Modification to the Automatic Ionization Chamber

The automatic ionization chamber has been described previously [1,2]. It has proven quite reliable in service and has many desirable features, especially for balloon-borne equipment. A disadvantage has been that the time of discharge was dependent upon the potential applied to the quartz fiber. Thus, during the comparison of the instrument to be used with the standards, careful measurement of the potential used on the standards was required. Furthermore, care was required to make sure that the battery used during the flight remained constant in potential. It has now been found that the time between rechargings can be made nearly independent of the potential of the fiber by inserting a metal conductor inside and insulating it from the outer conductor surrounding the quartz fiber, and making the potential of this inner conductor the same as that of the fiber

Techniques Useful in Evacuating and Pressurizing Metal Chambers

The aforementioned problems arose in connection with the automatic ionization chamber described previously (1). It was fund that the functioning of these instruments was more consistent if the ion chamber was baked at 350°C for several hours and then filled with pure argon. This procedure resulted in the elimination of organic impurities from the inner surfaces. The impurities, settling on the gold-coated quartz fiber and the collector, apparently altered the contact, resulting in some uncertainty in the recharging. The baking procedure has completely curved this difficulty

Contrast Gain Shapes Visual Time

Traditionally time perception has been considered the product of a central, generic, cognitive mechanism. However, evidence is emerging for a distributive system with modality-specific sensory components (Morrone et al., 2005; Johnston et al., 2006). Here we show that fast contrast adaptation, which can be observed in the retina, induces a change in apparent duration. The perceived duration of a subsecond interval containing a 50% luminance contrast drifting pattern is compressed when it follows a high (90%) as compared to a low (10%) contrast interval. The duration effect cannot be attributed to changes in latency at onset relative to offset, can be dissociated from the effect of contrast context on apparent speed or apparent contrast per se and it occurs in a retinocentric frame of reference. The temporal compression is limited to high drift temporal frequencies (≥10 Hz) and is not observed for equiluminant chromatic stimuli. This pattern of results indicates a major role for the magnocellular pathway in the neural encoding and representation of visual time

Rigour in research: theory in the research approach

Purpose – The purpose of this paper is to reexamine the importance of theory in research. The paper focuses on discussing the underlying principles that influence the research approach. Design/methodology/approach – This is a theoretical paper that discusses the importance of theory in research and opens up the area for discussion and debate. Findings – The paper contributes to the research methodology literature by adopting a sense making perspective, and focusing on the ontological and epistemological dimension of research. The paper furthers the debate on the link between theory and research, as the basis for developing further theory. Research limitations/implications – The paper provides a limited focus to management research and has not at this stage engaged in any practical testing of the ideas. Practical implications – There is an opportunity for changing practice at a variety of levels in engaging with research. These include implications for researchers, teachers, students and practitioners. Originality/value – The paper re-emphasises the importance in understanding philosophical concerns which underpins research activity. It is designed as a tool for discussion and guidance. </jats:sec

A Model of 1D and 2D Motion Processing in the Primate Brain

Velocity encoding in the primate brain can be modelled by a spatiotemporal gradient approach, with neurons characterized as spatio-temporal derivative operators (Johnston et al. 1999). This strategy works well for moving 1D spatial patterns, but it can produce systematic errors, as it can be overly influenced by the direction of the local spatial gradient of the image brightness. For 2D pattern it is possible to develop a similar spatio-temporal approach, in which the system solves a set of over-determined linear equations directly, to provide an estimate for the 2D image motion. However, in this case the matrix one needs to invert is indeterminate for 1D image pattern. This can be accommodated by introducing a constant on the diagonal of the matrix, as is done in ridge regression. However, the constant, however chosen, will introduce different degrees of error at each location due to the variation in the magnitudes of the spatio-temporal derivatives. Here we return to a geometric view of the solution of a system of linear equations through Cramer’s rule and formulate a geometrical strategy which delivers the 2D solution when the image pattern has 2D structure but which defaults automatically to the 1D computation (Johnston et al. 1999), when the image structure is 1D. The model makes the key prediction of the existence of neurons that respond to 2D pattern (plaids) but not 1D pattern (gratings), sometimes referred to as super pattern cells, which do not fit well into current theories of primate motion processing

From Image Gradients to a Perceptual Metric Space

How do we achieve a sense of spatial dimension from a sense of location? There are three predominant ideas about how we achieve this; spatial isomorphism, in which what we see reflects differences in distance or size in the brain; that spatial extent depends upon motor sensations or intentions related to eye movements; and that distance is computed from the degree of correlation in neural activity between adjacent locations, with distance inversely proportional to the correlation. There are problems with each of these approaches, for example, neural correlation may depend more on image structure than adjacency - consider the case of images containing repeating lines or sine gratings. Here a new computational strategy is outlined and assessed. Human image motion computation naturally relies on a set of linear temporal filters which can be defined in a window of around 100ms. However, gradient motion models can be reformulated to operate on just two frames, with image frame sums and differences taking the place of extended temporal derivative filters. This approach constitutes an image gradient approach to computing retinal disparity. This strategy can itself be re-purposed to compute the separation of points in a single image, rather than computing image displacement in the left and right eye’s images. This new strategy allows us to compute spatial separation, on the basis of a non-spatial measure, the image brightness difference, and a local spatial brightness gradient

Characterization of the airway epithelial bioelectric mechanisms associated with the effects of epithelium-derived relaxing factor in guinea pig-isolated trachea

In response to elevated serosal or mucosal tonicity, guinea-pig tracheal epithelium releases the non-nitric oxide, non-prostanoid, epithelium-derived relaxing factor (EpDRF), which subsequently diffuses to the underlying airway smooth muscle to initiate relaxation. Hypertonicity-induced smooth muscle relaxation via EpDRF involves epithelial Na+ and Cl- channels and is preceded by a depolarization of the transepithelial potential difference (Vms). By utilizing two different experimental systems, this study sought to characterize further the airway epithelial bioelectric mechanisms associated with the effects of EpDRF in guinea-pig isolated trachea.;First, this study attempted to elucidate which epithelial ion channels and/or transporters are involved in the depolarization of the Vms. This was accomplished by determining the effect of ion channel and transporter inhibitors on in vitro transepithelial short-circuit current responses to elevated mucosal tonicity in guinea-pig tracheal segments mounted in Ussing chambers. The data from these studies indicate that apical Na + channels and the basolateral Na+-K+-2Cl - cotransporter are intimately involved in the epithelial bioelectric response to elevated mucosal tonicity, and thus, may play an important role in the synthesis, release, and/or effects of EpDRF.;Secondly, this study sought to determine the consequences of altered epithelial ion transport, following LPS-treatment (4 mg/kg, i.p.; 18 hr post-treatment), on EpDRF-induced smooth muscle relaxation and its associated bioelectric events as well as airway reactivity to methacholine (MCh). In vitro tracheal smooth muscle contractile and relaxant responses as well as V ms responses were measured utilizing the isolated and modified isolated, perfused trachea apparatuses while the two-chambered, whole-body plethysmograph was used to measure in vivo airway reactivity. This study has shown that EpDRF-induced smooth muscle relaxation and its associated bioelectric events are either increased, decreased, or not changed following LPS-induced alterations of epithelial ion transport. In addition, LPS-treatment causes in vivo airway hyporeactivity to MCh. These results suggest that the effects of EpDRF on smooth muscle reactivity are modulated by changes in the electrical activity of the epithelium which can ultimately impact on airway reactivity to MCh

Geomorphology of Deposits from the 2004 Indian Ocean Tsunami, Tamil Nadu, Southeastern India

In low latitudes, geologically suitable repositories for tsunami deposits are not well defined. This project characterizes the geomorphic environments on the southeastern coast of India that preserved depositional evidence of the catastrophic tsunami created by the Mw9.0-9.3 Sumatra-Andaman earthquake on December 26, 2004. The Indian coast is particularly interesting because it is approximately 1300 km from the subduction-zone source of tsunamis across the Indian Ocean, and therefore only the largest events are capable of reaching it. The main objective of this study was to identify the settings where recognizable tsunami deposits from the 2004 event have been preferentially preserved in the stratigraphic record until 2008. These results will be useful in future attempts to discover and identify paleotsunami deposits in the geological record from India, and elsewhere

The role of the harmonic vector average in motion integration

The local speeds of object contours vary systematically with the cosine of the angle between the normal component of the local velocity and the global object motion direction. An array of Gabor elements whose speed changes with local spatial orientation in accordance with this pattern can appear to move as a single surface. The apparent direction of motion of plaids and Gabor arrays has variously been proposed to result from feature tracking, vector addition and vector averaging in addition to the geometrically correct global velocity as indicated by the intersection of constraints (IOC) solution. Here a new combination rule, the harmonic vector average (HVA), is introduced, as well as a new algorithm for computing the IOC solution. The vector sum can be discounted as an integration strategy as it increases with the number of elements. The vector average over local vectors that vary in direction always provides an underestimate of the true global speed. The HVA, however, provides the correct global speed and direction for an unbiased sample of local velocities with respect to the global motion direction, as is the case for a simple closed contour. The HVA over biased samples provides an aggregate velocity estimate that can still be combined through an IOC computation to give an accurate estimate of the global velocity, which is not true of the vector average. Psychophysical results for type II Gabor arrays show perceived direction and speed falls close to the IOC direction for Gabor arrays having a wide range of orientations but the IOC prediction fails as the mean orientation shifts away from the global motion direction and the orientation range narrows. In this case perceived velocity generally defaults to the HVA