Using e + e − collision data samples with center-of-mass energies ranging from 2.000 to 2.644 GeV, collected by the BESIII detector at the BEPCII collider, and with a total integrated luminosity of 300 pb −1 , a partial-wave analysis is performed for the process e + e − → K + K − π 0 π 0 . The total Born cross sections for the process e + e − → K + K − π 0 π 0 , as well as the Born cross sections for the subprocesses e + e − → φπ 0 π 0 , K + (1460)K − , K + 1 (1400)K − , K + 1 (1270)K − and K * + (892)K * − (892), are measured versus the center-of-mass energy. The corresponding results for e + e − → K + K − π 0 π 0 and φπ 0 π 0 are consistent with those of BaBar and have much improved precision. By analyzing the cross sections for the four subprocesses, K + (1460)K − , K + 1 (1400)K − , K + 1 (1270)K − and K * + (892)K * − (892), a structure with mass M = (2126.5 ± 16.8 ± 12.4) MeV/c 2 and width Γ = (106.9 ± 32.1 ± 28.1) MeV is observed with an overall statistical significance of 6.3σ, although with very limited significance in the subprocesses e + e − → K + 1 (1270)K − and K * + (892)K * − (892). The resonant parameters of the observed structure suggest it can be identified with the φ(2170), thus the results provide valuable input to the internal nature of the φ(2170).

The photodissociation dynamics of jet-cooled CHBrI were investigated in the near-ultraviolet (UV) region from 280-310 nm using velocity map imaging. We report the translational and internal energy distributions of the CHBr radical and ground state I ( P) or spin-orbit excited I ( P) fragments determined by velocity map imaging of the ionized iodine fragments following 2 + 1 resonance-enhanced multiphoton ionization of the nascent neutral iodine products. The velocity distributions indicate that most of the available energy is partitioned into the internal energy of the CHBr radical with only modest translational excitation imparted to the cofragments, which is consistent with a simple impulsive model. Furthermore, from extrapolation of the velocity distribution results, the first determination of the C-I bond dissociation energy of CHBrI is presented in this work to be D = 16 790 ± 590 cm. The ion images appear anisotropic, indicative of a prompt dissociation, and the derived anisotropy parameters are consistently positive. Additionally, the angular distributions report on the electronic excited state dynamics, which validate recent works characterizing the electronic states responsible for the first absorption band of CHBrI. In the current work, photolysis of CHBrI on the red edge of the absorption spectrum reveals an additional channel producing I ( P) fragments.

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Abstract:In view of the requirements for mechanical properties and service life above 650 • C, a high-Mn austenitic hot work die steel, instead of traditional martensitic hot work die steel such as H13, was developed in the present study. The effect of heat treatment on the microstructure and mechanical properties of the newly developed work die steel was studied. The results show that the microstructure of the high-Mn as-cast electroslag remelting (ESR) ingot is composed of γ-Fe, V(C,N), and Mo 2 C. V(C,N) is an irregular multilateral strip or slice shape with severe angles. Most eutectic Mo 2 C carbides are lamellar fish-skeleton-like, except for a few that are rod-shaped. With increasing solid solution time and temperature, the increased hardness caused by solid solution strengthening exceeds the effect of decreased hardness caused by grain size growth, but this trend is reversed later. As a result, the hardness of specimens after various solid solution heat treatments increases first and then decreases. The optimal combination of hardness and austenitic grain size can be obtained by soaking for 2 h at 1170 • C. The maximum Rockwell hardness (HRC) is 47.24 HRC, and the corresponding austenite average grain size is 58.4 µm. When the solid solution time is 3 h at 1230 • C, bimodality presented in the histogram of the austenite grain size as a result of further progress in secondary recrystallization. Compared with the single-stage aging, the maximum impact energy of the specimen after two-stage aging heat treatment was reached at 16.2 J and increased by 29.6%, while the hardness decreased by 1-2 HRC. After two-stage aging heat treatment, the hardness of steel reached the requirements of superior grade H13, and the maximum impact energy was 19.6% higher than that of superior grade H13, as specified in NADCA#207-2003.

In the background that hot-working die steels have been widely used in the hot stamping process of high strength steels for manufacturing car bodies and parts, solid lubricant materials are promising for decreasing the friction and wear on die surfaces at high temperatures. In this work, hexagonal boron nitride was used to lubricate the sliding interface of ceramic Si3N4 against die steel H13 at 800 ℃, and its frictional behavior was investigated at different contact pressures and rotating speeds by pin-on-disk testing. Tribological characteristics of hexagonal boron nitride solid lubricant were analyzed through 3D laser scanning confocal microscope and energy-dispersive spectroscopy. The results show that the wear behavior of hexagonal boron nitride powder lubricating film featured two stages: gradual undermining and complete damage. The formation-broken dynamic cycle of partial lubricating film constantly occurred at the frictional interface until the film was completely destroyed. In a short period, the hexagonal boron nitride lubricant can reduce the friction coefficient efficiently compared with dry friction, and the die substrate showed basically no abrasion because a layer of plasticity accumulated on the die surface, which protected the substrate. In a certain range, the boundary-lubricating film became damaged rapidly with increasing load, and high speed was not conducive to the stability of the lubricating film.

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We report the density measurement through e-3He elastic scattering with a 1.23 GeV electron beam in Jefferson Lab experiment E06-010. The extracted 3He density is (9.26±0.06) amagats and the N2/3He ratio is (1.49±0.08)%. In addition, these results are consistent with the deduced target densities based on pressure broadening measurement.