Abstract.We have observed HNC 1-0, CN 1-0 & 2-1 line emission in a sample of 13 IR luminous (LIRGs, LIR > 10 11 L ) starburst and Seyfert galaxies. HNC 1-0 is detected in 9, CN 1-0 is detected in 10 and CN 2-1 in 7 of the galaxies and all are new detections. We also report the first detection of HC3N (10-9) emission in Arp 220. The excitation of HNC and CN emission requires densities n > 10 4 cm −3 . We compare their intensities to that of the usual high density tracer HCN. The I(HCN) I(HNC) 1-0 and I(HCN) I(CN)1-0 line intensity ratios vary significantly, from 0.5 to > ∼ 6, among the galaxies. This implies that the actual properties of the dense gas is varying among galaxies who otherwise have similar I(CO) I(HCN)line intensity ratios. We suggest that the HNC emission is not a reliable tracer of cold (10 K) gas at the center of LIR galaxies, as it often is in the disk of the Milky Way. Instead, the HNC abundance may remain substantial, despite high gas temperatures, because the emission is emerging from regions where the HCN and HNC formation and destruction processes are dominated by ion-neutral reactions which are not strongly dependent on kinetic temperature. We find five galaxies (Mrk 231, NGC 7469, NGC 7130, IC 694 and NGC 2623) where the I(HCN) I(HNC)intensity ratio is close to unity. Four are classified as active galaxies and one as a starburst. In other active galaxies, however, the I(HCN) I(HNC)is >4. The CN emission is on average a factor of two fainter than the HCN for the luminous IR galaxies, but the variation is large and there seems to be a trend of reduced relative CN luminosity with increasing IR luminosity. This trend is discussed in terms of other PDR tracers such as the [C II] 158 µm line emission. One object, NGC 3690, has a CN luminosity twice that of HCN and its ISM is thus strongly affected by UV radiation. We discuss the I(HCN) I(HNC)and I(HCN) I(CN)line ratios as indicators of starburst evolution. However, faint HNC emission is expected both in a shock dominated ISM as well as for a cloud ensemble dominated by dense warm gas in the very early stages of a starburst. Additional information will help resolve the dichotomy.

Abstract. We present results of a multi-transition study of the dense molecular gas in the central part of the hybrid star-burst/Seyfert galaxies NGC 4945 and the Circinus galaxy. From the results of radiative transfer calculations, we estimate in NGC 4945 nH 2 = 3 10 3 −10 4 cm −3 and T kin ≈ 100 K and in Circinus nH 2 = 2 10 3 −10 5 cm −3 and T kin ≈ 50−80 K for the molecular hydrogen density and kinetic temperature, respectively. As well as density/temperature tracing molecules, we have observed C17 O and C 18 O in each galaxy and the value of C18 O/C 17 O ≈ 6 for the isotopic column density ratio suggests that both have relatively high populations of massive stars. Finally, although star formation is present, the radiative transfer results combined with the high HCN/CO and (possibly) HCN/FIR, radio/FIR ratios may suggest that, in comparison with Circinus, a higher proportion of the dense gas emission in NGC 4945 may be located in the hypothesised central nuclear disk as opposed to dense star forming cloud cores. Contrary to the literature, which assumes that all of the far-infrared emission arises from star formation, our results suggest that in NGC 4945 some of this emission could arise from an additional source, and so we believe that a revision of the star formation rate estimates may be required for these two galaxies.

The replacement and repair of bone lost due to trauma, cancer, or congenital defects is a major clinical challenge. Skeletal tissue engineering is a potentially powerful strategy in modern regenerative medicine, and research in this field has increased greatly in recent years. Tissue engineering strategies seek to translate research findings in the fields of materials science, stem cell biology, and biomineralization into clinical applications, demanding the use of appropriate in vivo models to investigate bone regeneration of the long bone. However, identification of the optimal in vivo segmental bone defect model from the literature is difficult due to the use of different animal species (large and small mammals), different bones (weight-bearing and nonweight bearing), and multiple protocols, including the use of various scaffolds, cells, and bioactives. The aim of this review is to summarize the available animal models for evaluating long bone regeneration in vivo. We highlight the differences not only in species and sites but also in defect size, means of defect creation, duration of study, and fixation method. A critical evaluation of the most clinically relevant models is addressed to guide the researcher in his/her choice of the most appropriate model to use in future hypothesis-driven investigations.

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