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David Merritt

Publications and source records attributed to David Merritt.

8 recordsLinked to original sources
PubMed2005

Core collapse via coarse dynamic renormalization.

In the context of the recently developed "equation-free" approach to computer-assisted analysis of complex systems, we extract the self-similar solution describing core collapse of a stellar system from numerical experiments. The technique allows us to sidestep the core "bounce" that occurs in direct N-body simulations due to the small-N correlations that develop in the late stages of collapse, and hence to follow the evolution well into the self-similar regime.

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PubMed2005

Characterization of in vivo expanded OspA-specific human T-cell clones.

A panel of CD4 T-cell clones was isolated from synovial fluid by single cell flow cytometry from a patient with treatment-resistant Lyme arthritis using a DRB1*0401 major histocompatibility complex (MHC) class II tetramer covalently loaded with outer surface protein A (OspA) peptide164-175, an immunodominant epitope of Borrelia burgdorferi. Sequencing of the T-cell receptors of the OspA reactive clones showed significant skewing of the T-cell receptor repertoire. Of the 101 T-cell clones sequenced, 81 possessed TCR beta chains that were present in at least one other clone isolated. Complete sequencing of both alpha and beta chains of a subset of clones showed that at least two distinct T-cell clones were expanded in vivo. Binding studies using a panel of Ala-substituted peptide ligands were performed to determine potential MHC binding sites of the OspAp164-175 to DRB1*0401. In addition, T-cell clones were tested functionally for their reactivity to the wild-type peptide as well as to altered peptide ligands (APLs) and peptide libraries based on the OspA epitope in order to determine the TCR contact residues and the stringency in T cell recognition. We are among the first to define the characteristics of TCR usage of T cells isolated from an inflamed immune compartment in an individual with an autoimmune disease potentially triggered by a microbial antigen.

Amino Acid Sequence↗
PubMed2005

Henry Kandrup's ideas about relaxation of stellar systems.

Henry Kandrup wrote prolifically on the problem of relaxation of stellar systems. His picture of relaxation was significantly more refined than the standard description in terms of phase mixing and violent relaxation. In this article, I summarize Henry's work in this and related areas.

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PubMed2005

Evolution of binary supermassive black holes via chain regularization.

A chain regularization method is combined with special purpose computer hardware to study the evolution of massive black hole binaries at the centers of galaxies. Preliminary results with up to N = 0.26 x 10(6) particles are presented. The decay rate of the binary is shown to decrease with increasing N, as expected on the basis of theoretical arguments. The eccentricity of the binary remains small.

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PubMed2004

Evolution of the dark matter distribution at the galactic center.

Annihilation radiation from neutralino dark matter at the Galactic center (GC) would be greatly enhanced if the dark matter were strongly clustered around the supermassive black hole (SBH). The existence of a dark matter "spike" is made plausible by the observed, steeply rising stellar density near the GC SBH. Here the time-dependent equations describing gravitational interaction of the dark matter with the stars are solved. Scattering of dark matter particles by stars would substantially lower the dark matter density near the GC SBH over 10 Gyr, due both to kinetic heating and to capture of dark matter particles by the SBH. This evolution implies a decrease by several orders of magnitude in the observable flux of annihilation products compared with models that associate a steep, dark matter spike with the SBH.

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PubMed2002

Tracing black hole mergers through radio lobe morphology.

Binary supermassive black holes are produced by galactic mergers as the black holes from the two galaxies fall to the center of the merged system and form a bound pair. The two black holes will eventually coalesce in an enormous burst of gravitational radiation. Here we show that the orientation of a black hole's spin axis would change dramatically even in a minor merger, leading to a sudden flip in the direction of any associated jet. We identify the winged or X-type radio sources with galaxies in which this has occurred. The inferred coalescence rate is similar to the overall galaxy merger rate, implying that of the order of one merger event per year could be detected by gravitational wave interferometers.

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PubMed2002

Dark matter spikes and annihilation radiation from the galactic center.

The annihilation rate of weakly interacting cold dark matter particles at the galactic center could be greatly enhanced by the growth of a density spike around the central supermassive black hole (SBH). Here we discuss the effects of hierarchical mergers on the central spike. Mergers between halos containing SBHs lead to the formation of SBH binaries which transfer energy to the dark matter particles, lowering their density. The predicted flux of annihilation photons from the galactic center is several orders of magnitude smaller than in models that ignore the effects of SBHs and mergers. Measurement of the annihilation radiation could in principle be used to constrain the merger history of the galaxy.

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