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43.
Thermal Climate Variations and Potential Modification of the Cropping Pattern in Bangladesh 总被引：1，自引：0，他引：1
R. Mahmood 《Theoretical and Applied Climatology》1998,61(3-4):231-243
Summary Changes in the thermal climate due to inter-annual climatic variability can potentially modify existing cropping pattern
by forcing farmers to rearrange transplanting and harvesting dates. In the present study, a crop climate model, the YIELD,
has been applied to 12 meteorological stations located in major rice growing regions in Bangladesh to estimate the effect
of thermal climate variations on the transplanting and harvesting dates of boro rice and the resultant potential changes in
cropping pattern and spatial shift. The abnormal thermal climate scenarios have been created by synthetically perturbing mean
air temperatures (Tair) up to −5 °C to +5 °C with an interval of 1 °C for each of these stations. Historical meteorological records of air temperature
in Bangladesh have been used to prepare these scenarios. The study finds that under abnormally cool conditions transplanting
dates will be pushed well into February to avoid plant injury and harvesting dates will be moved into the monsoon. The growing
seasons will be longer under cooler than normal thermal conditions. Under abnormally warm conditions harvesting dates will
be established well into March and will cause reduction of yield due to a shorter growing season. These conditions will also
cause spatial shift in crop potential and changes in the cropping pattern. Due to a longer boro rice growing season farmers
will lose a significant amount of cropping land which is usually used for low and deep water rice cultivation. New crops will
need to be introduced during the beginning of a year to overcome the loss of production under abnormally cool conditions.
Wheat and potato can be good options for the farmers for such conditions. New aus rice variety needs to be introduced after
the boro harvesting under warmer than the normal conditions to overcome the loss of yield due to a shorter growing season.
Received September 16, 1996 Revised September 8, 1997 相似文献
44.
Rezaul Mahmood Mark Meo David R. Legates Mark L. Morrissey 《The Professional geographer》2003,55(2):259-273
Agricultural practices in Bangladesh are largely dependent on the monsoonal rainfall. Historically, Bangladesh often experiences severe droughts and floods during the monsoon months, with significant crop losses during both extreme conditions. This article provides a quantitative assessment of potential monsoon‐season aman rice for four transplanting dates: 1 June, 1 July, 15 July, and 15 August. A crop‐growth simulation model, the CERES‐Rice, is applied to sixteen locations representing major rice‐growing regions of Bangladesh to determine baseline yield estimates for four transplanting dates. The applications were conducted for 1975 through 1987. Average potential yield in Bangladesh is 6,907, 5,039, 3,637, and 1,762 kg ha?1 for the above transplanting dates, respectively. In other words, Bangladesh would obtain 27 percent, 48 percent, and 75 percent less yield for 1 July, 15 July, and 15 August transplanting, respectively, than for 1 June transplanting. Potential yield vulnerability is the least for 1 June transplanting (up to 5 percent) and the highest (up to 66 percent) for 15 July transplanting date. The model applications show that regional variations exist for potential yield and yield vulnerability for a particular transplanting date. In addition, response of yield and vulnerability for a region changes with transplanting dates. 相似文献
45.
Efficiency of carrier-phase integer ambiguity resolution for precise GPS positioning in noisy environments 总被引：1，自引：0，他引：1
Precise GPS positioning relies on tracking the carrier-phase. The fractional part of carrier-phase can be measured directly
using a standard phase-locked loop, but the integer part is ambiguous and the ambiguity must be resolved based on sequential
carrier-phase measurements to ensure the required positioning precision. In the presence of large phase-measurement noise,
as can be expected in a jamming environment for example, the amount of data required to resolve the integer ambiguity can
be large, which requires a long time for any generic integer parameter estimation algorithm to converge. A key question of
interest in significant applications of GPS where fast and accurate positioning is desired is then how the convergence time
depends on the noise amplitude. Here we address this question by investigating integer least-sqaures estimation algorithms.
Our theoretical derivation and numerical experiments indicate that the convergence time increases linearly with the noise
variance, suggesting a less stringent requirement for the convergence time than intuitively expected, even in a jamming environment
where the phase noise amplitude is large. This finding can be useful for practical design of GPS-based systems in a jamming
environment, for which the ambiguity resolution time for precise positioning may be critical. 相似文献
46.
47.
Sahar Ghafari Ardavan Ghorbani Mehdi Moameri Raoof Mostafazadeh Mahmood Bidarlord 《山地科学学报》2018,15(6):1209-1228
This study provides a checklist of species distributed at the altitude gradient of Moghan-Sabalan rangelands in Ardabili province, Northwest Iran. We evaluated the changes in species composition, growth types of species, Raunkiaer’s life forms, geographical distribution, threat and endemicity status, and palatability of species along two altitudinal gradients in the sampling plots, which were conducted in eleven sites/habitats with 300 meters above sea level (masl) altitude intervals (from 100 to 3300 masl). We assessed the plant species composition with special reference to the gradient analysis, and identified overall 396 species, which was comprising 44 families and 194 genera. Results showed that Asteraceae family is by far the most species-rich family, followed by Poaceae, Fabaceae, Caryophyllaceae and Brassicaceae. Among the genera, Astragalus is the most diverse genus, followed by Allium, Veronica and Bromus, Galium, Silene and Ranunculus. Results indicated that the number of species increased as the altitude increased to 1200–1500 masl, but then starts to decline to 3300 masl. Family-to-genera ratio was 1:4.4, the family-tospecies ratio was 1:9, and the genera-to-species ratio was 1:2.04. Growth type of species analysis shows that the frequency of perennial plants was higher in the study area followed by annual species while the lower group was biennial species. The number of annuals showed a decreasing trend towards higher altitude. Hemicryptophytes and therophytes were the most frequent life forms constituted each with (41.9%). Hemicryptophytes showed an increasing trend with altitude, while therophytes showed a decreasing trend with altitude increase, followed by geophytes, chamaephytes, and phanerophytes. Results showed more than half of the species of the study area belonged to Iran-Turanian region and these species showed an increasing trend with altitude. In contrast, Sahara-Sindian species comprise a minor component of the spectrum, with decreasing trend with altitude. The rare and endangered species out of the surveyed taxonomic groups comprised 53 species in total which 29 of them are considered lower risk (LR), 13 data deficient (DD), 5 vulnerable (Vu) and with 3 rare (R) and identified endemic plants comprised 24 species. Some 56.6% species were identified as class III, 22.6% were class I and 20.8% were class II as the palatability variation. Moghan-Sabalan rangelands require strong conservation management policies in case of species loss and changing natural communities due to the occurrence of conversion into cropland, over-grazing and other anthropogenic effects. 相似文献
48.
Fractal measures of drainage network to investigate surface deformation from remote sensing data: A paradigm from Hindukush (NE-Afghanistan) 总被引：1，自引：0，他引：1
This approach represents the relative susceptibility of the topography of the earth to active deformation by means of geometrical distinctiveness of the river networks. This investigation employs the fractal analysis of drainage system extracted from ASTER Global Digital Elevation Model (GDEM-30m resolution). The objective is to mark active structures and to pinpoint the areas robustly influenced by neotectonics. This approach was examined in the Hindukush, NE-Afghanistan. This region is frequently affected by deadly earthquakes and the modern fault activities and deformation are driven by the collision between the northward-moving Indian subcontinent and Eurasia. This attempt is based on the fact that drainage system is strained to linearize due to neotectonic deformation. Hence, the low fractal dimensions of the Kabul, Panjsher, Laghman, Andarab, Alingar and Kocha Rivers are credited to active tectonics. A comprehensive textural examination is conducted to probe the linearization, heterogeneity and connectivity of the drainage patterns. The aspects for these natural textures are computed by using the fractal dimension (FD), lacunarity (LA) and succolarity (SA) approach. All these methods are naturally interrelated, i.e. objects with similar FD can be further differentiated with LA and/or SA analysis. The maps of FD, LA and SA values are generated by using a sliding window of 50 arc seconds by 50 arc seconds (50" × 50"). Afterwards, the maps are interpreted in terms of regional susceptibility to neotectonics. This method is useful to pinpoint numerous zones where the drainage system is highly controlled by Hindukush active structures. In the North-Northeast of the Kabul block, we recognized active tectonic blocks. The region comprising, Kabul, Panjsher, Andrab, Alingar and Badakhshan is more susceptible to damaging events. This investigation concludes that the fractal analysis of the river networks is a bonus tool to localize areas vulnerable to deadly incidents influencing the Earth’s topography and consequently intimidate human lives. 相似文献
49.
50.
Nonlinear ion acoustic solitary wave structures in electron-positron-ion (e-p-i) magnetized rotating plasmas is studied. The electron and positron species are assumed to be nonthermal and follow the kappa distribution function. The Korteweg de Vries (kdV) equation is derived by employing the reductive perturbation technique for solitary wave in the nonlinear regime. The variation in the amplitude and width of the solitary wave are discussed with the effects of positron concentration, temperature ratio of kappa distributed electrons to positrons, spectral index of the positrons, direction of propagation of the wave with magnetic field and effective gyrofrequency of the rotating nonthermal plasmas. The numerical results are also presented for illustration. 相似文献