The Hubble Constant from Observations of the Brightest Red Giant Stars in a Virgo-Cluster Galaxy

The Virgo and Fornax clusters of galaxies play central roles in determining the Hubble constant H_0. A powerful and direct way of establishing distances for elliptical galaxies is to use the luminosities of the brightest red-giant stars (the TRGB luminosity, at M_I = -4.2). Here we report the direct observation of the TRGB stars in a dwarf elliptical galaxy in the Virgo cluster. We find its distance to be 15.7 +- 1.5 Megaparsecs, from which we estimate a Hubble constant of H_0 = 77 +- 8 km/s/Mpc. Under the assumption of a low-density Universe with the simplest cosmology, the age of the Universe is no more than 12-13 billion years.Comment: 12 pages, LaTeX, with 2 postscript figures; in press for Nature, July 199

Adaptation to motor-visual and motor-auditory temporal lags transfer across modalities

Previous research has shown that the timing of a sensor-motor event is recalibrated after a brief exposure to a delayed feedback of a voluntary action (Stetson et al. 2006). Here, we examined whether it is the sensory or motor event that is shifted in time. We compared lag adaption for action-feedback in visuo-motor pairs and audio-motor pairs using an adaptation-test paradigm. Participants were exposed to a constant lag (50 or 150 ms) between their voluntary action (finger tap) and its sensory feedback (flash or tone pip) during an adaptation period (~3 min). Immediately after that, they performed a temporal order judgment (TOJ) task about the tap-feedback test stimulus pairings. The modality of the feedback stimulus was either the same as the adapted one (within-modal) or different (cross-modal). The results showed that the point of subjective simultaneity (PSS) was uniformly shifted in the direction of the exposed lag within and across modalities (motor-visual, motor-auditory). This suggests that the TRE of sensor-motor events is mainly caused by a shift in the motor component

Dark Matter in the Milky Way's Dwarf Spheroidal Satellites

The Milky Way's dwarf spheroidal satellites include the nearest, smallest and least luminous galaxies known. They also exhibit the largest discrepancies between dynamical and luminous masses. This article reviews the development of empirical constraints on the structure and kinematics of dSph stellar populations and discusses how this phenomenology translates into constraints on the amount and distribution of dark matter within dSphs. Some implications for cosmology and the particle nature of dark matter are discussed, and some topics/questions for future study are identified.Comment: A version with full-resolution figures is available at http://www.cfa.harvard.edu/~mwalker/mwdsph_review.pdf; 70 pages, 22 figures; invited review article to be published in Vol. 5 of the book "Planets, Stars, and Stellar Systems", published by Springe

Performance control after arthroscopic arthrolysis with capsulectomy in fresh-frozen elbow joints

Background and objective Posttraumatic or postoperative movement restrictions in elbow joints can often occur (including capsular contracture) and can generate everyday limitations. In persistent elbow stiffness, arthroscopic arthrolysis with removal of the dorsal and ventral capsule portions can be carried out. The purpose of this study was to assess the efficacy of arthroscopic capsulectomy by means of an in vitro anatomical study. Methods A standardized elbow arthroscopy with ventral and dorsal capsulectomy was performed and image-documented in five fresh-frozen elbow specimens. Subsequently, open dissection of the elbow joint was performed to analyze the amount of residual capsule by means of photodocumentation of the specimens. Results Regardless of the surgeon and surgical experience, anterior and posterior remnants of the capsule remained in all specimens. Dorsal capsule strands around the standard arthroscopy portals were noticed particularly more often in the area of the high dorsolateral camera portal. An incomplete capsulectomy was seen on the ulnar side at the level of the posterior medial ligament (PML) in the immediate vicinity of the ulnar nerve. Ventrally, a capsulectomy was performed from the radial side and also the ulnar side until the brachialis muscle and additionally a complete capsulectomy as far as the anterior medial ligament (AML) and radial collateral ligament (RCL) was achieved. The capsule was completely resected in a proximal direction. Distally, irrelevant capsular remnants were found in the region of the annular ligament and distal of the tip of the coronoid process. Conclusion Arthroscopic arthrolysis can be performed with a high degree of radicality. The radicality must be self-critically taken into account in one's own action. The radicality of the portal change may even be higher ventrally than with an isolated column procedure. On the other hand, it must be critically considered that posteriorly, the PML cannot be adequately addressed by means of arthroscopy due to the risk of ulnar nerve injury. Portal changes might help to enable a more complete visualization of the joint capsule and may avoid leaving possibly relevant remnants of the capsule. If a release of the PML is required, this may have to be carried out in combination with an ulnar nerve release in a mini-open technique