Osteoarthritis (OA) is a degenerative disease resulting in irreversible, progressive destruction of articular cartilage
. The etiology of OA is complex and involves a variety of factors, including ...genetic predisposition, acute injury and chronic inflammation
. Here we investigate the ability of resident skeletal stem-cell (SSC) populations to regenerate cartilage in relation to age, a possible contributor to the development of osteoarthritis
. We demonstrate that aging is associated with progressive loss of SSCs and diminished chondrogenesis in the joints of both mice and humans. However, a local expansion of SSCs could still be triggered in the chondral surface of adult limb joints in mice by stimulating a regenerative response using microfracture (MF) surgery. Although MF-activated SSCs tended to form fibrous tissues, localized co-delivery of BMP2 and soluble VEGFR1 (sVEGFR1), a VEGF receptor antagonist, in a hydrogel skewed differentiation of MF-activated SSCs toward articular cartilage. These data indicate that following MF, a resident stem-cell population can be induced to generate cartilage for treatment of localized chondral disease in OA.
We present a new ‘supercalibration’ technique for measuring systematic distortions in the wavelength scales of high-resolution spectrographs. By comparing spectra of ‘solar twin’ stars or asteroids ...with a reference laboratory solar spectrum, distortions in the standard thorium–argon calibration can be tracked with ∼10 m s−1 precision over the entire optical wavelength range on scales of both echelle orders (∼50–100 Å) and entire spectrographs arms (∼1000–3000 Å). Using archival spectra from the past 20 yr, we have probed the supercalibration history of the Very Large Telescope-Ultraviolet and Visible Echelle Spectrograph (VLT-UVES) and Keck-High Resolution Echelle Spectrograph (HIRES) spectrographs. We find that systematic errors in their wavelength scales are ubiquitous and substantial, with long-range distortions varying between typically ±200 m s−1 per 1000 Å. We apply a simple model of these distortions to simulated spectra that characterize the large UVES and HIRES quasar samples which previously indicated possible evidence for cosmological variations in the fine-structure constant, α. The spurious deviations in α produced by the model closely match important aspects of the VLT-UVES quasar results at all redshifts and partially explain the HIRES results, though not self-consistently at all redshifts. That is, the apparent ubiquity, size and general characteristics of the distortions are capable of significantly weakening the evidence for variations in α from quasar absorption lines.
Abstract
Previous, large samples of quasar absorption spectra have indicated some evidence for relative variations in the fine-structure constant (Δα/α) across the sky. However, they were likely ...affected by long-range distortions of the wavelength calibration, so it is important to establish a statistical sample of more reliable results from multiple telescopes. Here we triple the sample of Δα/α measurements from the Subaru Telescope which have been ‘supercalibrated’ to correct for long-range distortions. A blinded analysis of the metallic ions in six intervening absorption systems in two Subaru quasar spectra provides no evidence for α variation, with a weighted mean of Δα/α = 3.0 ± 2.8stat ± 2.0sys parts per million (1σ statistical and systematic uncertainties). The main remaining systematic effects are uncertainties in the long-range distortion corrections, absorption profile models, and errors from redispersing multiple quasar exposures on to a common wavelength grid. The results also assume that terrestrial isotopic abundances prevail in the absorbers; assuming only the dominant terrestrial isotope is present significantly lowers Δα/α, though it is still consistent with zero. Given the location of the two quasars on the sky, our results do not support the evidence for spatial α variation, especially when combined with the 21 other recent measurements which were corrected for, or resistant to, long-range distortions. Our spectra and absorption profile fits are publicly available.
ABSTRACT
We present a study of the metal-enriched cool halo gas traced by Mg ii absorption around 228 galaxies at z ∼ 0.8–1.5 within 28 quasar fields from the MUSE Analysis of Gas around Galaxies ...survey. We observe no significant evolution in the Mg ii equivalent width versus impact parameter relation and in the Mg ii covering fraction compared to surveys at z ≲ 0.5. The stellar mass, along with distance from galaxy centre, appears to be the dominant factor influencing the Mg ii absorption around galaxies. With a sample that is 90 per cent complete down to a star formation rate of ≈0.1 $\rm M_\odot yr^{-1}$ and up to impact parameters ≈250–350 kpc from quasars, we find that the majority ($67^{+12}_{-15}$ per cent or 14/21) of the Mg ii absorption systems are associated with more than one galaxy. The complex distribution of metals in these richer environments adds substantial scatter to previously reported correlations. Multiple galaxy associations show on average five times stronger absorption and three times higher covering fraction within twice the virial radius than isolated galaxies. The dependence of Mg ii absorption on galaxy properties disfavours the scenario in which a widespread intragroup medium dominates the observed absorption. This leaves instead gravitational interactions among group members or hydrodynamic interactions of the galaxy haloes with the intragroup medium as favoured mechanisms to explain the observed enhancement in the Mg ii absorption strength and cross-section in rich environments.
Stem cell regulation and hierarchical organization of human skeletal progenitors remain largely unexplored. Here, we report the isolation of a self-renewing and multipotent human skeletal stem cell ...(hSSC) that generates progenitors of bone, cartilage, and stroma, but not fat. Self-renewing and multipotent hSSCs are present in fetal and adult bones and can also be derived from BMP2-treated human adipose stroma (B-HAS) and induced pluripotent stem cells (iPSCs). Gene expression analysis of individual hSSCs reveals overall similarity between hSSCs obtained from different sources and partially explains skewed differentiation toward cartilage in fetal and iPSC-derived hSSCs. hSSCs undergo local expansion in response to acute skeletal injury. In addition, hSSC-derived stroma can maintain human hematopoietic stem cells (hHSCs) in serum-free culture conditions. Finally, we combine gene expression and epigenetic data of mouse skeletal stem cells (mSSCs) and hSSCs to identify evolutionarily conserved and divergent pathways driving SSC-mediated skeletogenesis.
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•PDPN+CD146−CD73+CD164+ marks a self-renewing, multipotent human skeletal stem cell•hSSCs can be isolated from fetal, adult, BMP2-treated human adipose stroma, and iPSCs•hSSCs undergo local expansion in response to acute skeletal injury•Comparison of mouse and human SSCs reveals evolutionary differences in skeletogenesis
Identification of a human skeletal stem cell reveals conserved and species-specific pathways in skeletal development, and response to injury and will guide future regenerative approaches.
Quasar absorption lines provide a precise test of whether the fine-structure constant, α, is the same in different places and through cosmological time. We present a new analysis of a large sample of ...quasar absorption-line spectra obtained using the Ultraviolet and Visual Echelle Spectrograph (UVES) on the Very Large Telescope (VLT) in Chile. We apply the many-multiplet method to derive values of Δα/α≡ (α
z
−α0)/α0 from 154 absorbers, and combine these values with 141 values from previous observations at the Keck Observatory in Hawaii. In the VLT sample, we find evidence that α increases with increasing cosmological distance from Earth. However, as previously shown, the Keck sample provided evidence for a smaller α in the distant absorption clouds. Upon combining the samples, an apparent variation of α across the sky emerges which is well represented by an angular dipole model pointing in the direction RA = 17.3 ± 1.0 h and Dec. =−61°± 10°, with amplitude
. The dipole model is required at the 4.1σ statistical significance level over a simple monopole model where α is the same across the sky (but possibly different from the current laboratory value). The data sets reveal remarkable consistencies: (i) the directions of dipoles fitted to the VLT and Keck samples separately agree; (ii) the directions of dipoles fitted to z < 1.6 and z > 1.6 cuts of the combined VLT+Keck samples agree; and (iii) in the equatorial region of the dipole, where both the Keck and VLT samples contribute a significant number of absorbers, there is no evidence for inconsistency between Keck and VLT. The amplitude of the dipole is clearly larger at higher redshift. Assuming a dipole-only (i.e. no-monopole) model whose amplitude grows proportionally with 'lookback-time distance' (r=ct, where t is the lookback time), the amplitude is (1.1 ± 0.2) × 10−6 GLyr−1 and the model is significant at the 4.2σ confidence level over the null model (Δα/α≡ 0). We apply robustness checks and demonstrate that the dipole effect does not originate from a small subset of the absorbers or spectra. We present an analysis of systematic effects, and are unable to identify any single systematic effect which can emulate the observed variation in α. To the best of our knowledge, this result is not in conflict with any other observational or experimental result.
We documented occurrence and relative abundance (henceforth abundance) of five woodpecker species in 36 forested green spaces in Portland, Oregon (USA), to estimate minimum area requirements (MAR; ...0.5 probability of occurrence) and to test for potential influences of green space area and type (heavily treed manicured green spaces vs. undeveloped natural forests), habitat features, and landscape composition on the abundance of woodpeckers. Abundances of all species increased with green space area. Manicured and natural green spaces did not differ in canopy cover or total basal area, but woodpecker abundances were greater in natural than manicured green spaces for all species except Northern Flickers (Colaptes auratus). Flickers and Downy Woodpeckers (Picoides pubescens) were most abundant, MAR of both were under 1.5 ha, and both were found in essentially all green spaces. Hairy (P. villosus) and Pileated (Dryocopus pileatus) woodpeckers were least abundant, and with MAR of 34 and 51 ha, respectively, exhibited pronounced area sensitivity. Red-breasted Sapsuckers (Sphyrapicus ruber) were intermediate in abundance and MAR to the 2 former and 2 latter species. The most important habitat variables associated with variation in abundance among green spaces were the contribution of deciduous trees to the canopy (Downy Woodpecker +, Pileated Woodpecker +, and Northern Flicker –), canopy cover (Hairy Woodpecker + and Northern Flicker +), and log density (Hairy Woodpecker +, Red-breasted Sapsucker –). At the landscape level, lower woodpecker abundance was associated with increased urbanization (Red-breasted Sapsucker and Northern Flicker), while increasing forest cover influenced abundance of Northern Flicker (–) and Pileated Woodpecker (+). Highest woodpecker abundances were thus found in large green spaces with complex understories that were embedded in relatively undeveloped treed landscapes. Management of forested urban green spaces should prioritize needs of the area-sensitive species because ensuring their continued presence benefits the entire avian community. How to Cite Baz, A., and M. T. Murphy (2023). Woodpeckers in the city: Abundances are highest in large green spaces with complex understories. Ornithological Applications 125:duad013. Woodpeckers provide ecosystem services by acting as ecosystem engineers, habitat modifiers, and facilitator species. However, we know little about woodpecker requirements for persistence in urban settings. We documented minimum area requirements (MAR) and sources of variation in abundance of 5 woodpecker species in 36 green spaces in Portland, Oregon, in 2015 and 2016. Except for the ground-foraging Northern Flicker, MAR increased with body size, ranging from 1.3 ha for the small Downy Woodpeckers (27.5 g) to 51 ha for the large Pileated Woodpecker (300 g). Abundance of all species increased with green space area, and except for Northern Flickers, was higher in natural than manicured green spaces. Species responses to habitat and landscape variables differed, but abundances were generally higher in green spaces with high basal area of deciduous trees, closed canopy, and where landscapes were less urbanized and had higher tree cover. Management policies should be driven by the needs of species with the largest MAR and greatest dependence on structurally complex vegetation structure. Documentamos la presencia y abundancia relativa (en adelante, abundancia) de cinco especies de pájaros carpinteros en 36 espacios verdes boscosos en Portland, Oregón (EEUU), para estimar los requisitos mínimos de superficie (RMS; 0,5 probabilidad de ocurrencia) y evaluar posibles influencias de la superficie y el tipo de espacio verde (espacios verdes cuidados con árboles podados versus bosques naturales poco desarrollados), las características del hábitat y la composición del paisaje en la abundancia de los pájaros carpinteros. Las abundancias de todas las especies aumentaron con la superficie del espacio verde. Los espacios verdes cuidados y naturales no se diferenciaron en la cobertura del dosel o el área basal total, pero las abundancias de pájaros carpinteros fueron mayores en los espacios verdes naturales que en los cuidados para todas las especies, excepto para Colaptes auratus. C. auratus y Picoides pubescens fueron las especies más abundantes, y los RMS de ambas estuvieron por debajo de 1,5 ha y se encontraron en prácticamente todos los espacios verdes. P. villosus y Dryocopus pileatus fueron las especies menos abundantes y, con RMS de 34 y 51 ha, respectivamente, mostraron una fuerte sensibilidad a la superficie. Sphyrapicus ruber tuvo una abundancia y un RMS intermedio en comparación con las 2 especies nombradas inicialmente y las 2 posteriores. Las variables de hábitat más importantes asociadas con la variación en la abundancia entre los espacios verdes fueron la contribución de árboles caducifolios al dosel (P. pubescens +, D. pileatus + y C. auratus –), la cobertura del dosel (P. villosus + y C. auratus +), y la densidad de troncos (P. villosus +, S. ruber –). A nivel del paisaje, una menor abundancia de pájaros carpinteros se asoció con una mayor urbanización (S. ruber y C. auratus), mientras que el aumento de la cobertura boscosa influyó en la abundancia de C. auratus (–) y D. pileatus (+). Las mayores abundancias de pájaros carpinteros se encontraron en espacios verdes grandes con sotobosques complejos que estuvieron inmersos en paisajes arbolados relativamente poco desarrollados. La gestión de los espacios verdes boscosos urbanos debe priorizar las necesidades de las especies sensibles a la superficie, ya que asegurar su presencia continua beneficia a toda la comunidad de aves.
Abstract
We present two measurements of the temperature–density relationship (TDR) of the intergalactic medium (IGM) in the redshift range 2.55 < z < 2.95 using a sample of 13 high-quality quasar ...spectra and high resolution numerical simulations of the IGM. Our approach is based on fitting the neutral hydrogen column density $N_{\rm H\, \small {I}}$ and the Doppler parameter b of the absorption lines in the Lyα forest. The first measurement is obtained using a novel Bayesian scheme that takes into account the statistical correlations between the parameters characterizing the lower cut-off of the $b\hbox{--}N_{\rm H\, \small {I}}$ distribution and the power-law parameters T0 and γ describing the TDR. This approach yields T0/103 K = 15.6 ± 4.4 and γ = 1.45 ± 0.17 independent of the assumed pressure smoothing of the small-scale density field. In order to explore the information contained in the overall $b\hbox{--}N_{\rm H\, \small {I}}$ distribution rather than only the lower cut-off, we obtain a second measurement based on a similar Bayesian analysis of the median Doppler parameter for separate column-density ranges of the absorbers. In this case, we obtain T0/103 K = 14.6 ± 3.7 and γ = 1.37 ± 0.17 in good agreement with the first measurement. Our Bayesian analysis reveals strong anticorrelations between the inferred T0 and γ for both methods as well as an anticorrelation of the inferred T0 and the pressure smoothing length for the second method, suggesting that the measurement accuracy can in the latter case be substantially increased if independent constraints on the smoothing are obtained. Our results are in good agreement with other recent measurements of the thermal state of the IGM probing similar (over-)density ranges.
ABSTRACT
Sun-like stars are a new probe of variations in the fine-structure constant, α, via the solar twins approach: velocity separations of close pairs of absorption lines are compared between ...stars with very similar stellar parameters, i.e. effective temperature, metallicity, and surface gravity within 100 K, 0.1 dex, and 0.2 dex of the Sun’s values. Here, we assess possible systematic errors in this approach by analysing ≳10 000 archival exposures from the High-Accuracy Radial Velocity Planetary Searcher (HARPS) of 130 stars covering a much broader range of stellar parameters. We find that each transition pair’s separation shows broad, low-order variations with stellar parameters that can be accurately modelled, leaving only a small residual, intrinsic star-to-star scatter of 0–33 m s−1 (average ≈7 m s−1, ≈1 × 10−4 Å at 5000 Å). This limits the precision available from a single pair in a single star. We consider potential systematic errors from a range of instrumental and astrophysical sources (e.g. wavelength calibration, charge transfer inefficiency, stellar magnetic activity, line blending) and conclude that variations in elemental abundances, isotope ratios, and stellar rotational velocities may explain this star-to-star scatter. Finally, we find that the solar twins approach can be extended to solar analogues – within 300 K, 0.3 dex, and 0.4 dex of the Sun’s parameters – without significant additional systematic errors, allowing a much larger number of stars to be used as probes of variation in α, including at much larger distances.
ABSTRACT
The rich absorption spectra of Sun-like stars are enticing probes for variations in the fine-structure constant, α, which gauges the strength of electromagnetism. While individual line ...wavelengths are sensitive to α, they are also sensitive to physical processes in the stellar atmospheres, which has precluded their use so far. Here we demonstrate a new differential approach using solar twins: velocity separations between close pairs of transitions are compared across stars with very similar physical properties, strongly suppressing astrophysical and instrumental systematic errors. We utilize 423 archival exposures of 18 solar twins from the High-Accuracy Radial velocity Planetary Searcher (HARPS), in which calibration errors can be reduced to ≲3 m s−1. For stars with ≈10 high-signal-to-noise ratio spectra (≥200 per pixel), velocity separations between pairs are measured with ≈10 m s−1 statistical precision. A companion paper assesses a range of systematic error sources using 130 stars, with a greater range of stellar parameters, providing accurate corrections for astrophysical effects and a residual, intrinsic star-to-star scatter of 0–13 m s−1. Within these uncertainties, we find no evidence for velocity separation differences in 17 transition pairs between solar twins. In a second companion paper, this is found to limit local (≲50 pc) variations in α to ≈50 parts per billion, ∼2 orders of magnitude less than other Galactic constraints.
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