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1.
We have used the technique of expansion in Empirical Orthogonal Functions (EOFs) to develop regional models of the critical frequencies of E and F2 layers (foE, foF2), peak height (hmF2), and semi-thickness of F2 layer (YmF2) over Pakistan. In the present study levels of solar activity specified by Smoothed Sunspot Number (R) from 10 to 200 are taken into account. The magnetic dip angle for the model ranges from 30° to 60°. We have compared the regional model and the International Reference Ionosphere (IRI) with measurements of three ionosondes in Pakistan. The model parameters foE and foF2 are found overall comparable to the observed hourly median values during daytime at Karachi (geographic latitude = 24.95°N, longitude = 67.13°E, magnetic inclination = 37°), Multan (30.18°N, 71.48°E, 45°) and Islamabad (33.75°N, 73.13°E, 51.5°) during the years 1988, 1996 and 2000. For hmF2 the computed values by regional and IRI model for the year 1995 are found close to each other. However, for YmF2the results are better during daytime as compared to nighttime.  相似文献   

2.
Plants grown on long-term space missions will likely be grown in low pressure environments (i.e., hypobaria). However, in hypobaria the transpiration rates of plants can increase and may result in wilting if the water is not readily replaced. It is possible to reduce transpiration by increasing the partial pressure of CO2 (pCO2), but the effects of pCO2 at high levels (>120 Pa) on the growth and transpiration of plants in hypobaria are not known. Therefore, the effects of pCO2 on the growth and transpiration of radish (Raphanus sativus var. Cherry Bomb II) in hypobaria were studied. The fresh weight (FW), leaf area, dry weight (DW), CO2 assimilation rates (CA), dark respiration rates (DR), and transpiration rates from 26 day-old radish plants that were grown for an additional seven days at different total pressures (33, 66 or 101 kPa) and pCO2 (40 Pa, 100 Pa and 180 Pa) were measured. In general, the dry weight of plants increased with CO2 enrichment and with lower total pressure. In limiting pCO2 (40 Pa) conditions, the transpiration for plants grown at 33 kPa was approximately twice that of controls (101 kPa total pressure with 40 Pa pCO2). Increasing the pCO2 from 40 Pa to 180 Pa reduced the transpiration rates for plants grown in hypobaria and in standard atmospheric pressures. However, for plants grown in hypobaria and high pCO2 (180 Pa) leaf damage was evident. Radish growth can be enhanced and transpiration reduced in hypobaria by enriching the gas phase with CO2 although at high levels leaf damage may occur.  相似文献   

3.
Though H2CO, H2CS, H2CCC, H2CCCC, H2CCO have been identified in cool interstellar molecular clouds, identification of H2CC is still awaited. To analyze its spectrum, collisional rate coefficients are required. We have calculated collisional rate coefficients for rotational transitions between 23 levels of ortho and para H2CC for kinetic temperatures 10, 20, 30, 40, and 50 K. The scattering problem is analyzed using the computer code MOLSCAT where the colliding partner is He atom. The interaction between H2CC and He has been calculated with GAUSSIAN 2003. For the interaction potential obtained with GAUSSIAN 2003, MOLSCAT is used to derive the parameters q(L,M,M|E)q(L,M,M|E) as a function of energy E   of the colliding partner. After averaging the parameters q(L,M,M|E)q(L,M,M|E) over a Maxwellian distribution, the parameters Q(L,M,M|T)Q(L,M,M|T) as a function of the kinetic temperature T in the cloud are obtained. Finally, the collisional rate coefficients have been calculated.  相似文献   

4.
The purpose of this research work is to validate the ionospheric models (IRI and CHIU) to assess its suitability and usefulness as an operational tool. The ionospheric model is a computer model designed to predict the state of the global ionosphere for 24 h. The scope was limited to conduct comparisons between the predicted F2 layer critical frequencies (f0F2) against observed ionosonde data. The ionospheric prediction model (IPM) was designed to predict by using monthly median sunspot number, while the observation data are taken from two digital ionospheric sounding stations (Okinawa, 26.28N, 127.8E and Wakkanai, 45.38N, 141.66E) which lies within the mid-latitude region of the globe. Analysis of the f0F2 data from stations for year (2001) with high solar activity and year (2004) with low solar activity, four months (March, June, September and December) chosen based primarily on data availability. From results it seen that the ratio between monthly median predicted and observed f0F2 values for each model used in this research work and for the chosen months was nonlinear with local time, so the empirical formula for applying correction factors were determined, these formula can be used to correct the error occurred in predicted f0F2 value.  相似文献   

5.
NeQuick ionospheric electron density model, which has been developed to version 2, produces the full electron density profile in the ionosphere. Each part of the profile is modeled using Epstein layer formalism. Simple empirical relations are used to compute the thicknesses of each layer. In order to validate the B2bot parameter in the NeQuick model during high solar activity, we use the data at Hainan, China (109.1°E, 19.5°N; Geomagnetic coordinates: 178.95°E, 8.1°N), measured with DPS-4, and study the diurnal and seasonal variations of B2bot, ΔB2 (B2best − B2NeQuick 2) and the seasonal median values of B2best/B2NeQuick 2 at that region. The results show that, (1) The differences between B2best and B2NeQuick 2 have diurnal and seasonal variations. (2) The diurnal variations of B2NeQuick 2 are smaller than those of B2best. (3) Generally, except for early morning the experimental values are properly reproduced. (4) Generally, during morning the NeQuick model has an underestimation. The magnitude of underestimation varies with LT and season.  相似文献   

6.
Plants can provide a means for removing carbon dioxide (CO2) while generating oxygen (O2) and clean water for life support systems in space. To study this, 20 m2 stands of potato (Solanum tuberosum L.) plants were grown in a large (113 m3 vol.), atmospherically closed chamber. Photosynthetic uptake of CO2 by the stands was detected about 10 DAP (days after planting), after which photosynthetic rates rose rapidly as stand ground cover and total light interception increased. Photosynthetic rates peaked ca. 50 DAP near 45 μmol CO2 m−2 s−1 under 865 μmol m−2 s−1 PPF (average photosynthetic photon flux), and near 35 μmol CO2 m−2 s−1 under 655 μmol m−2 s−1 PPF. Short term changes in PPF caused a linear response in stand photosynthetic rates up to 1100 μmol m−2 s−1 PPF, with a light compensation point of 185 μmol m−2 s−1 PPF. Comparisons of stand photosynthetic rates at different CO2 concentrations showed a classic C3 response, with saturation occurring near 1200 μmol mol−1 CO2 and compensation near 100 μmol mol−1 CO2. In one study, the photoperiod was changed from 12 h light/12 h dark to continuous light at 58 DAP. This caused a decrease in net photosynthetic rates within 48 h and eventual damage (scorching) of upper canopy leaves, suggesting the abrupt change stressed the plants and/or caused feedback effects on photosynthesis. Dark period (night) respiration rates increased during early growth as standing biomass increased and peaked near 9 μmol CO2 m−2 s−1 ca. 50 DAP, after which rates declined gradually with age. Stand transpiration showed a rapid rise with canopy ground cover and peaked ca. 50 DAP near 8.9 L m−2 d−1 under 860 μmol m−2 s−1 PPF and near 6.3 L m−2 d−1 under 650 μmol m−2 s−1 PPF. Based on the best photosynthetic rates from these studies, approximately 25 m2 of potato plants under continuous cultivation would be required to support the CO2 removal and O2 requirements for one person.  相似文献   

7.
This paper reports a study of spatial and temporal variations of columnar averaged concentration of CO2 and CH4 over India using SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) and Greenhouse gas Observing SATellite (GOSAT) data. Comparison of these data with the global view National Oceanic and Atmospheric Administration (NOAA) land data and also location specific flask data is made. The temporal variation in column averaged global CO2 is similar to that over India and it is also similar to the NOAA surface flask data and global view. The variation in NOAA surface CH4 is location dependent and its global view appears to vary seasonally in opposite phase with the column averaged CH4 values from satellites, reflecting the limited comparability of surface and column averaged data. Over India the CO2 maximum is in May and minimum in August/September while for CH4 the maximum is in September and minimum in February/March. The seasonal variation of CH4 over India is correlated with the eastern coastal rice cultivation.  相似文献   

8.
The ability to generate O2 and absorb CO2 of several co-cultured vegetable plants in an enclosed system was studied to provide theoretical reference for the future man-plant integrated tests. Four kinds of salad plants (Lactuca sativa L. var. Dasusheng, Lactuca sativa L. var. Youmaicai, Gynura bicolor and Cichorium endivia L.) were grown in the CELSS Integration Test Platform (CITP). The environmental factors including O2 and CO2 concentration were continuously monitored on-line and the plant biomass was measured at the end of the test. The changing rules of O2 and CO2 concentration in the system were basically understood and it was found that the O2 generated by the plants could satisfy the respiratory needs of 1.75 persons by calculation. It was also found that the plants could absorb the CO2 breathed out by 2 persons when the light intensity was raised to 550 mmol m−2 s−1 PPF. The results showed that the co-cultured plants hold good compatibility and excellent O2-generating and CO2-absorbing capability. They could also supply some fresh edible vegetable for a 2-person crew.  相似文献   

9.
H∞滤波在惯导系统地面快速对准中的应用   总被引:7,自引:0,他引:7  
阐述了H滤波器的设计过程,并将H滤波方法应用于惯导系统地面初始对准.文中建立了惯导系统的误差模型,并对其进行了可观性分析,利用H滤波方法对可观子系统进行了滤波计算,给出了在噪声统计特性未知方差有界情况下惯导系统初始对准的仿真曲线,仿真结果表明该方法克服了卡尔曼滤波对噪声的苛刻要求,滤波效果能够满足工程需要,进一步说明H滤波应用于惯导系统初始对准是有效的.为提高对准速度,文中给出了方位误差角的一种快速估计方法,结果表明该方法是可行的.  相似文献   

10.
A near rectilinear halo orbit (NRHO) is regarded as a potential orbit for a future deep space station that can effectively support sustainable crewed lunar exploration missions. In this paper, the L2 southern NRHOs are selected as the research object, and a direct transfer trajectory from an NRHO to a low lunar orbit (LLO) is designed and analyzed. First, based on the circular restricted three-body problem, the characteristics of NRHOs are discussed including geometric behaviour, stability and synodic resonance. Second, optimal direct transfer trajectories are obtained by combining a local gradient optimization with a numerical continuation strategy. A reachable domain calculation model is established. Finally, simulations are carried out to verify the feasibility of the trajectory design method. The relationship between the velocity change and the reachable domain is further analysed through simulation calculations.  相似文献   

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