Search Results

It is agreed that stilus tablets are very important documentary sources, however they are the most difficult to decipher. The difficulties in deciphering them is due to the rough surface of the tablets, the low brightness contrast of the incisions, the dense wood-grain lines, and the badly stained and pitted nature of the tablets. All of these posit a challenge for conventional two-dimensional (2D) image analysis. This chapter aims to provide a system that would aid the historian in interpreting stilus tablets by improving the legibility of the tablets. It provides novel ways of determining the texts incised on the tablets. One of these is the use of three-dimensional (3D) image analysis techniques. Such a technique is capable of detecting incisions, compared to the 2D image analysis, and is portable and inexpensive. Another method that can be used is the use of shadow stereo. This method employs low raking angle light close to the plane of the tablet at different elevations. The chapter also discusses the image formation process and the process of choosing elevations for each azimuth direction. The chapter also includes a discussion on realizing the shadow stereo algorithm.

The quality of the retinal image depends on optical factors such as chromatic and spherical aberrations and on the spacing of the receptors. An account of these factors is followed by a description of mechanisms responsible for the accommodation of the lens. First, the machinery of accommodation and the three types of accommodation are described. These are tonic accommodation, proximal accommodation, and accommodation induced by image blur. Induction of accommodation by image blur depends on blur detection and detection of the attributes of blur that indicate the required direction of accommodation. The chapter ends with a discussion of anisometropia and aniseikonia.

Phase contrast, the contrast transfer function (CTF), kinematical scattering and the weak-phase object approximation are central concepts for image formation. The physics is described in great detail with one hundred formulas, leading up to the fundamental relation between electron wave phases and structure factor phases. Through-focus series are discussed as a means to collect all the information from a structure projection – some data may be lost in one HRTEM image because it falls on a node (= zero cross-over of the CTF) but this data can be obtained from another image taken at another defocus value. It is shown that singly and doubly scattered electron waves are transferred differently by the objective lens to the image. Thus, they can be separated in image processing, especially if a few images of different focus are combined.

Fundamental transmission electron microscopy covers the topics of resolution, electron optics, image recording systems and image distortions and how they can be handled by hardware (Cs-correctors) and software. The interaction of electrons with matter starts with the individual atom and the atomic scattering factor. Special emphasis is placed on elastically scattered electrons, since those are the ones used for forming images of the atomic structure. The use of inelastically scattered electrons is briefly mentioned, for example in HAADF – high-angle annular dark field imaging of atomic structure.

The preparation of metal nanoparticles for plasmonics according to the LaMer Diagram is described, and this knowledge is extended to single-crystalline nanoparticles with variations in crystal habit, nanorods, and nanoplates. This is reinforced by knowledge of the preparation of photographic Ag and AgX nanoparticles. Formation mechanisms of reduction sensitization and latent image centres (Ag₂ and Ag_n with n≥4) serve as nuclei for Ag nanoparticles. Photographic development provides knowledge of the growth of small Ag_n clusters in the presence of silver ions and reducing agents. Descriptions of the growth of AgX nanoparticles include protective colloids and apparatus for this. Mechanisms for preparing all the possible single-crystalline nanoparticles with fcc structure, tabular nanoparticles, core/shell, and epitaxial nanoparticles with different AgXs, together with methods of preparing nanoparticles with monodispersity and enhanced anisotropy in shape and arranging them, are also discussed.

This chapter examines how the brain represents our sensory world in order to serve as the basis for perception. It is hypothesized that by studying the neural mechanisms for setting up and processing a visual scene in the brain, we will learn principles that will apply to the neural mechanisms for setting up and processing a smell image in the brain. Confirming this hypothesis offers a new perspective on how smells are represented in our brains and how these representations contribute to the perception of flavor. The chapter discusses the following principles: the initial image representation in a two-dimensional sheet, lateral inhibition, contrast enhancement, temporal transients, center-surround inhibition, and feature extraction—all of which play essential roles in the formation of neural images in all sensory systems.

This chapter provides an overview of the structure and function of insect photoreceptors, highlighting some problems (and solutions) peculiar to aquatic insect taxa. The physical properties of light underwater are described and their potential restrictions considered throughout the subsequent discussions of visual function. First is a discussion of the basic structure and the different types of compound eye, and the basic optical units, the ommatidia. The structure of compound eyes influences how they function, including image formation, movement detection, resolution, sensitivity to light levels, and wavelength (e.g., colour vision and polarization sensitivity). The following sections consider the other eye types, ocelli and stemmata, which are less complex than compound eyes, but still provide important kinds of photosensory information to aquatic insects. The final section provides a brief discussion of bioluminescence, which a few aquatic insects use in communication.

This chapter begins by identifying various kinds of imaging techniques. It then examines the role played by the amount of light and presence of fluorophore in the imaging process. the latter part of the chapter identifies the features of confocal microscopy and stimulated emission depletion (STED) microscopy. Sample problems are also provided at the end of the chapter.

Visual−deprivation experiments on cats and monkeys have showed that complete unilateral eye occlusion of these animals until twelve weeks of age can produce a permanent amblyopia and a decrease in cell density along the geniculocortical pathway. Reversal of the amblyopia was possible if the occlusion was removed before eight weeks of age in monkeys. Although this critical age is established for animals, the exact critical period has not been determined for humans, partly because of the problem with assessment of infant vision. This chapter focuses on the relationship between visual development and age at surgery for patients with total congenital cataract. In patients with total congenital cataract, retinal image formation is severely degraded from birth until the lens is removed by surgery and the optics is restored by a contact lens.

This chapter starts by looking at wave-particle character of electrons. It also explains the Ewald reflecting sphere construction for electron diffraction and provides an analysis of electron diffraction patterns. It also illustrates the precession and rotation electron diffraction techniques, Shechtman's identification of quasiperiodic crystals, Kikuchi patterns in the electron microscope and electron backscattered (EBSD) patterns in the scanning electron microscope, and image formation and resolution in the electron microscope.

This chapter takes central coin types as its starting point, and compares the trajectory of representations of imperial (grand) mothers on central coin types with those on other types of evidence in selected cases, focusing expecially on the Julio-Claudian and Severan dynasties. It questions assumptions about the level of interaction between the different media, which differs from one reign to the next. Developments in the representation of (imperial) women in various sources, in certain regions of the Empire, and in the Empire as a whole form the wider discourses within which imperial image formation is placed. The chapter also traces the parallels between increasing visibility of imperial mothers and grandmothers in centralized media—especially in the Eastern parts of the Empire—and a similar process in local civic representations. Where central notions cohered with these local expectations, a ‘shared field of experience’ made reciprocal interaction possible.