Program representation size in an intermediate language with intersection and union types

The CIL compiler for core Standard ML compiles whole programs using a novel typed intermediate language (TIL) with intersection and union types and flow labels on both terms and types. The CIL term representation duplicates portions of the program where intersection types are introduced and union types are eliminated. This duplication makes it easier to represent type information and to introduce customized data representations. However, duplication incurs compile-time space costs that are potentially much greater than are incurred in TILs employing type-level abstraction or quantification. In this paper, we present empirical data on the compile-time space costs of using CIL as an intermediate language. The data shows that these costs can be made tractable by using sufficiently fine-grained flow analyses together with standard hash-consing techniques. The data also suggests that non-duplicating formulations of intersection (and union) types would not achieve significantly better space complexity.National Science Foundation (CCR-9417382, CISE/CCR ESS 9806747); Sun grant (EDUD-7826-990410-US); Faculty Fellowship of the Carroll School of Management, Boston College; U.K. Engineering and Physical Sciences Research Council (GR/L 36963, GR/L 15685

Manufacture, observation, and test of membranes with locatable single pores

A method for generating single pores down to 0.1 μm diameter in the center of a large circular foil is described, based on nuclear tracks. The foil is framed by a tension ring which enables one to handle the foils in a well‐defined precise way. The single pore has a lateral displacement of ±0.1 mm with respect to the tension ring center. The foils used are polycarbonate of the type Makrofol and have thicknesses between 2 and 10 μm. For calibration of the single pore diameters, multiple nuclear tracks between 0.1 and 3.5 μm diameter are etched and observed by microscopy. The microscopic observations are compared with gas‐flow measurements, using two alternative methods: multiple holes are tested under viscous flow conditions of N2 gas at normal temperature and pressure; single holes are tested under collisionless flow conditions of 4He gas at liquid‐nitrogen temperature, using a capacitance method.Peer reviewe

Neural Substrates of Semantic Prospection – Evidence from the Dementias

The ability to envisage personally relevant events at a future time point represents an incredibly sophisticated cognitive endeavor and one that appears to be intimately linked to episodic memory integrity. Far less is known regarding the neurocognitive mechanisms underpinning the capacity to envisage non-personal future occurrences, known as semantic future thinking. Moreover the degree of overlap between the neural substrates supporting episodic and semantic forms of prospection remains unclear. To this end, we sought to investigate the capacity for episodic and semantic future thinking in Alzheimer’s disease (n = 15) and disease-matched behavioral-variant frontotemporal dementia (n = 15), neurodegenerative disorders characterized by significant medial temporal lobe (MTL) and frontal pathology. Participants completed an assessment of past and future thinking across personal (episodic) and non-personal (semantic) domains, as part of a larger neuropsychological battery investigating episodic and semantic processing, and their performance was contrasted with 20 age- and education-matched healthy older Controls. Participants underwent whole-brain T1-weighted structural imaging and voxel-based morphometry analysis was conducted to determine the relationship between gray matter integrity and episodic and semantic future thinking. Relative to Controls, both patient groups displayed marked future thinking impairments, extending across episodic and semantic domains. Analyses of covariance revealed that while episodic future thinking deficits could be explained solely in terms of episodic memory proficiency, semantic prospection deficits reflected the interplay between episodic and semantic processing. Distinct neural correlates emerged for each form of future simulation with differential involvement of prefrontal, lateral temporal, and medial temporal regions. Notably, the hippocampus was implicated irrespective of future thinking domain, with the suggestion of lateralization effects depending on the type of information being simulated. Whereas episodic future thinking related to right hippocampal integrity, semantic future thinking was found to relate to left hippocampal integrity. Our findings support previous observations of significant MTL involvement for semantic forms of prospection and point to distinct neurocognitive mechanisms which must be functional to support future-oriented forms of thought across personal and non-personal contexts

Regularized Multigrid Optimization for Material Reconstruction from Single Medical X-ray Images

This thesis presents a novel technique for the estimation of 3D structural and material composition of anatomies imaged with X-rays. These estimates are produced from a single image with associated X-ray detector data. This method is made possible with access to software for X-ray simulation and segmentation, both developed by and provided to us by IBEX Innovations. This work combines existing concepts from optimization and multi-grid methods to present a novel concept for using domain knowledge to sufficiently constrain an otherwise unsolvable problem to produce valuable output. Specifically, it is shown that by transforming knowledge about the shape and composition of anatomies into regularizing functions, we can produce models of their internal structure that are accurate enough to simulate X-ray scatter, and thereby remove noise from the final images in a physics-guided way. By introducing weighted penalties for results that do not conform to expectations from domain knowledge, which are informed by IBEX’s neural network for X-ray segmentation, we can estimate the shape and material composition of a 3D object from a single image which - in theory - does not contain enough information to produce such a model. This work makes use of an X-ray simulation tool and associated data created by IBEX innovations and provided to us. We have created an optimization algorithm that iteratively processes this data with the IBEX simulation tool, then updates the estimated material composition of the imaged anatomy by imposing regularizing functions that penalize models that do not conform to our expectations about real anatomies. This is implemented on multi-grid, showing improved reconstruction quality and speed by producing coarse models first, followed by a custom algorithm for optimally selecting coarsening and refining of the model to produce the most accurate model. By using IBEX’s simulation algorithm, we show that we can constrain an otherwise ill-posed problem. These novel tools allow us to solve the problem of estimating 3D material composition from a single image, by considering simple features of organic shapes such as continuity and smoothness. We demonstrate that with access to sufficiently powerful simulation tools, even simple assumptions about our target facilitate intuitive material estimations. The algorithm presented in this thesis has certain limitations. We are only able to produce models of anatomies at low resolutions, constructed of just two distinct materials, without fully capturing the 3D structure of the anatomy. Nonetheless, we demonstrate that it is possible to capture enough structural information to produce an accurate scatter estimate, which would not be possible without the research we present here. These limitations are imposed to simplify our solutions such that they can be found using conventional hardware, and to constrain our problem into the scope of feasibility. Furthermore, the choice to limit our models to 2.5D and just two materials reflects the models used by IBEX Innovations and their X-ray simulation method, which we require for our optimization. To our understanding, no other published work in this field has applied an approach like ours to X-ray image reconstruction. Inferring from a single image not just depth information, but also an abstraction of information about the internal structure, in a way that is physically motivated. We hope that this concept could be applied to other problems in future, where systems are well understood but hindered by limited data availability or high capture costs

Rhodopseudomonas palustris : a model of bacterial differentiation

Differentiation in the budding photosynthetic bacterium Rhodopseudomonas palustris was studied both in its own right and in the context of other comparable bacteria; particularly R. acidophila and Rhodomicrobium vannielii. Together, these three Rhodospirillaceae present a gradient of morphogenetic complexity ideally suited to differentiation studies. Semi-defined conditions were determined which gave consistent morphology and fast growth rates. Heterogeneous cultures of R. palustris were then synchronised by selecting swarmer cells by sucrose gradient sedimentation. Morphology and ultrastructure of the cell division cycle exhibited by R. palustria were examined in some detail and compared with R. acidophila. Both organisms exhibited differentiation at the sub-cellular level and by dividing to give two dissimilar cells. The distribution of cell types, stepwise doublings, particle volume distributions, optical density changes, cell motility, protein and DNA synthesis and probably also RNA synthesis were all examined during synchronous growth of R. palustris. Penicillin treatment showed that cell growth was by polar, unidirectional synthesis of wall material, Nalidixic acid, which inhibits DNA replication, modified the cell development by inhibiting cell division and giving rise to abnormal cell elongation. Studies with nalidixic acid also confirmed that there was periodic DNA synthesis during the normal cell cycle. Observations on the location of cell division in elongated cells after removal of the nalidixic acid, considered alongside the polar unidirectional mode of cell growth, allowed a model correlating chromosome replication and cell envelope growth to be proposed. Some preliminary investigations were made of mutants of R. palustris. Temperature-sensitive mutants were obtained, but these did not appear to be blocked at any particular stage of development. A phage specific for one strain of H. palustris was investigated and appeared to be temperature-sensitive in some step of its growth cycle. This might permit its use for transduction. Both temperature-sensitive mutants and a method of genetic transfer were considered invaluable for further studies of the control of R. palustris differentiation