In situ analysis of neuronal dynamics and positional cues in the patterning of nerve connections

Recently developed imaging techniques permit individual cells to be uniquely labeled and followed over time as development proceeds in intact vertebrate embryos. Small groups of cells in the developing eye rudiment of the frog Xenopus have been labeled with the vital dyes DiI, lysinated fluorescein dextran (LFD) or lysinated rhodamine dextran (LRD). Individual optic axons and their growth cones were clearly visible in the intact living animal using confocal microscopy or epifluorescence microscopy with a low light level video camera and computer-based video image enhancement. To follow the dynamics of single optic nerve fiber terminal arborizations, small groups of cells, or even single retinal ganglion cells, were labeled with DiI, and the resulting labeled optic nerve fibers were imaged using a confocal microscope. The images show a profound alteration in morphology from day to day, demonstrating that optic nerve terminal arborizations are dynamic structures constantly extending and retracting branches. To follow the topography of the developing projection and analyze the cues that guide its formation, small groups of eyebud cells from LFD- and LRD-labeled donor embryos were grafted to an unlabeled host in either a location equivalent to that from which they had been removed (homotopic grafts) or a non-equivalent location (heterotopic grafts). Axons from homotopic grafts projected to the tectum as expected from the adult topography of the retinotectal projection. Dorsoventral topography was present from the time that the optic nerve fibers were observable in the tectum, in agreement with previous work. Nasotemporal topography was subtle or absent for the first few days, and then slowly refined. The importance of positional cues was tested by performing heterotopic eyebud grafts, in which the labeled eyebud cells are grafted to inappropriate places in the host eyebud. The heterotopic grafts appeared to integrate with the ectopic site in the eyebud in a functional manner. They should, therefore, project to the tectum together with their new neighbors if neighbor interactions or activity-based cues were of primary importance in the initial patterning of the map. However, the experiments showed that the axons from heterotopic grafts always behaved in a fashion appropriate to their position of origin in the donor, regardless of their final position in the host. These observations indicate that small groups of eyebud cells (as small as a single cell) possess positional information that plays a dominant role in guiding the optic nerve fibers to their target sites in the tectum

The basics of gravitational wave theory

Einstein's special theory of relativity revolutionized physics by teaching us that space and time are not separate entities, but join as ``spacetime''. His general theory of relativity further taught us that spacetime is not just a stage on which dynamics takes place, but is a participant: The field equation of general relativity connects matter dynamics to the curvature of spacetime. Curvature is responsible for gravity, carrying us beyond the Newtonian conception of gravity that had been in place for the previous two and a half centuries. Much research in gravitation since then has explored and clarified the consequences of this revolution; the notion of dynamical spacetime is now firmly established in the toolkit of modern physics. Indeed, this notion is so well established that we may now contemplate using spacetime as a tool for other science. One aspect of dynamical spacetime -- its radiative character, ``gravitational radiation'' -- will inaugurate entirely new techniques for observing violent astrophysical processes. Over the next one hundred years, much of this subject's excitement will come from learning how to exploit spacetime as a tool for astronomy. This article is intended as a tutorial in the basics of gravitational radiation physics.Comment: 49 pages, 3 figures. For special issue of New Journal of Physics, "Spacetime 100 Years Later", edited by Richard Price and Jorge Pullin. This version corrects an important error in Eq. (4.23); an erratum is in pres

Scholarly collaboration across time zones

The barriers to global collaboration of yesteryear were, for example, country boundaries and time zones. Today however, in a world where communication is thriving on new technologies, these barriers have been overcome, not only by the technology itself, but also by the collaborators in a desire (and need) to extend knowledge, seize opportunities and build partnerships. This chapter reports on one such collaboration: a case study where the focus is the writing of a scholarly article between authors from Australia, England and South Africa. The challenges of different time zones, academic calendars, and managing the collaboration are outlined in this chapter. Findings from the case study suggests that the key elements of success are related to the individuals and project management techniques, and not the technology per se. The constructivist learning theory as well as the e-Moderation model are supported by this work and thus extend their application to the academic writing process

Using gravitational-wave standard sirens

Gravitational waves (GWs) from supermassive binary black hole (BBH) inspirals are potentially powerful standard sirens (the GW analog to standard candles) (Schutz 1986, 2002). Because these systems are well-modeled, the space-based GW observatory LISA will be able to measure the luminosity distance (but not the redshift) to some distant massive BBH systems with 1-10% accuracy. This accuracy is largely limited by pointing error: GW sources generally are poorly localized on the sky. Localizing the binary independently (e.g., through association with an electromagnetic counterpart) greatly reduces this positional error. An electromagnetic counterpart may also allow determination of the event's redshift. In this case, BBH coalescence would constitute an extremely precise (better than 1%) standard candle visible to high redshift. In practice, gravitational lensing degrades this precision, though the candle remains precise enough to provide useful information about the distance-redshift relation. Even if very rare, these GW standard sirens would complement, and increase confidence in, other standard candles.Comment: 10 pages, 8 figures. ApJ, in pres

Information technology team projects in higher education: an international viewpoint

It is common to find final or near final year undergraduate Information Technology students undertaking a substantial development project; a project where the students have the opportunity to be fully involved in the analysis, design, and development of an information technology service or product. This involvement has been catalyzed and prepared for during their previous studies where the students have been told and shown how to develop similar systems. It is the belief that only through this ‘real’ project do they get the chance to experience something similar to what is expected of them when they embark on their chosen profession; that is, as an information technology professional. The high value of ‘near real life’ educational experience is recognized by many universities across the globe. The aim of this paper is to present examples from three countries - Australia, United Kingdom and South Africa, of the delivery of these team, capstone or industrial experience projects; their curricula and management processes. Academics from institutions in each of the countries share experiences, challenges and pitfalls encountered during the delivery of these information technology projects within their institutions. An overview of each institution’s strategies is provided and highlights specific issues such as the selection of projects, allocation of teams to projects, legal requirements, assessment methods, challenges and benefits. The pedagogies presented here are not exhaustive; however, the three institutions do have in common the implementation of a combination of constructivism with a community of practice approach in delivering the project unit. The three universities recognize the need for industrial experience and learning of applied skills, and therefore make these projects a compulsory part of the curriculum. The projects tend to be real life business problems which are solved over a period of two semesters, and in the case of Cape Town it could be two consecutive years of two semesters each. These projects tend to involve practical development (for example databases and web sites). The process of project-to-team allocation is generally similar in all cases. Despite their differences, team work related problems are quite similar in all three cases presented, and seem to appear as a result of team work complexity, and the number of stakeholders involved. The intention of this paper is not to propose solutions to these problems (as these would be context dependent), but to draw the attention to the main problem categories for similar schemes, these are; • project selection, • management of students, • management of academic staff, • student team motivation, • equality and diversity, • passengers, and • assessment. Furthermore, it is not the intention of the authors to portray one approach as better than another, however, the approaches are representative of how team projects are being delivered across the globe, and in particular, in the contributing institutions. It is hoped that the assimilation and dissemination of information regarding the various approaches presented will nurture further discussion, and open communication across the globe with the view to enhancing the teaching and learning experience of such projects

Within-Subject Joint Independent Component Analysis of Simultaneous fMRI/ERP in an Auditory Oddball Paradigm

The integration of event-related potential (ERP) and functional magnetic resonance imaging (fMRI) can contribute to characterizing neural networks with high temporal and spatial resolution. This research aimed to determine the sensitivity and limitations of applying joint independent component analysis (jICA) within-subjects, for ERP and fMRI data collected simultaneously in a parametric auditory frequency oddball paradigm. In a group of 20 subjects, an increase in ERP peak amplitude ranging 1–8 μV in the time window of the P300 (350–700 ms), and a correlated increase in fMRI signal in a network of regions including the right superior temporal and supramarginal gyri, was observed with the increase in deviant frequency difference. JICA of the same ERP and fMRI group data revealed activity in a similar network, albeit with stronger amplitude and larger extent. In addition, activity in the left pre- and post-central gyri, likely associated with right hand somato-motor response, was observed only with the jICA approach. Within-subject, the jICA approach revealed significantly stronger and more extensive activity in the brain regions associated with the auditory P300 than the P300 linear regression analysis. The results suggest that with the incorporation of spatial and temporal information from both imaging modalities, jICA may be a more sensitive method for extracting common sources of activity between ERP and fMRI