1,374 research outputs found
The 11 Micron Emissions of Cabon Stars
A new classification scheme of the IRAS LRS carbon stars is presented. It comprises the separation of 718 probable carbon stars into 12 distinct self-similar spectral groupings. Continuum temperatures are assigned and range from 470 to 5000 K. Three distinct dust species are identifiable: SiC, alpha:C-H, and MgS. In addition to the narrow 11 + micron emission feature that is commonly attributed to SiC, a broad 11 + micron emission feature, that is correlated with the 8.5 and 7.7 micron features, is found and attributed to alpha:C-H. SiC and alpha:C-H band strengths are found to correlate with the temperature progression among the Classes. We find a spectral sequence of Classes that reflects the carbon star evolutionary sequence of spectral types, or alternatively developmental sequences of grain condensation in carbon-rich circumstellar shells. If decreasing temperature corresponds to increasing evolution, then decreasing temperature corresponds to increasing CIO resulting in increasing amounts of carbon rich dust, namely alpha:C-H. If decreasing the temperature corresponds to a grain condensation sequence, then heterogeneous, or induced nucleation scenarios are supported. SiC grains precede alpha:C-H and form the nuclei for the condensation of the latter material. At still lower temperatures, MgS appears to be quite prevalent. No 11.3 micron PAH features are identified in any of the 718 carbon stars. However, one of the coldest objects, IRAS 15048-5702, and a few others, displays an 11.9 micron emission feature characteristic of laboratory samples of coronene. That feature corresponds to the C-H out of plane deformation mode of aromatic hydrocarbon. This band indicates the presence of unsaturated, sp(sup 3), hydrocarbon bonds that may subsequently evolve into saturated bonds, sp(sup 2), if, and when, the star enters the planetary nebulae phase of stellar evolution. The effusion of hydrogen from the hydrocarbon grain results in the evolution in wavelength of this 11.9 micron emission feature to the 11.3 micron feature
The 11 Micron Emissions of Carbon Stars
A new classification scheme of the IRAS LRS carbon stars is presented. It comprises the separation of 718 probable carbon stars into 12 distinct self-similar spectral groupings. Continuum temperatures are assigned and range from 470 to 5000 K. Three distinct dust species are identifiable: SiC, alpha:C-H, and MgS. In addition to the narrow 11 + micron emission feature that is commonly attributed to SiC, a broad 11 + micron emission feature, that is correlated with the 8.5 and 7.7 micron features, is found and attributed to alpha:C-H. SiC and alpha:C-H band strengths are found to correlate with the temperature progression among the Classes. We find a spectral sequence of Classes that reflects the carbon star evolutionary sequence of spectral types, or alternatively developmental sequences of grain condensation in carbon-rich circumstellar shells. If decreasing temperature corresponds to increasing evolution, then decreasing temperature corresponds to increasing C/O resulting in increasing amounts of carbon rich dust, namely alpha:C-H. If decreasing the temperature corresponds to a grain condensation sequence, then heterogeneous, or induced nucleation scenarios are supported. SiC grains precede alpha:C-H and form the nuclei for the condensation of the latter material. At still lower temperatures, MgS appears to be quite prevalent. No 11.3 micron PAH features are identified in any of the 718 carbon stars. However, one of the coldest objects, IRAS 15048-5702, and a few others, displays an 11.9 micron emission feature characteristic of laboratory samples of coronene. That feature corresponds to the C-H out of plane deformation mode of aromatic hydrocarbon. This band indicates the presence of unsaturated, sp(sup 3), hydrocarbon bonds that may subsequently evolve into saturated bonds, sp(sup 2), if, and when, the star enters the planetary nebulae phase of stellar evolution. The effusion of hydrogen from the hydrocarbon grain results in the evolution in wavelength of this 11.9 micron emission feature to the 11.3 micron feature
Landscape of solutions in constraint satisfaction problems
We present a theoretical framework for characterizing the geometrical
properties of the space of solutions in constraint satisfaction problems,
together with practical algorithms for studying this structure on particular
instances. We apply our method to the coloring problem, for which we obtain the
total number of solutions and analyze in detail the distribution of distances
between solutions.Comment: 4 pages, 4 figures. Replaced with published versio
Performance of an environmental test to detect Mycobacterium bovis infection in badger social groups
A study by Courtenay and others (2006) demonstrated that
the probability of detecting Mycobacterium bovis by PCR in
soil samples from the spoil heaps of main badger setts correlated
with the prevalence of excretion (infectiousness) of
captured badgers belonging to the social group. It has been
proposed that such a test could be used to target badger culling
to setts containing infectious animals (Anon 2007). This
short communication discusses the issues surrounding this
concept, with the intention of dispelling any misconceptions
among relevant stakeholders (farmers, policy makers and
conservationists)
Smoking and quitting behaviour by sexual orientation: a cross-sectional survey of adults in England
Objective:
To assess associations between sexual orientation and smoking and quitting behaviour among adults in England.
Methods:
Data were collected from 112,537 adults (≥16y) participating in a nationally-representative monthly cross-sectional survey between 07/2013 and 02/2019. Sexual orientation was self-reported as heterosexual, bisexual, lesbian/gay, or prefer-not-to-say. Main outcomes were smoking status, e-cigarette use, cigarettes per day, time to first cigarette, motivation to stop smoking, motives for quitting, use of cessation support, and past‐year quit attempts. Associations were analysed separately for men and women using multivariable regression models adjusted for relevant covariates.
Results:
Smoking prevalence is now similar between gay (21.6%), prefer-not-to-say (20.5%) and heterosexual men (20.0%), and lesbian (18.3%) and heterosexual women (16.9%), but remains higher among bisexual men (28.2%, ORadj 1.41, 95%CI 1.11; 1.79) and bisexual women (29.8%, ORadj 1.64, 95%CI 1.33; 2.03) and lower among prefer-not-to-say women (14.5%, ORadj 0.85, 95%CI 0.72; 0.99). Among smokers, bisexuals were less addicted than heterosexuals, with bisexual men smoking fewer cigarettes per day (Badj -2.41, 95%CI -4.06; -0.75) and bisexual women less likely to start smoking within 30 minutes of waking (ORadj 0.66, 95% CI0.45; 0.95) than heterosexuals. However, motivation to stop smoking and quit attempts did not differ significantly.
Conclusions:
In England, differences in smoking prevalence among people with different sexual orientations have narrowed, primarily driven by a larger decline in smoking rates among sexual minority groups than heterosexuals. Bisexual men and women remain more likely to smoke but have lower levels of addiction while being no less likely to try to quit
NASA space station automation: AI-based technology review. Executive summary
Research and Development projects in automation technology for the Space Station are described. Artificial Intelligence (AI) based technologies are planned to enhance crew safety through reduced need for EVA, increase crew productivity through the reduction of routine operations, increase space station autonomy, and augment space station capability through the use of teleoperation and robotics
Exhaustive enumeration unveils clustering and freezing in random 3-SAT
We study geometrical properties of the complete set of solutions of the
random 3-satisfiability problem. We show that even for moderate system sizes
the number of clusters corresponds surprisingly well with the theoretic
asymptotic prediction. We locate the freezing transition in the space of
solutions which has been conjectured to be relevant in explaining the onset of
computational hardness in random constraint satisfaction problems.Comment: 4 pages, 3 figure
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