Analysis of stellar spectra with 3D and NLTE models

Models of radiation transport in stellar atmospheres are the hinge of modern astrophysics. Our knowledge of stars, stellar populations, and galaxies is only as good as the theoretical models, which are used for the interpretation of their observed spectra, photometric magnitudes, and spectral energy distributions. I describe recent advances in the field of stellar atmosphere modelling for late-type stars. Various aspects of radiation transport with 1D hydrostatic, LTE, NLTE, and 3D radiative-hydrodynamical models are briefly reviewed.Comment: 21 pages, accepted for publication as a chapter in "Determination of Atmospheric Parameters of B, A, F and G Type Stars", Springer (2014), eds. E. Niemczura, B. Smalley, W. Pyc

Analysis of heterogeneity in T2_2-weighted MR images can differentiate pseudoprogression from progression in glioblastoma

$\textbf{Purpose}$ To develop an image analysis technique that distinguishes pseudoprogression from true progression by analyzing tumour heterogeneity in $T_2$-weighted images using topological descriptors of image heterogeneity called Minkowski functionals (MFs). $\textbf{Methods}$ Using a retrospective patient cohort ($n$ = 50), and blinded to treatment response outcome, unsupervised feature estimation was performed to investigate MFs for the presence of outliers, potential confounders, and sensitivity to treatment response. The progression and pseudoprogression groups were then unblinded and supervised feature selection was performed using MFs, size and signal intensity features. A support vector machine model was obtained and evaluated using a prospective test cohort. $\textbf{Results}$ The model gave a classification accuracy, using a combination of MFs and size features, of more than 85% in both retrospective and prospective datasets. A different feature selection method (Random Forest) and classifier (Lasso) gave the same results. Although not apparent to the reporting radiologist, the $T_2$-weighted hyperintensity phenotype of those patients with progression was heterogeneous, large and frond-like when compared to those with pseudoprogression. $\textbf{Conclusion}$ Analysis of heterogeneity, in $T_2$-weighted MR images, which are acquired routinely in the clinic, has the potential to detect an earlier treatment response allowing an early change in treatment strategy. Prospective validation of this technique in larger datasets is required.Funded by Medical Research Council/ Royal College of Radiologists (UK) Clinical Research Fellowship (G1000265); Cancer Research UK Clinical Research Fellowship; Addenbrookes Charitable Trust Award to TCB. Cancer Research UK Programme grant (C197/ A3514) to KMB

DNA damage by lipid peroxidation products: implications in cancer, inflammation and autoimmunity

Oxidative stress and lipid peroxidation (LPO) induced by inflammation, excess metal storage and excess caloric intake cause generalized DNA damage, producing genotoxic and mutagenic effects. The consequent deregulation of cell homeostasis is implicated in the pathogenesis of a number of malignancies and degenerative diseases. Reactive aldehydes produced by LPO, such as malondialdehyde, acrolein, crotonaldehyde and 4-hydroxy-2-nonenal, react with DNA bases, generating promutagenic exocyclic DNA adducts, which likely contribute to the mutagenic and carcinogenic effects associated with oxidative stress-induced LPO. However, reactive aldehydes, when added to tumor cells, can exert an anticancerous effect. They act, analogously to other chemotherapeutic drugs, by forming DNA adducts and, in this way, they drive the tumor cells toward apoptosis. The aldehyde-DNA adducts, which can be observed during inflammation, play an important role by inducing epigenetic changes which, in turn, can modulate the inflammatory process. The pathogenic role of the adducts formed by the products of LPO with biological macromolecules in the breaking of immunological tolerance to self antigens and in the development of autoimmunity has been supported by a wealth of evidence. The instrumental role of the adducts of reactive LPO products with self protein antigens in the sensitization of autoreactive cells to the respective unmodified proteins and in the intermolecular spreading of the autoimmune responses to aldehyde-modified and native DNA is well documented. In contrast, further investigation is required in order to establish whether the formation of adducts of LPO products with DNA might incite substantial immune responsivity and might be instrumental for the spreading of the immunological responses from aldehyde-modified DNA to native DNA and similarly modified, unmodified and/or structurally analogous self protein antigens, thus leading to autoimmunity

A C-13 CP/MAS NMR study of the structure and dynamics of [(eta(5)-C5H5)(2)Fe-2(CO)(4)] included in gamma-cyclodextrin: Evidence for terminal-bridging exchange in the cis isomer

The novel inclusion compound of γ-cyclodextrin with the binuclear metal carbonyl complex (η5C5)2Fe 2(CO)4 as guest molecule is reported. 13C CP/MAS NMR spectroscopy, in the temperature range 100 to 353 K, is used to probe the structure and dynamics of the included molecules. Specifically, below ca. 240 K evidence is presented for the existence of both cis and trans isomers of included (η5-C5H5)2Fe 2(CO)4. Analysis of the temperature-dependence of the NMR line shapes shows that the microenvironment provided by the γ-cyclodextrin cavity allows much more extensive dynamic rearrangements of the guest molecules, in comparison to pure cis- or trans-(η5-C 5H5)2Fe2(CO)4, for which no isomerization or bridging-terminal carbonyl exchange processes are observed in this temperature regime. Notably, even at 100 K, bridging-terminal carbonyl exchange for the included trans isomer is rapid on the exchange-broadening time scale. However, the inclusion cavity is still more dynamically restrictive than a solution environment, and the rates of various exchange processes are usefully modified compared to those detected in solution. For (η5-C 5H5)2Fe2(CO)4 included in γ-cyclodextrin, contrary to the situation found in solution, the rate of bridging-terminal carbonyl exchange in the cis isomer is greater than the rate of cis-trans isomerization; in solution direct bridging-terminal exchange in the cis isomer could not be studied because indirect exchange via isomerization to the trans form, which undergoes rapid bridging-terminal exchange, is always significantly faster. By restricting isomerization, the inclusion environment thus confirms for the first time that the cis isomer is capable of carbonyl exchange and would allow the study of its rate and activation parameters. © 2006 American Chemical Society