摘要:

In the small regular virus particles, the (infective) nucleic acid is protected in a protein container built from many identical protein molecules. Early x-ray diffraction work showed that these subunit molecules are arranged with helical symmetry to form rod-shaped particles, or with icosahedral symmetry to form isometric particles. Current work on the rod-shaped, tobacco mosaic virus is directed towards e 10 Å resolution electron density map of the virus; a parallel study on crystals of the protein subunits has so far yielded a 15 Å map. The structures of two isometric viruses have been obtained to a resolution of 25 Å; both of these have extra, non-icosahedral, local symmetry of a type which had been predicted on theoretical grounds.

ISSN:0010-7514    

DOI:10.1080/00107517208205665

出版商:Taylor & Francis Group    

年代:1972

数据来源: Taylor

摘要:

Two contemporary developments in the field of protein structure determination are described. The first of these is an approach to the phase problem which is radically different from the classical method of isomorphous replacement and which is still at a developmental stage, whilst the second is concerned with the optimization of the interpretation of electron density maps which are below atomic resolution.

ISSN:0010-7514    

DOI:10.1080/00107517208205666

出版商:Taylor & Francis Group    

年代:1972

数据来源: Taylor

摘要:

Electron nuclear double resonance (endor) is a powerful tool for investigating the immediate surroundings of a centre with unpaired electrons in a solid. One can determine the nature of all neighbouring nuclei with nuclear magnetic moments, and can often determine their precise position in the crystal structure. Hence this technique may be used to map the positions of the neighbouring ions around the centre, and to discover the chemical nature of these ions.

ISSN:0010-7514    

DOI:10.1080/00107517208205667

出版商:Taylor & Francis Group    

年代:1972

数据来源: Taylor

摘要:

This article reviews recent work on the possible variability of basic physical constants, such as the charge of the electron e, Planck's constanthand the gravitational constantG. The problem was first raised by Dirac as early as 1937. Its present state is here discussed, together with new suggestions which include Gamow's hypothesis that the fine-structure constant varies directly with time (e2/hc ∞ t), the hypothesis (e2∞t, h ∞ t, G ∞ t) and the hypothesis (e4∞t, h2∞t, G=constant).

ISSN:0010-7514    

DOI:10.1080/00107517208205668

出版商:Taylor & Francis Group    

年代:1972

数据来源: Taylor

摘要:

Bubble Chamber Film Analysis, or Film Analysis as it is often called, is broadly the retrieval and interpretation of information on elementary particle interactions recorded on photographs of particle interactions in bubble chambers. A very brief account of bubble chambers is given to explain their usefulness as particle detectors. Essentially bubbles are formed along the tracks of all the charged particles involved in an interaction-a set of stereo-photographs is taken to record this information. The article describes how photographs are scanned (examined) for interactions of interest, and how the film images of tracks from such interactions are measured. The geometric reconstruction of the events from the measurements, and the interpretation of reconstructed events using kinematic fitting procedures, are discussed. When this stage of analysis is reached, events with the same interpretation (which involve the same reaction) are assembled and can be used to study that reaction. The remainder of the article deals with such studies in elementary particle physics, and emphasizes the role of film analysis in the detection and measurement of the quantum numbers of excited particle states for which the bubble chamber technique is an invaluable tool.

ISSN:0010-7514    

DOI:10.1080/00107517208205669

出版商:Taylor & Francis Group    

年代:1972

数据来源: Taylor

摘要:

Theory of Elasticity. By L. D. Landau and E. M. Lifshitz. (Pergamon Press, 1970.) [Pp. vii + 165.] £3 0s. 0d. Scope: Treatise/textbook. Level: Specialist/postgraduate; undergraduate.

ISSN:0010-7514    

DOI:10.1080/00107517208205670

出版商:Taylor & Francis Group    

年代:1972

数据来源: Taylor

ISSN:0010-7514    

DOI:10.1080/00107517208205671

出版商:Taylor & Francis Group    

年代:1972

数据来源: Taylor