脉冲激光在板状介质中的爆轰破坏

本文从激光作用时间内介质存在“假膨胀”的假设出发，采用圆柱模型研究了脉冲激光在板状介质内部产生的爆轰破坏机理。文中认为，当固体介质为各向同性且为板状时，可采用圆柱轴对称模型，并将激光作用点置于圆柱坐标系的原点。脉冲激光作用时，介质吸收光能导致圆柱体内压力增大，但在激光作用时间内体积不变，从而得到介质产生的压力脉冲的迁移效应。对位移波方程应用Ｌａｐｌａｃｅ变换和Ｆａｒｔｏｎｇｅｎ定理得到了位移波的解析解。     

Minimization of treatment time for in vitro 1.1 MHz destruction of Pseudomonas aeruginosa biofilms by high-intensity focused ultrasound

Medical implants are prone to colonization by bacterial biofilms. Normally, surgery is required to replace the infected implant. One promising noninvasive modality is to destroy biofilms with high-intensity focused ultrasound. In our study, Pseudomonas aeruginosa biofilms were grown on implant-mimicking graphite disks in a flow chamber for 3 days prior to exposing them to ultrasound pulses. Exposure time at each treatment location was varied between 5, 15 and 30 s. Burst period was varied between 1, 3, 6 and 12 milliseconds (ms). The pulses were 20 cycles in duration at 1.1 MHz from a spherically focused transducer (f/1, 63 mm focal length), creating peak compressional and rarefactional pressures at the graphite disk surface of 30 and 13 MPa, respectively. P. aeruginosa were tagged with green fluorescent protein, and killed cells were visualized using propidium iodide before determining the extent of biofilm destruction. The exposure-induced temperature rise was measured to be less than 0.2 °C at the focus, namely the interface between graphite disk and water. Then, the temperature rise was measured at the focus between the graphite disk and a tissue-mimicking phantom to evaluate therapy safety. Two thresholds, of bacteria destruction increase and of complete bacteria removal, respectively, were identified to divide our eight exposure conditions. Results indicated that 30-s exposure and 6-ms pulse period were sufficient to destroy the biofilms. However, the 15-s exposure and 3-ms pulse period were viewed as optimum when considering exposure time, efficacy, and safety.     

Oxidative Aromatization of 4,7-Dihydro-6-nitroazolo[1,5-a]pyrimidines: Synthetic Possibilities and Limitations,Mechanism of Destruction,and the Theoretical and Experimental Substantiation

The reaction tolerance of the multicomponent process between 3-aminoazoles, 1-morpholino-2-nitroalkenes, and aldehydes was studied. The main patterns of this reaction have been established. Conditions for the oxidation of 4,7-dihydro-6-nitroazolo[1,5-a]pyrimidines were selected. Previous claims that the 4,7-dihydro-6-nitroazolo[1,5-a]pyrimidines could not be aromatised have now been refuted. Compounds with an electron-donor substituent at position seven undergo decomposition during oxidation. The phenomenon was explained based on experimental data, electro-chemical experiment, and quantum-chemical calculation. The mechanism of oxidative degradation has been proposed.     

Coherent Destruction of Tunneling of Bosons with Effective Three-Body Interactions

The tunneling dynamics of dilute boson gases with three-body interactions in a periodically driven double wells are investigated both theoretically and numerically.In our findings,when the system is with only repulsive twobody interactions or only three-body interactions,the tunneling will be suppressed;while in the case of the coupling between two- and three-body interactions,the tunneling can be either suppressed or enhanced.Particularly,when attractive three-body interactions are twice large as repulsive two-body interactions,CDT occurs at isolated points of driving force,which is similar to the linear case.Considering different interaction,the system can experience different transformation from coherent tunneling to coherent destruction of tunneling(CDT).The quasi-energy of the system as the function of the periodically driving force shows a triangular structure,which provides a deep insight into the tunneling dynamics of the system.     

Thermal-exergetic behavior of a vertical double-tube heat exchanger with bubble injection

The use of air bubbles as a heat transfer improvement technique for heat exchangers has been proposed by some researchers. The vertical motion of tiny bubbles because of density difference with liquid provides extra vibration, eddies, turbulences, and consequently further heat transfer rate. The variety of affected parameters, such as injection method, air mass flow rate, bubbles size, number of perforations that forms bubbles, etc., has added to the complexity of this phenomena so that any change in the said parameters significantly influences the thermal-exergetic behavior of the heat exchanger. The quality and quantity of the impact of bubbles on the thermal performance of heat exchangers are different for any type of them. Moreover, each type of heat exchanger requires a specific injection method depending on the heat exchanger structure. In the present research, an injection way is proposed for vertical double-tube heat exchangers, and the effect of bubbles on thermal-exergetic characteristics is experimentally studied and discussed, which have not been performed before. Nondimensional exergy destruction, number of heat transfer units, and effectiveness are the main evaluated parameters in the present paper. Results showed a significant thermal improvement of the heat exchanger under the bubble injection.     

Exergy Analysis Using a Theoretical Formulation of a Geothermal Power Plant in Cerro Prieto,México

The purpose of this research is the calculation of the exergy destruction of the single-flash and double-flash cycles of a geothermal power plant located on the ladder of the 233 m Cerro Prieto volcano, on the alluvial plain of the Mexicali Valley, Mexico. The methodology developed in this research presents thermodynamic models for energy and exergy flows, which allows determining the contribution of each component to the total exergy destruction of the system. For the case-base, the results indicate that for the single-flash configuration the efficiency of the first and second law of thermodynamics are 0.1888 and 0.3072, as well as the highest contribution to the total exergy destruction is provided by the condenser. For the double-flash configuration, the efficiency of the first and second law of thermodynamics are 0.3643 and 0.4983. The highest contribution to the total exergy destruction is provided by the condenser and followed by the low-pressure turbine.     

皮秒双脉冲LA-LIBS对合金样品的微损元素分析

研究了基于一台皮秒Nd∶YAG激光器实现合金样品的双脉冲激光剥离-激光诱导击穿光谱(LA-LIBS)微损元素分析。实验采用低能量的532 nm二倍频激光烧蚀并剥离出微量样品,然后采用较高能量的延时1064 nm激光对剥离出的样品进行二次激发,以增强等离子体中的原子辐射强度和提高光谱检测灵敏度。实验分别研究了烧蚀激光脉冲和二次激发光脉冲的能量对信号强度的影响。在烧蚀激光脉冲能量为10 μJ,二次激发光脉冲能量为2.5 mJ的条件下,LA-LIBS中Cu Ⅰ 324.75 nm原子谱线的强度与单脉冲LIBS相比改善了86倍,激光烧蚀坑洞的直径小于10 μm。研究表明：基于一台皮秒Nd∶YAG激光器,采用双脉冲LA-LIBS技术可以较好地实现对固体样品的微损元素分析。该技术在贵重样品分析和高空间分辨的二维元素显微分析中具有一定的应用价值。     

The Design Optimization of a Plasma Reactor for Chemical Waste Destruction

The heat flux and destruction and removal efficiency (DRE) measurements have been made on 100, 150 and 200 mm diameter plasma reactors to optimize the performance. The DRE was measured for pressure and gas atomization techniques of waste injection using both argon and CO₂ gases. As a result, the design of the reactor was optimized and the waste throughput was increased by ~17% with improved destruction performance. The 150 mm diameter reactor was found to perform better using gas atomization of feed injection using carbon dioxide at the given power and waste feed rate.     

Effect of mineral fillers on thermal properties and flammability ofcis-1,4-polyisoprene vulcanizates

The effect of mineral fillers such as Ultrasil VN-3, Ze?O?Sil P-45, Aerosil 200, Frantex 8, Kaolin and precipitated calcium carbonate on the thermal properties sulphur vulcanizates ofcis-1,4-polyisoprene were studied by means of thermal analysis. It was found that the addition of a mineral filler did not change the nature of the thermal processes in isoprene vulcanizates essentially, but it distinctly affected the positions of the peaks recorded in the DTA curves. The mineral fillers affected the temperatures and rates of degradation and destruction of polyisoprene cross-linked with sulphur. The presence of a mineral filler brought about a decrease in the flammability ofcis-1,4-polyisoprene sulphur vulcanizates.     

Optimization of a New Design of Molten Salt-to-CO2 Heat Exchanger Using Exergy Destruction Minimization

One of the ways to make cost-competitive electricity, from concentrated solar thermal energy, is increasing the thermoelectric conversion efficiency. To achieve this objective, the most promising scheme is a molten salt central receiver, coupled to a supercritical carbon dioxide cycle. A key element to be developed in this scheme is the molten salt-to-CO₂ heat exchanger. This paper presents a heat exchanger design that avoids the molten salt plugging and the mechanical stress due to the high pressure of the CO₂, while improving the heat transfer of the supercritical phase, due to its compactness with a high heat transfer area. This design is based on a honeycomb-like configuration, in which a thermal unit consists of a circular channel for the molten salt surrounded by six smaller trapezoidal ducts for the CO₂. Further, an optimization based on the exergy destruction minimization has been accomplished, obtained the best working conditions of this heat exchanger: a temperature approach of 50 °C between both streams and a CO₂ pressure drop of 2.7 bar.