Psychophysical evidence for competition between real and illusory contour processing

Luminance defined and illusory contours provide vital information about object borders. However, real and illusory contour cues tend to be used under different contexts and can interfere with one another. Although some cells in visual cortex process both real and illusory contours equivalently, recent studies (Ramsden et al 2001) suggest competitive interactions between real (feedforward) and illusory (feedback) contour processing in primate V1 and V2. To test this hypothesis psychophysically, we designed stimuli in which illusory contours are presented with and without the presence of real line components. If real and illusory contour cues are processed by the same mechanism, then the presence of both cues should enhance the percept. If the illusory percept is degraded by the presence of real lines, then independent real and illusory mechanisms are suggested. The perception of a Kanisza-triangle, presented for 250 msec, was measured under three conditions: 1) virtual contour alone, 2) with a short parallel real line superimposed on the virtual contour or 3) with a short orthogonal real line abutting the virtual contour. The real lines were varied from sub- to supra-threshold contrasts. In a 2AFC paradigm three subjects fixated on a spot in the triangle center and indicated whether the side of the triangle was bent outwards or inwards. We found that real lines degraded the percept of the illusory contour (i.e. increased angular thresholds). Such interference occurred even at subthreshold real line contrasts and, in some subjects, was greater for the parallel than orthogonal real line. Our results support the presence of separate mechanisms for the processing of real and illusory contours and suggest that, under some circumstances, real cues can interfere with the processing of illusory cues. We suggest that such interferences occurs by the feedforward influences of the lines which interfere with the feedback influences prominent during illusory contour processing

Contaminant mobility as a result of sediment inundation : literature review and laboratory scale pilot study on mining contaminated sediments

This report presents a literature review of soil and sediment inundation methodologies and describes a pilot scale laboratory inundation study. Changing weather conditions, subsequent flooding events, and the increased frequency of such events both in the UK and worldwide is highlighting the need to research the area of contaminant mobility from soils and sediments under inundated conditions. The findings of such investigations impact on a wide variety of sectors, including human and ecological health, agriculture, building, transport, world economy and climate change. Standardised methodologies for the investigation of contaminant mobility resulting from soil/sediment inundation episodes are not available. Most research has been conducted in the agricultural sector for nutrient transport, as part of soil fertility and plant nutrition studies. Only recently has work been undertaken for studying potentially harmful element transport in inundated sediments/soils. A pilot scale laboratory study was undertaken using contaminated bank sediment samples collected from the Rookhope Burn catchment, Northern England, UK, with the aim to examine the extent of contaminant mobilisation from flooded sediments. The catchment has been affected by historical mining and processing of lead and zinc ore and is representative of several catchments affected by the environmental legacy related to mining in the Northern Pennine Orefield. Bank sediment Pb and Zn concentrations were found significantly above both the TEL and PEL sediment quality criteria, posing potentially a significant hazard to aquatic organisms. The source of the Pb and Zn in the sediments is related to the underlying mineralisation, mining activities and mine water discharges in the catchment. Abundances of original sulphide ore and authigenic metal-bearing phases were expected to vary through the catchment. The study design simulated rising flood water, a slow saturation of the sediment in order to induce a slow change in physico-chemical properties, followed by a 3 month (88 day) stagnation period. Natural day-night cycles were simulated by undertaking the study on the bench top during the winter of 2009/2010 (November to February). The chemical changes in the inundation water during the experiment were monitored and the sediment pore water at the end of the inundation period analysed. The inundation water pH remained alkaline to neutral, while redox measurements indicated oxic conditions in the water column throughout the inundation period. The pilot study showed that inundation of river bank sediments from the Rookhope Burn may be a significant pathway for contaminants in the catchment and that mobilisation from the sediments may pose a hazard to environmental receptors in the area, particularly with respect to Pb and Zn contamination. The different degrees and different rates of metal losses to the overlying water column observed during the flooding of the Rookhope Burn bank sediments demonstrated that the significance of metal mobilisation was dictated by the sediment composition. The inundation water composition monitored during the sediment flooding was used to indirectly infer possible processes that control contaminant fluxes from the sediments to the overlying water. Dissolved Pb concentration in the inundation water reflected the original concentration in the solid material and in sediments that had XRD-detectable galena and cerussite the dissolved Pb concentration reached a maximum value of 395 μg l-1. Cerussite, which is commonly formed as coatings on galena during the sulphide weathering, was close or supersaturated in those solutions, suggesting that the lead carbonate mineral phase provided a continuous source of Pb to these solutions. The initial dissolved Zn in the inundation waters was independent of the original concentration in the sediments. Sediments downstream a mine water discharge showed a greater availability of easily mobilised Zn, producing high initial Zn concentration in the inundation water, despite the relatively low Zn concentration in the inundated sediment. The Zn/SO4 and Cd/Zn molar ratios were both consistent with sphalerite mineral oxidation. The final inundation water solutions had the highest Zn concentrations for those sediment samples where sphalerite was detected by XRD. Redox sensitive elements such as Fe and Mn could not unequivocally indicate the presence of reducing conditions within the flooded sediments and the redox measurements were carried out only in the overlying water column (ORP above 200-350 mV). Low organic matter content and sandy texture would not have favoured the rapid formation of an anoxic layer. Yet, only extending the ORP measurements to the submerged sediment would determine the presence of flooding-induced reducing conditions. Reductive dissolution of Mn oxyhydroxides would result in release of Mn into solution, along with other trace metals, such as Pb and Zn. Mn increased in the inundation water throughout most or all the inundation period for some of the studied sediments. Their final pore water composition was significantly enriched in Mn (1300- 6500 μg l-1). Saturation indices indicated both rhodocrosite (MnCO3) and Mn oxides reached saturation. Therefore, it was not possible to preclude either the role of rhodocrosite as solubility controlling solid phase or the reductive dissolution of Mn oxides for accounting the enhanced Mn concentrations in the pore water and overlying water column without a better characterisation of the solid phase and monitoring of the sediment redox conditions. Amendments to the inundation test design have been recommended, which comprise: set-up to allow for the continuous monitoring of pore water dynamics and allow for the collection of pore water at the different times and measurement of pore water pH and Eh; inclusion of a blank test cell, to test the influence of the properties and the volume of the inundation water; inclusion of flow-cell tests to assess the influence of moving or stagnant inundation water; the inclusion of abiotic blanks to identify the role microbes play in the solubilisation of contaminants. complementary characterisation of the solid phase material and metal distribution in the sediment before and after the inundation experiment

Coarse topology, enlargeability, and essentialness

Using methods from coarse topology we show that fundamental classes of closed enlargeable manifolds map non-trivially both to the rational homology of their fundamental groups and to the K-theory of the corresponding reduced C*-algebras. Our proofs do not depend on the Baum--Connes conjecture and provide independent confirmation for specific predictions derived from this conjecture.Comment: 21 pages, 2 figures. Revised version. To appear in Ann. Sci. Ecole Norm. Su

Normal background concentrations (NBCs) of contaminants in English soils : final project report

The British Geological Survey (BGS) has been commissioned by the Department for Environment, Food and Rural Affairs (Defra) to give guidance on what are normal levels of contaminants in English soils in support of the Part 2A Contaminated Land Statutory Guidance. This has initially been done by studying the distribution of four contaminants – arsenic, lead, benzo[a]pyrene (BaP) and asbestos – in topsoils from England. This work was extended to a further four contaminants (cadmium, copper, nickel and mercury) which enabled methodologies developed to be tested on a larger range of contaminants. The first phase of the Project gathered data sets that were: nationally extensive; systematically collected so a broad range of land uses were represented; and collected and analysed to demonstrably and acceptable levels of quality. Information on the soil contaminant concentrations in urban areas was of particular importance as the normal background is considered to be a combination of both natural and diffuse anthropogenic contributions to the soil. Issues of soil quality are most important in areas where these affect most people, namely, the urban environment. The two principal data sets used in this work are the BGS Geochemical Baseline Survey of the Environment (G-BASE) rural and urban topsoils (37,269 samples) and the English NSI (National Soil Inventory) topsoils (4,864 samples) reanalysed at the BGS laboratories by X-ray fluorescence spectrometry (XRFS) so both data sets were highly compatible. These two data sets provide results for most inorganic element contaminants, though results explored for mercury and BaP are drawn from a variety of different and much less extensive data sets

Minimal kernels of Dirac operators along maps

Let $M$ be a closed spin manifold and let $N$ be a closed manifold. For maps $f\colon M\to N$ and Riemannian metrics $g$ on $M$ and $h$ on $N$, we consider the Dirac operator $D^f_{g,h}$ of the twisted Dirac bundle $\Sigma M\otimes_{\mathbb{R}} f^*TN$. To this Dirac operator one can associate an index in $KO^{-dim(M)}(pt)$. If $M$ is $2$-dimensional, one gets a lower bound for the dimension of the kernel of $D^f_{g,h}$ out of this index. We investigate the question whether this lower bound is obtained for generic tupels $(f,g,h)$

Letter from Laura B. Roe to John Muir, [ca. 1912] Aug 10.

[3]- for you meet so many - I just want to say I was most glad to meet and know you for the short time I did in a place so beloved by us both - and so you may know how much I am going to enjoy having you within my book -Hoping soon to hear from you and hoping too that you may recall me, I am very sincerely yoursLaura B. Roe(Mrs. George H. Roe of Ross Valley, Marin Co., Ca.)[1][letterhead]Aug. 10thMy dear Mr. Muir,I am wondering if you will remember me - Mrs Roe of Ross Valley, whom you met at Camp Ahwahnee a few days before you left this year?I got you to write in a friends book, and was most unselfish about05247 [2]it for I wanted your autograph in a book of my own.You told me when I returned to Ross or S. F. that if I would send one, I chose Yosemite, and put an inside wrapper on it addressed to me that you would write me a something on the fly leaf.Now I am back at sea level, sighing still for Yosemite, and I have my book, but write this first to know if you are at home, or whether you went to Alaska and have not yet returned.I am going to ask the favor of an answer to this as soon as you do return, and have a chance to open your mail, and then I will send the book to you, already for return shipment.If I am at all clear to yo

Warning: Environmental Law May Be Hazardous to the Environment

A book review essay considering Cases and Materials on Environmental Law, by Oscar S. Gray (1970)

Letter to the Court from the Office of the Attorney General, Washington

RE: United States v. Anderson, Civil No. 364