Constellation design for responsive visiting based on ground track adjustment

2017 ◽  
Vol 232 (12) ◽  
pp. 2300-2316
Author(s):  
Xiang Yu ◽  
Kun Liu ◽  
Qifeng Chen
Keyword(s):  
Search Algorithm ◽  
Design Methods ◽  
Pattern Search ◽  
User Requirements ◽  
Ground Track ◽  
Constellation Design ◽  
Short Period ◽  
The Difference ◽  
Orbit Period ◽  
Global Reach

Many responsive civilian or military space missions require that a certain ground site of interest be visited in a fairly short period (e.g., 12 h or less). To this end, a constellation must be utilized, since a single satellite is usually unable to fulfill such a task if the ground site is selected on the whole terrestrial surface responding to random user requirements. In this paper, the design approaches of such a constellation for responsive visiting based on ground track adjustment are investigated. By using the difference in orbit period between the maneuvered satellite and the reference satellite to make the ground track shift, reachable domain belts are generated. In terms of orbit maneuvering, two- and one-impulse maneuvers are analyzed and compared. Based on the reachable domain belts of a single satellite, two constellation design methods are proposed. The first one is an analytical method which is presented to achieve global reach and implemented by uniformly splicing together the widest belts of all satellites within the range of [0°, 180°]. The second one is an optimized method proposed to further reduce the number of satellites, by splicing together all the reachable domain belts rather than only the widest belts in the equator. A hybrid algorithm that consists of the genetic algorithm and the pattern search algorithm is proposed to minimize the number of satellites. Numerical examples are provided to illustrate the two proposed constellation design methods and validate the global reach performance.

Comparison of two asynchronous QCT methods

2020 ◽  
Vol 24 (4) ◽  
pp. 108-118
Author(s):  
A. V. Petraikin ◽  
A. K. Smorchkova ◽  
N. D. Kudryavtsev ◽  
K. A. Sergunova ◽  
Z. R. Artyukova ◽  
...  
Keyword(s):  
Bone Densitometry ◽  
Pearson Correlation ◽  
Calibration Data ◽  
Mineral Density ◽  
Quantitative Ct ◽  
Short Period ◽  
Potassium Hydrogen ◽  
Patients At Risk ◽  
Ray Density ◽  
The Difference

Rationale. Quantitative CT (QCT) bone densitometry with asynchronous calibration not require a phantom during the scan procedure. Based on calibration data it converts X-ray density in HU to bone mineral density (BMD). Given the large number of CT studies performed on patients at risk of osteoporosis, there is a need for a hands-on method capable of assessing BMD in a short period of time without tailored software or protocols.Goal. To develop a method for QCT bone densitometry using an PHK (PHantom Kalium), to compare the volume BMD measurements with the QCT data with asynchronous calibration provided by software from a reputable developer.Methods. The studies were performed at 64-slice CT unit with body scanning parameters. The BMD was measured using two techniques: 1) QCT with asynchronous calibration using software from a reputable developer; 2) QCT using a PHK phantom (QCT-PHK). For convert the HU to BMD values, we scanned the PHK phantom and calculate correction factor. Phantom contains “vertebrae” filled with potassium hydrogen phosphate in different concentrations. In both methods, the BMD values measured for LI–II, and sometimes for ThXII, LIII.Results. The study enrolled 65 subjects (11 male and 54 female patients); median age 69.0 years. A comparison of the vertebrae BMD measured by QCT and QCT-PHK revealed a significant linear Pearson correlation r = 0.977 (p < 0.05). The Bland–Altman analysis demonstrated a lack of relationship between the difference in measurements and the average BMD and a systematic BMD; bias of +4.50 mg/ml in QCT vs. QCT-PHK. Differences in the division into groups osteoporosis / osteopenia / norm according to the ACR criteria for the two methods were not significant.Conclusion. The developed asynchronous QCT-PHK method measure BMD comparable to the widely used QCT with asynchronous calibration. This method can be used for opportunistic screening for osteoporosis.

Dynamic Path Planning Algorithm Based on Chaos Genetic Vehicle Navigation

2011 ◽  
Vol 142 ◽  
pp. 12-15
Author(s):  
Ping Feng
Keyword(s):  
Path Planning ◽  
Search Algorithm ◽  
Traffic Condition ◽  
Planning Time ◽  
Dynamic Path Planning ◽  
Short Period ◽  
Planning Algorithm ◽  
Dynamic Path ◽  
Path Planning Algorithm ◽  
Chaos Genetic Algorithm

The paper puts forward the dynamic path planning algorithm based on improving chaos genetic algorithm by using genetic algorithms and chaos search algorithm. In the practice of navigation, the algorithm can compute at the best path to meet the needs of the navigation in such a short period of planning time. Furthermore,this algorithm can replan a optimum path of the rest paths after the traffic condition in the sudden.

scholarly journals THE ELIMINATION OF IRON AND ITS DISTRIBUTION IN THE LIVER AND SPLEEN IN EXPERIMENTAL ANEMIA

1917 ◽  
Vol 25 (5) ◽  
pp. 675-691 ◽  
Author(s):  
Harry Dubin ◽  
Richard M. Pearce
Keyword(s):  
Sodium Oleate ◽  
Immune Serum ◽  
The Body ◽  
Bile Pigment ◽  
Striking Increase ◽  
Short Period ◽  
The Difference ◽  
Ultimate Fate ◽  
Cell Fragments ◽  
Severe Type

Blood destruction due to a single injury, as by sodium oleate, or acting through a short period of time, as by toluylenediamine or hemolytic immune serum, is not characterized, in the absence of hemoglobinuria, by an increased elimination of iron in the urine. This holds, not only for the evanescent injury caused by sodium oleate, but also for the severe type caused by hemolytic immune serum, in which a progressive destruction of the blood may persist for 2 weeks or more with constant evidence of the disintegration of erythrocytes as shown by bile pigment in the urine. This finding is in accord with previous investigations of anemia in both man and animals. Likewise, no striking increase is evident, under such circumstances, in the percentage of iron excreted in the feces. The total amount of iron in the feces has been notably increased in two experiments with hemolytic serum, but as the percentage was not appreciably altered, the difference depends presumably on variations in the bulk of feces rather than upon increased elimination. This evidence of the power of the body to conserve the iron rephagocytosis is negligible, is to be fragmented one by one, while still circulating, to a fine, hemoglobin-containing dust. The cell fragments are rapidly removed from the blood, but their ultimate fate remains to be determined. The facts indicate that they are removed from the blood by the spleen, and under exceptional conditions, by the bone marrow.

scholarly journals IDENTIFICATION OF A ROBUST LICHEN INDEX FOR THE DECONVOLUTION OF LICHEN AND ROCK MIXTURES USING PATTERN SEARCH ALGORITHM (CASE STUDY: GREENLAND)

2016 ◽  
Vol XLI-B7 ◽  
pp. 973-979
Author(s):  
S. Salehi ◽  
M. Karami ◽  
R. Fensholt
Keyword(s):  
Search Algorithm ◽  
Mineral Exploration ◽  
Optimization Procedure ◽  
Hyperspectral Data ◽  
Pattern Search ◽  
Rock Outcrops ◽  
Bare Rock ◽  
Mixed Pixel ◽  
Mixing Ratios ◽  
Linear Mixtures

Lichens are the dominant autotrophs of polar and subpolar ecosystems commonly encrust the rock outcrops. Spectral mixing of lichens and bare rock can shift diagnostic spectral features of materials of interest thus leading to misinterpretation and false positives if mapping is done based on perfect spectral matching methodologies. Therefore, the ability to distinguish the lichen coverage from rock and decomposing a mixed pixel into a collection of pure reflectance spectra, can improve the applicability of hyperspectral methods for mineral exploration. The objective of this study is to propose a robust lichen index that can be used to estimate lichen coverage, regardless of the mineral composition of the underlying rocks. The performance of three index structures of ratio, normalized ratio and subtraction have been investigated using synthetic linear mixtures of pure rock and lichen spectra with prescribed mixing ratios. Laboratory spectroscopic data are obtained from lichen covered samples collected from Karrat, Liverpool Land, and Sisimiut regions in Greenland. The spectra are then resampled to Hyperspectral Mapper (HyMAP) resolution, in order to further investigate the functionality of the indices for the airborne platform. In both resolutions, a Pattern Search (PS) algorithm is used to identify the optimal band wavelengths and bandwidths for the lichen index. The results of our band optimization procedure revealed that the ratio between R<sub>894-1246</sub> and R<sub>1110</sub> explains most of the variability in the hyperspectral data at the original laboratory resolution (R<sup>2</sup>=0.769). However, the normalized index incorporating R<sub>1106-1121</sub> and R<sub>904-1251</sub> yields the best results for the HyMAP resolution (R<sup>2</sup>=0.765).

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