43,787 research outputs found
High thermal conductance across c-BN/diamond interface
No full textHigh thermal conductivity electronic components with low interfacial thermal resistance are of technological importance and fundamental interest of research. Diamond, a superhard material with ultrahigh thermal conductivity at room temperature, is desirable for microelectronics thermal management. Cubic polymorph of boron nitride (c-BN) is a promising material due to wide bandgap and diamond like structure and properties. To understand the nature in thermal transport of diamond, c-BN and the most commonly used silicon (Si) semiconductor, ab initio phonon Boltzmann transport equations are employed to investigate lattice vibrational properties of these three materials. At 300 K, the predicted thermal conductivity of Si, diamond and c-BN reached 142, 2112, and 736 W/(m·K), respectively. What's more, heat transport phenomena across the interfaces of Si/diamond, c-BN/diamond and Si/c-BN are unfolded. In comparison, the interfacial thermal conductance of c-BN/diamond is ten-fold of Si/diamond; besides, the thermal conductance across Si/c-BN interface is 20.2% larger than that of Si/diamond at 300 K and 18.9% larger at 340 K. These findings provide us new vision and potential solution to heat dissipation of high-local-power density devices, shedding light on future thermal management of c-BN and diamond related electronics.Peer reviewe
Verification of C-detectability using Petri nets
No full textDetectability describes the property of a system to uniquely determine, after a finite number of observations, the current and the subsequent states. In this paper, we extend detectability to C-detectability that only requires that a given set of crucial states can be distinguished from other states. We define four types of C-detectability in the framework of labeled Petri nets: strong C-detectability, weak C-detectability, periodically strong C-detectability, and periodically weak C-detectability. Moreover, we propose efficient approaches to verify such properties in the case of bounded labeled Petri net systems. The proposed approaches use the notion of basis marking and thus do not require an exhaustive enumeration of the reachability space
ZrO2/C nanosphere enables high-efficiency nitrogen reduction to ammonia at ambient conditions
No full textElectrochemical synthesis of ammonia via nitrogen reduction reaction is a rational route to save energy and relieve pollution compared to the traditional Haber-Bosch process. In this report, ZrO2 nanosphere derived from thermolysis of Zr-based biphenyl-4,4 '-dicarboxylic acid MOFs (ZrO2/C) as a non-noble metal catalyst with large specific surface area and porous structure is proposed to fix nitrogen to ammonia at ambient conditions. Such catalyst achieves Faradaic efficiency of 11.86 % and a NH3 yield rate of 10.72 mu g h(-1) mg(cat.)(-1) at -0.6 V vs. the reversible hydrogen electrode in 0.1 M Na2SO4. First-principles calculations confirm the alternating reaction at the catalyst surface
Kinematic Simulation and Structure Analysis of a Morphing Flap
No full textThis thesis presents a study on the design and analysis of a morphing flap
structure integrated with actuation mechanism for potential application to large
aircraft. Unlike the conventional rigid flap mounted on the wing trailing edge,
the morphing flap is designed as a unitized structural system integrated with
three primary components: the upper and lower flexible skins reinforced by
stringers, an eccentric beam actuation mechanism (EBAM) with discs fixed on it,
and the connection of the discs with the stringers. Based on the EBAM concept
proposed by Dr Guo in previous research [1], the current study has been
focused on the EBAM design and optimization, kinematic simulation and
structural modelling of the morphing flap.
Although a lot of efforts have been made to develop the morphing flap in
previous research, it is lack of detailed design of the disc-skin linkage and clear
view on the mechanism optimization in relation to the shape requirement. The
main objective of this research is to meet the morphing shape requirements and
calculate the actuation torque for a specified morphing flap. Firstly effort was
made to design and optimize the disc shape and locations in the EBAM for the
best matching of the specified morphing shape with minimum actuation torque
demand. It is found that minimum three discs are required and their locations
have little effect on the actuation torque. Secondly attention was focused on
designs of the disc and a C-linkage with the stringers. To ensure that the C-
linkage works in practice, a twisted stringer flange design was proposed. Thirdly
the actuation mechanism was integrated with the stiffened skin to play the role
of an active rib in the flap structure. Based on the design, FE modelling and
analysis of the morphing flap structure was carried out. The behaviour of the
morphing flap under the internal actuation and external aerodynamic load was
applied for stress analysis and detailed design of the structures. Finally the
kinematics of the integrated morphing flap was simulated by using CATIA to
demonstrate the feasibility and the effectiveness of the improved design
Improved measurement of the branching fraction of h c → γη′/η and search for h c → γπ 0
No full textAbstract The processes h c → γP (P = η′, η, π 0) are studied with a sample of (27.12 ± 0.14) × 108 ψ(3686) events collected by the BESIII detector at the BEPCII collider. The decay h c → γη is observed for the first time with the significance of 9.0 σ, and the branching fraction is determined to be (3.77 ± 0.55 ± 0.13 ± 0.26) × 10 −4, while B (h c → γη′) is measured to be (1.40 ± 0.11 ± 0.04 ± 0.10) × 10 −3, where the first uncertainties are statistical, the second systematic, and the third from the branching fraction of ψ(3686) → π 0 h c . The combination of these results allows for a precise determination of R h c = B h c → γη B h c → γ η ′ , which is calculated to be (27.0 ± 4.4 ± 1.0)%. The results are valuable for gaining a deeper understanding of η − η′ mixing, and its manifestation within quantum chromodynamics. No significant signal is found for the decay h c → γπ 0, and an upper limit is placed on its branching fraction of B (h c → γπ 0) < 5.0 × 10 −5, at the 90% confidence level
Solidification microstructure and tensile deformation mechanisms of selective electron beam melted Ni3Al-based alloy at room and elevated temperatures
No full textSelective electron beam melting (SEBM) was used to process crack-free Ni3Al-based IC21 alloy (low density superalloy) containing ~85% γ′-volume fraction. There are distinct differences between dendrites and inter-dendritic regions with the presence of coarse γ+γ′ eutectic and secondary solidification microconstituents (Cr and Mo-rich) in the latter. The pronounced inter-dendritic eutectic regions suggest that a significant elemental partitioning between the liquid and solid occurred during the SEBM. The terminal liquid is trapped at boundaries between dendrites and grains, as evidenced by the liquid films on cracked surfaces. In contrast to extensive studies indicating the segregation of Zr and B, we show unambiguously the segregation of Si to low melting point liquid films and thereby enhancing the susceptibility to solidification cracking in IC21 produced by SEBM. The tensile specimens extracted from the crack-free IC21 samples exhibit superior properties at room temperature (RT) and 1000 °C. The RT deformation mechanism is characterised by cutting γ′-phase with two paired dislocations and antiphase boundaries in between. At 1000 °C tensile deformation, the well-developed γ/γ′ interfacial dislocation networks are in good agreement with their promising high-temperature performance (σ = 518 ± 10 MPa, σ = 560 ± 16 MPa, 20.5% for ductility)
Ring-polymer molecular dynamics: Rate coefficient calculations for energetically symmetric (near thermoneutral) insertion reactions (X + H[subscript 2]) → HX + H(X = C([superscript 1]D), S([superscript 1]D))
No full textFollowing our previous study of prototypical insertion reactions of energetically asymmetric type with the RPMD (Ring-Polymer Molecular Dynamics) method [Y. Li, Y. Suleimanov, and H. Guo, J. Phys. Chem. Lett. 5, 700 (2014)], we extend it to two other prototypical insertion reactions with much less exothermicity (near thermoneutral), namely, X + H[subscript 2] → HX + H where X = C([superscript 1] D), S([superscript 1] D), in order to assess the accuracy of this method for calculating thermal rate coefficients for this class of reactions. For both chemical reactions, RPMD displays remarkable accuracy and agreement with the previous quantum dynamic results that make it encouraging for the future application of the RPMD to other barrier-less, complex-forming reactions involving polyatomic reactants with any exothermicity.United States. Dept. of Energy. Office of Basic Energy Sciences (Massachusetts Institute of Technology. Energy Frontier Research Center for Excitonics. Combustion Energy Frontier Research Center. Award DE-SC0001198)MIT Energy Initiativ
Reply to the Comment by Chien, Guo, and Levin
No full textA Reply to the Comment by C.-C. Chien, H. Guo, and K. Levi
Experimental Investigation of Heat Transfer with Ash Deposition in Ultra-Low Temperature WHRS of Coal-fired Power Plant
No full textWaste Heat Recovery Systems (WHRS) have been widely adopted in coal-fired power station boilers, though their heat transfer performance is poor under ultra-low tube temperature circumstances. In this study, we have carried out experiments to reveal heat transfer deterioration and its relation with ash deposition when probe tube temperature varies from 90°C to ultra-low 40°C. Results reveal that gas-side Nusselt number has two rapid drops as the probe outer wall temperature decreases. The first drop occurs when the wall temperature is about 32°C lower than the acid dew temperature, where the deposited ash thickens due to the condensed concentrated sulfuric acid and slight corrosion is observable. The second drop occurs when the wall temperature is about 10°C greater than the water dew temperature, where the corrosion becomes severe because the concentration of sulfuric acid decreases. For engineering applications, we suggest that the tube outer wall temperature be greater than the first drop temperature to deflate poor heat transfer and surface corrosion.Peer reviewe
Search for new hadronic decays of h c and observation of h c → p p ¯ η
No full textAbstract A search for the hadronic decays of the h c meson to the final states p p ¯ π + π − π 0, p p ¯ η , and p p ¯ π 0 via the process ψ(3686) → π 0 h c is performed using (4.48 ± 0.03) × 108 ψ(3686) events collected with the BESIII detector. The decay channel h c → p p ¯ η is observed for the first time with a significance greater than 5σ and a branching fraction of (6.41 ± 1.74 ± 0.53 ± 1.00) × 10 −4, where the uncertainties are statistical, systematic, and that from the branching fraction of ψ(3686) → π 0 h c . Strong evidence for the decay h c → p p ¯ π + π − π 0 is found with a significance of 4.9σ and a branching fraction of (3.84 ± 0.83 ± 0.69 ± 0.58) × 10 −3. The significances include systematic uncertainties. No clear signal of the decay h c → p p ¯ π 0 is found, and an upper limit of 6.59 × 10 −4 on its branching fraction is set at the 90% confidence level
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