4,167 research outputs found
Galaxy Clustering Around Nearby Luminous Quasars
We examine the clustering of galaxies around a sample of 20 luminous low
redshift (z<0.30) quasars observed with the Wide Field Camera-2 on the Hubble
Space Telescope. The HST resolution makes possible galaxy identification
brighter than V=23.5 and as close as 2'' to the quasar. We find a significant
enhancement of galaxies within a projected separation of < 100 kpc/h of the
quasars. If we model the qso/galaxy correlation function as a power law with a
slope given by the galaxy/galaxy correlation function, we find that the ratio
of the qso/galaxy to galaxy/galaxy correlation functions is . The
galaxy counts within r<15 kpc/h of the quasars are too high for the density
profile to have an appreciable core radius ( > 100 kpc). Our results reinforce
the idea that low redshift quasars are located preferentially in groups of
10-20 galaxies rather than in rich clusters. We see no significant difference
in the clustering amplitudes derived from radio-loud and radio-quiet
subsamples.Comment: 16 pages, 3 figures (included), 2 tables, Apj in pres
Strategies for Product Variety: Lessons From the Auto Industry
Driven by the market\u27s pull fir increasingly differentiated products and by manufacturers\u27 push to seek finely targeted niche segments, the variety of products offered in most industries has increased steadily over the last several decades. The pull comes from customers who seem to reward companies that can offer high variety while matching the price and quality of competitors with narrower product lines. Modern marketing methods accelerate this trend by identifying once-obscure specifics of consumer preferences. As more companies compete internationally, product markets become more crowded and product differentiation more important, both to make a product stand out in a popular product category and to help tailor a product to niche markets. The push comes from new firm capabilities as the increased sophistication and declining price of flexible, programmable automation bring the opportunity for greater product variety within the grasp of many more companies
Preservation of glaciochemical time-series in snow and ice from the Penny Ice Cap, Baffin Island
A detailed investigation of major ion concentrations of snow and ice in the summit region of Penny Ice Cap (PIC) was performed to determine the effects of summer melt on the glaciochemical time-series. While ion migration due to meltwater percolation makes it difficult to confidently count annual layers in the glaciochemical profiles, time-series of these parameters do show good structure and a strong one year spectral component, suggesting that annual to biannual signals are preserved in PIC glaciochemical records
Improving Patient Decision-Making in Health Care
Outlines regional variations within Minnesota in rates of patients with similar conditions receiving elective surgery, the concept of shared decision making, treatment choices for eight conditions, and steps for ensuring patients make informed decisions
Addressing present pitfalls in 3D printing for tissue engineering to enhance future potential
Additive manufacturing in tissue engineering has significantly advanced in acceptance and use to address complex problems. However, there are still limitations to the technologies used and potential challenges that need to be addressed by the community. In this manuscript, we describe how the field can be advanced not only through the development of new materials and techniques but also through the standardization of characterization, which in turn may impact the translation potential of the field as it matures. Furthermore, we discuss how education and outreach could be modified to ensure end-users have a better grasp on the benefits and limitations of 3D printing to aid in their career development
Holocene loess deposition and soil formation as competing processes, Matanuska Valley, southern Alaska
Although loess–paleosol sequences are among the most important records of Quaternary climate change and past dust deposition cycles, few modern examples of such sedimentation systems have been studied. Stratigraphic studies and 22 new accelerator mass spectrometry radiocarbon ages from the Matanuska Valley in southern Alaska show that loess deposition there began sometime after ~6500 14C yr B.P. and has continued to the present. The silts are produced through grinding by the Matanuska and Knik glaciers, deposited as outwash, entrained by strong winds, and redeposited as loess. Over a downwind distance of ~40 km, loess thickness, sand content, and sand-pluscoarse- silt content decrease, whereas fine-silt content increases. Loess deposition was episodic, as shown by the presence of paleosols, at distances \u3e10 km from the outwash plain loess source. Stratigraphic complexity is at a maximum (i.e., the greatest number of loesses and paleosols) at intermediate (10–25 km) distances from the loess source. Surface soils increase in degree of development with distance downwind from the source, where sedimentation rates are lower. Proximal soils are Entisols or Inceptisols, whereas distal soils are Spodosols. Ratios of mobile CaO, K2O, and Fe2O3 to immobile TiO2 show decreases in surface horizons with distance from the source. Thus, as in China, where loess deposition also takes place today, eolian sedimentation and soil formation are competing processes. Study of loess and paleosols in southern Alaska shows that particle size can vary over short distances, loess deposition can be episodic over limited time intervals, and soils developed in stabilized loess can show considerable variability under the same vegetation
Numerical study of the strongly screened vortex glass model in an external field
The vortex glass model for a disordered high-T_c superconductor in an
external magnetic field is studied in the strong screening limit. With exact
ground state (i.e. T=0) calculations we show that 1) the ground state of the
vortex configuration varies drastically with infinitesimal variations of the
strength of the external field, 2) the minimum energy of global excitation
loops of length scale L do not depend on the strength of the external field,
however 3) the excitation loops themself depend sensibly on the field. From 2)
we infer the absence of a true superconducting state at any finite temperature
independent of the external field.Comment: 6 pages RevTeX, 5 eps-figures include
Clustering in the 1.2 Jy IRAS Galaxy Redshift Survey II: Redshift Distortions and \xi(r_p,\pi)
We examine the effect of redshift space distortions on the galaxy two-point
correlation function as a function of separations parallel
() and perpendicular () to the line of sight. We find that the
relative velocity dispersion of pairs of IRAS galaxies is \kms at r=1 \mpc, consistent with previous estimates derived
from optically selected galaxy catalogues. Unfortunately, the use of this
result to estimate via the Cosmic Virial Theorem is thwarted by large
systematic uncertainties. We also fit for the mean relative streaming velocity
of pairs, , which describes the growth of fluctuations on both
linear and nonlinear scales. We find that \kms at
\mpc, so that on average, approximately half the Hubble expansion velocity
of pairs at this separation is canceled by infall. At \mpc, the amplitude
of the streaming is lower and v_{12}(r) = 109^{+64}_{-47} \kms. Linear
perturbation theory then implies that on
scales \sim 10-15 \mpc. The amplitude of is sensitive to the
assumed shape of ; if the latter deviates substantially from a
virialized form on small scale, our best fit amplitude of can
deviate by a factor of two.Comment: 28 pages of uuencoded compressed postscript; figures include
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