Higher homotopy operations and cohomology

We explain how higher homotopy operations, defined topologically, may be identified under mild assumptions with (the last of) the Dwyer-Kan-Smith cohomological obstructions to rectifying homotopy-commutative diagrams.Comment: 28 page

On shocks driven by high-mass planets in radiatively inefficient disks. I. Two-dimensional global disk simulations

Recent observations of gaps and non-axisymmetric features in the dust distributions of transition disks have been interpreted as evidence of embedded massive protoplanets. However, comparing the predictions of planet-disk interaction models to the observed features has shown far from perfect agreement. This may be due to the strong approximations used for the predictions. For example, spiral arm fitting typically uses results that are based on low-mass planets in an isothermal gas. In this work, we describe two-dimensional, global, hydrodynamical simulations of disks with embedded protoplanets, with and without the assumption of local isothermality, for a range of planet-to-star mass ratios 1-10 M_jup for a 1 M_sun star. We use the Pencil Code in polar coordinates for our models. We find that the inner and outer spiral wakes of massive protoplanets (M>5 M_jup) produce significant shock heating that can trigger buoyant instabilities. These drive sustained turbulence throughout the disk when they occur. The strength of this effect depends strongly on the mass of the planet and the thermal relaxation timescale; for a 10 M_jup planet embedded in a thin, purely adiabatic disk, the spirals, gaps, and vortices typically associated with planet-disk interactions are disrupted. We find that the effect is only weakly dependent on the initial radial temperature profile. The spirals that form in disks heated by the effects we have described may fit the spiral structures observed in transition disks better than the spirals predicted by linear isothermal theory.Comment: 10 pages, 8 figures. ApJ, accepte

Annual Survey of Virginia Law: Planning, Zoning and Subdivision Law

In recent years, a debate has sharpened in Virginia concerning the limits of public power over private property and the determination of which arm of the government will exercise the public\u27s power in land use matters. This debate has continued into 1990 and 1991

Review of From Author to Text: Re-reading George Eliot\u27s Romola; George Eliot and Italy: Literary, Cultural and Politcal Influences from Dante to the Risorgimento

Each of these books took me by surprise. There is a curious tension between the incorporativeness of Andrew Thompson\u27s title, George Eliot and Italy, and his compendiously specific sub-title, Literary, Cultural and Political Influences from Dante to the Risorgimento, which somehow led me to expect something like a descriptive catalogue of alleged influences. Instead, I found a book which indeed has awkwardnesses, but which pursues an argument and offers valuable illumination of George Eliot\u27s whole career (and not just Romola, as might easily be assumed). Barbara Hardy memorably observed in 1959 that \u27Romola is undoubtedly a book which it is more interesting to analyse than simply to read\u27, an opinion to which I still subscribe after a fashion which has been profoundly qualified by the collection of essays on Romola assembled by Caroline Levine and Mark W. Turner, which added to other work on the novel in recent years makes it impossible \u27simply to read\u27 Romola. Levine and Turner and their contributors challenge the whole range of judgments and assumptions about the novel of which George Eliot herself declared \u27I began it a young woman, I finished it an old woman\u27

On local-to-global spectral sequences for the cohomology of diagrams

The aim of this paper is to construct and examine three candidates for local-to-global spectral sequences for the cohomology of diagrams of algebras with directed indexing. In each case, the $E^2$ -terms can be viewed as a type of local cohomology relative to a map or an object in the diagram.Comment: 27 pages; incorporated corrections based on referee's report and added a few reference

Goal-directed attention alters the tuning of object-based representations in extrastriate cortex

Humans survive in environments that contain a vast quantity and variety of visual information. All items of perceived visual information must be represented within a limited number of brain networks. The human brain requires mechanisms for selecting only a relevant fraction of perceived information for more in-depth processing, where neural representations of that information may be actively maintained and utilized for goal-directed behavior. Object-based attention is crucial for goal-directed behavior and yet remains poorly understood. Thus, in the study we investigate how neural representations of visual object information are guided by selective attention. The magnitude of activation in human extrastriate cortex has been shown to be modulated by attention; however, object-based attention is not likely to be fully explained by a localized gain mechanism. Thus, we measured information coded in spatially distributed patterns of brain activity with fMRI while human participants performed a task requiring selective processing of a relevant visual object category that differed across conditions. Using pattern classification and spatial correlation techniques, we found that the direction of selective attention is implemented as a shift in the tuning of object-based information representations within extrastriate cortex. In contrast, we found that representations within lateral prefrontal cortex (PFC) coded for the attention condition rather than the concrete representations of object category. In sum, our findings are consistent with a model of object-based selective attention in which representations coded within extrastriate cortex are tuned to favor the representation of goal-relevant information, guided by more abstract representations within lateral PFC

Inconsistent Divergence of Mitochondrial-DNA in the Spontaneously Hypertensive Rat

We have recently shown that the spontaneously hypertensive rat (SHR) and the Wistar-Kyoto (WKY) rat differ at a frequency of 1 per 62 bases in their nuclear DNA (Hypertension 1992;19:425-427). Given the origin of these strains this level of divergence was unexpected. To investigate the origin of this nuclear divergence we have examined mitochondrial DNA. Mitochondrial DNA was isolated from SHR and WKY rats, digested with several restriction enzymes, electrophoresed in 1.0% agarose gels, and the fragments visualized with ethidium bromide staining. This approach allowed us to analyze 220 base pairs of mitochondrial DNA. No differences were detected between SHR and WKY rats. Comparison with the King-Holtzman rat strain produced differences at an average of 1 per 52 base pairs. We also examined several SHR and WKY rats from within our colonies and found no differences suggesting intrastrain homogeneity for mitochondrial DNA phenotypes. These data indicate that the SHR and WKY rat share a recent, common maternal ancestor. This result is consistent with the published origins of the SHR and WKY rat strains. Together with the nuclear divergence results, the data suggest that the original Wistar colony from which SHR and WKY rats were derived was probably highly polymorphic for nuclear genes

Effects on Freshwater Organisms of Magnetic Fields Associated with Hydrokinetic Turbines

Underwater cables will be used to transmit electricity between turbines in an array (interturbine cables), between the array and a submerged step-up transformer (if part of the design), and from the transformer or array to shore. All types of electrical transmitting cables (as well as the generator itself) will emit EMF into the surrounding water. The electric current will induce magnetic fields in the immediate vicinity, which may affect the behavior or viability of animals. Because direct electrical field emissions can be prevented by shielding and armoring, we focused our studies on the magnetic fields that are unavoidably induced by electric current moving through a generator or transmission cable. These initial experiments were carried out to evaluate whether a static magnetic field, such as would be produced by a direct current (DC) transmitting cable, would affect the behavior of common freshwater fish and invertebrates