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The microscopic mechanism of the energy transfer in cyclotrimethylene trinitramine (RDX) is of particular importance for the study of the energy release process in high-energy materials. In this work, an effective vibrational Hamiltonian based on normal modes (NMs) has been introduced to study the energy transfer process of RDX. The results suggest that the energy redistribution in RDX can be characterized as an ultrafast process with a time scale of 25 fs, during which the energy can be rapidly localized to the –NNO2 twisting mode (vNNO2), the N–N stretching mode (vN–N), and the C–H stretching mode (vC–H). Here, the vNNO2 and vN–N modes are directly related to the cleavage and dissociation of the N–N bond in RDX and, therefore, can be referred to as "active modes." More importantly, we found that the energy can be rapidly transferred from the vC–H mode to the vNNO2 mode due to their strong coupling. From this perspective, the vC–H mode can be regarded as an "energy collector" that plays a pivotal role in supplying energy to the "active modes." In addition, the bond order analysis shows that the dissociation of the N–N bonds of RDX follows a combined twisting and stretching path along the N–N bond. This could be an illustration of the further exothermic decomposition triggered by the accumulation of vibrational energy. The present study reveals the microscopic mechanism for the vibrational energy redistribution process of RDX, which is important for further investigation of the energy transfer process in high-energy materials. [ABSTRACT FROM AUTHOR]

Steady-state and time-resolved infrared (IR) studies of cyclotetramethylene tetranitramine (HMX) were carried out, using the asymmetric nitro-stretch as probe, to investigate its solution structures and vibrational energy transfer processes in pure dimethyl sulfoxide (DMSO) and in a DMSO/water mixture. A linear IR spectrum in the nitro-stretching mode region shows two major bands and one minor band in DMSO but changes to the two major bands mainly picture when adding water as an antisolvent of HMX, suggesting a transition from well-solvated and less perfect β-conformation to a less-solvated and close-to-perfect β-conformation. The latter bears a similar asymmetric nitro-stretch vibration profile to the β-polymorph in the crystal form. Density functional theory computations of the nitro-stretching vibrations suggest that HMX in DMSO may be in a NO2 group rotated β-conformation. Two-dimensional IR cross-peak intensity reveals intramolecular energy transfer between the axial and equatorial nitro-groups in the β-HMX on the ps time scale, which is slightly faster in the mixed solvent case. The importance of water as an antisolvent in influencing the equilibrium solvation structure, as well as the vibrational and orientational relaxation dynamics of HMX, is discussed. [ABSTRACT FROM AUTHOR]

In China, many cities are building themselves the transit metropolis, and the reasonable evaluation of level of service (LOS) of public transport system (PTS) is one important aspect. However, to determine the overall LOS is hard because the distribution of service in PTS is not homogeneous with regard to time and space. To address this problem, this study proposes a general framework to determine the LOS scale of PTS based on the distribution of service quality. Under the framework, two classification methods are discussed. Method 1 uses two parameters, the mean and coefficient of variation to model the distribution, and Method 2 is an existing approach that only considers mean. Then the specific use of the framework is expounded for the service attribute of crowding, and Beijing subway line LOS is evaluated. The line LOS is divided into I-IV, whose threshold is expressed as a function of mean and coefficient of variation. The results show that 57.8% of the sample points are in the most crowding level IV in morning peak hours by Method 1, but 60.9% of sample points are in a comfortable level II by Method 2, and the former is more consistent with reality. In addition, it reveals which lines and time periods need to improve the service level. The research proves the feasibility of considering the service distribution to determine the overall LOS of PTS, and it is useful for capturing more detailed information of the system performance in time and space. This research can provide an approach for evaluating and helping to improve the overall service level of PTS for public transport authorities., Author(s): Min Wang [1]; Baohua Mao (corresponding author) [1]; Yanqiang Yang [1]; Ruijia Shi [2]; Junsheng Huang [1] 1. Introduction With the development of social economy and residents' living standards, [...]

To improve the driving comfort of continuously variable transmission (CVT) tractors, the shifting quality of hydrostatic power-split transmission with a standard planetary gear set was optimized. Firstly, the powertrain of the CVT and two shift strategies, direct-shift and bridge-shift, were introduced; then, a dynamic model of tractor shifting was constructed, and the models of key components such as wet clutches and proportional pressure valves were experimentally verified. Finally, the control parameters of the above two shifting strategies were optimized, and the acceleration impact and sliding energy loss caused by them were compared. The results showed the following: the minimum peak acceleration of the bridge-shift method was 0.385807 m/s2; the energy consumption of the bridge-shift method was significantly lower than that of the direct-shift method; the sliding friction work of clutches decreased by 14.92% and 75.84%, respectively, while their power loss decreased by 22.82% and 74.48%, respectively. [ABSTRACT FROM AUTHOR]

A simple kHz-rate spectral phosphor thermometry technique with sub-millisecond temporal resolution for contactless point measurements of short duration transient surface temperature changes was developed by employing a compact high-speed fiber-optic spectrometer, a high repetition rate pulsed green laser, and a fast decaying thermographic phosphor. Temperature changes were determined from the temperature-dependent emission spectra of the YAG:Ce phosphor using a spectral slope method. The precision of single-shot temperature measurements was better than 4% for temperatures up to 700 K. An application of the technique for time-resolved measurements of local transient temperature changes at 5 kHz during repetitive long CO2 laser pulse heating is presented. The measured temperature transients are well-predicted using a two-dimensional axisymmetric heat transfer model. [ABSTRACT FROM AUTHOR]