Search

Micrometer-sized spherical composites based on 2,4,6,8,10,12-hexanitrohexaazaisowurtzitane (CL-20) with fluororubber (F2604), dioctyl sebacate (DOS), and polyvinyl butyral (PVB) were prepared by an electrospray method. After preparation, the morphology, chemical bonds, thermal decomposition properties, mechanical sensitivity, and explosion performance were characterized. The main explosive CL-20 transformed from ε-CL-20 to β-CL-20 after electrospray preparation. With an insensitive additive mass ratio of 5 wt %, the CL-20/F2604 composite had the highest maximum peak exothermic temperature and the lowest mechanical sensitivity. The explosion pressures of the composites with the same mass ratio of additives decreased in the order CL-20/F2604CL-20/PVBCL-20/DOS and were lower than that of raw CL-20.

In a constant-volume chamber, the atomization characteristics of low-viscosity fuel sprays were studied under the effects of mass concentration and injection pressure. Microscopic spray parameters were measured via laser diffraction downstream of the nozzle at various axial and radial positions. The results showed that an increase in the mass concentration suppressed the atomization effect in a linear manner. The increase in injection pressure promoted droplet breakup; however, the trend gradually weakened and became more noticeable at high concentrations. Compared to the concentration, the influence of the injection pressure on the atomization characteristics was dominant. Although low concentration and high injection pressure promoted droplet breakup, they also increased the probability of droplet collision, resulting in droplet aggregation. This was more evident in low-viscosity fuels. The droplet size increased in the axial direction owing to the aggregation. However, the diameter decreased in the radial direction owing to the outward deflection of small droplets caused by air turbulence and entrainment. In addition, the high-velocity airflow significantly promoted droplet breakup near the nozzle and spray axis regions and suppressed the aggregation effect. Nevertheless, lower-viscosity fuels maintained smaller droplet sizes and better atomization throughout the spraying process, which was easier to achieve than that in higher-viscosity fuels. Overall, low concentration, high injection pressure and low viscosity of the fuel have beneficial effects on the droplet breakup. This is important to enhance the atomization effect of the fuel.

Among all the CL-20/HMX-based energetic composites, CL-20/HMX/PVAc sample 1 possesses the highest maximum burn pressure value of 33.3 kPa.

Background To explore the clinical efficacy and safety of Kirschner wires (KW) as blocking screws technique in extra-articular fractures of the distal tibia treated with intramedullary nail (IMN). Methods 61 patients treated with IMN for extra-articular fractures of the distal tibia assisted with KW as blocking screws technique or Poller screws (PS) technique. The operation time, times of fluoroscopy, number of blocking screws used, blood loss and time to union were compared between the two groups. Also, the functional outcomes of the two groups were compared using range of motion (ROM), visual analogue scale (VAS), American Orthopedic Foot and Ankle Society (AOFAS), and Lysholm scores. Results Compared with the PS group, the operation time of the KW group was significantly shorter, the times of fluoroscopy and the amount of blood loss during the surgery of KW were also significantly reduced (P 0.05). Conclusion In the treatment of extra-articular fractures of the distal tibia with nails, KW as blocking screws technique is safe and reliable.

Unmanned aerial vehicle (UAV)-enabled wireless power transfer (WPT) has recently emerged as a promising technique to provide sustainable energy supply for widely distributed low-power ground devices (GDs) in large-scale wireless networks. Compared with the energy transmitters (ETs) in conventional WPT systems which are deployed at fixed locations, UAV-mounted aerial ETs can fly flexibly in the three-dimensional (3D) space to charge nearby GDs more efficiently. This paper provides a tutorial overview on UAV-enabled WPT and its appealing applications, in particular focusing on how to exploit UAVs’ controllable mobility via their 3D trajectory design to maximize the amounts of energy transferred to all GDs in a wireless network with fairness. First, we consider the single-UAV-enabled WPT scenario with one UAV wirelessly charging multiple GDs at known locations. To solve the energy maximization problem in this case, we present a general trajectory design framework consisting of three innovative approaches to optimize the UAV trajectory, which are multi-location hovering, successive-hover-and-fly, and time-quantization-based optimization, respectively. Next, we consider the multi-UAV-enabled WPT scenario where multiple UAVs cooperatively charge many GDs in a large area. Building upon the single-UAV trajectory design, we propose two efficient schemes to jointly optimize multiple UAVs’ trajectories, based on the principles of UAV swarming and GD clustering, respectively. Furthermore, we consider two important extensions of UAV-enabled WPT, namely UAV-enabled wireless powered communication networks (WPCN) and UAV-enabled wireless powered mobile edge computing (MEC), by integrating the emerging WPCN and MEC techniques, respectively. For both cases, we investigate the UAV trajectory design jointly with communication/computation resource allocations to optimize the system performance, subject to the energy availability constraints at GDs. Finally, open problems in UAV-enabled WPT and promising directions for its future research are discussed.

Most of the previous studies have investigated the detonation and combustion characteristics of hydrogen and air mixtures, but the change process of hydrogen-air recombination reaction at ambient temperature is unclear. In this study, the variation of temperature and hydrogen conversion during the H2-air mixture reaction catalyzed by Pt/C catalyst was examined. Experiments were carried out in a small-scale cylindrical vessel to investigate the effects of hydrogen volume fraction, catalyst mass, and inlet gas flow rate on the reaction process. The results revealed that the reaction temperature climbed as the hydrogen volume fraction increased, with a peak value achieved when the hydrogen volume fraction reached 35 vol%, and subsequently reduced as the hydrogen volume fraction increased further. The increase of the inlet gas flow rate also promoted the growth of reaction temperature. However, there was no significant linear relationship between the rise of catalyst mass and the change of reaction temperature.

Accidents involving hydrogen explosions occur frequently, yet systematic methods of explosion suppression have not been investigated and applied. Therefore, this paper studied the deflagration characteristics in hydrogen with the addition of propane in the tube filled with mesh aluminium alloys (MAAs). The effects of different propane contents and different filling densities (the mass of MAAs per unit volume in a vessel) on the explosion suppression of the premixed gas are examined. The results show that propane and MAAs can effectively suppress the hydrogen-air explosion. However, MAAs have multiple suppression/promotion effects on the propane-hydrogen explosion. Based on the mathematical model, the dominant effect of MAAs changes abruptly toward the promoting effect when the hydrogen content exceeds 72.26% of the premixed gas stoichiometric concentration. It is also found that an increase in filling density would have a beneficial effect on explosion suppression. The study results provide references for preventing hydrogen and hydrogenated hydrocarbon fuels explosions and optimizing the performance of MAAs.

In order to improve the energy level of fuel air explosive(FAE) with delayed secondary igniters, high energetic metal powders were added to liquid fuels mainly composed of ether and isopropyl nitrate. Metal powders’ explosive properties and reaction mechanisms in FAE were studied by high-speed video, pressure test system, and infrared thermal imager. The results show that compared with pure liquid fuels, the shock wave overpressure, maximum surface fireball temperature and high temperature duration of the mixture were significantly increased after adding high energetic metal powder. The overpressure values of the liquid-solid mixture at all measuring points were higher than that of the pure liquid fuels. And the maximum temperature of the fireball was up to 1700 °C, which was higher than that of the pure liquid fuels. After replacing 30% of aluminum powder with boron or magnesium hydride, the shock wave pressure of the mixture was further increased. The high heat of combustion of boron and the hydrogen released by magnesium hydride could effectively increase the blast effect of the mixture. The improvement of the explosion performance of boron was better than magnesium hydride. It shows that adding high energetic metal powder to liquid fuels can effectively improve the explosion performance of FAE.

OBJECTIVE: To analyze the expression of type Ⅱ inflammatory-related cytokines in nasal secretions of patients with eosinophilic chronic rhinosinusitis with nasal polyps(ECRSwNP), and to preliminarily explore the role of type Ⅱ inflammatory cytokines in nasal secretions in predicting ECRSwNP. METHODS: A prospective analysis was made of 91 patients with CRSwNP who underwent endoscopic sinus surgery in Peking University Third Hospital from November 2020 to June 2021. All the selected patients had their SNOT-22 score, Lund-Mackay score and blood eosinophilia collected before surgery. Percentage and absolute value; the nasal secretions of patients were collected before operation, and enzyme-linked immunosorbent assay was used to detect the typeⅡinflammatory cytokines(IL-4, IL-5, IL-13, IL-25, IL-33, Eotaxin-3, periostin), intraoperative nasal polyp tissue was collected for eosinophil count. According to the proportion of eosinophils in the tissue≥10%, they were divided into ECRSwNP group and nECRSwNP group. The clinical baseline data and type Ⅱ inflammatory cytokines were compared between the two groups, and the related factors of ECRSwNP were evaluated by univariate logistic regression analysis. The receiver operating characteristic(ROC) curve was used to evaluate the predictive potential of each clinical index. RESULTS: The SNOT-22 score, Lund-Mackay score, blood eosinophil percentage and absolute value in the ECRSwNP group were higher than those in the nECRSwNP group(P < 0.05). In the nECRSwNP group(P < 0.01). Logistic regression analysis found that IL-5, Eotaxin-3 and blood eosinophil percentage were risk factors for ECRSwNP(P < 0.05). ROC analysis found that IL-5, Eotaxin-3 and blood eosinophil percentage had predictive diagnostic value(P < 0.01), among which blood eosinophil percentage had the greatest predictive value(AUC=0.756). The prediction model composed of Eotaxin-3, SNOT-22 score, sinus CT Lund-Mackay score, blood eosinophil percentage and blood eosinophil absolute value had better prediction effect on ECRSwNP(AUC=0.873). CONCLUSION: Type Ⅱ inflammatory cytokines IL-5 and Eotaxin-3 in nasal secretions may be involved as biomarkers for early diagnosis of ECRSwNP.

This study seeks to discover the change of cloud's expansion rate with self-designed shock wave dispersion system. Transmission, diffraction and reflection could be observed intuitively when shock waves passed through solid particle layers. Results show that the longitudinal motion of particle group greatly influenced cloud's volume growth, thus, the maximum rate of longitudinal expansion of clouds was almost twice that of lateral expansion. The cloud growth rate and volume acceleration increased with smaller particle size, thicker particle layer and stronger shock wave intensity. Also, the expansion rate initially had a drastic decrease, small particles made clouds volume acceleration unstable and experienced a subsequent swift rise. Shock wave intensity influenced diffraction and reflection formation waves as well as the cloud's shape and expansion rate. This study therefore proposed a controlling model for cloud's expansion rate, which could illustrate differences between acceleration stage of dynamic action and deceleration stage of resistance action.

The etiologies of chronic rhinosinusitis with nasal polyps (CRSwNP)-associated olfactory dysfunction have several potentially overlapping hypotheses. Understanding the association of tissue eosinophils and mucous inflammatory cytokines with olfactory function and identifying predictors of olfactory outcomes in patients with nasal polyposis after surgery is fundamental for future clinical care and research.Eighty-five patients who underwent endoscopic surgery for nasal polyposis were enrolled in this study. Olfactory measurements were performed before surgery and 3-6 months after surgery using a TT olfactometer. Baseline characteristics of CRSwNP patients were collected, and Spearman's rho correlation was performed to assess the association of olfactory function with tissue eosinophils and mucous inflammatory cytokines. A multivariate logistic regression model was used to assess the independent predictors of olfactory outcomes after surgery.Here, 85 CRSwNP patients, including 25 patients without olfactory disorder and 60 patients with hypo-anosmia, were evaluated. Of the 60 patients with preoperative hypo-anosmia, 22 did not have improved olfactory function, and 38 demonstrated normal olfactory function after surgery based on the TT olfactometer results. The levels of tissue eosinophil, interleukin-5 (IL-5), IL-13, eotaxin-3, and periostin in the preoperative hypo-anosmia group were higher than those in the preoperative normosmia group. Tissue eosinophil count, IL-5, and periostin levels in patients without olfactory improvement were higher than those in patients with olfactory improvement. The tissue eosinophil count, blood eosinophil count, and nasal mucus levels of IL-5, eotaxin-3, and periostin were significantly correlated with olfactory function in all patients with CRSwNP. The IL-5 level remained a strong predictor of poor olfactory outcomes after surgery.Both tissue eosinophils and mucous inflammatory cytokines, including IL-5, IL-13, eotaxin-3, and periostin, may contribute to the pathogenesis of CRSwNP-associated olfactory dysfunction. Higher IL-5 levels are associated with a lower chance of olfactory function recovery after each surgical revision.

To explore an effective way to prevent and control the hydrogen explosion accidents, closed explosion experiments involving hydrogen-air mixtures were carried out in a 2 m-long cylindrical tube under the influences of mesh aluminum alloys (MAAs) and spherical nonmetallic materials (SNMs). The results show that with the increase of filling diameter, the overpressure of hydrogen-air mixtures under the influence of MAAs and SNMs decreases gradually in general, and the flame velocity shows a same trend. MAAs and SNMs have a promotion/suppressing double functions on the deflagration of hydrogen-air mixtures and SNMs show a better suppressing effect than MAAs. It is also found that the deflagration to detonation transition (DDT) is more difficult achieved for larger filling density and larger filling diameter of MAAs and SNMs. In addition, several different DDT mechanisms are discussed in detail, including DDT caused by Mach-stem reflection and by direct initiation due to shock focusing. Based on a mathematical model, a prediction value of 184.30 kg/m3 (filling density of MAAs) may be satisfy the explosion-suppression evaluation criteria according to the Chinese standard AQ3001-2005. These results provide references for preventing explosions of hydrogen-air mixtures and for optimizing the performance of MAAs and SNMs.

An experimental study was carried out to investigate the flame propagation and thermal hazard of the premixed N2O/fuel mixtures, including NH3, C3H8 and C2H4. The study provided the high speed video images and data about the flame locations, propagation patterns, overpressures and the quenching diameters during the course of combustion in different channels to elucidate the dynamics of various combustion processes. The onset decomposition temperature was determined using high-performance adiabatic calorimetry. It was shown that the order of the flame acceleration rate and thermal hazard was N2O/C2H4>N2O/C3H8>N2O/NH3.

The density functional theory (DFT) was applied to investigate the structure, optical properties, and non-bonded interactions of the cyclo-pentazolate salt [Mg(H2O)6(N5)2]·4H2O in the pressure range of 0–100 GPa. The results show that there is a structural transition at the pressure of 64 GPa, which has not been found in the experiments. As the pressure increases, the band gap gradually decreases with a sudden increase at the structural transition point. The analysis of DOS presents that the electronic localization in the crystal gradually weakens under the pressure. The structural transition point also exists in the hydrogen bonds and the Hirshfeld surfaces under compression. The absorption spectra of the cyclo-pentazolate salt at high pressures show some strong bands in the fundamental absorption region. The increasing pressure helps to improve the photoelectric performances of the crystal. Our studies are expected to provide a new understanding of the structural transition of the novel energetic materials under high pressures.

Experiments were conducted in a 2 m large duct with an internal diameter of 70 mm, to investigate the effects of the vent area and ignition position on pressure oscillations with different methane concentrations. The results showed that violent pressure oscillations occurred when methane concentrations were between 9.5 and 12 vol. % in the closed duct. End ignition was shown to dampen the pressure oscillations to a significant extent. In addition, vented explosions could also reduce the pressure oscillations where the amplitude of the pressure oscillations decreases with increasing vented area. For a vent area of 38.5 cm2, no pressure oscillations occurred in all tests. Central ignition produced the larger pressure peak only when the vent area was small.

Zirconium powder, a main potential dangerous source in nuclear industry, has been focused on its explosion characteristics in this paper. Experiments were performed in a 20 L cylindrical explosion vessel with the influences of initial ignition energy, ignition delay time and zirconium concentration. Results showed that the maximum explosion pressure of zirconium-air mixture rose with the increase of the initial ignition energy, and a peak value was obtained with the variation of the ignition delay time. Lower explosion limit with the initial ignition energy of 10 kJ is 10 g/m³. Furthermore, explosion severity parameters, including maximum explosion pressure, maximum rate of pressure rise and maximum explosion index of zirconium-air mixture, were also obtained with the coupling variation between initial ignition energy and dust concentration. Research results and data obtained are a supplement to the utilization and safety operation of zirconium powders.

Detonation characteristics of hydrocarbon fuels are important indexes for their safety evaluation and protection. To investigate the detonation characteristic of alkane homologs series and the influence of different molecular energies, alkane homologs series’ critical energy to direct detonation (hereinafter related to as critical energy) and detonation cellular width were measured by a self-designed shock tube. Then, the molecular total energy (E) and bond dissociation energy (BDE) of fuel molecules were calculated by the quantum chemistry method. After the comparison between detonation characteristics and molecular energies, it is found that for alkane homologs series, molecular total energy was found to have a good exponent relation between critical energy and detonation cellular width, which indicated that the detonation sensitivity of alkane homologs series can be predicted based on total energy of fuel molecules with preferable accuracy. Extra experiment and calculation was also carried out on gaseous hydrocarbon fuels (ethane, ethylene and acetylene) with same carbon atom number. Results indicated that the bond dissociation energy may have the impact on the detonation cellular width for these three gaseous fuels. The bigger bond dissociation energy leads to smaller cellular width.