Investigation of strength of isolated vertebrae, phase IV Final technical report, 29 Oct. 1965 - 28 Oct. 1966

Dynamic strength measurements of human vertebrae under axial compressio

Investigation of strength of isolated vertebrae Quarterly report, 30 Jan. - 29 May 1966

Strength of human vertebrae under various static and dynamic load

The symbiotic star CH Cygni. III. A precessing radio jet

VLA, MERLIN and Hubble Space Telescope imaging observations of the extended regions of the symbiotic system CH Cygni are analysed. These extensions are evidence of a strong collimation mechanism, probably an accretion disk surrounding the hot component of the system. Over 16 years (between 1985 and 2001) the general trend is that these jets are seen to precess. Fitting a simple ballistic model of matter ejection to the geometry of the extended regions suggests a period of 6520 +/- 150 days, with a precession cone opening angle of 35 +/- 1 degrees. This period is of the same order as that proposed for the orbital period of the outer giant in the system, suggesting a possible link between the two. Anomalous knots in the emission, not explained by the simple model, are believed to be the result of older, slower moving ejecta, or possibly jet material that has become disrupted through sideways interaction with the surrounding medium.Comment: 9 pages, 4 figure

Vortices in vibrated granular rods

We report the experimental observation of novel vortex patterns in vertically vibrated granular rods. Above a critical packing fraction, moving ordered domains of nearly vertical rods spontaneously form and coexist with horizontal rods. The domains of vertical rods coarsen in time to form large vortices. We investigate the conditions under which the vortices occur by varying the number of rods, vibration amplitude and frequency. The size of the vortices increases with the number of rods. We characterize the growth of the ordered domains by measuring the area fraction of the ordered regions as a function of time. A {\em void filling} model is presented to describe the nucleation and growth of the vertical domains. We track the ends of the vertical rods and obtain the velocity fields of the vortices. The rotation speed of the rods is observed to depend on the vibration velocity of the container and on the packing. To investigate the impact of the direction of driving on the observed phenomena, we performed experiments with the container vibrated horizontally. Although vertical domains form, vortices are not observed. We therefore argue that the motion is generated due to the interaction of the inclination of the rods with the bottom of a vertically vibrated container. We also perform simple experiments with a single row of rods in an annulus. These experiments directly demonstrate that the rod motion is generated when the rods are inclined from the vertical, and is always in the direction of the inclination.Comment: 6 pages, 10 figure, 2 movies at http://physics.clarku.edu/vortex uses revtex

S-band Polarization All Sky Survey (S-PASS): survey description and maps

We present the S-Band Polarization All Sky Survey (S-PASS), a survey of polarized radio emission over the southern sky at Dec~$< -1^\circ$ taken with the Parkes radio telescope at 2.3~GHz. The main aim was to observe at a frequency high enough to avoid strong depolarization at intermediate Galactic latitudes (still present at 1.4 GHz) to study Galactic magnetism, but low enough to retain ample Signal-to-Noise ratio (S/N) at high latitudes for extragalactic and cosmological science. We developed a new scanning strategy based on long azimuth scans, and a corresponding map-making procedure to make recovery of the overall mean signal of Stokes $Q$ and $U$ possible, a long-standing problem with polarization observations. We describe the scanning strategy, map-making procedure, and validation tests. The overall mean signal is recovered with a precision better than 0.5\%. The maps have a mean sensitivity of 0.81 mK on beam--size scales and show clear polarized signals, typically to within a few degrees of the Galactic plane, with ample S/N everywhere (the typical signal in low emission regions is 13 mK, and 98.6\% of the pixels have S/N $> 3$). The largest depolarization areas are in the inner Galaxy, associated with the Sagittarius Arm. We have also computed a Rotation Measure map combining S-PASS with archival data from the WMAP and Planck experiments. A Stokes $I$ map has been generated, with a sensitivity limited to the confusion level of 9 mK.Comment: Accepted for publication on MNRAS. Maps are available for download at the website indicated in the manuscrip

Radio and gamma-ray constraints on dark matter annihilation in the Galactic center

We determine upper limits on the dark matter (DM) self-annihilation cross section for scenarios in which annihilation leads to the production of electron--positron pairs. In the Galactic centre (GC), relativistic electrons and positrons produce a radio flux via synchroton emission, and a gamma ray flux via bremsstrahlung and inverse Compton scattering. On the basis of archival, interferometric and single-dish radio data, we have determined the radio spectrum of an elliptical region around the Galactic centre of extent 3 degrees semi-major axis (along the Galactic plane) and 1 degree semi-minor axis and a second, rectangular region, also centered on the GC, of extent 1.6 degrees x 0.6 degrees. The radio spectra of both regions are non-thermal over the range of frequencies for which we have data: 74 MHz -- 10 GHz. We also consider gamma-ray data covering the same region from the EGRET instrument (about GeV) and from HESS (around TeV). We show how the combination of these data can be used to place robust constraints on DM annihilation scenarios, in a way which is relatively insensitive to assumptions about the magnetic field amplitude in this region. Our results are approximately an order of magnitude more constraining than existing Galactic centre radio and gamma ray limits. For a DM mass of m_\chi =10 GeV, and an NFW profile, we find that the velocity-averaged cross-section must be less than a few times 10^-25 cm^3 s^-1.Comment: 14 pages, 9 figures. Version accepted for publication in PRD. Reference section updated/extended

Comparing [CII], HI, and CO dynamics of nearby galaxies

The HI and CO components of the interstellar medium (ISM) are usually used to derive the dynamical mass M_dyn of nearby galaxies. Both components become too faint to be used as a tracer in observations of high-redshift galaxies. In those cases, the 158 $\mu$m line of atomic carbon [CII] may be the only way to derive M_dyn. As the distribution and kinematics of the ISM tracer affects the determination of M_dyn, it is important to quantify the relative distributions of HI, CO and [CII]. HI and CO are well-characterised observationally, however, for [CII] only very few measurements exist. Here we compare observations of CO, HI, and [CII] emission of a sample of nearby galaxies, drawn from the HERACLES, THINGS and KINGFISH surveys. We find that within R_25, the average [CII] exponential radial profile is slightly shallower than that of the CO, but much steeper than the HI distribution. This is also reflected in the integrated spectrum ("global profile"), where the [CII] spectrum looks more like that of the CO than that of the HI. For one galaxy, a spectrally resolved comparison of integrated spectra was possible; other comparisons were limited by the intrinsic line-widths of the galaxies and the coarse velocity resolution of the [CII] data. Using high-spectral-resolution SOFIA [CII] data of a number of star forming regions in two nearby galaxies, we find that their [CII] linewidths agree better with those of the CO than the HI. As the radial extent of a given ISM tracer is a key input in deriving M_dyn from spatially unresolved data, we conclude that the relevant length-scale to use in determining M_dyn based on [CII] data, is that of the well-characterised CO distribution. This length scale is similar to that of the optical disk.Comment: Accepted for publication in the Astronomical Journa

Dynamics of viscoelastic membranes

We determine both the in-plane and out-of-plane dynamics of viscoelastic membranes separating two viscous fluids in order to understand microrheological studies of such membranes. We demonstrate the general viscoelastic signatures in the dynamics of shear, bending, and compression modes. We also find a screening of the otherwise two-dimensional character of the response to point forces due to the presence of solvent. Finally, we show that there is a linear, hydrodynamic coupling between the in-plane compression modes of the membrane and the out-of-plane bending modes in the case where the membrane separates two different fluids or environments