scholarly journals Carbon Stars and Interstellar Dust

1977 ◽  
Vol 45 ◽  
pp. 181-185
Author(s):  
Stanisław Krawczyk ◽  
Janina Krempeć ◽  
Janusz Gertner
Keyword(s):  
Thermal Radiation ◽  
Interstellar Dust ◽  
Carbonaceous Material ◽  
The Other ◽  
Major Constituent ◽  
Interstellar Matter ◽  
Carbon Stars ◽  
Intrinsic Polarization ◽  
Infrared Excess ◽  
Infrared Observations

Extensive recent infrared observations of carbon stars (Gillet et al. 1971, Hackwell 1972, Morrison and Simon 1973) have shown that spectra of some cool variable carbon stars reveal infrared excesses, which are believed to be due to thermal radiation of the dust envelopes surrounding these stars. Observations of the visual intrinsic polarization made by Dyck et al. (1971) have confirmed this discovery. The relation existing between stars loosing their mass and those revealing the infrared excess (Geisel 1970) gives evidence for the reality of mass loss from cool variable carbon stars. On the other hand, several investigations (Kamijo 1967, Donn et al. 1968, Salpeter 1974), although differing considerably in details, do agree that conditions in the atmospheres of cool carbon stars are appropriate for the condensation of carbon grains. Hence, it is believed that evolutionary advanced cool variable carbon stars supply carbonaceous material, mainly graphite, into the interstellar matter, in which carbon seems to be the major constituent (Donn et al. 1968).

Stable isotope measurements of meteorites and cosmic dust grains

1987 ◽  
Vol 323 (1572) ◽  
pp. 313-322 ◽  
Keyword(s):  
Stable Isotope ◽  
Solar System ◽  
Deep Sea ◽  
Interstellar Dust ◽  
Carbonaceous Material ◽  
Red Giants ◽  
Interstellar Matter ◽  
Evolved Stars ◽  
Isotopic Measurements ◽  
Isotope Measurements

Although it was well known that a high 13 C abundance was a common feature of the spectra of evolved stars, it took over 50 years to find evidence of carbonaceous instellar dust, which might have been ejected from such objects, in the Solar System. However, it is now established that dust probably produced in novae and red giants can be located in primitive meteorites and the latest state of knowledge in respect of such components is reviewed herein. Nitrogen isotopic measurements have been helpful in distinguishing another form of dust that is carbonaceous but does not have a distinctive 13 C abundance. Likewise they suggest a non-carbonaceous material (possibly a sulphide) present in the meteorite Bencubbin could be a relict of supernovae outbursts. None of the components seen in meteorites can be detected in deep-sea spheres or stratospheric grains to provide a link between interstellar matter and comets. Until now interstellar dust has been the realm of observing astronomers and theoretians; stable isotope measurements are responsible for recognizing a material which it should be possible to isolate and study in the laboratory.

Temporal variability of disinfection by-products concentration in urban public water system

2013 ◽  
Vol 14 (4) ◽  
pp. 393-398
Keyword(s):  
Drinking Water ◽  
Water Samples ◽  
Temporal Variability ◽  
Water System ◽  
The Other ◽  
Major Constituent ◽  
System P ◽  
Public Water System ◽  
Drinking Water Samples ◽  
By Products

The occurrence of trihalomethanes (THMs) was studied in the drinking water samples from urban water supply network of Karachi city that served more than 18 million people. Drinking water samples were collected from 58 locations in summer (May-August) and winter (November-February) seasons. The major constituent of THMs detected was chloroform in winter (92.34%) and summer (93.07%), while the other THMs determined at lower concentrations. Summer and winter concentrations of total THMs at places exceed the levels regulated by UEPA (80 μg l-1) and WHO (100 μg l-1). GIS linked temporal variability in two seasons showed significantly higher median concentration (2.5%-23.06%) of THMs compared to winter.

scholarly journals Optical/infrared observations of RV Tauri stars

1987 ◽  
Vol 122 ◽  
pp. 537-540
Author(s):  
M. J. Goldsmith ◽  
A. Evans ◽  
J. S. Albinson ◽  
M. F. Bode
Keyword(s):  
Dust Formation ◽  
Infrared Excess ◽  
Infrared Observations ◽  
Dust Shells ◽  
Discernible Difference

Optical/infrared observations of RV Tauri stars obtained at SAAO have allowed the natures of the dust shells around stars with infrared excess to be investigated. The data suggest that dust formation occurs sporadically and that some stars have multiple shells. There is no photometrically discernible difference between carbon- and oxygen-rich stars or their dust shells. There is some evidence that stars with higher metallicity have more dust.

scholarly journals On Newcomb's method of investigating periodicities and its application to Brückner's weather cycle

1914 ◽  
Vol 90 (619) ◽  
pp. 349-355
Keyword(s):  
Thermal Radiation ◽  
The Other ◽  
New Method ◽  
Critical Examination ◽  
Numerical Work ◽  
Average Value ◽  
Other Hand ◽  
Relationship Of ◽  
The Relationship ◽  
Great Simplicity

During the last few years of his life Prof. Simon Newcomb was keenly interested in the problem of periodicities, and devised a new method for their investigation. This method is explained, and to some extent applied, in a paper entitled "A Search for Fluctuations in the Sun's Thermal Radiation through their Influence on Terrestrial Temperature." The importance of the question justifies a critical examination of the relationship of the older methods to that of Newcomb, and though I do not agree with his contention that his process gives us more than can be obtained from Fourier's analysis, it has the advantage of great simplicity in its numerical work, and should prove useful in a certain, though I am afraid, very limited field. Let f ( t ) represent a function of a variable which we may take to be the time, and let the average value of the function be zero. Newcomb examines the sum of the series f ( t 1 ) f ( t 1 + τ) + f ( t 2 ) f ( t 2 + τ) + f ( t 3 ) f ( t 3 + τ) + ..., where t 1 , t 2 , etc., are definite values of the variable which are taken to lie at equal distances from each other. If the function be periodic so as to repeat itself after an interval τ, the products are all squares and each term is positive. If, on the other hand, the periodic time be 2τ, each product will be negative and the sum itself therefore negative. It is easy to see that if τ be varied continuously the sum of the series passes through maxima and minima, and the maxima will indicated the periodic time, or any of its multiples.

Physical a priori solar radiation pressure models for GNSS satellites with the focus on BDS

2021 ◽  
Author(s):  
Bingbing Duan ◽  
Urs Hugentobler ◽  
Inga Selmke ◽  
Stefan Marz
Keyword(s):  
Optical Properties ◽  
Solar Radiation ◽  
Thermal Radiation ◽  
Radiation Pressure ◽  
Total Mass ◽  
A Priori ◽  
Solar Radiation Pressure ◽  
The Other ◽  
Time Range ◽  
Satellite Attitude

<p>A physical a priori box-wing solar radiation pressure (SRP) model is widely used by most analysis centers for Galileo and QZSS (Quasi-Zenith Satellite System) satellites, complemented by an ECOM or ECOM2 (Empirical CODE Orbit Model) model. For the other constellations, for instance GPS and GLONASS satellites, optical properties of satellite surfaces are not publicly available, especially for GPS Block IIF and GLONASS satellites. By fixing satellite surface areas and total mass to the values from some unpublished documents, we estimate satellite surface optical properties based on true GNSS measurements covering long time periods (typically this should be longer than a full beta angle time range to reduce correlations between parameters). Meanwhile, various physical effects are considered, such as yaw bias, radiator emission and thermal radiation of solar panels. We find that yaw bias of GPS Block IIA and IIR satellites does not dominate the Y-bias, it is likely that heat generated in the satellite is radiated from louvers or heat pipes on the Y side of the satellite. It is also noted that the ECOM Y0 estimates of both GPS and GLONASS satellites show clear anomaly during eclipse seasons. This indicates that the radiator emission is present when the satellite crosses shadows. Since satellite attitude during eclipse seasons could be different from the nominal yaw, potential radiator effect in the –X surface could be wrongly absorbed by the ECOM Y0 as well. By considering all the estimated parameters in an a priori model we observe clear improvement in satellite orbits, especially for GLONASS satellites. China’s Beidou-3 satellites are now providing PNT (positioning, navigation and timing) service globally. Satellite attitude, dimensions and total mass are publicly available. Also, the absorption optical properties of each satellite surface are given. With all this information, we estimate the other optical properties of Beidou satellites considering similar yaw bias, radiator and thermal radiation effects as those in GPS and GLONASS satellites.</p>

On the capture of interstellar matter by stars

1940 ◽  
Vol 36 (3) ◽  
pp. 314-322 ◽  
Author(s):  
R. d'E. Atkinson
Keyword(s):  
Radial Velocity ◽  
The Other ◽  
Interstellar Matter ◽  
Centre Of Gravity ◽  
Compelling Reason ◽  
Other Hand ◽  
The Mean ◽  
The One ◽  
The Individual ◽  
Capture Radius

The derivation given by Hoyle and Lyttleton for an accretion formula proposed by them is examined. A number of arguments against its validity are put forward, especially that on the one hand their capture radius depends on the theorem that if the velocity of certain masses of gas after collision is less than the velocity of escape at the point, they will not in fact escape, while on the other hand it is clear (and is now admitted) that the gas cannot in fact move with this velocity at all. It is also shown that since, ex hypothesi, the individual molecules will all, on the average, retain their hyperbolic velocities, there is not the compelling reason for their capture that there appeared to be in Hoyle and Lyttleton's argument, where only the mean radial velocity of the centre of gravity of the mass was considered. Further, it seems improbable that the temperature of the interstellar matter can be low enough for the initial assumptions of their theory to hold.

scholarly journals Characterization of microbial aggregates in relation to membrane biofouling in submerged membrane bioreactors

2021 ◽  
Author(s):  
Heather Elizabeth Kraemer
Keyword(s):  
Laser Scanning ◽  
Extracellular Polymeric Substances ◽  
Municipal Wastewater ◽  
Pilot Scale ◽  
Membrane Bioreactors ◽  
Laser Scanning Microscopy ◽  
The Other ◽  
Major Constituent ◽  
Confocal Laser ◽  
Microbial Flocs

The purpose of this study was to characterize microbial aggregates and extracellular polymeric substances (EPS) that contribute to biofouling of submerged polymeric microfiltration membranes. Two issues were addressed in this study, (1) the influence operational and recovery cleanings of membranes have on biofouling amelioration and (2) the influence physicochemical properties of microbial flocs have on biofouling. The experiments in this study employed two pilot scale Zee Weed™ membrane bioreactors (MBRs). In one MBR, a ZW-I0 module was installed to treat secondary municipal wastewater at a sludge retention time (SRT) of30 days and operated under permeate/relaxation conditions. In the other MBR, two ZW -10 modules were installed to treat secondary municipal wastewater at an SRT of 12 days. One module operated under permeate/relaxation conditions, while the other operated under permeate/backwash conditions. Sludge samples from the MBRs were characterized by measuring the surface charge, hydrophobicity, and EPS composition of the microbial flocs. Membrane fibre samples were collected from each ZW -10 module during permeation and after recovery cleanings. The biofoulant on the membrane was analyzed using confocal laser scanning microscopy (CLSM) after simultaneous staining with the lectins concanavalin A (ConA), wheat germ agglutinin (WGA), and soybean agglutinin (SBA). The CLSM analysis of the membrane fibres sampled showed that the biofoulant on the membrane was composed of a heterogeneous colonization of microbes and EPS known to contain glucose, mannose, N -acetylglucosamine, and galactose. The dominant carbohydrate in the biofoulant was shown to be N -acetylglucosamine, which is part of both the cell wall of bacteria and the extracellular matrix. The reversible biofoulant was composed of individual cells, aggregates of cells, and EPS. The major constituent of the irreversible biofoulant was inferred to be EPS, which was observed as a fibrous network of material that remained adhered to the membrane after recovery cleaning the modules with a 2000 ppm hypochlorite solution. By using a permeate backwash rather than relaxation as an operational cleaning method, the rate of biofouling may be reduced. The rate of biofoulant accumulation on hydrophilic membranes may be reduced at higher SR Ts because the biomass at higher SR Ts has a higher hydrophobicity when compared to the biomass at lower SRTs.

scholarly journals Systematic study of AGB stars in the intermediate-age globular clusters in the Magellanic Clouds

1999 ◽  
Vol 191 ◽  
pp. 573-578
Author(s):  
T. Tanabé ◽  
S. Nishida ◽  
Y. Nakada ◽  
T. Onaka ◽  
I. S. Glass ◽  
...  
Keyword(s):  
Mass Loss ◽  
Globular Clusters ◽  
Near Infrared ◽  
Magellanic Clouds ◽  
Agb Stars ◽  
Carbon Stars ◽  
Infrared Observations ◽  
The Past ◽  
Intense Mass ◽  
Infrared Stars

We performed systematic infrared observations of the intermediate-age Magellanic Clouds clusters NGC 419, NGC 1783 and NGC 1978. Mid-infrared stars discovered in NGC 419 and NGC 1978 are very red and must be undergoing intense mass loss (comparable to superwinds). They are probably carbon stars but do not seem to show any FIR excesses. Three optically visible carbon stars as well as (at least) 2 near-infrared carbon stars observed with ISOPHOT show 60 μm excesses which may indicate mass loss in the past. It seems that the MIR stars are fainter than the AGB tip luminosity and that their Mbols are close to those of the transition luminosity from M type to C stars. Therefore, these MIR stars may not be in the final stage of the AGB phase. This may suggest that AGB stars lose mass heavily at some other time, possibly during the transition from M type to C stars.

Sign in / Sign up

Export Citation Format

Share Document