RESUMEN
The adsorbed nanobubbles inside the nanochannels can cause fluid transport blockages, which will obviously degrade the nanodevice performance and reduce the lifetime. However, due to small-scale effects, the removal of nanobubbles is a huge challenge at the nanoscale. Herein, molecular dynamics simulations are carried out to study the effect of the electrostatic field on underwater nitrogen nanobubbles confined in nanochannels. It is found that the nanobubbles will collapse under an appropriate electrostatic field, thereby unblocking the transport of water in the nanochannels. The formation of ordered water structures induced by electrostatic fields plays an important role in the removal of nanobubbles from the nanochannels. Our findings provide a convenient, controllable, and remote way to address the blockage problem of nanobubbles in nanochannels, which may have potential applications in improving the performance of fuel cells.
RESUMEN
Atmospheric drag is an important influencing factor in precise orbit determination and the prediction of low-orbit space debris. It has received widespread attention. Currently, calculating atmospheric drag mainly relies on different atmospheric density models. This experiment was designed to explore the impact of different atmospheric density models on the orbit prediction of space debris. In the experiment, satellite laser ranging data published by the ILRS (International Laser Ranging Service) were used as the basis for the precise orbit determination for space debris. The prediction error of space debris orbits at different orbital heights using different atmospheric density models was used as a criterion to evaluate the impact of atmospheric density models on the determination of space-target orbits. Eight atmospheric density models, DTM78, DTM94, DTM2000, J71, RJ71, JB2006, MSIS86, and NRLMSISE00, were compared in the experiment. The experimental results indicated that the DTM2000 atmospheric density model is best for determining and predicting the orbits of LEO (low-Earth-orbit) targets.
RESUMEN
Atmospheric drag is an important factor affecting orbit determination and prediction of low-orbit space debris. To obtain accurate ballistic coefficients of space debris, we propose a calculation method based on measured optical angles. Angle measurements of space debris with a perigee height below 1400 km acquired from a photoelectric array were used for orbit determination. Perturbation equations of atmospheric drag were used to calculate the semi-major-axis variation. The ballistic coefficients of space debris were estimated and compared with those published by the North American Aerospace Defense Command in terms of orbit prediction error. The 48 h orbit prediction error of the ballistic coefficients obtained from the proposed method is reduced by 18.65% compared with the published error. Hence, our method seems suitable for calculating space debris ballistic coefficients and supporting related practical applications.
RESUMEN
A simple, compact sensor involving a continuous-wave 3.38⯵m distributed feedback laser in combination with a novel compact dense-pattern multipass cell was demonstrated for simultaneous measurement of atmospheric methane and water vapor. The calibration-free direct absorption spectroscopy approach was adopted for data generation and processing. Allan deviation analysis indicates that minimum detection limits (1σ) of 11.0â¯ppb for CH4 and 100â¯ppm for H2O were achieved with a 1-s integration time at an optimum pressure of 50â¯Torr. Atmospheric environmental mixing ratios of these two gases were recorded and analyzed. This newly developed mid-infrared dual-gas sensor is very suitable for trace gas sensing in weight-limited unmanned aerial vehicle- or balloon-embedded field observations.
RESUMEN
A continuous-wave mid-infrared radiation from difference frequency generation by mixing a continuous-wave Ti: sapphire laser and a continuous-wave YAG laser in a 15 mm long BaGa4Se7 crystal is demonstrated for the first time. The tunable range from 3.15 to 7.92 µm was achieved by rotating the crystal to fulfill the type I phase-matching condition. A maximum DFG power of 1.41 µW was obtained at 5 µm. Meanwhile the experimental DFG power conversion efficiency was 20.2 µW/W2, with a length-normalized slope efficiency of 15.5 µW/cmW2. The conversion efficiency decreases rapidly from 50 µW/cmW2 at 3.15 µm to 1 µW/cmW2 at 7.92 µm. The wavelength acceptance bandwidth and the angular acceptance bandwidth were measured to be 16.4 cm-1 and 44' for DFG at 5.1 µm, respectively.
RESUMEN
The accuracy of absorption spectral parameters is very important for the trace gas measurement based on absorption spectroscopy techniques, especially for the isotopic abundance measurement of gas molecules. For some of the applications, spectral parameters listed in HITRAN database were used to retrieve the trace gas concentration. However, these parameters have uncertainty, in order to validate spectroscopic parameters near 2.0 µm of CO2 lines, which are to be used in detecting the CO2 concentration and isotopic abundance, spectra of those lines were recorded at room temperature using a distributed feed-back (DFB) diode laser. The recorded absorption spectra were fitted to Voigt profile. Line position, intensity, self-broadening coefficient and N2-broadening coefficient were deduced from those data. The results show a good consistency in comparison with those listed in HITRAN2012 database. The discrepancy of most line intensities and self-broadening coefficients are less than 2%. The CO2 concentration and Δ(13 CO2 ) in real atmosphere inside laboratory are 440 ppm and -9 per hundred respectively. These results provide a reliable basis for real time and on line detecting the CO2 concentration and Δ(13 CO2) in the wavelength range.