Multiple parietal reach regions in humans: cortical representations for visual and proprioceptive feedback during on-line reaching

Reaching toward a visual target involves at least two sources of information. One is the visual feedback from the hand as it approaches the target. Another is proprioception from the moving limb, which informs the brain of the location of the hand relative to the target even when the hand is not visible. Where these two sources of information are represented in the human brain is unknown. In the present study, we investigated the cortical representations for reaching with or without visual feedback from the moving hand, using functional magnetic resonance imaging. To identify reach-dominant areas, we compared reaching with saccades. Our results show that a reach-dominant region in the anterior precuneus (aPCu), extending into medial intraparietal sulcus, is equally active in visual and nonvisual reaching. A second region, at the superior end of the parieto-occipital sulcus (sPOS), is more active for visual than for nonvisual reaching. These results suggest that aPCu is a sensorimotor area whose sensory input is primarily proprioceptive, while sPOS is a visuomotor area that receives visual feedback during reaching. In addition to the precuneus, medial, anterior intraparietal, and superior parietal cortex were also activated during both visual and nonvisual reaching, with more anterior areas responding to hand movements only and more posterior areas responding to both hand and eye movements. Our results suggest that cortical networks for reaching are differentially activated depending on the sensory conditions during reaching. This indicates the involvement of multiple parietal reach regions in humans, rather than a single homogenous parietal reach region

A qualitative analysis of the interfaces between urban underground metro infrastructure and its environment in London

As urban environments densify and cities across the world employ urban underground metros for the effective rapid movement of millions of people a day, there is an essential need to ensure the safe continued presence and operation of those metros. To achieve this, the authors argue there is a need for a more detailed qualitative analysis of how urban underground metro infrastructure and its environment interface. Failure to do so could potentially lead to the development of inaccurate asset management data. This would subsequently lead to the implementation of flawed Building Information Modelling processes for 2, 3, and 4D modelling and mapping, of existing and proposed infrastructure. Following a review of existing asset management approaches which confirms the need for qualitative approaches to the analyses of the interfaces, this paper presents findings from a detailed case study, in the Bayswater area of the City of Westminster in West London, UK.The processes employed for the detailed case study form part of proposed (ultimately) standardised approaches to the gathering, analysis, and sharing, of multi-disciplinary evidence-based data, developed by the authors. Such data is essential to enable effective asset and urban management processes, now and for the future

The generalized Fenyes-Nelson model for free scalar field theory

The generalized Fenyes--Nelson model of quantum mechanics is applied to the free scalar field. The resulting Markov field is equivalent to the Euclidean Markov field with the times scaled by a common factor which depends on the diffusion parameter. This result is consistent between Guerra's earlier work on stochastic quantization of scalar fields. It suggests a deep connection between Euclidean field theory and the stochastic interpretation of quantum mechanics. The question of Lorentz covariance is also discussed.Comment: 6 page

Soil carbon changes in cultivated land converted to grasses in south-central Saskatchewan

Non-Peer ReviewedSoils play an important role in the carbon cycle. Under natural conditions, soil organic carbon forms an equilibrium with the environment. Disruption to this equilibrium can transform the soils into either a source or a sink for atmospheric CO2. Mensah (2000) found in the Black and Gray soil zone that the conversion of marginal cultivated land to grassland resulted in an increase in soil organic carbon of 0.6 Mg C ha-1 yr-1 to 1.2 Mg ha-1 yr-1 (0-15 cm depth) across the landscape over a ten year period. However, little information is available on carbon sequestration rates from grassland restoration in the Brown and Dark Brown soil zones of the southern Prairies. The Missouri Coteau region in southern Saskatchewan is comprised predominantly of Brown and Dark Brown soils that, due to steep topography and stoniness, pose limitations for production of annual crops. The effect of conversion to grassland on the forms and distribution of soil carbon was examined using side-by-side paired cultivated and grassland catenae that had been in a grass seed-down for about eight years. Total soil organic carbon in the 0-15 cm depth of the shoulder, midslope and footslope positions were measured. The shoulder positions showed the greatest increase in soil organic carbon from grass seed-down, with an average apparent increase in soil carbon of 1.62 Mg ha-1 yr-1. Carbon distribution with depth was found to be dependent upon the cropping history of the cultivated equivalent as well as the parent material. Greatest apparent carbon gains were observed when the cultivated comparable was in a cereal-fallow rotation and the lowest gain from grass seed-down occurred when the cultivated comparable contained a legume in rotation

The 1:1 resonance in Extrasolar Systems: Migration from planetary to satellite orbits

We present families of symmetric and asymmetric periodic orbits at the 1/1 resonance, for a planetary system consisting of a star and two small bodies, in comparison to the star, moving in the same plane under their mutual gravitational attraction. The stable 1/1 resonant periodic orbits belong to a family which has a planetary branch, with the two planets moving in nearly Keplerian orbits with non zero eccentricities and a satellite branch, where the gravitational interaction between the two planets dominates the attraction from the star and the two planets form a close binary which revolves around the star. The stability regions around periodic orbits along the family are studied. Next, we study the dynamical evolution in time of a planetary system with two planets which is initially trapped in a stable 1/1 resonant periodic motion, when a drag force is included in the system. We prove that if we start with a 1/1 resonant planetary system with large eccentricities, the system migrates, due to the drag force, {\it along the family of periodic orbits} and is finally trapped in a satellite orbit. This, in principle, provides a mechanism for the generation of a satellite system: we start with a planetary system and the final stage is a system where the two small bodies form a close binary whose center of mass revolves around the star.Comment: to appear in Cel.Mech.Dyn.Ast

Identifying the major variables controlling transport of water and analytes from an alluvial aquifer to streams

Reliable information on groundwater (GW) lateral flow characteristics is required for estimation of GW extraction, environmental flow requirements, contaminant loading from GW to surface water bodies (SWB), and aquifer remediation purposes. Lateral flow from a shallow alluvial aquifer was investigated applying parametric and non-parametric statistics to flux-theory based outputs obtained using time series hydraulic head (HH) and analyte concentration data. The emphasis of the investigation was to identify the major variables that control the export of contaminants from GW to SWB. Point measurements from 4 shallow wells (10-12 m deep) installed along a 1.1 km transect perpendicularly crossing a creek were undertaken at 7 - 12 day intervals from January through June (wet season) over 3 years in a wet tropical catchment in north-eastern Australia. The HH during two wet seasons at north upslope varied from 4.84 m to 12.37 m with mean, median, and coefficient of variation (CV) of 8.86 m, 8.73 m, and 17% respectively. At the downslope the corresponding values were 3.59-6.21 m, 4.81 m, 4.58 m, and 13%, respectively. Similar temporal trends were observed at the south upslope and downslopes. Nitrate-N concentrations at the north upslope varied from 23 to 1340 µg L-1 with mean, median, and CV of 691 µg L-1, 609 µg L-1 and 23%, respectively. Similar trends were observed at north downslope and at up- and down-slopes of southern transect. The lateral hydraulic gradient (LHG) from north upslope to downslope varied from 4.12 x 10-3 to 9.92 x 10-3 m m-1 and the corresponding flow velocity (Vx) from 3.63 x 10-3 to 3.48 x 10-2 m d-1. Nitrate-N flux from north upslope to downslope varied from 1.0 x 10-4 to 4.4 x10-3 g m-2 d-1, similar trends were observed for EC and Cl and also along southern transect. These suggest that analyte fluxes followed the LHG indicating conservative transport of the former from upslopes to downslopes. The conservative transport was reconfirmed by significant associations between HH and analyte fluxes; R2 18-70% for EC, 24-52% for Cl, and 52-76% for nitrate. Travel time for 650 m, computed using mean Vx varied from 5.8 to 69 yrs and the variations depended on the values of saturated soil hydraulic conductivity (Ks) used. The results indicate contaminant export extrapolations from point measurements to landscape scales depended on our ability to incorporate spatial and temporal variabilities in Vx and analyte fluxes, reliable information in Ks, and macropore bypass flow. We believe this is one of the few studies that have coupled flux-theory and statistics to identify and assess the major variables that control contaminant export from GW to SWB

A comparison of Noether charge and Euclidean methods for Computing the Entropy of Stationary Black Holes

The entropy of stationary black holes has recently been calculated by a number of different approaches. Here we compare the Noether charge approach (defined for any diffeomorphism invariant Lagrangian theory) with various Euclidean methods, specifically, (i) the microcanonical ensemble approach of Brown and York, (ii) the closely related approach of Ba\~nados, Teitelboim, and Zanelli which ultimately expresses black hole entropy in terms of the Hilbert action surface term, (iii) another formula of Ba\~nados, Teitelboim and Zanelli (also used by Susskind and Uglum) which views black hole entropy as conjugate to a conical deficit angle, and (iv) the pair creation approach of Garfinkle, Giddings, and Strominger. All of these approaches have a more restrictive domain of applicability than the Noether charge approach. Specifically, approaches (i) and (ii) appear to be restricted to a class of theories satisfying certain properties listed in section 2; approach (iii) appears to require the Lagrangian density to be linear in the curvature; and approach (iv) requires the existence of suitable instanton solutions. However, we show that within their domains of applicability, all of these approaches yield results in agreement with the Noether charge approach. In the course of our analysis, we generalize the definition of Brown and York's quasilocal energy to a much more general class of diffeomorphism invariant, Lagrangian theories of gravity. In an appendix, we show that in an arbitrary diffeomorphism invariant theory of gravity, the ``volume term" in the ``off-shell" Hamiltonian associated with a time evolution vector field $t^a$ always can be expressed as the spatial integral of $t^a {\cal C}_a$, where ${\cal C}_a = 0$ are the constraints associated with the diffeomorphism invariance.Comment: 29 pages (double-spaced) late

From attention to memory along the dorsal-ventral axis of the medial prefrontal cortex: some methodological considerations

Distinctions along the dorsal-ventral axis of medial prefrontal cortex (mPFC), between anterior cingulate (AC), prelimbic (PL) and infralimbic (IL) sub-regions, have been proposed on a variety of neuroanatomical and neurophysiological grounds. Conventional lesion approaches (as well as some electrophysiological studies) have shown that these distinctions relate to function in that a number behavioural dissociations have been demonstrated, particularly using rodent models of attention, learning and memory. For example, there is evidence to suggest that AC has a relatively greater role in attention, whereas IL is more involved in executive function. However, the well-established methods of behavioral neuroscience have the limitation that neuromodulation is not addressed. The neurotoxin 6-hydroxydopamine has been used to deplete dopamine (DA) in mPFC sub-regions, but these lesions are not selective anatomically and noradrenalin is typically also depleted. Microinfusion of drugs through indwelling cannulae provides an alternative approach, to address the role of neuromodulation and moreover that of specific receptor subtypes within mPFC sub-regions, but the effects of such treatments cannot be assumed to be anatomically restricted either. New methodological approaches to the functional delineation of the role of mPFC in attention, learning and memory will also be considered. Taken in isolation, the conventional lesion methods which have been a first line of approach may suggest that a particular mPFC sub-region is not necessary for a particular aspect of function. However, this does not exclude a neuromodulatory role and more neuropsychopharmacological approaches are needed to explain some of the apparent inconsistencies in the results

On the dynamics of Extrasolar Planetary Systems under dissipation. Migration of planets

We study the dynamics of planetary systems with two planets moving in the same plane, when frictional forces act on the two planets, in addition to the gravitational forces. The model of the general three-body problem is used. Different laws of friction are considered. The topology of the phase space is essential in understanding the evolution of the system. The topology is determined by the families of stable and unstable periodic orbits, both symmetric and non symmetric. It is along the stable families, or close to them, that the planets migrate when dissipative forces act. At the critical points where the stability along the family changes, there is a bifurcation of a new family of stable periodic orbits and the migration process changes route and follows the new stable family up to large eccentricities or to a chaotic region. We consider both resonant and non resonant planetary systems. The 2/1, 3/1 and 3/2 resonances are studied. The migration to larger or smaller eccentricities depends on the particular law of friction. Also, in some cases the semimajor axes increase and in other cases they are stabilized. For particular laws of friction and for special values of the parameters of the frictional forces, it is possible to have partially stationary solutions, where the eccentricities and the semimajor axes are fixed.Comment: Accepted in Celestial Mechanics and Dynamical Astronom

From attention to memory along the dorsal-ventral axis of the medial prefrontal cortex: some methodological considerations

Distinctions along the dorsal-ventral axis of medial prefrontal cortex (mPFC), between anterior cingulate (AC), prelimbic (PL) and infralimbic (IL) sub-regions, have been proposed on a variety of neuroanatomical and neurophysiological grounds. Conventional lesion approaches (as well as some electrophysiological studies) have shown that these distinctions relate to function in that a number behavioural dissociations have been demonstrated, particularly using rodent models of attention, learning and memory. For example, there is evidence to suggest that AC has a relatively greater role in attention, whereas IL is more involved in executive function. However, the well-established methods of behavioral neuroscience have the limitation that neuromodulation is not addressed. The neurotoxin 6-hydroxydopamine has been used to deplete dopamine (DA) in mPFC sub-regions, but these lesions are not selective anatomically and noradrenalin is typically also depleted. Microinfusion of drugs through indwelling cannulae provides an alternative approach, to address the role of neuromodulation and moreover that of specific receptor subtypes within mPFC sub-regions, but the effects of such treatments cannot be assumed to be anatomically restricted either. New methodological approaches to the functional delineation of the role of mPFC in attention, learning and memory will also be considered. Taken in isolation, the conventional lesion methods which have been a first line of approach may suggest that a particular mPFC sub-region is not necessary for a particular aspect of function. However, this does not exclude a neuromodulatory role and more neuropsychopharmacological approaches are needed to explain some of the apparent inconsistencies in the results