Computational study of the aero-optical imaging degradation of hypersonic vehicles under time-varying velocities.

Researches on hypersonic vehicles have been a hotspot in the field of aerospace because of the pursuits for higher speed by human being. Infrared imaging guidance is playing a very important role in modern warfare. When an Infrared Ray(IR) imaging guided missile is flying in the air at high speed, its optical dome suffers from serious aero-optic effects because of air flow. The turbulence around the dome and the thermal effects of the optical window would cause disturbance to the wavefront from the target. Therefore, detected images will be biased, dithered and blurred, and the capabilities of the seeker for detecting, tracking and recognizing are weakened. In this paper, methods for thermal and structural analysis with Heat Transfer and Elastic Mechanics are introduced. By studying the aero-thermal effects and aero-thermal radiation effects of the optical window, a 3D analysis model of the optical window is established by using finite element method. The direct coupling analysis is employed as a solving strategy. The variation regularity of the temperature field is obtained. For light with different incident angles, the influence on the ray propagation caused by window deformation is analyzed with theoretical calculation and optical/thermal/structural integrated analysis method respectively.

The aero-optical effects induced by the complex flow structure around a hypersonic optical dome is highly unsteady, which leads to significant differences in the imaging quality under different exposure times. It is of great significance to study the influence of exposure time on imaging quality for guiding the design of imaging guidance seekers and improving imaging guidance accuracy. Based on the hypersonic gun wind tunnel, an aero-optical effect measurement platform was built to measure the wavefront from transient exposure to long exposure. With the increase of exposure time, the accuracy of high-order optical path difference (OPD) reconstruction by low-order Zernike polynomials increased from 62.2% to 88.6%. The increase of exposure time was helpful to reduce the complexity of the wavefront spatial distribution structure. In principle, it could reduce the difficulty of wavefront adaptive correction systems. With the increase of exposure time, the ${{\rm OPD}_{\rm rms}}$OPDrms corresponding to ${{\rm OPD}_{\rm high-order}}$OPDhigh-order increased gradually, the amplitude decreased gradually, and the difference of ${{\rm OPD}_{\rm rms}}$OPDrms decreased gradually at different times. Under different exposure times, the large-aperture approximation principle could achieve a better prediction of Strehl ratio values. With the increase of exposure time, the imaging integral resolution, $R$R, decreased obviously, and it was stable at about ${1.43}{R_0}$1.43R0. Compared with that, $R$R was improved by about 30% when the exposure time was 6 ns.

According to the aero-thermal effects and aero-thermal radiation effects of the optical window, the thermo-optic effect, the elasto-optical effect and the thermal deformation of the optical window are analyzed using finite element analysis method. Also, the peak value and its location of the point spread function, which is caused by the thermo-optic effect and the dome thermal deformation, are calculated with the variance of time. Furthermore, the temperature gradient influence to the transmission of optical window, the variation trend of transmission as well as optical window radiation with time are studied based on temperature distribution analysis. The simulations results show that: When the incident light is perpendicular to the optical window, image shift is mainly caused by its thermal deformation, and the value of image shift is very small. Image shift is determined only by the angle of the incident light. With a certain incident angle, image shift is not affected by the gradient refractive index change. The optical window transmission is mainly affected by temperature gradient and thus not neglectable to image quality. Therefore, the selection of window cooling methods, needs not only consider the window temperature but try to eliminate the temperature gradient. When calculating the thermal radiation, the optical window should be regarded as volume radiation source instead of surface radiator. The results provide the basis for the optical window design, material selection and the later image processing.

Changes in the ultimate properties brought about by outdoor weathering during the rainy season of polypropylene (PP) films were studied. The results obtained showed that the draw ratio λd, tensile stress σb, breaking ratio λb, breaking factor (BF), work draw Ud, and work for rupture Ur all increased with increase in outdoor exposure time, attaining a maximum at about 240-h exposure time, before decreasing with further increases in exposure time. On the other hand, the draw ratio δs remained practically constant up to about 100-h exposure time. The changes in the former set of properties were corroborated by the changes in the apparent crystallinity of the PP samples. In addition, it was shown that a 504-h exposure time was not enough to reduce the properties to damaging levels. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 2533–2540, 1998

Changes in the ultimate properties brought about by outdoor weathering during the rainy season of polypropylene (PP) films were studied. The results obtained showed that the draw ratio λd, tensile stress σb, breaking ratio λb, breaking factor (BF), work draw Ud, and work for rupture Ur all increased with increase in outdoor exposure time, attaining a maximum at about 240-h exposure time, before decreasing with further increases in exposure time. On the other hand, the draw ratio δs remained practically constant up to about 100-h exposure time. The changes in the former set of properties were corroborated by the changes in the apparent crystallinity of the PP samples. In addition, it was shown that a 504-h exposure time was not enough to reduce the properties to damaging levels. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 2533–2540, 1998

When an optically guided hypersonic vehicle flies in the atmosphere, the scene is viewed through an optical dome. Because of hypersonic friction with the atmosphere, the optical dome is inevitably covered by a serious shock wave, which threatens to alter the dome's physical parameters and further induce wavefront distortion and degradation of images. By studying the physical phenomena occurring within the optical dome in such an adverse environment, this paper identifies the relationship between the variation of the dome's optical characteristics and the infrared image degradation. The research indicates that the image quality degrades sharply as the vehicle's Mach number increases. Simulations also show that while the thermo-optic effect, elastic-optic effect, thermal deformation, and variation of transmittance have little effect on the optical system, the thermal radiation severely degrades images when vehicles fly at hypersonic speeds

This study addressed the antifouling efficiency of commercially available chlorine at different concentrations (0.5%, 1%, and 2%) and exposure times (0.5 min, 1 min, 5 min, and 15 min). The rapid and non-destructive FIRe (fluorescence induction and relaxation) technique was used to evaluate the effects of the biocide on diatom dominated biofilms. The efficiency of chlorine in removing diatoms from the developed biofilms increased with an increase in concentration and exposure time. The fluorescence measurements revealed low F v /F m and high σPSII values for chlorine-treated Navicula and Amphora biofilms indicating that chlorination was efficient in damaging the photosystem-II reaction centers. Chlorination also caused mortality of diatom cells by damaging the cell body. In natural biofilms, the biocidal effect of chlorine was species specific; species of Amphiphrora, Navicula, Cylindrotheca, and Coscinodiscus showed an increase in the density of the population, but species of Pleurosigma, Amphora, and Thalassionema did not increase in density after chlorine treatment. It was also demonstrated that diatoms can colonize, grow and photosynthesize on chlorine-treated surfaces. Under pulse chlorination (treatment every 6 h), irrespective of chlorine concentration, the development of biofouling decreased with an increase in exposure time. Differences between exposure times of 1 to 15 min were not significant. Additionally, transmission levels of the control (non-chlorine-treated) fouled coupons reduced significantly (∼20%) compared to the chlorine-treated fouled coupons (<2%). These results suggest that chlorine can be used as a biocide to control the development of diatom biofilms.

The high-temperature structure stability of high Al content Ni-based single crystal superalloy was studied, the microstructure was observed, and the micro-mechanism of the thermal stability of the material was analyzed. The results show that the exposure time and exposure temperature have significant effects on the stability of the alloy’s high-temperature structure. With the increase of exposure temperature and/or exposure time, the γ’ phase in the material becomes coarser, gradually connects and grows, and the stability of the material structure is obviously reduced. Compared with standard heat-treated alloys after high temperature exposure, The absolute value of the γ’ and γ phases misfit increases significantly. With the increase of exposure time, although the absolute value of the two-phase misfit continues to increase, the increase of its absolute value gradually slows down. The long-term structural stability of the alloy under continuous exposure to high temperature environment is good.

Современные требования, предъявляемые к качеству товарной нефти, способствуют разработке новых и совершенствованию существующих технологий ее подготовки. Интенсификация десорбции сероводорода с помощью ультразвукового воздействия является одним из направлений при разработке новых технологий очистки нефти. Были проведены экспериментальные исследования определения эффективности применения ультразвукового излучения при различных условиях. С повышением температуры эффективность возрастает, причем наиболее существенно для нефти с высокой вязкостью. При вязкости нефти более 400 мПас увеличение удельной акустической мощности практически не влияет на снижение содержания сероводорода, тогда как при вязкости менее 150 мПас повышение мощности от 100 до 200 кВт/м3 позволяет интенсифицировать выделение сероводорода из жидкой фазы примерно в два раза. Увеличение продолжительности воздействия на нефть ультразвуковых волн также способствует более полной десорбции сероводорода из нефти. Однако, увеличение продолжительности и удельной акустической мощности не всегда является экономически оправданным. Оптимальным является воздействие на нефть в течение 417 минут с удельной акустической мощностью 1050 кВт/м3. Согласно полученным результатам установлено, что ультразвуковая обработка позволяет улучшить процесс перехода сероводорода из нефти в газовую фазу и может использоваться на горячих ступенях сепарации с целью снижения расхода реагентанейтрализатора сероводорода. Current requirements to stock tank oil quality promote development and improvement of oil treatment technologies. One of the promising methods is enhancement of hydrogen sulfide stripping via ultrasonic treatment. Experimental studies have been carried out to determine the efficiency of ultrasonic radiation under various conditions. The efficiency increases with temperature growth, especially for highviscosity oils. For oil viscosity over 400 MPas, specific sound power increase has little or no impact on H2S stripping, while in case of viscosity below 150 MPas increase of sound power from 100 to 200 kW/m3 enhances hydrogen sulfide separation twofold. Increase of ultrasonic exposure time also contributes to a more complete H2S removal. However, increase of exposure time and specific sound power is not always economically viable. An optimum exposure time is from 4 to 17 minutes at specific sound power of 1050 kW/m3. The obtained results show that ultrasonic oil treatment improves transition of hydrogen sulfide from oil to the gas phase and can be used at thermal stages of separation to reduce consumption of H2S chemical scavenger.

Ultraviolet (UV) radiation significantly affects insect life and, as a result, has been widely used to control different invertebrate pests. The current results demonstrate that when Bemisia tabaci first instar nymphs are exposed to UV-A light for 12, 24, 48, and 72 h, their developmental and biological parameters are negatively affected by UV-A exposure; the effect increased with an increase in exposure time. We hypothesized that UV-A light is compatible with other biological control agents. Results showed that when the entomopathogenic fungus Cordyceps fumosorosea was applied to third instar nymphs of B. tabaci previously exposed to UV-A light, the LC50 was 3.4% lower after 72 h of exposure to UV-A light compared to the control. However, when the fungus was exposed to UV-A light, its virulence decreased with an increase in UV-A exposure time. The parasitism rate of Encarsia formosa against 24 h UV-A-exposed third instar nymphs of B. tabaci increased while the adult emergence from parasitized nymphs was not affected after UV-A light exposure. Parasitism rate was significantly reduced however following E. formosa exposure to UV-A light; but again, adult emergence was not affected from parasitized nymphs. The percentage mortality of E. formosa increased with increasing exposure time to UV-A light. The enzyme activity of SOD, CAT, GST, and AChE and the energy reserve contents were negatively affected due to UV-A exposure. Collectively, this study has demonstrated that UV-A light significantly suppresses the immune system of B. tabaci and that UV-A light is compatible with other biological control agents if it is applied separately from the biological agent.

Neurotoxicity, oxidative stress biomarkers and haematological responses in African catfish (Clarias gariepinus) exposed to polyvinyl chloride microparticles

Kinetic models for production of propionic acid by Propionibacter freudenrechii subsp. shermanii and Propionibacterium freudenreichii subsp. freudenreichii in date syrup during sonication treatments

Aiming at the problem that multiple Unmanned Aerial Vehicles (UAVs) attack the stationary target cooperatively under time-varying velocity, the cooperative guidance law with finite time convergence on two-dimensional plan and the three-dimensional cooperative guidance laws with impact time constraint are designed separately in this paper. Firstly, based on the relative motion equation between UAV and target on two-dimensional plane, the time cooperative guidance model of multiple UAVs is established. Then based on the consistency theory and graph theory, a distributed time cooperative guidance law is designed, which can ensure that the impact time of all UAVs can be quickly consistent in a limited time. Next, the cooperative guidance problem is expanded from two-dimensional plane to three-dimensional space, the motion model between UAV and target in three-dimensional space is established and the expression of time-to-go estimation under time-varying velocity is derived. Finally, according to whether there is the communication among UAVs under the condition of time-varying velocity, a multiple UAVs three-dimensional cooperative guidance law based on desired impact time and a multiple UAVs three-dimensional cooperative guidance law based on coordination variables are designed, respectively. The simulation results show that the cooperative guidance law with finite time convergence on two-dimensional plan and the three-dimensional cooperative guidance law with impact time constraint proposed in this paper are effective, which can both realize the saturation attack under the time-varying velocity.

A study was conducted to determine the effect of microwave pre-treatment on de-husking characteristics and quality parameters of foxtail millet. Foxtail millet was treated at three microwave power levels (900 W, 720 W and 540 W) for three different exposure time (120 s, 100 s and 80 s). Increase in grain surface temperature from 64.68˚C to 81.66˚C and decrease in de-husking time from 191 s to 88 s were observed with increase in microwave power level and exposure time. De-husking yield increased initially with increase in microwave power and exposure time, reaching a maximum of 85.64 % (720 W, 120 s), and thereafter decreased. The lowest de-husking yield of 72.12 % was observed at 900 W and 100 s exposure time. The increase in broken content from 0.20 % to 19.61 %, and reduction in head yield from 99.80 % to 85.40 % was observed with increase in microwave power and exposure time. The colour change was not significant (@ p≤0.05) in all the treatments. Cooking time of the de-husked grain decreased with increase in microwave power level and exposure time from 544 s to 442 s. De-husking yield of 91.97 % was predicted at optimal conditions of 732 W microwave power and 80 s exposure time.

The induced modifications of the optical properties in UV-irradiated Makrofol-E with different wavelengths were investigated. Makrofol-E samples were irradiated by UV of wavelengths 254, 302, and 365 nm for different durations. It was found that Makrofol-E shows substantial modifications in its optical characteristics upon exposure to UV of wavelengths 302 and 254 nm, but no modifications were observed at 365 nm. UV-irradiated Makrofol-E with wavelengths 254 and 302 nm exhibits shoulder bands at 297 nm in UV–visible spectra. For an exposure time less than 20 h, the band absorbance strengths depend on the exposure time and approximately increases linearly, but for prolonged exposure times, the band absorbance strengths become almost saturated. The optical energy band gaps obtained from the direct and indirect allowed transition in K-space. Both of them decrease with the increase in exposure time for wavelengths of 254 and 302 nm. Urbach's energy increases with increase in the exposure time for both wavelengths of 254 and 302 nm. The number of carbon atoms in a cluster increases with the increase in the exposure time.