scholarly journals Graphite Grains and Graphite-Core-Ice-Mantle Grains

1965 ◽  
Vol 7 ◽  
pp. 167-184
Author(s):  
N. C. Wickramasinghe
Keyword(s):  
Ad Hoc ◽  
Narrow Range ◽  
Interstellar Extinction ◽  
Characteristic Size ◽  
Size Parameter ◽  
Grain Sizes ◽  
Desirable Feature ◽  
The Galaxy ◽  
The Mean ◽  
Grain Model

Among the First Requirements for a Grain Model is that it should explain the observed interstellar extinction law or laws as they are now understood; a desirable feature of such a model is that as few ad hoc assumptions be made as possible.A criticism of the classical ice grain theory is that a very narrow range of grain sizes (or a size distribution with a size parameter specified to within a few percent) must be postulated in order to obtain a fit with the mean extinction law. (See refs. 1 and 2.) While it is true that regional variations in the extinction law have recently been detected (refs. 3 and 4), the best available evidence indicates that the extinction law is quite uniform when averaged over individual large regions which are widely distributed in the galaxy. (See ref. 5 and paper by Nandy in the present compilation.) The restriction of particle size to a radius within a few percent of an arbitrarily specified value (r ≈ 3 X 10-5 cm) demanded on the basis of pure ice absorption is therefore considered quite unsatis-factory, particularly in view of the fact that no characteristic size parameter emerges from the Oort-van de Hulst theory for the formation and destruction of grains. (See ref. 6.)

scholarly journals Analysis of Interstellar Extinction towards the Hypergiant Cyg OB2 No. 12

2016 ◽  
Vol 25 (1) ◽  
Author(s):  
O. V. Maryeva ◽  
E. L. Chentsov ◽  
V. P. Goranskij ◽  
S. V. Karpov
Keyword(s):  
Interstellar Extinction ◽  
Stellar Association ◽  
The Galaxy ◽  
The Mean

AbstractThe Cyg OB2 stellar association hosts an entire zoo of unique objects, and among them – an enigmatic star Cyg OB2 No. 12 (Schulte 12, MT 304). MT 304 is enigmatic not only due to its highest luminosity (according to various estimates, it is one of the brightest stars in the Galaxy), but also because its reddening is anomalously large, greater than the mean reddening in the association. To explain the nature of anomalous reddening (

A discussion on infared astronomy - Expected infrared spectra of gaseous nebulae

1969 ◽  
Vol 264 (1150) ◽  
pp. 241-247 ◽  
Keyword(s):  
Infrared Spectra ◽  
Galactic Plane ◽  
Interstellar Extinction ◽  
Mount Everest ◽  
Gaseous Nebulae ◽  
The Galaxy ◽  
The Mean ◽  
Spiral Arm

If we are asked why we want to use the infrared to observe gaseous nebulae, we might reply with George Mallory, who was asked why he wanted to climb Mount Everest, ‘Because its there’. More specifically, one reason is the very great space penetration possible in the infrared. Diffuse nebulae characteristically are close to the galactic plane, and interstellar extinction therefore prevents the observation of distant objects. At MATHS FORMULA the mean range to which diffuse nebulae can easily be observed is about 1500 parsecs (pc), while many of these nebulae are so reddened as to be nearly unobservable at Hβ. It is for this reason that at present the observation of diffuse nebulae is almost entirely limited to our own spiral arm and its immediate neighbours. However, because of the decrease of interstellar extinction to longer wavelengths, at 1 μm the range of observation would be about 3000 pc; at 2 μm about 10 000 pc, comparable with the distance to the centre of the Galaxy; and at 10μm, about 100 000 pc, far larger than the diameter of the Galaxy. (The form of the interstellar reddening curve is from Whitford 1958.)

scholarly journals Interstellar Extinction in the Magellanic Clouds

1984 ◽  
Vol 108 ◽  
pp. 341-351
Author(s):  
K. Nandy
Keyword(s):  
Interstellar Dust ◽  
Interstellar Extinction ◽  
Magellanic Clouds ◽  
Absorption Feature ◽  
Early Type ◽  
Distribution Law ◽  
Broad Absorption ◽  
Grain Sizes ◽  
The Galaxy ◽  
The Difference

The extinction properties of interstellar dust in the Large and Small Magellanic Clouds have been systematically investigated, using recent UV observations of early type Cloud members along with complementary visible data. The extinction curves differ systematically from the standard Galactic curve. The latter shows a broad absorption feature centred near 2200Å in virtually all sight lines but this is absent or only weakly present in the SMC; also the SMC extinction in the far UV is the largest known relative to EB-V. Dust in the LMC appears to be intermediate in extinction properties between the SMC and normal Galactic material. However, exceptions from the average extinction curves have been found in both Clouds.Model computations show that the range of grain sizes and their number distribution law may not be significantly different in the Clouds and the Galaxy; the difference in extinction laws can be accounted for by varying the graphite contribution relative to silicate.

SOME FEATURES OF THE EQUILIBRIUM COASTAL PROFILE FOR DIFFERENT INITIAL BED SLOPES BASED ON MODELLING STUDY

2017 ◽  
Author(s):  
Dmitry Korzinin ◽  
Dmitry Korzinin ◽  
Igor Leontiev ◽  
Igor Leontiev
Keyword(s):  
Time Scales ◽  
Wave Impact ◽  
Grain Sizes ◽  
Equilibrium Profiles ◽  
Equilibrium Profile ◽  
The Mean ◽  
Wave Conditions ◽  
Bed Slope ◽  
Coastal Profile ◽  
Modelling Study

Modelling study of the equilibrium profiles formed on sandy coasts of different bed slopes and grain sizes under the various wave conditions was realized by using the CROSS-P and Xbeach morphodynamic models. A special criterion taking into account a total volume of bed deformations per one hour was suggested to determine the conditions of profile stabilization. For both models the time scales of equilibrium profile formation were found to be the same. However, the deformation magnitudes differed significantly. Bed deformations were computed on the whole profile length over the 200-hours duration of wave impact. It was concluded that both models predict a trend of the bed slope toward a stable value. CROSS-P model shows the widening of accumulative terrace during the profile evolution. The mean slope of the equilibrium profile was found to depend on the initial bed slope.

Solid, slightly soluble phosphorus compounds as nutrient source in activated sludge treatment of forest industry wastewaters

1997 ◽  
Vol 35 (2-3) ◽  
pp. 131-138 ◽  
Author(s):  
Pirjo-Riitta Rantala ◽  
Hannu Wirola
Keyword(s):  
Activated Sludge ◽  
The Other ◽  
Phosphorus Compounds ◽  
Forest Industry ◽  
Phosphorus Concentration ◽  
Nutrient Source ◽  
Sludge Treatment ◽  
Grain Sizes ◽  
Soluble Phosphorus ◽  
The Mean

The aim of the study was to determine if solid, slightly soluble compounds can be used as nutrient source in activated sludge treatment plants instead of liquid phosphoric acid. Four different solid materials were tested in lab-scale solubility tests to find compounds which are least soluble. Two materials were chosen for further studies: apatite and raw phosphate. The use of apatite and raw phosphate as nutrient source was studied in lab-scale activated sludge reactors along with a control reactor where phosphorus was added in liquid form. The phosphorus dosage, measured as elementary phosphorus, was the same for all three reactors. The reactors were fed with pre-clarified chemi-thermomechanical pulp mill (CTMP) wastewater. There were no significant differences in the reductions of organic matter between the three reactors. The mean effluent concentration of total phosphorus was 3 mg P/l in the control reactor and less than 1 mg P/1 in the other two reactors. The soluble phosphorus concentration was more than 2 mg P/l in the control reactor and less than 0.5 mg P/l in the other two. Apatite was an even better nutrient source than raw phosphate. Further lab-scale tests were conducted using two different grain sizes of apatite. No significant differences were found between the studied grain sizes (<0.074 mm and 0.074 mm-0.125 mm). Apatite was then used in full-scale at a CTMP-mill two different times. The experiments showed that the mean concentrations of phosphorus can be reduced radically by using apatite as a nutrient source instead of liquid phosphorus. Solid phosphorus compounds are a viable alternative to reduce the phosphorus load from forest industry wastewater treatment plants.

scholarly journals Technical note: Inherent benchmark or not? Comparing Nash–Sutcliffe and Kling–Gupta efficiency scores

2019 ◽  
Vol 23 (10) ◽  
pp. 4323-4331 ◽  
Author(s):  
Wouter J. M. Knoben ◽  
Jim E. Freer ◽  
Ross A. Woods
Keyword(s):  
Time Series ◽  
Coefficient Of Variation ◽  
Ad Hoc ◽  
Model Performance ◽  
Technical Note ◽  
Mean Flow ◽  
Model Adequacy ◽  
Robust Model ◽  
The Mean ◽  
Adequacy Assessment

Abstract. A traditional metric used in hydrology to summarize model performance is the Nash–Sutcliffe efficiency (NSE). Increasingly an alternative metric, the Kling–Gupta efficiency (KGE), is used instead. When NSE is used, NSE = 0 corresponds to using the mean flow as a benchmark predictor. The same reasoning is applied in various studies that use KGE as a metric: negative KGE values are viewed as bad model performance, and only positive values are seen as good model performance. Here we show that using the mean flow as a predictor does not result in KGE = 0, but instead KGE =1-√2≈-0.41. Thus, KGE values greater than −0.41 indicate that a model improves upon the mean flow benchmark – even if the model's KGE value is negative. NSE and KGE values cannot be directly compared, because their relationship is non-unique and depends in part on the coefficient of variation of the observed time series. Therefore, modellers who use the KGE metric should not let their understanding of NSE values guide them in interpreting KGE values and instead develop new understanding based on the constitutive parts of the KGE metric and the explicit use of benchmark values to compare KGE scores against. More generally, a strong case can be made for moving away from ad hoc use of aggregated efficiency metrics and towards a framework based on purpose-dependent evaluation metrics and benchmarks that allows for more robust model adequacy assessment.

scholarly journals How Does the Cause of Infantile Hemiparesis Influence Other Conditioning Factors? A Preliminary Study in a Spanish Population

Children ◽  
2021 ◽  
Vol 8 (5) ◽  
pp. 323
Author(s):  
Rocío Palomo-Carrión ◽  
Rita Pilar Romero-Galisteo ◽  
Helena Romay-Barrero ◽  
Inés Martínez-Galán ◽  
Cristina Lirio-Romero ◽  
...  
Keyword(s):  
Ad Hoc ◽  
Cross Sectional Study ◽  
Motor Dysfunction ◽  
Sensory Loss ◽  
Speech Impairments ◽  
Cross Sectional ◽  
Conditioning Factors ◽  
Age Of Diagnosis ◽  
The Mean ◽  
Preliminary Study

Infantile hemiparesis may be associated with significant morbidity and may have a profound impact on a child’s physical and social development. Infantile hemiparesis is associated with motor dysfunction as well as additional neurologic impairments, including sensory loss, mental retardation, epilepsy, and vision, hearing, or speech impairments. The objective of this study was to analyze the association between the cause of infantile hemiparesis and birth (gestational age), age of diagnosis, and associated disorders present in children with infantile hemiparesis aged 0 to 3 years. An observational and cross-sectional study was performed. A simple and anonymous questionnaire was created ad hoc for parents of children diagnosed with infantile hemiparesis aged between 0 and 3 years about the situation regarding the diagnosis of hemiparesis, birth, cause of hemiparesis, and presence of other associated disorders. Perinatal stroke (60.1%) was the most common cause of hemiparesis, and the most typical associated disorder was epilepsy (34.2%), with the second largest percentage in this dimension corresponding to an absence of associated disorders (20.7%). The most frequent birth was “no premature” (74.1%). The mean age of diagnosis of infantile hemiparesis was registered at 8 months (IQR: 0–36). Knowing the possible association between different conditioning factors and the cause of infantile hemiparesis facilitates the prevention of severe sequelae in children and family, implementing an early comprehensive therapeutic approach in children with infantile hemiparesis.

scholarly journals Nautilus multi-grain model: Importance of cosmic-ray-induced desorption in determining the chemical abundances in the ISM

2018 ◽  
Vol 615 ◽  
pp. A20 ◽  
Author(s):  
Wasim Iqbal ◽  
Valentine Wakelam
Keyword(s):  
Grain Size ◽  
Surface Temperature ◽  
Gas Phase ◽  
Numerical Models ◽  
Cosmic Ray ◽  
Grain Sizes ◽  
Small Grains ◽  
Grain Model ◽  
Grain Surface ◽  
The Impact

Context. Species abundances in the interstellar medium (ISM) strongly depend on the chemistry occurring at the surfaces of the dust grains. To describe the complexity of the chemistry, various numerical models have been constructed. In most of these models, the grains are described by a single size of 0.1 μm. Aims. We study the impact on the abundances of many species observed in the cold cores by considering several grain sizes in the Nautilus multi-grain model. Methods. We used grain sizes with radii in the range of 0.005 μm to 0.25 μm. We sampled this range in many bins. We used the previously published, MRN and WD grain size distributions to calculate the number density of grains in each bin. Other parameters such as the grain surface temperature or the cosmic-ray-induced desorption rates also vary with grain sizes. Results. We present the abundances of various molecules in the gas phase and also on the dust surface at different time intervals during the simulation. We present a comparative study of results obtained using the single grain and the multi-grain models. We also compare our results with the observed abundances in TMC-1 and L134N clouds. Conclusions. We show that the grain size, the grain size dependent surface temperature and the peak surface temperature induced by cosmic ray collisions, play key roles in determining the ice and the gas phase abundances of various molecules. We also show that the differences between the MRN and the WD models are crucial for better fitting the observed abundances in different regions in the ISM. We show that the small grains play a very important role in the enrichment of the gas phase with the species which are mainly formed on the grain surface, as non-thermal desorption induced by collisions of cosmic ray particles is very efficient on the small grains.

scholarly journals Determination of cervical stenosis in rugby players using an alternative radiographic method

2018 ◽  
Vol 4 (1) ◽  
pp. e000411
Author(s):  
Gustavo C Bornholdt ◽  
Bruno Siqueira Campos Lopes ◽  
Pedro Francisco Senne Paz ◽  
Arnaldo José Hernandez ◽  
André Pedrinelli
Keyword(s):  
Cervical Canal ◽  
Cervical Stenosis ◽  
Size Parameter ◽  
Cervical Injury ◽  
Radiographic Method ◽  
Institutional Review ◽  
Vertebral Bodies ◽  
The Mean ◽  
Rugby Players

PurposeTo find a radiographic method that best correlates with the mean subaxial cervical space available for the cord (MSCSAC) by using a fixed size parameter as radiographic reference, in contrast to the use of vertebral bodies as reference in the mean subaxial cervical Torg ratio (MTorg).MethodsThe study was approved by an institutional review board and written informed consent was obtained. Radiographs and cervical neck MRI were obtained from 18 male rugby athletes (age 18–30 years). Rheumatic disease, symptomatic cervical orthopaedic disease and previous cervical injury were used as exclusion criteria. MSCSAC and MTorg were calculated for each individual as the space available for the cord and Torg ratio averages from C3 to C6, respectively. A new radiographic method, using a metal bar as a size parameter (the corrected diameter of the cervical canal - CDCC), was also calculated for each individual, as well as its average from C3 to C6 (mean corrected diameter of the cervical canal - MCDCC). Values obtained for MCDCC and MTorg were correlated with those obtained by the MSCSAC using Pearson’s coefficient.ResultsFour volunteers were excluded due to previous cervical injury. In total, 14 subjects had their radiographs and MRIs analysed. Pearson’s correlation between MSCSAC and MTorg was 0.5706 (p=0.033). The correlation between MSCSAC and MCDCC was 0.6903 (p=0.006).ConclusionMCDCC correlates better than MTorg with MSCSAC and may be a better radiographic option than MTorg for cervical stenosis evaluation.

Elaboration, Structure and Mössbauer Spectroscopy of Nanostructured Fe100−xSix Powders Elaborated by Mechanical Alloying

SPIN ◽  
2017 ◽  
Vol 07 (02) ◽  
pp. 1750002 ◽  
Author(s):  
M. Hemmous ◽  
A. Guittoum
Keyword(s):  
Magnetic Field ◽  
Solid Solution ◽  
Mechanical Alloying ◽  
Hyperfine Magnetic Field ◽  
Lattice Parameter ◽  
X Ray Diffraction ◽  
X Ray ◽  
Grain Sizes ◽  
The Mean ◽  
Xrd Studies

We have studied the effect of the silicon concentration on the structural and hyperfine properties of nanostructured Fe[Formula: see text]Six powders ([Formula: see text], 20, 25 and 30[Formula: see text]at.%) prepared by mechanical alloying. The X-ray diffraction (XRD) studies indicated that after 72[Formula: see text]h of milling, the solid solution bcc-[Formula: see text]-Fe(Si) is formed. The grain sizes, [Formula: see text]D[Formula: see text] (nm), decreases with increasing Si concentration and reaches a minimum value of 11[Formula: see text]nm. We have found that the lattice parameter decreases with increasing Si concentration. The changes in values are attributed to the substitutional dissolution of Si in Fe matrix. From the adjustment of Mössbauer spectra, we have shown that the mean hyperfine magnetic field, [Formula: see text]H[Formula: see text] (T), decreases with increasing Si concentration. The substitutional dependence of [Formula: see text]H[Formula: see text] (T) can be attributed to the effect of p electrons Si influencing electrons d of Fe.

Sign in / Sign up

Export Citation Format

Share Document