Load-Flow in Multiphase Distribution Networks: Existence, Uniqueness, Non-Singularity, and Linear Models

This paper considers unbalanced multiphase distribution systems with generic topology and different load models, and extends the Z-bus iterative load-flow algorithm based on a fixed-point interpretation of the AC load-flow equations. Explicit conditions for existence and uniqueness of load-flow solutions are presented. These conditions also guarantee convergence of the load-flow algorithm to the unique solution. The proposed methodology is applicable to generic systems featuring (i) wye connections; (ii) ungrounded delta connections; (iii) a combination of wye-connected and delta-connected sources/loads; and, (iv) a combination of line-to-line and line-to-grounded-neutral devices at the secondary of distribution transformers. Further, a sufficient condition for the non-singularity of the load-flow Jacobian is proposed. Lastly, linear load-flow models are derived, and their approximation accuracy is analyzed. Theoretical results are corroborated through experiments on IEEE test feeders.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2018

Evolution of Inclusions During the 1473 K (1200 °C) Heating Process of EH36 Shipbuilding Steel

Evolution behaviors of inclusions of EH36 shipbuilding steel during 1473 K (1200 °C) heating have been studied in conjunction with ex situ scanning electron microscope (SEM) examination and in situ confocal scanning laser microscopy (CSLM) observations. It has been found that Al-Ca-O-S complex inclusions dominate the particles in the cast billet. However, TiN inclusions are profusely populated after heating. Moreover, possible strategies governing austenite growth are offered here.

36 MATERIALS SCIENCE↗
DOE OSTI2018

An Embedded 3D Fracture Modeling Approach for Simulating Fracture-Dominated Fluid Flow and Heat Transfer in Geothermal Reservoirs

An efficient modeling approach is described for incorporating arbitrary 3D, discrete fractures, such as hydraulic fractures or faults, into modeling fracture-dominated fluid flow and heat transfer in fractured geothermal reservoirs. This technique allows 3D discrete fractures to be discretized independently from surrounding rock volume and inserted explicitly into a primary fracture/matrix grid, generated without including 3D discrete fractures in prior. An effective computational algorithm is developed to discretize these 3D discrete fractures and construct local connections between 3D fractures and fracture/matrix grid blocks of representing the surrounding rock volume. The constructed gridding information on 3D fractures is then added to the primary grid. This embedded fracture modeling approach can be directly implemented into a developed geothermal reservoir simulator via the integral finite difference (IFD) method or with TOUGH2 technology This embedded fracture modeling approach is very promising and computationally efficient to handle realistic 3D discrete fractures with complicated geometries, connections, and spatial distributions. Compared with other fracture modeling approaches, it avoids cumbersome 3D unstructured, local refining procedures, and increases computational efficiency by simplifying Jacobian matrix size and sparsity, while keeps sufficient accuracy. Several numeral simulations are present to demonstrate the utility and robustness of the proposed technique. Our numerical experiments show that this approach captures all the key patterns about fluid flow and heat transfer dominated by fractures in these cases. Thus, this approach is readily available to simulation of fractured geothermal reservoirs with both artificial and natural fractures.

15 GEOTHERMAL ENERGY↗
DOE OSTI2018

Crystal-on-crystal chips for in situ serial diffraction at room temperature

Recent developments in serial crystallography have been driven by two scientific goals – first, static structure determination from nano or microcrystals that are difficult for cryocrystallography, and second, direct observations of transient structural species in biochemical reactions at near atomic resolution.

Ren, Zhong↗
DOE OSTI2017

Stationary state distribution and efficiency analysis of the Langevin equation via real or virtual dynamics

Langevin dynamics has become a popular tool to simulate the Boltzmann equilibrium distribution. When the repartition of the Langevin equation involves the exact realization of the Ornstein-Uhlenbeck noise, in addition to the conventional density evolution, there exists another type of discrete evolution that may not correspond to a continuous, real dynamical counterpart. This virtual dynamics case is also able to produce the desired stationary distribution. Different types of repartition lead to different numerical schemes, of which the accuracy and efficiency are investigated through studying the harmonic oscillator potential, an analytical solvable model. By analyzing the asymptotic distribution and characteristic correlation time that are derived by either directly solving the discrete equations of motion or using the related phase space propagators, it is shown that the optimal friction coefficient resulting in the minimum characteristic correlation time depends on the time interval chosen in the numerical implementation. In conclusion, when the recommended “middle” scheme is employed, both analytical and numerical results demonstrate that, for good numerical performance in efficiency as well as accuracy, one may choose a friction coefficient in a wide range from around the optimal value to the high friction limit.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

RACK1 promotes radiation resistance in esophageal cancer via regulating AKT pathway and Bcl-2 expression

RACK1 is a seven Trp-Asp 40 repeat protein, which interacts with a wide range of kinases and proteins. RACK1 plays an important role in the proliferation and progression of various cancers. The aim of this study is to detect the role of RACK1 in the radioresistance in esophageal cancer. The results indicated that downregulation of RACK1 reduced the colony formation ability, proliferation ability and resistance of cells to radiation effection through regulating the radiation-related proteins including pAKT, Bcl-2 and Bim; whereas upregulation of RACK1 promoted the ability and radioresistance of ESCC cells. Our findings suggest that RACK1 promotes proliferation and radioresistance in ESCC cells by activating the AKT pathway, upregulating Bcl-2 expression and downregulating protein levels of Bim. Our study fills in gaps in the field of RACK1 and radiation resistance and may provide new possibilities for improving strategies of radiotherapy in esophageal cancer. - Highlights: • RACK1 is proposed to influence the proliferation ability of cells after irradiation. • Present the relationship between RACK1 and radiation resistance of esophageal cancer. • Analyze the mechanism by which RACK1 plays a role in radiation resistance.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2017

Metalorganic chemical vapor deposition-regrown Ga-rich InGaP films on SiGe virtual substrates for Si-based III-V optoelectronic device applications

Ga-rich InGaP materials are attractive applications for yellow-green spectral range optoelectronics such as light-emitting diodes and solar cells on silicon substrate. Bulk, Ga-rich InGaP films grown by metalorganic chemical vapor deposition on SiGe virtual substrates were investigated in the V/III compositional ratio range of 44.3–402 using chamber pressures from 100 to 200 mbar. These films were nominally lattice matched to the SiGe virtual substrate with a bandgap energy of 2.07–2.09 eV at low temperature (10 K). The authors show that the surface morphology of the Ga-rich InGaP films was dependent on the growth conditions, including the V/III gas phase ratio, pressure, and growth rate. By optimizing the growth conditions, the authors achieved improved surface morphologies of the Ga-rich InGaP films. The hillock density of the films produced using a V/III gas phase ratio of 44.3 and 75.4, a growth pressure of 100 mbar, and a growth rate of 0.9 μm/h was about an order of magnitude lower (30.3–50 × 104 cm−2) than that observed using higher V/III gas phase ratios such as 201 and 402. An increase in luminescence efficiency of Ga-rich InGaP materials was observed when the hillock density is lower. The authors discuss the mechanisms of the hillock formation.

Kim, TaeWan↗
DOE OSTI2017

Tunable thermal expansion in framework materials through redox intercalation

Thermal expansion properties of solids are of fundamental interest and control of thermal expansion is important for practical applications but can be difficult to achieve. Many framework type materials show negative thermal expansion when internal cages are empty but positive thermal expansion when additional atoms or molecules fill internal voids present, offering a potential route for control. Here we show that redox intercalation offers an effective method to control thermal expansion from positive to zero to negative by insertion of Li ions into the simple negative thermal expansion framework material ScF 3 , doped with 10% Fe to enable reduction. The small concentration of intercalated Li ions has a strong influence through steric hindrance of transverse fluoride ion vibrations, which directly controls the thermal expansion. As a result, redox intercalation of guest ions is thus likely to be a general and effective method for controlling thermal expansion in the many known framework materials with phonon-driven negative thermal expansion.

36 MATERIALS SCIENCE↗
DOE OSTI2016

First-principles calculations of K-shell X-ray absorption spectra for warm dense nitrogen

X-ray absorption spectrum is a powerful tool for atomic structure detection on warm dense matter. Here, we perform first-principles molecular dynamics and X-ray absorption spectrum calculations on warm dense nitrogen along a Hugoniot curve. From the molecular dynamics trajectory, the detailed atomic structures are examined for each thermodynamical condition. The K-shell X-ray absorption spectrum is calculated, and its changes with temperature and pressure along the Hugoniot curve are discussed. The warm dense nitrogen systems may contain isolated nitrogen atoms, N{sub 2} molecules, and nitrogen clusters, which show quite different contributions to the total X-ray spectrum due to their different electron density of states. The changes of X-ray spectrum along the Hugoniot curve are caused by the different nitrogen structures induced by the temperature and the pressure. Some clear signatures on X-ray spectrum for different thermodynamical conditions are pointed out, which may provide useful data for future X-ray experiments.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Near-zero temperature coefficient of resistivity associated with magnetic ordering in antiperovskite Mn{sub 3+x}Ni{sub 1−x}N

The near-zero temperature coefficient of resistivity (NZ-TCR) behavior is reported in the antiperovskite compounds Mn{sub 3+x}Ni{sub 1−x}N (0 ≤ x ≤ 0.333). Our results indicate that the broad temperature range (above 275 K extending to above 220 K) of NZ-TCR is obtained by Mn doping at the Ni site. The short-range magnetic ordering is revealed by both neutron powder diffraction and inverse magnetic susceptibility. Further, we find a strong correlation between the anomalous resistivity change of Mn{sub 3+x}Ni{sub 1−x}N from the metal-like to the NZ-TCR behavior and the lack of the long-range magnetic ordering. The possible mechanism of NZ-TCR behavior is discussed using the spin-disorder scattering model.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗