Hominin tracks in southern Africa: a review and an approach to identification

Three Late Pleistocene hominin tracksites have been reported from coastal aelioanites in South Africa. Two have been dated to 124 ka and 117 ka , and the third is inferred to be 90 ka. There are no other globally reported sites for probable Homo sapiens tracks older than 46 ka. Given this documented record, a search for further hominin tracksites in southern Africa may well yield additional positive results. However, this is a field that demands scientific rigour, as false positive tracksites (pseudotracks) may occur. Criteria have been developed for the identification of fossil vertebrate tracks and hominin tracks, but these are specific neither to southern Africa nor to aeolianites.An important caveat is that the tracks of shod humans would not fulfil these criteria. Preservation of tracks varies with facies and is known to be suboptimal in aeolianites. An analysis of the tracks from the three documented South African sites, along with pseudotracks and tracks of questionable provenance, allows for the proposal and development of guidelines for fossil hominin track identification that are of specific relevance to southern Africa. Such guidelines have broader implications for understanding the constraints that track preservation and substrate have on identifying diagnostic morphological features.Palaeontological Scientific Trust (PAST)JNC201

Improved Cosmological Constraints from Gravitational Lens Statistics

We combine the Cosmic Lens All-Sky Survey (CLASS) with new Sloan Digital Sky Survey (SDSS) data on the local velocity dispersion distribution function of E/S0 galaxies, $\phi(\sigma)$, to derive lens statistics constraints on $\Omega_\Lambda$ and $\Omega_m$. Previous studies of this kind relied on a combination of the E/S0 galaxy luminosity function and the Faber-Jackson relation to characterize the lens galaxy population. However, ignoring dispersion in the Faber-Jackson relation leads to a biased estimate of $\phi(\sigma)$ and therefore biased and overconfident constraints on the cosmological parameters. The measured velocity dispersion function from a large sample of E/S0 galaxies provides a more reliable method for probing cosmology with strong lens statistics. Our new constraints are in good agreement with recent results from the redshift-magnitude relation of Type Ia supernovae. Adopting the traditional assumption that the E/S0 velocity function is constant in comoving units, we find a maximum likelihood estimate of $\Omega_\Lambda = 0.74$--0.78 for a spatially flat unvierse (where the range reflects uncertainty in the number of E/S0 lenses in the CLASS sample), and a 95% confidence upper bound of $\Omega_\Lambda<0.86$. If $\phi(\sigma)$ instead evolves in accord with extended Press-Schechter theory, then the maximum likelihood estimate for $\Omega_\Lambda$ becomes 0.72--0.78, with the 95% confidence upper bound $\Omega_\Lambda<0.89$. Even without assuming flatness, lensing provides independent confirmation of the evidence from Type Ia supernovae for a nonzero dark energy component in the universe.Comment: 35 pages, 15 figures, to be published in Ap

Hinge for Use in a Tension Stiffened and Tendon Actuated Manipulator

A tension stiffened and tendon actuated manipulator is provided performing robotic-like movements when acquiring a payload. The manipulator design can be adapted for use in-space, lunar or other planetary installations as it is readily configurable for acquiring and precisely manipulating a payload in both a zero-g environment and in an environment with a gravity field. The manipulator includes a plurality of link arms, a hinge connecting adjacent link arms together to allow the adjacent link arms to rotate relative to each other and a cable actuation and tensioning system provided between adjacent link arms. The cable actuation and tensioning system includes a spreader arm and a plurality of driven and non-driven elements attached to the link arms and the spreader arm. At least one cable is routed around the driven and non-driven elements for actuating the hinge

The DEEP2 Galaxy Redshift Survey: Spectral classification of galaxies at z~1

We present a Principal Component Analysis (PCA)-based spectral classification, eta, for the first 5600 galaxies observed in the DEEP2 Redshift Survey. This parameter provides a very pronounced separation between absorption and emission dominated galaxy spectra - corresponding to passively evolving and actively star-forming galaxies in the survey respectively. In addition it is shown that despite the high resolution of the observed spectra, this parameter alone can be used to quite accurately reconstruct any given galaxy spectrum, suggesting there are not many `degrees of freedom' in the observed spectra of this galaxy population. It is argued that this form of classification, eta, will be particularly valuable in making future comparisons between high and low-redshift galaxy surveys for which very large spectroscopic samples are now readily available, particularly when used in conjunction with high-resolution spectral synthesis models which will be made public in the near future. We also discuss the relative advantages of this approach to distant galaxy classification compared to other methods such as colors and morphologies. Finally, we compare the classification derived here with that adopted for the 2dF Galaxy Redshift Survey and in so doing show that the two systems are very similar. This will be particularly useful in subsequent analyses when making comparisons between results from each of these surveys to study evolution in the galaxy populations and large-scale structure.Comment: 10 pages, 9 figures, Accepted for publication in Ap

A Large Structure of Galaxies At Redshift z~3 and its Cosmological Implications

We report the discovery of a highly significant concentration of galaxies at a redshift of =3.090. The structure is evident in a redshift histogram of photometrically selected ``Lyman break'' objects in a 9' by 18' field in which we have obtained 78 spectroscopic redshifts in the range 2.0 < z <3.4. The dimensions of the structure projected on the plane of the sky are at least 11'by 8', or 14h_{70}^{-1} by 10h_{70}^{-1} Mpc (comoving; \Omega_M=1). The concentration contains 15 galaxies and one faint (R=21.7) QSO. We consider the structure in the context of a number of cosmological models and argue that Lyman-break galaxies must be very biased tracers of mass, with an effective bias on mass scale M~10^{15}M_{\sun} ranging from b~2 for \Omega_M=0.2 to b >~6 for \Omega_M=1. In a Cold Dark Matter scenario the large bias values suggest that individual Lyman-break galaxies are associated with dark halos of mass M~10^{12} M_{\sun}, reinforcing the interpretation of these objects as the progenitors of massive galaxies at the present epoch. Preliminary results of spectroscopy in additional fields suggest that such large structures are common at z~3, with about one similar structure per survey field. The implied space density is consistent with the possibility that we are observing moderately rich clusters of galaxies in their early non-linear evolution. Finally, the spectrum of one of the QSOs discovered in our survey (z_{em} = 3.356) exhibits metal line absorption systems within the 3 redshift bins having the largest number of galaxies in field, z = 2.93, 3.09, and 3.28. These results are the first from an ongoing ``targeted'' redshift survey designed to explore the nature and distribution of star-forming galaxies in the redshift range 2.7 <~ z <~ 3.4.Comment: 24 pages including 5 ps figures, LaTeX, uses aaspp4.sty, to appear in the Astrophysical Journal. Also available at ftp://astro.caltech.edu/users/ccs/spike_preprint.ps.g

Aeroelastic Response and Protection of Space Shuttle External Tank Cable Trays

Sections of the Space Shuttle External Tank Liquid Oxygen (LO2) and Liquid Hydrogen (LH2) cable trays are shielded from potentially damaging airloads with foam Protuberance Aerodynamic Load (PAL) Ramps. Flight standard design LO2 and LH2 cable tray sections were tested with and without PAL Ramp models in the United States Air Force Arnold Engineering Development Center s (AEDC) 16T transonic wind tunnel to obtain experimental data on the aeroelastic stability and response characteristics of the trays and as part of the larger effort to determine whether the PAL ramps can be safely modified or removed. Computational Fluid Dynamic simulations of the full-stack shuttle launch configuration were used to investigate the flow characeristics around and under the cable trays without the protective PAL ramps and to define maximum crossflow Mach numbers and dynamic pressures experienced during launch. These crossflow conditions were used to establish wind tunnel test conditions which also included conservative margins. For all of the conditions and configurations tested, no aeroelastic instabilities or unacceptable dynamic response levels were encountered and no visible structural damage was experienced by any of the tested cable tray sections. Based upon this aeroelastic characterization test, three potentially acceptable alternatives are available for the LO2 cable tray PAL Ramps: Mini-Ramps, Tray Fences, or No Ramps. All configurations were tested to maximum conditions, except the LH2 trays at -15 deg. crossflow angle. This exception is the only caveat preventing the proposal of acceptable alternative configurations for the LH2 trays as well. Structural assessment of all tray loads and tray response measurements from launches following the Shuttle Return To Flight with the existing PAL Ramps will determine the acceptability of these PAL Ramp alternatives

The global oscillation network group site survey. II. Results

The Global Oscillation Network Group (GONG) Project will place a network of instruments around the world to observe solar oscillations as continuously as possible for three years. The Project has now chosen the six network sites based on analysis of survey data from fifteen sites around the world. The chosen sites are: Big Bear Solar Observatory, California; Mauna Loa Solar Observatory, Hawaii; Learmonth Solar Observatory, Australia; Udaipur Solar Observatory, India; Observatorio del Teide, Tenerife; and Cerro Tololo Interamerican Observatory, Chile. Total solar intensity at each site yields information on local cloud cover, extinction coefficient, and transparency fluctuations. In addition, the performance of 192 reasonable components analysis. An accompanying paper describes the analysis methods in detail; here we present the results of both the network and individual site analyses. The selected network has a duty cycle of 93.3%, in good agreement with numerical simulations. The power spectrum of the network observing window shows a first diurnal sidelobe height of 3 × 10⁻⁴ with respect to the central component, an improvement of a factor of 1300 over a single site. The background level of the network spectrum is lower by a factor of 50 compared to a single-site spectrum

Comparison of Jet Quenching Formalisms for a Quark-Gluon Plasma "Brick"

We review the currently available formalisms for radiative energy loss of a high-momentum parton in a dense strongly interacting medium. The underlying theoretical framework of the four commonly used formalisms is discussed and the differences and commonalities between the formalisms are highlighted. A quantitative comparison of the single gluon emission spectra as well as the energy loss distributions is given for a model system consisting of a uniform medium with a fixed length of L=2 fm and L=5 fm (the `Brick'). Sizable quantitative differences are found. The largest differences can be attributed to specific approximations that are made in the calculation of the radiation spectrum.Comment: 30 pages, 24 figures update version2: added curves with large x to Figure 14, Higher Twist curves to Figs 19, 20, plus some changes in the text (introduction/summary, discussion of Fig 14 and HT section