440 research outputs found
Preventive conservation strategies for sustainable urban pollution control in museums
The last 40 years have seen major changes in the sources and concentrations of urban pollution (nitrogen dioxide, sulfur dioxide, hydrogen sulfide, and particulates). During this time, research has advanced our understanding of the impact of pollutants on objects in urban museums. As a consequence, pollutant control has become an important aspect of preventive conservation. There is also increased awareness of the need for pollution control strategies that are sustainable at an organizational and global level. This report, prepared by a chemist, a conservator, and two building scientists, reviews strategies for minimizing the impact of urban pollution on museum collections. The results of new research funded by the UK government identify current (1999) internal pollution levels in both naturally ventilated and air-conditioned museums with particle and gaseous filtration, in relation to external concentrations, ventilation strategies, and the characteristics of the internal fabric and finishes of these buildings. The last 40 years have seen major changes in the sources and concentrations of urban pollution (nitrogen dioxide, sulfur dioxide, hydrogen sulfide, and particulates). During this time, research has advanced our understanding of the impact of pollutants on objects in urban museums. As a consequence, pollutant control has become an important aspect of preventive conservation. There is also increased awareness of the need for pollution control strategies that are sustainable at an organizational and global level. This report, prepared by a chemist, a conservator, and two building scientists, reviews strategies for minimizing the impact of urban pollution on museum collections. The results of new research funded by the UK government identify current (1999) internal pollution levels in both naturally ventilated and air-conditioned museums with particle and gaseous filtration, in relation to external concentrations, ventilation strategies, and the characteristics of the internal fabric and finishes of these buildings
Investigation of Substituted-Benzene Dopants for Charge Exchange Ionization of Nonpolar Compounds by Atmospheric Pressure Photoionization
Atmospheric pressure photoionization (APPI) using a dopant enables both polar and nonpolar compounds to be analyzed by LC/MS. To date, the charge exchange ionization pathway utilized for nonpolar compounds has only been efficient under restrictive conditions, mainly because the usual charge exchange reagent ions—the dopant photoions themselves—tend to be consumed in proton transfer reactions with solvent and/or dopant neutrals. This research aims to elucidate the factors affecting the reactivities of substituted-benzene dopant ions; another, overriding, objective is to discover new dopants for better implementing charge exchange ionization in reversed-phase LC/MS applications. The desirable properties for a charge exchange dopant include low reactivity of its photoions with solvent and dopant neutrals and high ionization energy (IE). Reactivity tests were performed for diverse substituted-benzene compounds, with substituents ranging from strongly electron withdrawing (EW) to strongly electron donating (ED). The results indicate that both the tendency of a dopant's photoions to be lost through proton transfer reactions and its IE depend on the electron donating/withdrawing properties of its substituent(s): ED groups decrease reactivity and IE, while EW groups increase reactivity and IE. Exceptions to the reactivity trend for dopants with ED groups occur when the substituent is itself acidic. All told, the desirable properties for a charge exchange dopant tend towards mutual exclusivity. Of the singly-substituted benzenes tested, chloro- and bromobenzene provide the best compromise between low reactivity and high IE. Several fluoroanisoles, with counteracting EW and ED groups, may also provide improved performance relative to the established dopants
Lyman-alpha absorption around nearby galaxies
We have used STIS aboard HST to search for Lyman-alpha (Lya) absorption lines
in the outer regions of eight nearby galaxies using background QSOs and AGN as
probes. Lya lines are detected within a few hundred km/s of the systemic
velocity of the galaxy in all cases. We conclude that a background
line-of-sight which passes within 26-200 h-1 kpc of a foreground galaxy is
likely to intercept low column density neutral hydrogen with log N(HI) >~ 13.0.
The ubiquity of detections implies a covering factor of ~ 100% for low N(HI)
gas around galaxies within 200 h-1 kpc. We discuss the difficulty in trying to
associate individual absorption components with the selected galaxies and their
neighbors, but show that by degrading our STIS data to lower resolutions, we
are able to reproduce the anti-correlation of Lya equivalent width and impact
parameter found at higher redshift. We also show that the equivalent width and
column density of Lya complexes (when individual components are summed over ~
1000 km/s) correlate well with a simple estimate of the volume density of
galaxies brighter than M(B) = -17.5 at the same redshift as a Lya complex. We
do not reject the hypothesis that the selected galaxies are directly
responsible for the observed Lya lines, but our analysis indicates that
absorption by clumpy intragroup gas is an equally likely explanation. (Abriged)Comment: Accepted for publication in Nov 20, 2002 issue of ApJ. Paper with all
figures can be found at http://www.astro.princeton.edu/~dvb/lyapaper.ps
(preferable). Minor typos fixe
Space Telescope Imaging Spectrograph slitless observations of Small Magellanic Cloud Planetary Nebulae: a study on morphology, emission line intensity, and evolution
A sample of 27 Planetary Nebulae (PNs) in the Small Magellanic Clouds (SMC)
have been observed with the Hubble Space Telescope Imaging Spectrograph
(HST/STIS) to determine their morphology, size, and the spatial variation of
the ratios of bright emission lines. The morphologies of SMC PNs are similar to
those of LMC and Galactic PNs. However, only a third of the resolved SMC PNs
are asymmetric, compared to half in the LMC. The low metallicity environment of
the SMC seems to discourage the onset of bipolarity in PNs. We measured the
line intensity, average surface brightness (SB), and photometric radius of each
nebula in halpha, hbeta, [O III] lambda4959 and 5007, [NII] 6548 and 6584, [S
II] lambda6716 and 5731, He I 6678, and [OI] 6300 and 6363. We show that the
surface brightness to radius relationship is the same as in LMC PNs, indicating
its possible use as a distance scale indicator for Galactic PNs. We determine
the electron densities and the ionized masses of the nebulae where the [S II]
lines were measured accurately, and we find that the SMC PNs are denser than
the LMC PNs by a factor of 1.5. The average ionized mass of the SMC PNs is 0.3
Msun. We also found that the median [O III]/hbeta intensity ratio in the SMC is
about half than the corresponding LMC median. We use Cloudy to model the
dependence of the [O III]/hbeta ratio on the oxygen abundance. Our models
encompass very well the average observed physical quantities. We suggest that
the SMC PNs are principally cooled by the carbon lines, making it hard to study
their excitation based on the optical lines at our disposal.Comment: Accepted for publication in the Astrophysical Journal, 30 pages, 13
figures, 6 tables. For high resolution version of Figs 1 to 6, see
http://archive.stsci.edu/hst/mcpn/home.htm
Thermal Pressures in Neutral Clouds inside the Local Bubble, as Determined from C I Fine-Structure Excitations
High-resolution spectra covering absorption features from interstellar C I
were recorded for four early-type stars with spectrographs on HST, in a program
to measure the fine-structure excitation of this atom within neutral clouds
inside or near the edge of the Local Bubble, a volume of hot (T ~ 10^6 K) gas
that emits soft x-rays and extends out to about 100 pc away from the Sun. The
excited levels of C I are populated by collisions, and the ratio of excited
atoms to those in the ground level give a measure of the local thermal
pressure. Absorptions from the two lowest levels of C I were detected toward
alpha Del and delta Cyg, while only marginal indications of excited C I were
obtained for gamma Ori, and lambda Lup. Along with temperature limits derived
by other means, the C I fine-structure populations indicate that for the clouds
in front of gamma Ori, delta Cyg and alpha Del, 10^3 < p/k < 10^4 cm^{-3}K at
about the +-1 sigma confidence level in each case. The results for lambda Lup
are not as well constrained, but still consistent with the other three stars.
The results indicate that the thermal pressures are below generally accepted
estimates p/k > 10^4 cm^{-3}K for the Local Bubble, based on the strength of
x-ray and EUV emission from the hot gas. This inequality of pressure for these
neutral clouds and their surroundings duplicates a condition that exists for
the local, partly-ionized cloud that surrounds the Sun. An appendix in the
paper describes a direct method for determining and eliminating small spectral
artifacts arising from variations of detector sensitivity with position.Comment: 33 pages, 7 figures, submitted to the Astrophysical Journa
Interstellar and Circumstellar Optical & Ultraviolet Lines Towards SN1998S
We have observed SN1998S which exploded in NGC3877, with the UES at the WHT
and with the E230M echelle of STIS aboard HST. Both data sets were obtained at
two seperate epochs. From our own Galaxy we detect interstellar absorption
lines of CaII, FeII, MgI, and probably MnII from the edge of the HVC Complex M.
We derive gas-phase abundances which are very similar to warm disk clouds in
the local ISM, which we believe argues against the HVC material having an
extragalactic origin. At the velocity of NGC3877 we detect interstellar MgI,
MgII, MnII, CaII, & NaI. Surprisingly, one component is seen to increase by a
factor of ~1 dex in N(NaI) and N(MgI) between the two epochs over which the
data were taken. Unusually, our data also show narrow Balmer, HeI, and
metastable FeII P-Cygni profiles, with a narrow absorption component
superimposed on the bottom of the profile's absorption trough. Both the broad
and narrow components of the optical lines are seen to increase substantially
in strength between the two epochs. Most of the low-ionization absorption can
be understood in terms of gas co-rotating with the disk of NGC 3877, providing
the SN is at the back of an HI disk with a similar thickness to that of our own
Galaxy. However, the variable absorption components, and the classic P-Cygni
emission profiles, most likely arise in slow-moving circumstellar outflows
originating from the red supergiant progenitor of SN1998S. [Abridged.]Comment: Accepted by ApJ, 26 pages including 9 figure
Risk of prostate cancer after isolated high-grade prostatic intraepithelial neoplasia (HGPIN) detected on extended core needle biopsy : a UK hospital experience.
Background High-grade prostatic intraepithelial neoplasia (HGPIN) is a precursor lesion to prostate cancer (CaP). UK-based studies examining the occurrence of isolated HGPIN and subsequent risk of CaP are lacking. Our aim was to assess the occurrence of HGPIN in a regional UK population and to determine whether in a retrievable cohort of such patients that had repeat extended core biopsies, there was an elevated risk of CaP. Methods A retrospective analysis of the pathology database was conducted at our institution (Lancashire Teaching Hospitals NHS Foundation Trust) for prostate biopsies recorded between January 2001 and December 2005 (all extended core biopsies). Those patients with isolated HGPIN on 1st set of biopsies were identified and, their clinical characteristics and pathological findings from subsequent biopsies (if any) were determined. The risk of CaP on subsequent biopsies based on presenting baseline PSA was stratified. Results Of 2,192 biopsied patients, there were 88 cases of isolated HGPIN of which 67 patients underwent one or more repeat biopsies. In this repeat-biopsy group, 28 CaP diagnoses were made. Age at first biopsy (P 20 ng/ml – 87.5%. Conclusion Based on our results, we recommend delaying the 1st repeat biopsy at low PSA range but to have a shorter interval to repeat biopsies at intermediate and higher PSA ranges
Monitoring of lung edema by microwave reflectometry during lung ischemia-reperfusion injury in vivo
It is still unclear whether lung edema can be monitored by microwave reflectometry and whether the measured changes in lung dry matter content (DMC) are accompanied by changes in PaO(2) and in pro-to anti-inflammatory cytokine expression (IFN-gamma and IL-10). Right rat lung hili were cross-clamped at 37 degrees C for 0, 60, 90 or 120 min ischemia followed by 120 min reperfusion. After 90 min (DMC: 15.9 +/- 1.4%; PaO(2): 76.7 +/- 18 mm Hg) and 120 min ischemia (DMC: 12.8 +/- 0.6%; PaO(2): 43 +/- 7 mm Hg), a significant decrease in DMC and PaO(2) throughout reperfusion compared to 0 min ischemia (DMC: 19.5 +/- 1.11%; PaO(2): 247 +/- 33 mm Hg; p < 0.05) was observed. DMC and PaO(2) decreased after 60 min ischemia but recovered during reperfusion (DMC: 18.5 +/- 2.4%; PaO(2) : 173 +/- 30 mm Hg). DMC values reflected changes on the physiological and molecular level. In conclusion, lung edema monitoring by microwave reflectometry might become a tool for the thoracic surgeon. Copyright (c) 2006 S. Karger AG, Basel
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