A robust method for fitting peculiar velocity field models

We present a new method for fitting peculiar velocity models to complete flux limited magnitude-redshifts catalogues, using the luminosity function of the sources as a distance indicator.The method is characterised by its robustness. In particular, no assumptions are made concerning the spatial distribution of sources and their luminosity function. Moreover, selection effects in redshift are allowed. Furthermore the inclusion of additional observables correlated with the absolute magnitude -- such as for example rotation velocity information as described by the Tully-Fisher relation -- is straightforward. As an illustration of the method, the predicted IRAS peculiar velocity model characterised by the density parameter beta is tested on two samples. The application of our method to the Tully-Fisher MarkIII MAT sample leads to a value of beta=0.6 \pm 0.125, fully consistent with the results obtained previously by the VELMOD and ITF methods on similar datasets. Unlike these methods however, we make a very conservative use of the Tully-Fisher information. Specifically, we require to assume neither the linearity of the Tully-Fisher relation nor a gaussian distribution of its residuals. Moreover, the robustness of the method implies that no Malmquist corrections are required. A second application is carried out, using the fluxes of the IRAS 1.2 Jy sample as the distance indicator. In this case the effective depth of the volume in which the velocity model is compared to the data is almost twice the effective depth of the MarkIII MAT sample. The results suggest that the predicted IRAS velocity model, while successful in reproducing locally the cosmic flow, fails to describe the kinematics on larger scales.Comment: 10 pages, 14 figures, MNRAS in pres

Self-driven oscillation in Coulomb blockaded suspended carbon nanotubes

Suspended carbon nanotubes are known to support self-driven oscillations due to electromechanical feedback under certain conditions, including low temperatures and high mechanical quality factors. Prior reports identified signatures of such oscillations in Kondo or high-bias transport regimes. Here, we observe self-driven oscillations that give rise to significant conduction in normally Coulomb-blockaded low-bias transport. Using a master equation model, the self-driving is shown to result from strongly energy-dependent electron tunneling, and the dependencies of transport features on bias, gate voltage, and temperature are well reproduced.Comment: Main text + Appendices (8 pages, 10 figures

Spectral Classification of Galaxies Along the Hubble Sequence

We develop a straightforward and quantitative two-step method for spectroscopically classifying galaxies from the low signal-to-noise (S/N) optical spectra typical of galaxy redshift surveys. First, using \chi^2-fitting of characteristic templates to the object spectrum, we determine the relative contributions of the old stellar component, the young stellar component, and various emission line spectra. Then, we classify the galaxy by comparing the relative strengths of the components with those of galaxies of known morphological type. In particular, we use the ratios of (1) the emission line to absorption line contribution, (2) the young to old stellar contribution, and (3) the oxygen to hydrogen emission line contribution. We calibrate and test the method using published morphological types for 32 galaxies from the long-slit spectroscopic survey of Kennicutt (1992) and for 304 galaxies from a fiber spectroscopic survey of nearby galaxy clusters. From an analysis of a sample of long-slit spectra of spiral galaxies in two galaxy clusters, we conclude that the majority of the galaxies observed in the fiber survey are sufficiently distant that their spectral classification is unaffected by aperture bias. Our spectral classification is consistent with the morphological classification to within one type (e.g. E to S0 or Sa to Sb) for \gtsim 80% of the galaxies. Disagreements between the spectral and morphological classifications of the remaining galaxies reflect a divergence in the correspondence between spectral and morphological types, rather than a problem with the data or method.Comment: 13 pages, uuencoded gzip'ed ps-file that includes 8 of 9 Figures, accepted for publication in A

The LCO/Palomar 10,000 km/sec Cluster Survey. II. Constraints on Large-Scale Streaming

The LCO/Palomar 10,000 km/sec (LP10K) Tully-Fisher (TF) data set is used to test for bulk streaming motions on a ~150 Mpc scale. The sample consists of 172 cluster galaxies in the original target range of the survey, 9000-13,000 km/sec, plus an additional 72 galaxies with cz < 30,000 km/sec. A maximum-likelihood analysis that is insensitive to Malmquist and selection bias effects is used to constrain the bulk velocity parameters, and realistic Monte-Carlo simulations are carried out to correct residual biases and determine statistical errors. When the analysis is restricted to the original target range, the bias-corrected bulk flow is v_B=720 +/- 280 km/sec toward l=266, b=19. When all objects out to z=0.1 are included the result is virtually unchanged, v_B=700 +/- 250 km/sec toward l=272, b=10. The hypothesis that the Hubble flow has converged to the CMB frame at distances less than ~ 100 Mpc is ruled out at the 97% confidence level. The data are inconsistent with the flow vector found by Lauer & Postman. However, the LP10K bulk flow is consistent with that obtained from the SMAC survey of elliptical galaxies recently described by Hudson et al. If correct, the LP10K results indicate that the convergence depth for the Hubble flow is >~ 150 Mpc.Comment: 14 pages, 7 figures, uses emulateapj, submitted to the Astrophysical Journal. Also available at http://astro.stanford.edu/jeff

Fast measurement of carbon nanotube resonator amplitude with a heterojunction bipolar transistor

Carbon nanotube (CNT) electromechanical resonators have demonstrated unprecedented sensitivities for detecting small masses and forces. The detection speed in a cryogenic setup is usually limited by the CNT contact resistance and parasitic capacitance. We report the use of a heterojunction bipolar transistor (HBT) amplifying circuit near the device to measure the mechanical amplitude at microsecond timescales. A Coulomb rectification scheme, in which the probe signal is at much lower frequency than the mechanical drive signal, allows investigation of the strongly non-linear regime. The behaviour of transients in both the linear and non-linear regimes is observed and modeled by including Duffing and non-linear damping terms in a harmonic oscillator equation. We show that the non-linear regime can result in faster mechanical response times, on the order of 10 microseconds for the device and circuit presented, potentially enabling the magnetic moments of single molecules to be measured within their spin relaxation and dephasing timescales.Comment: Pages 1-5 are the main paper, pages 6-8 are supplementary materia