Bremsstrahlung from relativistic heavy ions in a fixed target experiment at the LHC

We calculate the emission of bremsstrahlung from lead and argon ions in A Fixed Target ExpeRiment (AFTER) that uses the LHC beams. With nuclear charges of $Ze$ equal $208$ and $18$ respectively, these ions are accelerated to energies of $7$ TeV$\times Z$. The bremsstrahlung peaks around $\approx 100$ GeV and the spectrum exposes the nuclear structure of the incoming ion. The peak structure is significantly different from the flat power spectrum pertaining to a point charge. Photons are predominantly emitted within an angle of $1/\gamma$ to the direction of ion propagation. Our calculations are based on the Weizs\"{a}cker-Williams method of virtual quanta with application of existing experimental data on photonuclear interactions.Comment: 9 pages, 3 figures. Submitted to Advances in High Energy Physic

Analysis of the Effects of Five Factors Relevant to In Vitro Chondrogenesis of Human Mesenchymal Stem Cells Using Factorial Design and High Throughput mRNA-Profiling

The in vitro process of chondrogenic differentiation of mesenchymal stem cells for tissue engineering has been shown to require three-dimensional culture along with the addition of differentiation factors to the culture medium. In general, this leads to a phenotype lacking some of the cardinal features of native articular chondrocytes and their extracellular matrix. The factors used vary, but regularly include members of the transforming growth factor β superfamily and dexamethasone, sometimes in conjunction with fibroblast growth factor 2 and insulin-like growth factor 1, however the use of soluble factors to induce chondrogenesis has largely been studied on a single factor basis. In the present study we combined a factorial quality-by-design experiment with high-throughput mRNA profiling of a customized chondrogenesis related gene set as a tool to study in vitro chondrogenesis of human bone marrow derived mesenchymal stem cells in alginate. 48 different conditions of transforming growth factor β 1, 2 and 3, bone morphogenetic protein 2, 4 and 6, dexamethasone, insulin-like growth factor 1, fibroblast growth factor 2 and cell seeding density were included in the experiment. The analysis revealed that the best of the tested differentiation cocktails included transforming growth factor β 1 and dexamethasone. Dexamethasone acted in synergy with transforming growth factor β 1 by increasing many chondrogenic markers while directly downregulating expression of the pro-osteogenic gene osteocalcin. However, all factors beneficial to the expression of desirable hyaline cartilage markers also induced undesirable molecules, indicating that perfect chondrogenic differentiation is not achievable with the current differentiation protocols

Muon Acceleration in Cosmic-ray Sources

Many models of ultra-high energy cosmic-ray production involve acceleration in linear accelerators located in Gamma-Ray Bursts magnetars, or other sources. These source models require very high accelerating gradients, $10^{13}$ keV/cm, with the minimum gradient set by the length of the source. At gradients above 1.6 keV/cm, muons produced by hadronic interactions undergo significant acceleration before they decay. This acceleration hardens the neutrino energy spectrum and greatly increases the high-energy neutrino flux. We rule out many models of linear acceleration, setting strong constraints on plasma wakefield accelerators and on models for sources like Gamma Ray Bursts and magnetars.Comment: 5 pgs. submitted for publicatio

The young centre of the Earth

We treat, as an illustrative example of gravitational time dilation in relativity, the observation that the center of the Earth is younger than the surface by an appreciable amount. Richard Feynman first made this insightful point and presented an estimate of the size of the effect in a talk; a transcription was later published in which the time difference is quoted as 'one or two days'. However, a back-of-the-envelope calculation shows that the result is in fact a few years. In this paper we present this estimate alongside a more elaborate analysis yielding a difference of two and a half years. The aim is to provide a fairly complete solution to the relativity of the 'aging' of an object due to differences in the gravitational potential. This solution - accessible at the undergraduate level - can be used for educational purposes, as an example in the classroom. Finally, we also briefly discuss why exchanging 'years' for 'days' - which in retrospect is a quite simple, but significant, mistake - has been repeated seemingly uncritically, albeit in a few cases only. The pedagogical value of this discussion is to show students that any number or observation, no matter who brought it forward, must be critically examined.Comment: Published version, apart from minor editing (e.g. corrections of 'center' to 'centre'

Experimental setup and principal component analysis (PCA).

<p><b>A.</b> Experimental setup with numbering of the different conditions. When not stated, the cell density was 10⁷ cells per mL. <b>B.</b> PCA on all conditions labelled by days in culture. <b>C.</b> PCA limited to conditions 1–32 on days 0 and 1. <b>D.</b> PCA limited to conditions 1–32 on days 0 and day 7.</p

List of culture supplements.

<p>List of culture supplements.</p