184 research outputs found
Spatial correlation between CH, CN and the diffuse interstellar band carriers
Observations are presented of the diffuse interstellar bands at 5780 and 5797 A and of the ultraviolet lines of CH and CN in the light of six bright stars which lie behind isolated interstellar clouds. It is found that CN and CH are only present when the 5797 band is deeper than the 5780 one. Comparisons with satellite measurements of the UV extinction show that the shape of the extinction curve is linked to the same band ratio in these stars. The results support a previous suggestion that the various components of the absorption spectrum of an isolated cloud (the extinction law, atomic and molecular features and the diffuse interstellar bands) all vary together
Spatial correlation between CH, CN and the diffuse interstellar band carriers
Observations are presented of the diffuse interstellar bands at 5780 and 5797 A and of the ultraviolet lines of CH and CN in the light of six bright stars which lie behind isolated interstellar clouds. It is found that CN and CH are only present when the 5797 band is deeper than the 5780 one. Comparisons with satellite measurements of the UV extinction show that the shape of the extinction curve is linked to the same band ratio in these stars. The results support a previous suggestion that the various components of the absorption spectrum of an isolated cloud (the extinction law, atomic and molecular features and the diffuse interstellar bands) all vary together
Effect of Alloying Additives and Casting Parameters on the Microstructure and Mechanical Properties of Silicon Bronzes
The studied silicon bronze (CuSi3Zn3Mn1) is characterised by good strength and corrosion resistance due to the alloying elements that are present in it (Si, Zn, Mn, Fe). This study analysed the casting process in green sand moulding, gravity die casting, and centrifugal casting with a horizontal axis of rotation. The influences of Ni and Zr alloying additives as well as the casting technology that was used were evaluated on the alloyâs microstructure and mechanical properties. The results of the conducted research are presented in the form of the influence of the technology (GS, GZ, GM) and the content of the introduced alloy additives on the mechanical parameters (UTS, A10, and Proof Stress, BHN). The analysis of the tests that were carried out made it possible to determine which of the studied casting technologies had the best mechanical properties. Microstructure of metal poured into metal mould was finer than that which was cast into moulding compound. Mechanical properties of castings made in moulding compound were lower than those that were cast into metal moulds. Increased nickel content affected the BHN parameter
Ultraviolet Extinction Properties in the Milky Way
We have assembled a homogeneous database of 417 ultraviolet (UV) extinction
curves for reddened sightlines having International Ultraviolet Explorer (IUE)
spectra. We have combined these with optical and 2MASS photometry allowing
estimates of the ratio of total-to-selective extinction, R(V), for the entire
sample. Fitzpatrick-Massa (FM) parameters have also been found for the entire
sample. This is the largest study of parameterized UV extinction curves yet
published and it covers a wide range of environments, from dense molecular
clouds to the diffuse interstellar medium (ISM), with extinctions A(V) ranging
from 0.50 to 4.80. It is the first to extend far beyond the solar neighborhood
and into the Galaxy at large, with 30 sightlines having distances > 5 kpc.
Previously, the longest sightlines with FM parameters and R(V) extended ~ 1
kpc. We find that (1.) the CCM extinction law applies for 93% of the
sightlines, implying that dust processing in the Galaxy is efficient and
systematic; (2.) the central wavelength of the 2175 A bump is constant; (3.)
the 2175 A bump width is dependent on environment. Only four sightlines show
systematic deviations from CCM, HD 29647, 62542, 204827, and 210121. These
sightlines all sample dense, molecule-rich clouds. The new extinction curves
and values of R(V) allow us to revise the CCM law.Comment: 32 pages, 12 figure
REPAIRtoireâa database of DNA repair pathways
REPAIRtoire is the first comprehensive database resource for systems biology of DNA damage and repair. The database collects and organizes the following types of information: (i) DNA damage linked to environmental mutagenic and cytotoxic agents, (ii) pathways comprising individual processes and enzymatic reactions involved in the removal of damage, (iii) proteins participating in DNA repair and (iv) diseases correlated with mutations in genes encoding DNA repair proteins. REPAIRtoire provides also links to publications and external databases. REPAIRtoire contains information about eight main DNA damage checkpoint, repair and tolerance pathways: DNA damage signaling, direct reversal repair, base excision repair, nucleotide excision repair, mismatch repair, homologous recombination repair, nonhomologous end-joining and translesion synthesis. The pathway/protein dataset is currently limited to three model organisms: Escherichia coli, Saccharomyces cerevisiae and Homo sapiens. The DNA repair and tolerance pathways are represented as graphs and in tabular form with descriptions of each repair step and corresponding proteins, and individual entries are cross-referenced to supporting literature and primary databases. REPAIRtoire can be queried by the name of pathway, protein, enzymatic complex, damage and disease. In addition, a tool for drawing custom DNAâprotein complexes is available online. REPAIRtoire is freely available and can be accessed at http://repairtoire.genesilico.pl/
An Ultra-High-Resolution Survey of the Interstellar ^7Li-to-^6Li Isotope Ratio in the Solar Neighborhood
In an effort to probe the extent of variations in the interstellar ^7Li/^6Li
ratio seen previously, ultra-high-resolution (R ~ 360,000), high
signal-to-noise spectra of stars in the Perseus OB2 and Scorpius OB2
Associations were obtained. These measurements confirm our earlier findings of
an interstellar ^7Li/^6Li ratio of about 2 toward o Per, the value predicted
from models of Galactic cosmic ray spallation reactions. Observations of other
nearby stars yield limits consistent with the isotopic ratio ~ 12 seen in
carbonaceous chondrite meteorites. If this ratio originally represented the gas
toward o Per, then to decrease the original isotope ratio to its current value
an order of magnitude increase in the Li abundance is expected, but is not
seen. The elemental K/Li ratio is not unusual, although Li and K are formed via
different nucleosynthetic pathways. Several proposals to account for the low
^7Li/^6Li ratio were considered, but none seems satisfactory.
Analysis of the Li and K abundances from our survey highlighted two sight
lines where depletion effects are prevalent. There is evidence for enhanced
depletion toward X Per, since both abundances are lower by a factor of 4 when
compared to other sight lines. Moreover, a smaller Li/H abundance is observed
toward 20 Aql, but the K/H abundance is normal, suggesting enhanced Li
depletion (relative to K) in this direction. Our results suggest that the
^7Li/^6Li ratio has not changed significantly during the last 4.5 billion years
and that a ratio ~ 12 represents most gas in the solar neighborhood. In
addition, there appears to be a constant stellar contribution of ^7Li,
indicating that one or two processes dominate its production in the Galaxy.Comment: 54 pages, accepted for publication in the Astrophysical Journa
Ultraviolet Survey of CO and H_2 in Diffuse Molecular Clouds: The Reflection of Two Photochemistry Regimes in Abundance Relationships
(Abridged) We carried out a comprehensive far-ultraviolet (UV) survey of
^12CO and H_2 column densities along diffuse molecular Galactic sight lines in
order to explore in detail the relationship between CO and H_2. We measured new
CO abundances from HST spectra, new H_2 abundances from FUSE data, and new CH,
CH^+, and CN abundances from the McDonald and European Southern Observatories.
A plot of log N(CO) versus log N(H_2) shows that two power-law relationships
are needed for a good fit of the entire sample, with a break located at log
N(CO, cm^-2) = 14.1 and log N(H_2) = 20.4, corresponding to a change in
production route for CO in higher-density gas. Similar logarithmic plots among
all five diatomic molecules allow us to probe their relationships, revealing
additional examples of dual slopes in the cases of CO versus CH (break at log N
= 14.1, 13.0), CH^+ versus H_2 (13.1, 20.3), and CH^+ versus CO (13.2, 14.1).
These breaks are all in excellent agreement with each other, confirming the
break in the CO versus H_2 relationship, as well as the one-to-one
correspondence between CH and H_2 abundances. Our new sight lines were selected
according to detectable amounts of CO in their spectra and they provide
information on both lower-density (< 100 cm^-3) and higher-density diffuse
clouds. The CO versus H_2 correlation and its intrinsic width are shown to be
empirically related to the changing total gas density among the sight lines of
the sample. We employ both analytical and numerical chemical schemes in order
to derive details of the molecular environments. In the low-density gas, where
equilibrium-chemistry studies have failed to reproduce the abundance of CH^+,
our numerical analysis shows that nonequilibrium chemistry must be employed for
correctly predicting the abundances of both CH^+ and CO.Comment: 40 pages in emulateapj style, to appear in the Astrophysical Journa
Effects of experience and body size on refuge choice in the crayfish Orconectes immunis
We investigated whether refuge size or experience with a refuge affected the refuge use of male Orconectes immunis crayfish. Individuals were given choices among seven refuges for 10 consecutive days. Refuges were formed from equal length but different diameter PVC pipe and placed in an array in a random sequence. Three treatments were used. In the Novel Refuge treatment, individuals were placed in a new test arena with a new arrangement of cleaned refuges every day. In the Nonremoval treatment, individuals were left in the same arena with the same set of refuges each day. In the Removal treatment, individuals were removed from the refuges each day but placed back in the same arena with the same set of refuges after the refuges had been cleaned. We found that refuge occupation was correlated with an individual\u27s size; smaller crayfish tended to use smaller refuges than larger crayfish, even though all crayfish could fit in all of the different sized refuges. When first tested, individuals initially chose larger refuges than they would subsequently settle in, suggesting that under duress, they were not as particular about refuge characteristics. Individuals in the Nonremoval and Removal treatments were significantly more consistent in their refuge use than those in the Novel Refuge treatment, suggesting that experience with a particular refuge increased use of that refuge. Individuals from the Novel Refuge treatment that were housed for a month with a single refuge did not increase their use of that sized refuge more than those that were housed without a refuge, indicating that simply occupying a refuge of a given size did not affect refuge preference
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