214 research outputs found
Benefits and limitations of composites in carrier-based aircraft
There are many unique aspects of Navy air missions that lead to the differentiation between the design and performance of ship and shore-based aircraft. The major aspects are discussed from which essentially all Navy aircraft design requirements derive. (1) Navy aircraft operate from carriers at sea imposes a broad spectrum of physical conditions, constraints, and requirements ranging from the harsh sea environment, the space limitations of a carrier, takeoff and landing requirements as well as for endurance at long distances from the carrier. (2) Because the carrier and its airwing are intended to be capable of responding to a broad range of contingencies, mission flexibility is essential (maximum weapon carriage, rapid reconfiguration, multiple mission capability). (3) The embarked aircraft provides the long range defense of the battle group against air, surface and subsurface launched antiship missiles. (4) The carrier and its aircraft must operate independently and outside of normal supply lines. Taking into account these aspects, the use of composite materials in the design and performance of naval aircraft is outlined, also listing advantages and disadvantages
Chesapeake Bay Baseline Data Acquisition: Final Report
This report forms one of several appendices which are the body of
the Chesapeake Bay Baseline Data Acquisition Final Report. These
appendices are as follows:
Appendix I. A Chesapeake Bay Directory
Appendix II. Submerged Aquatic Vegetation
Appendix III. Toxics in the Chesapeake Bay
Appendix IV. Eutrophication
Appendix V. Shellfish Bed Closures
Appendix VI. Dredging and Spoil Disposal
Appendix VII. Modification of Fisheries
Appendix VIII. Hydrologic Modifications
Appendix IX. Wetlands Alteration
Appendix X. Effects of Boating and Shipping on Water Quality
Appendix XI. Shoreline Erosio
The nature of the progenitor of the Type II-P supernova 1999em
We present high quality ground-based VRI images of the site of the Type II-P
SN1999em (in NGC1637) taken before explosion, which were extracted from the
CFHT archive. We determine a precise position of the SN on these images to an
accuracy of 0.17''. The host galaxy is close enough (7.5 +/- 0.5 Mpc) that the
bright supergiants are resolved as individual objects, however we show that
there is no detection of an object at the SN position before explosion that
could be interpreted as the progenitor star. By determining the sensitivity
limits of the VRI data, we derive bolometric luminosity limits for the
progenitor. Comparing these to standard stellar evolutionary tracks which trace
evolution up to the point of core carbon ignition, we initially derive an upper
mass limit of approximately 12M_sol. However we present evolutionary
calculations that follow 7-12M_sol stars throughout their C-burning lifetime
and show that we can restrict the mass of the progenitor even further. Our
calculations indicate that progenitors initially of 8-10M_sol, undergoing
expected mass loss, can also be excluded because a second dredge up sends them
to somewhat higher luminosities than a star of initially 12M_sol. These results
limit the progenitor's initial main-sequence mass to a very narrow range of 12
+/- 1 M_sol. We discuss the similarities between the Type II-P SNe 1999em and
1999gi and their progenitor mass limits, and suggest that SN Type II-P
originate only in intermediate mass stars of 8-12M_sol, which are in the red
supergiant region and that higher mass stars produce the other Type II
sub-types. (Abridged).Comment: Replaced with accepted version to appear in ApJ, 30 pages, inc. 6
figure
B-type supergiants in the SMC: Rotational velocities and implications for evolutionary models
High-resolution spectra for 24 SMC and Galactic B-type supergiants have been
analysed to estimate the contributions of both macroturbulence and rotation to
the broadening of their metal lines. Two different methodologies are
considered, viz. goodness-of-fit comparisons between observed and theoretical
line profiles and identifying zeros in the Fourier transforms of the observed
profiles. The advantages and limitations of the two methods are briefly
discussed with the latter techniques being adopted for estimated projected
rotational velocities (\vsini) but the former being used to estimate
macroturbulent velocities. Only one SMC supergiant, SK 191, shows a significant
degree of rotational broadening (\vsini 90 \kms). For the remaining
targets, the distribution of projected rotational velocities are similar in
both our Galactic and SMC samples with larger values being found at earlier
spectral types. There is marginal evidence for the projected rotational
velocities in the SMC being higher than those in the Galactic targets but any
differences are only of the order of 5-10 \kms, whilst evolutionary models
predict differences in this effective temperature range of typically 20 to 70
\kms. The combined sample is consistent with a linear variation of projected
rotational velocity with effective temperature, which would imply rotational
velocities for supergiants of 70 \kms at an effective temperature of 28 000 K
(approximately B0 spectral type) decreasing to 32 \kms at 12 000 K (B8 spectral
type). For all targets, the macroturbulent broadening would appear to be
consistent with a Gaussian distribution (although other distributions cannot be
discounted) with an half-width varying from approximately 20 \kms
at B8 to 60 \kms at B0 spectral types.Comment: 4 figures, 8 pages, submitted to Astronomy and Astrophysic
The transferrin receptor CD71 delineates functionally distinct airway macrophage subsets during idiopathic pulmonary fibrosis
RATIONALE: Idiopathic pulmonary fibrosis (IPF) is a devastating progressive disease with limited therapeutic options. Airway macrophages (AMs) are key components of the defence of the airways and are implicated in the pathogenesis of IPF. Alterations in iron metabolism have been described during fibrotic lung disease and in murine models of lung fibrosis. However, the role of transferrin receptor-1 (CD71)-expressing AMs in IPF is not known. OBJECTIVES: To assess the role of CD71 expressing AMs in the IPF-lung. METHODS: We utilized multi-parameter flow cytometry, gene expression analysis and phagocytosis/transferrin uptake assays to delineate the role of AMs expressing, or lacking, CD71 in the BAL of patients with IPF or healthy controls. MEASUREMENTS AND MAIN RESULTS: There was a distinct increase in proportions of AMs lacking CD71 in IPF patients in comparison to healthy controls. Levels of BAL transferrin were enhanced in IPF-BAL and furthermore, CD71- AMs had an impaired ability to sequester transferrin. CD71+ and CD71- AMs were phenotypically, functionally and transcriptionally distinct, with CD71- AMs characterised by reduced expression of markers of macrophage maturity, impaired phagocytosis and enhanced expression of pro-fibrotic genes. Importantly, proportions of AMs lacking CD71 were independently associated with worse survival, underlining the importance of this population in IPF and as a potential therapeutic target. CONCLUSIONS: Taken together these data highlight how CD71 delineates AM subsets which play distinct roles in IPF and furthermore, CD71- AMs may be an important pathogenic component of fibrotic lung disease
Genetics, recombination and clinical features of human rhinovirus species C (HRV-C) infections; interactions of HRV-C with other respiratory viruses
To estimate the frequency, molecular epidemiological and clinical associations of infection with the newly described species C variants of human rhinoviruses (HRV), 3243 diagnostic respiratory samples referred for diagnostic testing in Edinburgh were screened using a VP4-encoding region-based selective polymerase chain reaction (PCR) for HRV-C along with parallel PCR testing for 13 other respiratory viruses. HRV-C was the third most frequently detected behind respiratory syncytial virus (RSV) and adenovirus, with 141 infection episodes detected among 1885 subjects over 13 months (7.5%). Infections predominantly targeted the very young (median age 6–12 months; 80% of infections in those <2 years), occurred throughout the year but with peak incidence in early winter months. HRV-C was detected significantly more frequently among subjects with lower (LRT) and upper respiratory tract (URT) disease than controls without respiratory symptoms; HRV-C mono-infections were the second most frequently detected virus (behind RSV) in both disease presentations (6.9% and 7.8% of all cases respectively). HRV variants were classified by VP4/VP2 sequencing into 39 genotypically defined types, increasing the current total worldwide to 60. Through sequence comparisons of the 5′untranslated region (5′UTR), the majority grouped with species A (n = 96; 68%, described as HRV-Ca), the remainder forming a phylogenetically distinct 5′UTR group (HRV-Cc). Multiple and bidirectional recombination events between HRV-Ca and HRV-Cc variants and with HRV species A represents the most parsimonious explanation for their interspersed phylogeny relationships in the VP4/VP2-encoding region. No difference in age distribution, seasonality or disease associations was identified between HRV-Ca and HRV-Cc variants. HRV-C-infected subjects showed markedly reduced detection frequencies of RSV and other respiratory viruses, providing evidence for a major interfering effect of HRV-C on susceptibility to other respiratory virus infections. HRV-C's disease associations, its prevalence and evidence for interfering effects on other respiratory viruses mandates incorporation of rhinoviruses into future diagnostic virology screening
Chemical constituents of lawang root oil
Spectroscopic analysis of lawang root oil identified methyl salicylate as the major component. This result contrasts with the known composition of bark-derived lawang oil, in which eugenol is the major component. The validity of the compositional analysis was confirmed by extraction of an authentic sample of plant root tissue, and comparison with the commercially available essential oil
Terminal velocities of luminous, early-type SMC stars
Ultraviolet spectra from the Space Telescope Imaging Spectrograph (STIS) are
used to determine terminal velocities for 11 O and B-type giants and
supergiants in the Small Magellanic Cloud (SMC) from the Si IV and C IV
resonance lines. Using archival data from observations with the Goddard
High-Resolution Spectrograph and the International Ultraviolet Explorer
telescope, terminal velocities are obtained for a further five B-type
supergiants. We discuss the metallicity dependence of stellar terminal
velocities, finding no evidence for a significant scaling between Galactic and
SMC metallicities for Teff < 30,000 K, consistent with the predictions of
radiation driven wind theory for supergiant stars. A comparison of the
ratio between the SMC and Galactic samples, while
consistent with the above statement, emphasizes that the uncertainties in the
distances to galactic O-stars are a serious obstacle to a detailed comparison
with theory. For the SMC sample there is considerable scatter in this ratio at
a given effective temperature, perhaps indicative of uncertainties in stellar
masses.Comment: 28 pages, 8 figures, accepted by ApJ; minor revisions prior to
acceptanc
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