Antibodies to acetylcholine receptor in parous women with myasthenia: evidence for immunization by fetal antigen

The weakness in myasthenia gravis (MG) is mediated by autoantibodies against adult muscle acetylcholine receptors (AChR) at the neuromuscular junction; most of these antibodies also bind to fetal AChR, which is present in the thymus. In rare cases, babies of mothers with MG, or even of asymptomatic mothers, develop a severe developmental condition, arthrogryposis multiplex congenita, caused by antibodies that inhibit the ion channel function of the fetal AChR while not affecting the adult AChR. Here we show that these fetal AChR inhibitory antibodies are significantly more common in females sampled after pregnancy than in those who present before pregnancy, suggesting that they may be induced by the fetus. Moreover, we were able to clone high-affinity combinatorial Fab antibodies from thymic cells of two mothers with MG who had babies with arthrogryposis multiplex congenita. These Fabs were highly specific for fetal AChR and did not bind the main immunogenic region that is common to fetal and adult AChR. The Fabs show strong biases to VH3 heavy chains and to a single Vk1 light chain in one mother. Nevertheless, they each show extensive intraclonal diversification from a highly mutated consensus sequence, consistent with antigen-driven selection in successive steps. Collectively, our results suggest that, in some cases of MG, initial immunization against fetal AChR is followed by diversification and expansion of B cells in the thymus; maternal autoimmunity will result if the immune response spreads to the main immunogenic region and other epitopes common to fetal and adult AChR

Diffraction-Limited Imaging and Photometry of NGC 1068

The nearby Seyfert 2 Galaxy NGC 1068 was observed with speckle imaging techniques in the near-infrared H-band (1.6 microns) at the Hale 200-inch Telescope and K-band (2.2 microns) at the 10 m Keck I Telescope. Images with diffraction limited or near-diffraction limited resolutions of 0.''05 - 0.''1 were obtained and used to search for structure in the nuclear region. Images of the nucleus of NGC 1068 reveal an extended region of emission which accounts for nearly 50% of the nuclear flux at K-band. This region extends 10 pc on either side of an unresolved point source nucleus which is at most, 0.''02 or 1.4 pc in size. Both the point source and the newly imaged extended emission are very red, with identical H-K colors corresponding to a color temperature of 800 K. While the point source is of a size to be consistent with grains in thermal equilibrium with the nuclear source, the extended emission is not. It must consist either of nuclear emission which has been reflected off an extended dusty disk or of small grains raised to transiently high temperatures by reflected UV photons.Comment: accepted to AJ, AAS LaTeX and epsfig, 22 pages incl. 5 ps figure

The Cooling Flow to Accretion Flow Transition

Cooling flows in galaxy clusters and isolated elliptical galaxies are a source of mass for fueling accretion onto a central supermassive black hole. We calculate the dynamics of accreting matter in the combined gravitational potential of a host galaxy and a central black hole assuming a steady state, spherically symmetric flow (i.e., no angular momentum). The global dynamics depends primarily on the accretion rate. For large accretion rates, no simple, smooth transition between a cooling flow and an accretion flow is possible; the gas cools towards zero temperature just inside its sonic radius, which lies well outside the region where the gravitational influence of the central black hole is important. For accretion rates below a critical value, however, the accreting gas evolves smoothly from a radiatively driven cooling flow at large radii to a nearly adiabatic (Bondi) flow at small radii. We argue that this is the relevant parameter regime for most observed cooling flows. The transition from the cooling flow to the accretion flow should be observable in M87 with the {\it Chandra X-ray Observatory}.Comment: emulateapj.sty, 10 pages incl. 5 figures, to appear in Ap

Observations of Rapid Disk-Jet Interaction in the Microquasar GRS 1915+105

We present evidence that ~ 30 minute episodes of jet formation in the Galactic microquasar GRS 1915+105 may sometimes entirely be a superposition of smaller, faster phenomena. We base this conclusion on simultaneous X-ray and infrared observations in July 2002, using the Rossi X-ray Timing Explorer and the Palomar 5 meter telescope. On two nights, we observed quasi-periodic infrared flares from GRS 1915+105, each accompanied by a set of fast oscillations in the X-ray light curve (indicating an interaction between the jet and accretion disk). In contrast to similar observations in 1997, we find that the duration of each X-ray cycle matches the duration of its accompanying infrared flare, and we observed one instance in which an isolated X-ray oscillation occurred at the same time as a faint infrared "subflare" (of duration ~ 150 seconds) superimposed on one of the main flares. From these data, we are able to conclude that each X-ray oscillation had an associated faint infrared flare and that these flares blend together to form, and entirely comprise, the ~ 30 minute events we observed. Part of the infrared emission in 1997 also appears to be due to superimposed small flares, but it was overshadowed by infrared-bright ejections associated with the appearance of a sharp "trigger" spike in each X-ray cycle that were not present in 2002. We also study the evolution of the X-ray spectrum and find significant differences in the high energy power law component, which was strongly variable in 1997 but not in 2002. Taken together, these observations reveal the diversity of ways in which the accretion disk and jet in black hole systems are capable of interacting and solidify the importance of the trigger spike for large ejections to occur on ~ 30 minute timescales in GRS 1915+105.Comment: 17 pages, 9 figures; accepted for publication in The Astrophysical Journa

Measurement of the Branching Fractions for D^0 → π^-e^+v_e and D^0 → + K^-e^+V_e and Determination of │V_(cd)/V_(cs)│^2

Measurements of the exclusive branching fractions B(D^0→π^-e^+ν_e) and B(D^0→K^-e^+ν_e), using data collected at the ψ(3770) with the Mark III detector at the SLAC e^+e^- storage ring SPEAR, are used to determine the ratio of the Kobayashi-Maskawa matrix elements │V_(cd)/V_(cs)│^2 =0.057_(-0.015)^(+0.038)±0.005

Search for the decay D^0→K^0e^+e^-

A search for the decay of the charmed meson D^0→K^0e^+e^- is presented, based on data collected at the ψ(3770) resonance with the Mark III detector at the SLAC storage ring SPEAR. No evidence for this process is found, resulting in an upper limit on the decay branching ratio of 1.7×10^(-3) at the 90% confidence level

Optimal conditions for observing Josephson oscillations in a double-well Bose-gas condensate

The Josephson oscillations between condensates in a double-well trap are known theoretically to be strongly effected by the mean field interaction in dilute atomic gases. The most important effect is that the amplitude of oscillation in the relative population of the two wells is greatly suppressed due to the mean field interaction, which can make it difficult to observe the Josephson effect. Starting from the work of Raghavan, Smerzi, Fantoni, and Shenoy, we calculate the maximum amplitude of oscillation in the relative population as a function of various physical parameters, such as the trap aspect ratio, the Gaussian barrier height and width, and the total number of atoms in the condensate. We also compare results for ${}^{23}$Na and ${}^{87}$Rb. Our main new result is that the maximum amplitude of oscillation depends strongly on the aspect ratio of the harmonic trap and can be maximized in a ``pancake'' trap, as used in the experiment of Anderson and Kasevich.Comment: 8 pages with 5 embeded figure

Variability of Quasars at 10 microns

Twenty five low redshift quasars have been monitored for several decades at five near- and mid-infrared wavelengths to detect rapid variations which would indicate that a nonthermal component was present in the "10 micron bump". Such variability has apparently been detected in several radio loud quasars and in the radio quiet quasar PG1535+547. In addition, the structure function of PG1226+023 shows that an apparently periodic component is present in its near-infrared emission.Comment: AAS LaTex, 33 figures in 2 postscript files, AJ, accepte