We present the calibration and background model for the Proportional Counter Array on board the Rossi X-Ray Timing Explorer. The energy calibration is systematics-limited below 10 keV, with deviations from a power-law fit to the Crab Nebula plus pulsar of less than 1%. Unmodeled variations in the instrumental background amount to less than 2% of the observed background below 10 keV and less than 1% between 10 and 20 keV. Individual photon arrival times are accurate to 4.4 s at all times during the mission and to 2.5 s after 1997 April 29. The peak pointing direction of the five collimators is known to a precision of a few arcseconds.

The neural crest (NC) is a transient, multipotent, migratory cell population unique to vertebrates that gives rise to diverse cell lineages. Much of our knowledge of NC development comes from studies of organisms such as chicken and zebrafish because human NC is difficult to obtain because of its transient nature and the limited availability of human fetal cells. Here we examined the process of NC induction from human pluripotent stem cells, including human embryonic stem cells (hESCs) and induced pluripotent stem cells (iPSCs). We showed that NC cells could be efficiently induced from hESCs by a combination of growth factors in medium conditioned on stromal cells and that NC stem cells (NCSCs) could be purified by p75 using fluorescence-activated cell sorting (FACS). FACS-isolated NCSCs could be propagated in vitro in five passages and cryopreserved while maintaining NCSC identity characterized by the expression of a panel of NC markers such as p75, Sox9, Sox10, CD44, and HNK1. In vitro-expanded NCSCs were able to differentiate into neurons and glia (Schwann cells) of the peripheral nervous system, as well as mesenchymal derivatives. hESC-derived NCSCs appeared to behave similarly to endogenous embryonic NC cells when injected in chicken embryos. Using a defined medium, we were able to generate and propagate a nearly pure population of Schwann cells that uniformly expressed glial fibrillary acidic protein, S100, and p75. Schwann cells generated by our protocol myelinated rat dorsal root ganglia neurons in vitro. To our knowledge, this is the first report on myelination by hESC-or iPSC-derived Schwann cells. STEM CELLS TRANSLATIONAL MEDI-CINE 2012;1:266 -278

The 1999 November outburst of the transient pulsar SAX J2103.5+4545 was monitored with the large area detectors of the Rossi X-Ray Timing Explorer until the pulsar faded after a year. The 358 s pulsar was spun up for 150 days, at which point the flux dropped quickly by a factor of %7, the frequency saturated, and, as the flux continued to decline, a weak spin-down began. The pulses remained strong during the decay and the spin-up/flux correlation can be fitted to the Ghosh and Lamb derivations for the spin-up caused by accretion from a thin, pressure-dominated disk, for a distance of %3.2 kpc and a surface magnetic field of %1:2Â 10 13 G. During the bright spin-up part of the outburst, the flux was subject to strong orbital modulation, peaking %3 days after periastron of the eccentric 12.68 day orbit, while during the faint part, there was little orbital modulation. The X-ray spectra were typical of accreting pulsars, describable by a cutoff power law, with an emission line near the 6.4 keV of K fluorescence from cool iron. The equivalent width of this emission did not share the orbital modulation, but nearly doubled during the faint phase, despite little change in the column density. The outburst could have been caused by an episode of increased wind from a Be star, such that a small accretion disk was formed during each periastron passage. A change in the wind and disk structure apparently occurred after 5 months such that the accretion rate was no longer modulated or the diffusion time was longer. The distance estimate implies that the X-ray luminosity observed was between 1 Â 10 36 and 6 Â 10 34 ergs s À1 , with a small but definite correlation with the intrinsic power-law spectral index.

Cranial placodes are ectodermal regions that contribute extensively to the vertebrate peripheral sensory nervous system. The development of the ophthalmic trigeminal (opV) placode, which gives rise only to sensory neurons of the ophthalmic lobe of the trigeminal ganglion, is a useful model of sensory neuron development. While key differentiation processes have been characterized at the tissue and cellular levels, the signaling pathways governing opV placode development have not. Here we tested in chick whether the canonical Wnt signaling pathway regulates opV placode development. By introducing a Wnt reporter into embryonic chick head ectoderm, we show that the canonical pathway is active in Pax3+ opV placode cells as, or shortly after, they are induced to express Pax3. Blocking the canonical Wnt pathway resulted in the failure of targeted cells to adopt or maintain an opV fate, as assayed by the expression of various markers including Pax3, FGFR4, Eya2, and the neuronal differentiation markers Islet1, neurofilament, and NeuN, although, surprisingly, it led to upregulation of Neurogenin2, both in the opV placode and elsewhere in the ectoderm. Activating the canonical Wnt signaling pathway, however, was not sufficient to induce Pax3, the earliest specific marker of the opV placode. We conclude that canonical Wnt signaling is necessary for normal opV placode development, and propose that other molecular cues are required in addition to Wnt signaling to promote cells toward an opV placode fate.

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