Critical distance of far field for basic radiation element

Author(s):  
Sun Jiang_sheng ◽  
Gao Ben-qing
2011 ◽  
Vol 187 ◽  
pp. 826-830 ◽  
Author(s):  
Yu Xu ◽  
Bing Cheng Yuan ◽  
Hong Gang Zhang

With the distance between sonar system and target enlarging, the underwater target transits from near field to far field. Based on planar element scattering similarity, a novel algorithm is presented in this paper. In this thesis, an underwater target model is set up and meshed with triangular planar element by using the software of Ansys. Due to the sonar system is in far field to every planar element, the matrixes whose elements are the planar elements target strength can be calculated. In the course of an underwater target transits from near field to far field, the matrix whose elements are the planar elements target strength is becoming more and more similar to that in far field. Thus the correlation coefficient between the above two matrixes can be used to analyze the transition of an underwater target. Numerical calculation are presented, and the results show that the underwater target scattering characteristics in critical distance approximate the characteristics in far field, but the target strength which is calculated in critical distance is also should be modified little.


Author(s):  
N. Bonnet ◽  
M. Troyon ◽  
P. Gallion

Two main problems in high resolution electron microscopy are first, the existence of gaps in the transfer function, and then the difficulty to find complex amplitude of the diffracted wawe from registered intensity. The solution of this second problem is in most cases only intended by the realization of several micrographs in different conditions (defocusing distance, illuminating angle, complementary objective apertures…) which can lead to severe problems of contamination or radiation damage for certain specimens.Fraunhofer holography can in principle solve both problems stated above (1,2). The microscope objective is strongly defocused (far-field region) so that the two diffracted beams do not interfere. The ideal transfer function after reconstruction is then unity and the twin image do not overlap on the reconstructed one.We show some applications of the method and results of preliminary tests.Possible application to the study of cavitiesSmall voids (or gas-filled bubbles) created by irradiation in crystalline materials can be observed near the Scherzer focus, but it is then difficult to extract other informations than the approximated size.


Author(s):  
Patrick P. Camus

The theory of field ion emission is the study of electron tunneling probability enhanced by the application of a high electric field. At subnanometer distances and kilovolt potentials, the probability of tunneling of electrons increases markedly. Field ionization of gas atoms produce atomic resolution images of the surface of the specimen, while field evaporation of surface atoms sections the specimen. Details of emission theory may be found in monographs.Field ionization (FI) is the phenomena whereby an electric field assists in the ionization of gas atoms via tunneling. The tunneling probability is a maximum at a critical distance above the surface,xc, Fig. 1. Energy is required to ionize the gas atom at xc, I, but at a value reduced by the appliedelectric field, xcFe, while energy is recovered by placing the electron in the specimen, φ. The highest ionization probability occurs for those regions on the specimen that have the highest local electric field. Those atoms which protrude from the average surfacehave the smallest radius of curvature, the highest field and therefore produce the highest ionizationprobability and brightest spots on the imaging screen, Fig. 2. This technique is called field ion microscopy (FIM).


Author(s):  
Ingrid Diran

Agamben describes his posture as a reader as one of seeking a text’s Entwicklungsfähigkeit, or capacity for elaboration.1 In examining Agamben’s practices of reading, we can attend to the opposite phenomenon: the counter-elaboration that a text, in having being read by the philosopher, performs upon Agamben’s own thought. This reciprocal elaboration might constitute a paradigm for Agamben’s use of reading, according to his own idiosyncratic definition of use as an event in the middle voice, in which (according to a definition of Benveniste) the subject ‘effects an action only in affecting itself (il effectue en s’affectant)’ (UB 28). With this definition in mind, we could say that Agamben effects a text (he writes) only to the extent that he is also affected by another text (he reads). This is why Agamben’s position as a reader proves particularly important to any assessment of his work, quite aside from the problem of influence or intellectual genealogy. For this same reason, however, assessing Agamben’s relation to Antonio Negri – a figure with whom, by most measures, he is at odds – poses an unexpected challenge: how can Agamben’s thought be a use of Negri? Answering this question means not only assessing the critical distance between the two thinkers, but also taking this distance as a measure, in the Spinozan sense, of mutual affection.


2018 ◽  
Vol 189 (03) ◽  
pp. 312-322 ◽  
Author(s):  
Ivan Yu. Eremchev ◽  
M.Yu. Eremchev ◽  
Andrei V. Naumov

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