Functional brain organization of preparatory attentional control in visual search

Looking for an object that may be present in a cluttered visual display requires an advanced specification of that object to be created and then matched against the incoming visual input. Here, fast event-related fMRI was used to identify the brain networks that are active when preparing to search for a visual target. By isolating the preparation phase of the task it has been possible to show that for an identical stimulus, different patterns of cortical activation occur depending on whether participants anticipate a 'feature' or a 'conjunction' search task. When anticipating a conjunction search task, there was more robust activation in ventral occipital areas, new activity in the transverse occipital sulci and right posterior intraparietal sulcus. In addition, preparing for either type of search activated ventral striatum and lateral cerebellum. These results suggest that when participants anticipate a demanding search task, they develop a different advanced representation of a visually identical target stimulus compared to when they anticipate a nondemanding search. © 2013 Elsevier B.V. All rights reserved

Neural mechanisms of top-down control during visual search: effects of template complexity

Neural mechanisms of top-down control during visual search: effects of template complexit

Investigation of ion channel activity in alveolar epithelial cells. The development of lung slice in-vitro model.

The alveolar epithelium maintains lung fluid homeostasis by active ion transport. The molecular machinery required to create an osmotic gradient across the alveolar epithelium, which in turn moves water out of the airspaces, has been identified by number of experimental techniques. The alveolar epithelium, which covers 95% of the surface area of the lung, is composed of two morphologically distinct epithelial cell types: alveolar epithelial type one and alveolar epithelial type two cells. The much studied alveolar epithelial type two cell, which cover <5% of the surface, contain the myriad of ion channel and transports required to undertake fluid transport. The alveolar epithelial type one cell, which covers >95% of the surface area, is less well characterised. Direct functional electrophysiological measurements from the alveolar epithelial type one cell has proved difficult to obtain. In order to obtain novel recordings the unfilled lung slice experimental model was developed. This experimental model demonstrated excellent cellular viability. VIIIB2 mouse monoclonal antibody, a specific cell marker for alveolar epithelial type one cells, was used to obtain live cell immunohistochemistry, the first such reported in peripheral tissue. The results presented in this thesis represent the first published ion channel recordings from identified alveolar epithelial type one cells within a rat lung slice (Bourke, S. et al 2005). Cell-attached, patch-clamp recordings demonstrated the presence of a voltage-dependant, K+ selective ion channel with a measured unitary conductance of 21 pS. The findings contained within this thesis present a novel experimental technique to investigate the functional physiological role of the alveolar epithelial cells. The alveolar epithelium is reliant upon Ca2+ signalling mechanisms to undertake a number of normal physiological activities. The release of surfactant from the alveolar epithelial type two cell lamellar bodies relies on a Ca2+ dependant exocytosis step. To investigate further the function of Ca2+ in the alveolar cells, experiments were undertaken using Ca2+ fluorescent indicator dye Fluo-3. Slices demonstrated spontaneous Ca2+ oscillations. Application of a number of physiological and pharmacological substances failed to modulate the observed activity

The Envelope Kinematics and a Possible Disk Around the Class 0 Protostar within BHR7

We present a characterization of the protostar embedded within the BHR7 dark cloud, based on both photometric measurements from the near-infrared to millimeter and interferometric continuum and molecular line observations at millimeter wavelengths. We find that this protostar is a Class 0 system, the youngest class of protostars, measuring its bolometric temperature to be 50.5~K, with a bolometric luminosity of 9.3~L$_{\odot}$. The near-infrared and \textit{Spitzer} imaging show a prominent dark lane from dust extinction separating clear bipolar outflow cavities. Observations of $^{13}$CO ($J=2\rightarrow1$), C$^{18}$O ($J=2\rightarrow1$), and other molecular lines with the Submillimeter Array (SMA) exhibit a clear rotation signature on scales $<$1300~AU. The rotation can be traced to an inner radius of $\sim$170~AU and the rotation curve is consistent with an R$^{-1}$ profile, implying that angular momentum is being conserved. Observations of the 1.3~mm dust continuum with the SMA reveal a resolved continuum source, extended in the direction of the dark lane, orthogonal to the outflow. The deconvolved size of the continuum indicates a radius of $\sim$100~AU for the continuum source at the assumed distance of 400~pc. The visibility amplitude profile of the continuum emission cannot be reproduced by an envelope alone and needs a compact component. Thus, we posit that the resolved continuum source could be tracing a Keplerian disk in this very young system. If we assume that the continuum radius traces a Keplerian disk (R$\sim$120~AU) the observed rotation profile is consistent with a protostar mass of 1.0~$M_{\odot}$.Comment: 36 pages; 11 Figures, 2 Tables; Accepted to Ap

Organic Molecules in Low-Mass Protostellar Hot Cores: Submillimeter Imaging of IRAS 16293-2422

Arcsecond-resolution spectral observations toward the protobinary system IRAS 16293-2422 at 344 and 354 GHz were conducted using the Submillimeter Array. Complex organic molecules such as CH3OH and HCOOCH3 were detected. Together with the rich organic inventory revealed, it clearly indicates the existence of two, rather than one, compact hot molecular cores (smaller than or equal to 400 AU in radius) associated with each of the protobinary components identified by their dust continuum emission in the inner star-forming core.Comment: 11 pages, 3 figures, to be published in ApJ

A 1.3 mm SMA Survey of 29 Variable Young Stellar Objects

© 2018 ESO. Reproduced with permission from Astronomy & Astrophysics.Context. Young stellar objects (YSOs) may undergo periods of active accretion (outbursts), during which the protostellar accretion rate is temporarily enhanced by a few orders of magnitude. Whether or not these accretion outburst YSOs possess similar dust and gas reservoirs to each other, and whether or not their dust and gas reservoirs are similar as quiescent YSOs, are issues yet to be clarified.Aims. The aim of this work is to characterize the millimeter thermal dust emission properties of a statistically significant sample of long and short duration accretion outburst YSOs (i.e., FUors and EXors) and the spectroscopically identified candidates of accretion outbursting YSOs (i.e., FUor-like objects). Methods. We have carried out extensive Submillimeter Array (SMA) observations mostly at ~225 GHz (1.33 mm) and ~272 GHz (1.10 mm), from 2008 to 2017. We covered accretion outburst YSOs located at 3σ significance. Detected sources except for the two cases of V883 Ori and NGC 2071 MM3 were observed with ~1″ angular resolution. Overall our observed targets show a systematically higher millimeter luminosity distribution than those of the M ∗ > 0.3 MClass II YSOs in the nearby (400 pc) low-mass star-forming molecular clouds (e.g., Taurus, Lupus, Upp Scorpio, and Chameleon I). In addition, at 1 mm our observed confirmed binaries or triple-system sources are systematically fainter than the rest of the sources even though their 1 mm fluxes are broadly distributed. We may have detected ∼30-60% millimeter flux variability from V2494 Cyg and V2495 Cyg, from the observations separated by approximately one year.Peer reviewe