Energy gaps in amorphous covalent semiconductors

A calculation of approximate density of states for a disordered covalent semiconductor shows that the energy gap is due to the presence of short range order

Critical analysis of the 'generalized coherent wave approximation'

The formalism developed by Fletcher (1967) to take account of the presence of short range order in the calculation of the electronic energy spectrum of amorphous covalent semiconductors is examined critically and found to have fundamental difficulties

Ultrasonic evaluation of high voltage circuit boards

Preliminary observations indicate that an ultrasonic scanning technique may be useful as a quick, low cost, nondestructive method for judging the quality of circuit board materials for high voltage applications. Corona inception voltage tests were conducted on fiberglass-epoxy and fiberglass-polyimide high pressure laminates from 20 to 140 C. The same materials were scanned ultrasonically by utilizing the single transducer, through-transmission technique with reflector plate, and recording variations in ultrasonic energy transmitted through the board thickness. A direct relationship was observed between ultrasonic transmission level and corona inception voltage. The ultrasonic technique was subsequently used to aid selection of high quality circuit boards for the Communications Technology Satellite

2D Iterative MAP Detection: Principles and Applications in Image Restoration

The paper provides a theoretical framework for the two-dimensional iterative maximum a posteriori detection. This generalization is based on the concept of detection algorithms BCJR and SOVA, i.e., the classical (one-dimensional) iterative detectors used in telecommunication applications. We generalize the one-dimensional detection problem considering the spatial ISI kernel as a two-dimensional finite state machine (2D FSM) representing a network of the spatially concatenated elements. The cellular structure topology defines the design of the 2D Iterative decoding network, where each cell is a general combination-marginalization statistical element (SISO module) exchanging discrete probability density functions (information metrics) with neighboring cells. In this paper, we statistically analyse the performance of various topologies with respect to their application in the field of image restoration. The iterative detection algorithm was applied on the task of binarization of images taken from a CCD camera. The reconstruction includes suppression of the defocus caused by the lens, CCD sensor noise suppression and interpolation (demosaicing). The simulations prove that the algorithm provides satisfactory results even in the case of an input image that is under-sampled due to the Bayer mask

Evaluation of electrode shape and nondestructive evaluation method for welded solar cell interconnects

Resistance welds of solar cell interconnect tabs were evaluated. Both copper-silver and silver-silver welds were made with various heat inputs and weld durations. Parallel gap and annular gap weld electrode designs were used. The welds were analyzed by light microscope, electron microprobe and scanning laser acoustic microscope. These analyses showed the size and shape of the weld, the relationship between the acoustic micrographs, the visible electrode footprint, and the effect of electrode misalignment. The effect of weld heat input on weld microstructure was also shown

Short-Range Order and Pseudogaps in Elemental Amorphous Covalent Semiconductors

The role of short-range order in producing a pseudogap in the density of states ρ(E) of an elemental amorphous material is investigated. An approximate expression for ρ(E) which emphasizes short-range order and neglects all long-range order is derived from multiple-scattering theory. This expression is used to study the influence of short-range order consisting of two atoms, a single bond, and eight atoms in the staggered and eclipsed bonding configurations on ρ(E). The results of numerical calculation for amorphous sp3-bonded C, amorphous Si, and amorphous Ge are reported. These results suggest that the pseudogap in ρ(E) may be attributed to the short-range order

Morphology and Distribution of Volcanic Vents in the Orientale Basin from Chandrayaan-1 Moon Mineralogy Mapper (M3) Data

One of the most fundamental questions in the geological and thermal evolution of the Moon is the nature and history of mantle melting and its relationship to the formation and evolution of lunar multi-ringed basins. Mare volcanic deposits provide evidence for the nature, magnitude and composition of mantle melting as a function of space and time [1]. Many argue that mantle partial melts are derived from depths well below the influence of multiringed basin impact events [1], while others postulate that the formation of these basins can cause mantle perturbations that are more directly linked to the generation ascent and eruption of mare basalts [2,3]. In any case, longer-term basin evolution will considerably influence the state and orientation of stress in the lithosphere, and the location of mare volcanic vents in basins as a function of time [4]. Thus, the location, nature and ages of volcanic vents and deposits in relation to multi-ringed impact basins provides evidence for the role that these basins played in the generation of volcanism or in the influence of the basins on surface volcanic eruption and deposit concentration. Unfortunately, most lunar multi-ringed impact basins have been eroded by impacts or filled with lunar mare deposits [5-8], with estimates of the thickness of mare fill extending up to more than six km in the central part of some basins [9-11]. The interior of most basins (e.g., Crisium, Serenitatis, Imbrium, Humorum) are almost completely covered and obscured. Although much is known about the lava filling of multi-ringed basins, and particularly the most recent deposits [5-8], little is known about initial stages of mare volcanism and its relationship to the impact event. One multi-ringed basin, Orientale, offers substantial clues to the relationships of basin interiors and mare basalt volcanism

Carbon on Mercury's Surface - Origin, Distribution, and Concentration

Distinctive low-reflectance material (LRM) was first observed on Mercury in Mariner 10 flyby images. Visible to near-infrared reflectance spectra of LRM are flatter than the average reflectance spectrum of Mercury, which is strongly red sloped (increasing in reflectance with wavelength). From Mariner 10 and early MErcury, Surface, Space, ENvironment, GEochemistry, and Ranging (MESSENGER) flyby observations, it was suggested that a higher content of ilmenite, ulvospinel, carbon, or iron metal could cause both the characteristic dark, flat spectrum of LRM and the globally low reflectance of Mercury. Once MESSENGER entered orbit, low Fe and Ti abundances measured by the X-Ray and Gamma-Ray Spectrometers ruled out ilmenite, and ulvospinel as important surface constituents and implied that LRM was darkened by a different phase, such as carbon or small amounts of micro- or nanophase iron or iron sulfide dispersed in a silicate matrix. Low-altitude thermal neutron measurements of three LRM-rich regions confirmed an enhancement of 1-3 weight-percent carbon over the global abundance, supporting the hypothesis that LRM is darkened by carbon

The acquisition of Sign Language: The impact of phonetic complexity on phonology

Research into the effect of phonetic complexity on phonological acquisition has a long history in spoken languages. This paper considers the effect of phonetics on phonological development in a signed language. We report on an experiment in which nonword-repetition methodology was adapted so as to examine in a systematic way how phonetic complexity in two phonological parameters of signed languages — handshape and movement — affects the perception and articulation of signs. Ninety-one Deaf children aged 3–11 acquiring British Sign Language (BSL) and 46 hearing nonsigners aged 6–11 repeated a set of 40 nonsense signs. For Deaf children, repetition accuracy improved with age, correlated with wider BSL abilities, and was lowest for signs that were phonetically complex. Repetition accuracy was correlated with fine motor skills for the youngest children. Despite their lower repetition accuracy, the hearing group were similarly affected by phonetic complexity, suggesting that common visual and motoric factors are at play when processing linguistic information in the visuo-gestural modality