space acquisition
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2022 ◽  
Vol 11 (1) ◽  
pp. 56
Author(s):  
Xiaorong Gao ◽  
Haowen Yan ◽  
Xiaomin Lu ◽  
Pengbo Li

The major reason that the fully automated generalization of residential areas has not been achieved to date is that it is difficult to acquire the knowledge that is required for automated generalization and for the calculation of spatial similarity degrees between map objects at different scales. Furthermore, little attention has been given to generalization methods with a scale reduction that is larger than two-fold. To fill this gap, this article develops a hybrid approach that combines two existing methods to generalize residential areas that range from 1:10,000 to 1:50,000. The two existing methods are Boffet’s method for free space acquisition and kernel density analysis for city hotspot detection. Using both methods, the proposed approach follows a knowledge-based framework by implementing map analysis and spatial similarity measurements in a multiscale map space. First, the knowledge required for residential area generalization is obtained by analyzing multiscale residential areas and their corresponding contributions. Second, residential area generalization is divided into two subprocesses: free space acquisition and urban area outer boundary determination. Then, important parameters for the two subprocesses are obtained through map analysis and similarity measurements, reflecting the knowledge that is hidden in the cartographer’s mind. Using this acquired knowledge, complete generalization steps are formed. The proposed approach is tested using multiscale datasets from Lanzhou City. The experimental results demonstrate that our method is better than the traditional methods in terms of location precision and actuality. The approach is robust, comparatively insensitive to the noise of the small buildings beyond urban areas, and easy to implement in GIS software.


2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Hankyeol Lee ◽  
Jeongtaek Lee ◽  
Jang-Yeon Park ◽  
Seung-Kyun Lee

AbstractTwo-dimensional (2D) line scan-based dynamic magnetic resonance imaging (MRI) is examined as a means to capture the interior of objects under repetitive motion with high spatiotemporal resolutions. The method was demonstrated in a 9.4-T animal MRI scanner where line-by-line segmented k-space acquisition enabled recording movements of an agarose phantom and quail eggs in different conditions—raw and cooked. A custom MR-compatible actuator which utilized the Lorentz force on its wire loops in the scanner’s main magnetic field effectively induced the required periodic movements of the objects inside the magnet. The line-by-line k-space segmentation was achieved by acquiring a single k-space line for every frame in a motion period before acquisition of another line with a different phase-encode gradient in the succeeding motion period. The reconstructed time-course images accurately represented the objects’ displacements with temporal resolutions up to 5.5 ms. The proposed method can drastically increase the temporal resolution of MRI for imaging rapid periodic motion of objects while preserving adequate spatial resolution for internal details when their movements are driven by a reliable motion-inducing mechanism.


Author(s):  
Peter L. Hays

This chapter discusses opportunities and challenges facing the U.S. Space Force, a separate branch of the U.S. Armed Forces within the Department of the Air Force that was created in December 2019. Major initial priorities for the Space Force include developing space doctrine and incubating a space-minded culture; blunting counterspace threats; improving space acquisition; and accelerating creation of wealth in and from space. To assess the evolution of spacepower doctrine, the chapter uses Dennis Drew’s doctrine tree model and David Lupton’s four schools of thought about the strategic utility of space capabilities: sanctuary, survivability, control, and high ground. The chapter also addresses several cautions and concerns including the relatively small size of the Space Force; significant dissimilarities between creation of the U.S. Air Force in 1947 and the Space Force in 2019; unintended consequences in impeding airpower development from the United Kingdom’s creation of a relatively small and weak Royal Air Force in 1918; and potential concerns stemming from the highly politicized environment that birthed the Space Force. The chapter concludes by reminding readers that new organizations do not guarantee success and by urging application of the right lessons from past missteps.


2020 ◽  
Vol 85 (4) ◽  
pp. 1840-1854
Author(s):  
Robert W. Stobbe ◽  
Christian Beaulieu

Author(s):  
Sebastian Kozerke ◽  
Redha Boubertakh ◽  
Marc Miquel

This chapter introduces the different methods used to synchronize pulse sequences with both cardiac and respiratory motions, to suppress motion-related blurring and image artefacts. A single frame or a series of images (cine imaging) can be acquired at different time points (cardiac phases) throughout the cardiac cycle by detecting the patient’s heart rate, usually by using an electrocardiogram (ECG) or, in case of poor ECG signals, a pulse oximeter signal. Fast single-shot and segmented k-space acquisition techniques are introduced, and for segmented cine imaging, both prospective and retrospective gating techniques are described. To suppress breathing motion artefacts, acquisitions use respiratory motion techniques. For short acquisition durations, breath-holding is the easiest method to stop the patient’s breathing during data collection. However, for long scans, respiratory gating or respiratory navigated techniques can be used. The principles of these techniques and their applications are presented.


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