Vestiges of life in the oldest Greenland rocks? A review of early Archean geology in the Godthabsfjord region, and reappraisal of field evidence for > 3850 Ma life on Akilia.

The Godthåbsfjord region of West Greenland contains the most extensive, best exposed and most intensely studied early Archean rocks on Earth. A geological record has been described of numerous magmatic events between ~3.9 and 3.6 Ga, and evidence of life at >3.85 Ga and ~3.8-3.7 Ga has been proposed from two widely-separated localities. Some of these claims have recently been questioned, and the nature of the best preserved remnants of the oldest known terrestrial volcanic and sedimentary rocks in the Isua greenstone belt are being reinvestigated and substantially reinterpreted. The first part of this article reviews the evolution of geological research and interpretations, outlining the techniques by which the geological history has been determined and the ensuing controversies. The second part re-examines crucial field evidence upon which the antiquity of the oldest terrestrial life is claimed from the island of Akilia.

Skin surface electron microscopy in Pityrosporum folliculitis. The role of follicular occlusion in disease and the response to oral ketoconazole.

The yeast Pityrosporum orbiculare is thought to cause the folliculitis associated with seborrheic eczema. However, a combination of mechanical and microbiological factors may be involved, with follicular occlusion leading to yeast overgrowth and folliculitis. Scanning electron microscopy was used to investigate this hypothesis. Skin biopsy specimens obtained from patients with Pityrosporum folliculitis were examined by scanning electron microscopy before and after oral ketoconazole therapy. Patients with active disease showed occlusion of noninflamed follicles, which resolved after ketoconazole treatment. Follicular occlusion was not present in biopsy specimens obtained from unaffected controls nor was it related to the presence of P orbiculare. These findings suggest that follicular occlusion may be a primary event in the development of this folliculitis, with yeast overgrowth a secondary occurrence. The beneficial effect of ketoconazole in this disease may be due to direct effects on the follicle.

Skin surface electron microscopy in Pityrosporum folliculitis. The role of follicular occlusion in disease and the response to oral ketoconazole.

The yeast Pityrosporum orbiculare is thought to cause the folliculitis associated with seborrheic eczema. However, a combination of mechanical and microbiological factors may be involved, with follicular occlusion leading to yeast overgrowth and folliculitis. Scanning electron microscopy was used to investigate this hypothesis. Skin biopsy specimens obtained from patients with Pityrosporum folliculitis were examined by scanning electron microscopy before and after oral ketoconazole therapy. Patients with active disease showed occlusion of noninflamed follicles, which resolved after ketoconazole treatment. Follicular occlusion was not present in biopsy specimens obtained from unaffected controls nor was it related to the presence of P orbiculare. These findings suggest that follicular occlusion may be a primary event in the development of this folliculitis, with yeast overgrowth a secondary occurrence. The beneficial effect of ketoconazole in this disease may be due to direct effects on the follicle.

Rhodotorula rubra ventriculitis.

We describe a case of post-operative ventriculitis in an immunocompetent patient caused by an unusual organism, namely Rhodotorula rubra. The patient was treated successfully with antifungal agents.

Multiple resolution representation and probabilistic matching of 2-d gray-scale shape.

One approach to pattern classification is to match a structural description of a pattern to models which describe the structural properties of pattern classes. The central problem in structural pattern matching is to determine the correspondence between the symbols which comprise a model and symbols which describe a pattern. The difficulty of determining this correspondence depends critically on the representation that is used to describe patterns. This correspondence presents a probabilistic representation for structural models of pattern classes. Both pattern descriptions and models for pattern classes are based on symbols which represent grayscale information at multiple resolutions. A pattern description is given by a tree of symbols with attribute values. Structural models are represented by a tree of symbols with probabilistic attributes. The position and scale (resolution) of the symbols, as well as other ``features,'' are represented by these attributes. An algorithm is presented for determining the correspondence between symbols in a description of a pattern and symbols in a model of a pattern class. This algorithm uses the connectivity between symbols at different scales to constrain the search for correspondence. An interactive training program for learning models of pattern classes is described, and some conclusions from the work are presented.

A representation for shape based on peaks and ridges in the difference of low-pass transform.

This paper defines a multiple resolution representation for the two-dimensional gray-scale shapes in an image. This representation is constructed by detecting peaks and ridges in the difference of lowpass (DOLP) transform. Descriptions of shapes which are encoded in this representation may be matched efficiently despite changes in size, orientation, or position. Motivations for a multiple resolution representation are presented first, followed by the definition of the DOLP transform. Techniques are then presented for encoding a symbolic structural description of forms from the DOLP transform. This process involves detecting local peaks and ridges in each bandpass image and in the entire three-dimensional space defined by the DOLP transform. Linking adjacent peaks in different bandpass images gives a multiple resolution tree which describes shape. Peaks which are local maxima in this tree provide landmarks for aligning, manipulating, and matching shapes. Detecting and linking the ridges in each DOLP bandpass image provides a graph which links peaks within a shape in a bandpass image and describes the positions of the boundaries of the shape at multiple resolutions. Detecting and linking the ridges in the DOLP three-space describes elongated forms and links the largest peaks in the tree. The principles for determining the correspondence between symbols in pairs of such descriptions are then described. Such correspondence matching is shown to be simplified by using the correspondence at lower resolutions to constrain the possible correspondence at higher resolutions.

Fast computation of the difference of low-pass transform.

This paper defines the difference of low-pass (DOLP) transform and describes a fast algorithm for its computation. The DOLP is a reversible transform which converts an image into a set of bandpass images. A DOLP transform is shown to require O(N2) multiplies and produce O(N log(N)) samples from an N sample image. When Gaussian low-pass filters are used, the result is a set of images which have been convolved with difference of Gaussian (DOG) filters from an exponential set of sizes. A fast computation technique based on ``resampling'' is described and shown to reduce the DOLP transform complexity to O(N log(N)) multiplies and O(N) storage locations. A second technique, ``cascaded convolution with expansion,'' is then defined and also shown to reduce the computational cost to O(N log(N)) multiplies. Combining these two techniques yields an algorithm for a DOLP transform that requires O(N) storage cells and requires O(N) multiplies.