Archetypal analysis of galaxy spectra

Archetypal analysis represents each individual member of a set of data vectors as a mixture (a constrained linear combination) of the pure types or archetypes of the data set. The archetypes are themselves required to be mixtures of the data vectors. Archetypal analysis may be particularly useful in analysing data sets comprising galaxy spectra, since each spectrum is, presumably, a superposition of the emission from the various stellar populations, nebular emissions and nuclear activity making up that galaxy, and each of these emission sources corresponds to a potential archetype of the entire data set. We demonstrate archetypal analysis using sets of composite synthetic galaxy spectra, showing that the method promises to be an effective and efficient way to classify spectra. We show that archetypal analysis is robust in the presence of various types of noise.Comment: 6 pages, 5 figures, 1 style-file. Accepted for publication by MNRA

Wildland fire effects in silviculturally treated vs. untreated stands of New Mexico and Arizona

Stand-replacement fires, particularly in ponderosa pine (Pinus ponderosa) forests, have replaced high frequency, low-intensity historical fire regimes. We examined whether forest stands treated recently using silvicultural practices would be (1) less susceptible to stand-replacing crownfires, and (2) more ecologically and functionally resilient compared to untreated stands following extreme wildland fire. Reports detailing wildland fire behavior in treated stands remain largely anecdotal. We compared fire severity indices, fireline intensity (btu/ft/s), stand characteristics including canopy bulk density (kg/m3), and post-fire recovery indices in silviculturally treated vs. untreated forest stands in New Mexico and Arizona. Results indicated fire severity in pine-grassland forests was lowered when surface and aerial fuel loads were reduced. Specifically, as density (stems/ac) and basal area (ft2/ac) decreased and mean tree diameter (in) increased, fire severity and fireline intensity decreased. The more aggressive the treatment (i.e., where the canopy bulk density was reduced), the less susceptible forest stands were to crownfire. However, mechanical treatments where slash was scattered rendered stands susceptible to near stand-replacement type damage when wildfire occurred within 4 years of treatment. On our study sites, mechanical treatment followed by prescribed fire had the greatest impact toward mitigating fire severity (i.e., aerial and surface fuels were reduced). Treated stands were also more ecologically and functionally resilient than untreated forest stands following wildland fire

Fecundity of the black vine weevil, Brachyrhinus sulcatus (F.), fed on foliage of blueberry, cranberry and weeds from peat bogs

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Seeing the forest and the trees: A meta-analysis of information security policy compliance literature

A rich stream of research has identified numerous antecedents to employee compliance with information security policies. However, the breadth of this literature and inconsistencies in the reported findings warrants a more in-depth analysis. Drawing on 25 quantitative studies focusing on security policy compliance, we classified 105 independent variables into 17 distinct categories. We conducted a meta-analysis for each category’s relationship with security policy compliance and then analyzed the results for possible moderators. Our results revealed a number of illuminating insights, including (1) the importance of categories associated with employees’ personal attitudes, norms and beliefs, (2) the relative weakness of the link between compliance and rewards/punishment, and (3) the enhanced compliance associated with general security policies rather than specific policies (e.g., anti-virus). These findings can be used as a reference point from which future scholarship in this area can be guided

The oxidative costs of reproduction are group-size dependent in a wild cooperative breeder.

Life-history theory assumes that reproduction entails a cost, and research on cooperatively breeding societies suggests that the cooperative sharing of workloads can reduce this cost. However, the physiological mechanisms that underpin both the costs of reproduction and the benefits of cooperation remain poorly understood. It has been hypothesized that reproductive costs may arise in part from oxidative stress, as reproductive investment may elevate exposure to reactive oxygen species, compromising survival and future reproduction and accelerating senescence. However, experimental evidence of oxidative costs of reproduction in the wild remains scarce. Here, we use a clutch-removal experiment to investigate the oxidative costs of reproduction in a wild cooperatively breeding bird, the white-browed sparrow weaver, Plocepasser mahali. Our results reveal costs of reproduction that are dependent on group size: relative to individuals in groups whose eggs were experimentally removed, individuals in groups that raised offspring experienced an associated cost (elevated oxidative damage and reduced body mass), but only if they were in small groups containing fewer or no helpers. Furthermore, during nestling provisioning, individuals that provisioned at higher rates showed greater within-individual declines in body mass and antioxidant protection. Our results provide rare experimental evidence that reproduction can negatively impact both oxidative status and body mass in the wild, and suggest that these costs can be mitigated in cooperative societies by the presence of additional helpers. These findings have implications for our understanding of the energetic and oxidative costs of reproduction, and the benefits of cooperation in animal societies.This study was funded by a BBSRC David Phillips Fellowship and a Royal Society Research Grant to A.J.Y. and an NERC studentship to D.L.C. J.D.B. was supported by a Royal Society University Research Fellowship.This is the final version of the article. It first appeared from Royal Society Publishing via http://dx.doi.org/10.1098/rspb.2015.203

Immune response in a wild bird is predicted by oxidative status, but does not cause oxidative stress.

Final published versionCopyright: © 2015 Cram et al.The immune system provides vital protection against pathogens, but extensive evidence suggests that mounting immune responses can entail survival and fecundity costs. The physiological mechanisms that underpin these costs remain poorly understood, despite their potentially important role in shaping life-histories. Recent studies involving laboratory models highlight the possibility that oxidative stress could mediate these costs, as immune-activation can increase the production of reactive oxygen species leading to oxidative stress. However, this hypothesis has rarely been tested in free-ranging wild populations, where natural oxidative statuses and compensatory strategies may moderate immune responses and their impacts on oxidative status. Furthermore, the possibility that individuals scale their immune responses according to their oxidative status, conceivably to mitigate such costs, remains virtually unexplored. Here, we experimentally investigate the effects of a phytohaemagglutinin (PHA) immune-challenge on oxidative status in wild male and female white-browed sparrow weavers, Plocepasser mahali. We also establish whether baseline oxidative status prior to challenge predicts the scale of the immune responses. Contrary to previous work on captive animals, our findings suggest that PHA-induced immune-activation does not elicit oxidative stress. Compared with controls (n = 25 birds), PHA-injected birds (n = 27 birds) showed no evidence of a differential change in markers of oxidative damage or enzymatic and non-enzymatic antioxidant protection 24 hours after challenge. We did, however, find that the activity of a key antioxidant enzyme (superoxide dismutase, SOD) prior to immune-activation predicted the scale of the resulting swelling: birds with stronger initial SOD activity subsequently produced smaller swellings. Our findings (i) suggest that wild birds can mount immune responses without suffering from systemic oxidative stress, and (ii) lend support to biomedical evidence that baseline oxidative status can impact the scale of immune responses; a possibility not yet recognised in ecological studies of immunity.Biotechnology and Biological Sciences Research Council (BBSRC)Natural Environment Research Council (NERC)Royal SocietyUniversity of Bristo

VLA Observations of the "Eye of the Tornado"- the High Velocity \HII Region G357.63-0.06

The unusual supernova remnant candidate G357.7-0.1 and the compact source G357.63-0.06 have been observed with the Very Large Array at 1.4 and 8.3 GHz. The H92$\alpha$ line (8.3 GHz) was detected from the compact source with a surprising velocity of about -210 km/s indicating that this source is an \HII region, is most likely located at the Galactic center, and is unrelated to the SNR. The \HI absorption line (1.4 GHz) data toward these sources supports this picture and suggests that G357.7-0.1 lies farther away than the Galactic center.Comment: Latex, 14 pages including 4 figures. Accepted to A

Chlamydiae Enhance Self-Antigen Presentation in a Mechanism that is Dependent on Biosynthesis of Lipooligosaccharide

Chlamydia is a genus of obligate intracellular bacteria that undergo a unique, biphasic developmental cycle. The infectious and metabolically inert Elementary Bodies (EBs) begin the cycle of infection by attaching and invading a host cells. Once inside, the EBs differentiate into the metabolically active, dividing Reticulate Bodies (RBs) within their own cellular compartment. A significant portion of the chlamydial developmental cycle takes place within the host cell, which presents a challenge for the host immune system to detect and clear the infection. MHC Class I antigen presentation is the adaptive immune system’s answer to this problem by displaying both host and parasitic antigens, if present, to other cells such as CD8⁺ cytotoxic T cells. Previous research has identified chlamydial interactions with host-cell metabolism such as alteration of host transcription and translation. Other previous work has identified chlamydial antigens displayed in MHC Class I molecules. This body of work is the first to describe the impact of Chlamydia spp. infection on MHC Class I self-antigen presentation by enhancing presentation of peptides derived from defective ribosomal products (DRiPs). We hypothesize that enhancing self-antigen presentation is a novel immune evasion strategy by which Chlamyidae saturate MHC Class I molecules with self-antigen and therefore decrease the likelihood that chlamydial antigens are presented. Mechanisms of pathogenesis have often been used to elucidate host molecular pathways such as herpesvirus and the MHC Class I and MHC Class II antigen presentation pathways. The DRiPs pathway is currently unknown, and future endeavors will aim to utilize chlamydial infection to discover the molecular mechanisms of the DRiPs pathway. Additionally, we used a small molecule inhibitor of chlamydial lipooligosaccharide biosynthesis and identified the sensitivities of C. trachomatis L2, C. trachomatis J6276, C. muridarum, C. caviae, and C. suis to the drug. Treatment of infected cells with the inhibitor of LOS resulted in aberrant inclusions in some, but not all species as well as a differential effect on output of infectious EBs. Future experiments will seek to validate the use of the LOS inhibitor as an agent of selection in chlamydial recombination.Keywords: Chlamydia, Lipooligosaccharide, DRiPs, MHC Class