Weak Lensing Determination of the Mass in Galaxy Halos

We detect the weak gravitational lensing distortion of 450,000 background galaxies (20<R<23) by 790 foreground galaxies (R<18) selected from the Las Campanas Redshift Survey (LCRS). This is the first detection of weak lensing by field galaxies of known redshift, and as such permits us to reconstruct the shear profile of the typical field galaxy halo in absolute physical units (modulo H_0), and to investigate the dependence of halo mass upon galaxy luminosity. This is also the first galaxy-galaxy lensing study for which the calibration errors are negligible. Within a projected radius of 200 \hkpc, the shear profile is consistent with an isothermal profile with circular velocity 164+-20 km/s for an L* galaxy, consistent with typical disk rotation at this luminosity. This halo mass normalization, combined with the halo profile derived by Fischer et al (2000) from lensing analysis SDSS data, places a lower limit of (2.7+-0.6) x 10^{12}h^{-1} solar masses on the mass of an L* galaxy halo, in good agreement with satellite galaxy studies. Given the known luminosity function of LCRS galaxies, and the assumption that $M\propto L^\beta$ for galaxies, we determine that the mass within 260\hkpc of normal galaxies contributes $\Omega=0.16\pm0.03$ to the density of the Universe (for $\beta=1$) or $\Omega=0.24\pm0.06$ for $\beta=0.5$. These lensing data suggest that $0.6<\beta<2.4$ (95% CL), only marginally in agreement with the usual $\beta\approx0.5$ Faber-Jackson or Tully-Fisher scaling. This is the most complete direct inventory of the matter content of the Universe to date.Comment: 18 pages, incl. 3 figures. Submitted to ApJ 6/7/00, still no response from the referee after four months

Brightest Cluster Galaxies at the Present Epoch

We have observed 433 z<=0.08 brightest cluster galaxies (BCGs) in a full-sky survey of Abell clusters. The BCG Hubble diagram is consistent to within 2% of a Omega_m=0.3, Lambda=0.7 Hubble relation. The L_m-alpha relation for BCGs, which uses alpha, the log-slope of the BCG photometric curve of growth, to predict metric luminosity, L_m, has 0.27 mag residuals. We measure central stellar velocity dispersions, sigma, of the BCGs, finding the Faber-Jackson relation to flatten as the metric aperture grows to include an increasing fraction of the total BCG luminosity. A 3-parameter "metric plane" relation using alpha and sigma together gives the best prediction of L_m, with 0.21 mag residuals. The projected spatial offset, r_x, of BCGs from the X-ray-defined cluster center is a gamma=-2.33 power-law over 1<r_x<10^3 kpc. The median offset is ~10 kpc, but ~15% of the BCGs have r_x>100 kpc. The absolute cluster-dispersion normalized BCG peculiar velocity |Delta V_1|/sigma_c follows an exponential distribution with scale length 0.39+/-0.03. Both L_m and alpha increase with sigma_c. The alpha parameter is further moderated by both the spatial and velocity offset from the cluster center, with larger alpha correlated with the proximity of the BCG to the cluster mean velocity or potential center. At the same time, position in the cluster has little effect on L_m. The luminosity difference between the BCG and second-ranked galaxy, M2, increases as the peculiar velocity of the BCG within the cluster decreases. Further, when M2 is a close luminosity "rival" of the BCG, the galaxy that is closest to either the velocity or X-ray center of the cluster is most likely to have the larger alpha. We conclude that the inner portions of the BCGs are formed outside the cluster, but interactions in the heart of the galaxy cluster grow and extend the envelopes of the BCGs.Comment: Accepted for publication in the Astrophysical Journa

Microwave and hard X-ray observations of a solar flare with a time resolution of better than 100 MS

Simultaneous microwave and X-ray observations are presented for a solar flare detected on 1980 May 8 starting at 1937 UT. The X-ray observations were made with the Hard X-Ray Burst Spectrometer on the Solar Maximum Mission and covered the energy range from 28-490 keV with a time resolution of 10 ms. The microwave observations were made with the 5 and 45 foot antennas at the Itapetinga Radio Observatory at frequencies of 7 and 22 GHz, with time resolutions of 100 ms and 1 ms respectively. Detailed correlation analysis of the different time profiles of the event show that the major impulsive in the X-ray flux preceded the corresponding microwave peaks at 22 GHz by about 240ms. For this particular burst the 22 GHz peaks preceded the 7 GHz by about 1.5s. Observed delays of the microwave peaks are too large for a simple electron beam model but they can be reconciled with the speeds of shock waves in a thermal model

Advanced superconducting magnets investigation

Mathematical models for steady state behavior of composite superconductors and experimental verification using magnet coi

Super-resolution imaging and estimation of protein copy numbers at single synapses with DNA-PAINT

In the brain, the strength of each individual synapse is defined by the complement of proteins present or the "local proteome." Activity-dependent changes in synaptic strength are the result of changes in this local proteome and posttranslational protein modifications. Although most synaptic proteins have been identified, we still know little about protein copy numbers in individual synapses and variations between synapses. We use DNA-point accumulation for imaging in nanoscale topography as a single-molecule super-resolution imaging technique to visualize and quantify protein copy numbers in single synapses. The imaging technique provides near-molecular spatial resolution, is unaffected by photobleaching, enables imaging of large field of views, and provides quantitative molecular information. We demonstrate these benefits by accessing copy numbers of surface AMPA-type receptors at single synapses of rat hippocampal neurons along dendritic segments

Resistive Wall Tearing Mode Disruptions

This paper deals with resistive wall tearing mode (RWTM) disruptions. RWTMs are closely related to resistive wall modes (RWMs). The nonlinear behavior of these modes is strongly dependent on the resistive wall outside the plasma. A conducting wall is highly mitigating for RWTM disruptions. The consequence for ITER, which has a highly conducting wall, is that the thermal quench (TQ) time could be much longer than previously conjectured. Active feedback stabilization is another possible way to mitigate or prevent RWTM disruptions. Simulations of disruptions are reviewed for DIII-D and MST. MST has a longer resistive wall time than ITER, and disruptions are not observed experimentally when MST is operated as a standard tokamak. Simulations indicate that the RWTM disruption time scale is longer than the experimental shot time. In general, edge cooling by tearing mode island overlap or by impurity radiation causes contraction of the current profile, which destabilizes RWTMs. The equilibria studied here have a q = 2 rational surface close to the edge of the plasma, and low edge current density. A sequence of low edge current model equilibria hasmajor disruptions only for a resistive, not ideal, wall, and approximately edge q < 3. This is consistent with typical regimes of tokamak disruption avoidance, suggesting that typical tokamak disruptions could be RWTMs

MST Resistive Wall Tearing Mode Simulations

The Madison Symmetric Torus (MST) is a toroidal device that, when operated as a tokamak, is resistant to disruptions. Unlike most tokamaks, the MST plasma is surrounded by a close fitting highly conducting wall, with a resistive wall penetration time two orders of magnitude longer than in JET or DIII-D, and three times longer than in ITER. The MST can operate with edge q_a < 2, unlike standard tokamaks. Simulations presented here indicate that the MST is unstable to resistive wall tearing modes (RWTMs) and resistive wall modes (RWMs). They could in principle cause disruptions, but the predicted thermal quench time is much longer than the experimental pulse time. If the MST thermal quench time were comparable to measurements in JET and DIII-D, theory and simulations predict that disruptions would have been observed in MST. This is consistent with the modeling herein, predicting that disruptions are caused by RWTMs and RWMs. In the low q_a regime of MST, the RWTM asymptotically satisfies the RWM dispersion relation. The transition from RWTM to RWM occurs smoothly at q_a = m/n, where m,n are poloidal and toroidal mode numbers

Skewness as a probe of non-Gaussian initial conditions

We compute the skewness of the matter distribution arising from non-linear evolution and from non-Gaussian initial perturbations. We apply our result to a very generic class of models with non-Gaussian initial conditions and we estimate analytically the ratio between the skewness due to non-linear clustering and the part due to the intrinsic non-Gaussianity of the models. We finally extend our estimates to higher moments.Comment: 5 pages, 2 ps-figs., accepted for publication in PRD, rapid com