scholarly journals X. Bakerian lecture.—The structure and opacity of a stellar atmosphere

1929 ◽  
Vol 228 (659-669) ◽  
pp. 421-461 ◽  
Keyword(s):  
Chemical Composition ◽  
Radiation Pressure ◽  
Thermal Characteristics ◽  
Stellar Atmosphere ◽  
Mean Value ◽  
Abstract Problem ◽  
Net Flux ◽  
The Mean ◽  
Flash Spectrum ◽  
Two Parameters

The general problem .—“Stellar atmosphere" is the name given loosely to the outer portions of a star. The stellar atmosphere is divided observationally into three superincumbent layers, named the photospheric layers, the reversing layer and the chromosphere, in order of increasing level. The boundaries between these are only roughly defined, but broadly speaking the photospheric layers give rise to the continuous spectrum of the star, the reversing layer to the absorption-line spectrum and the chromosphere (when seen edgeways) to the flash spectrum. Mathematical analysis of the way in which gaseous material comprising the outer portions of a star may be expected to thin out into space confirms this threefold division. It also brings to light certain dynamical and thermal characteristics of the three layers. For example a definite temperature gradient in the photospheric layers shades off into an approximately isothermal state in the chromosphere; “local thermodynamic equilibrium” in the photospheric layers shades off into “monochromatic radiative equilibrium” in the upper chromosphere; and a somewhat unimportant general radiation pressure in the photospheric layers augments to a strong selective radiation-pressure in the reversing layer and chromosphere. The reversing layer is in most cases the transition layer. Assumptions valid for either photospheric layers or chromosphere separately cease to be so near their upper and lower boundaries respectively and so far it has not been possible to give a treatment which accurately deals with the regions of transition. In the present lecture it is proposed to consider chiefly the photospheric layers and the reversing layer. For these regions the dominant need is the determination of the general opacity—the fogginess—for this determines the depth we see into the star and so the pressures, densities, etc., at which the observed spectral phenomena originate. The abstract problem of the stellar atmosphere may be stated as follows. For many purposes the curvature of the outer regions of a star may be neglected and we consider only material stratified in parallel planes. The material is subject to ( a ) a gravitational field of acceleration g , ( b ) a net flux of energy of amount πF per unit area, incident on it from below and emergent into space above. This is determined by the evolution of energy in the interior of the star. The amount of energy actually incident on the atmospheric layers from below exceeds π F, but a portion is re-radiated downwards by the atmospheric layers, π F being the net amount passing through. If the atmospheric layers are in a steady state there is no accumulation of energy, and the net amount of energy crossing any surface of stratification is equal to that crossing any parallel surface, namely π F. The quantity F itself is the mean value of the emergent intensity of radiation at any point, or, what is the same thing, the mean intensity of radiation over the stellar disc. The abstract problem is:— Given the two parameters g and F, and given also the ultimate chemical composition of the material, to determine the distribution of temperature, pressure, density, ionization and chemical composition in the layers, and to determine also the complete intensity-distribution both in angle and in frequency, of the emergent radiation. The practical problem is to some extent the converse one of inferring the temperature and other physical quantities from the observed emergent radiation, i.e ., from the observed spectra, measured if possible spectro-photometrically. In many cases we do not know either g or F, and these also may have to be determined from the observed spectra.

scholarly journals Modern quantitative microstructure analysis on the example of aicu5mg1 alloys

2002 ◽  
pp. 109-114
Author(s):  
Biljana Zlaticanin ◽  
Branislav Radonjic ◽  
Branka Jordovic
Keyword(s):  
Grain Size ◽  
Chemical Composition ◽  
Linear Method ◽  
Titanium Content ◽  
Mean Value ◽  
Grain Refining ◽  
Relative Standard ◽  
Method Of Measurement ◽  
The Mean ◽  
Picture Analysis

Using an automatic, QUANTIMET 500 MC, device for quantitative picture analysis and applying linear method of measurement on the example of AlCu5Mg1 alloys, the grain size (min, max and medium values), as well as relative standard measuring errors (RSE), dendrite arm spacing (DAS) and length eutectic (Le) and also distribution by size (histogram) and volume participation of ?-hard solution and eutectic have been determined. We have also studied the influence of grain-refining additives AlTi5B1 for the same chemical composition of the aluminium-capper-magnesium alloy. It has been concluded that with the increase of titanium content, the mean value of grain size decreases. We have also examined hardness and pressure strength.

Variations of ventilation and diffusing capacity to perfusion determining the alveolar-arterial O2 difference: theory

1961 ◽  
Vol 16 (3) ◽  
pp. 507-510 ◽  
Author(s):  
Johannes Piiper
Keyword(s):  
Venous Blood ◽  
Mean Value ◽  
Alveolar Ventilation ◽  
Mixed Venous Blood ◽  
Pulmonary Perfusion ◽  
Diffusing Capacity ◽  
Unequal Distribution ◽  
The Mean ◽  
Two Parameters ◽  
Mixed Venous

The factors determining the alveolar-arterial O2 pressure difference, AaD, have been theoretically reinvestigated, taking into account the effect of unequal distribution of pulmonary diffusing capacity, D, to pulmonary perfusion, Q. It is shown that, for a given inspired gas and a given mixed venous blood, the AaD is determined by two parameters, the ratios diffusing capacity :perfusion, D/Q, and alveolar ventilation :perfusion, Va/Q. Two characteristics of both of these ratios, the mean value and the variation, affect the AaD. Submitted on May 23, 1960

Studies on Centrifugal Clutch of Frictional Lining Materials

2015 ◽  
Vol 642 ◽  
pp. 39-44
Author(s):  
Tse Chang Li ◽  
Yu Wen Huang ◽  
Jen Fin Lin
Keyword(s):  
Contact Pressure ◽  
Pressure Ratio ◽  
Mean Value ◽  
Frictional Torque ◽  
Sliding Velocity ◽  
Mean Values ◽  
The Mean ◽  
Two Parameters ◽  
Maximum Contact ◽  
Static Torque

Using the Taguchi method, a 5-factorial, 3-level orthogonal array (L’18 (35)) was used as the experimental layout for 18 kinds of frictional lining specimen. These specimens were prepared in order to investigate their performance in establish a relationship between Ts/Td (Ts: static torque; Td: dynamic torque) and dμ/dνx (μ: friction coefficient; νx: relative velocity of frictional lining and clutch drum) parameters. The frictional torque and the rotational speeds of the driveline, clutch, and clutch drum as functions of contact time for 100 clutch cycles are experimentally obtained dμ/dνx and Ts/Td. In the study, a sharp rise in maximum contact pressure ratio occurred when the relative sliding velocity reached the critical velocity, Vc. This increase in maximum contact pressure ratio generally led to an increase of the (initially negative) dμ/dνx value. The mean values of dμ/dνx and Ts/Td for the clutching tests with 100 cycles can be roughly divided into three groups dependent on the fluctuation intensities of these two parameters, for each of which there is a linear relationship. The maximum contact pressure ratio significantly increases even increasing the mean value of dμ/dνx.

The effect of phosphorus, potassium, and calcium on the growth, chemical composition, and symptoms of deficiency of white clover in a subtropical environment

1960 ◽  
Vol 11 (2) ◽  
pp. 149 ◽  
Author(s):  
CS Andrew
Keyword(s):  
Calcium Carbonate ◽  
Chemical Composition ◽  
Potassium Chloride ◽  
Sodium Phosphate ◽  
Nutrient Content ◽  
Mean Value ◽  
Flowering Stage ◽  
Visual Symptoms ◽  
The Mean ◽  
Subtropical Environment

The effect of the rates of application of sodium phosphate, potassium chloride, and calcium carbonate on growth, chemical composition, and visual symptoms of deficiency in Trifolium repens var. Irrigation White, grown in a low humic gley soil under subtropical conditions in Queensland, has been investigated. The surface soil is grossly deficient in phosphorus, potassium, and calcium and consists almost entirely of sand (92 per cent.). Additions of sodium phosphate, potassium chloride, and calcium carbonate each increased the yield of clover, increased the phosphorus, potassium, and calcium contents respectively, and conditioned the uptake of other nutrients. Plant material for chemical analyses consisted of petioles and leaves (less senescent and expanding leaves), harvested at the immediate pre-flowering stage of growth. Critical percentages for phosphorus, potassium, and calcium under these conditions were established at 0.23, 1.1, and 1.0 per cent. respectively. Visual symptoms of phosphorus, potassium, and calcium deficiencies are discussed in relation to yield and nutrient content. The sum of the equivalents of potassium, calcium, and magnesium is approximately constant. The mean value of 18 analyses covering all treatments was 136 m-equiv. per cent. with a range of 116-148.

scholarly journals Integration of Expectation Maximization using Gaussian Mixture Models and Naïve Bayes for Intrusion Detection

2021 ◽  
Vol 3 (2) ◽  
Author(s):  
Loka Raj Ghimire ◽  
Roshan Chitrakar(PHD)
Keyword(s):  
Intrusion Detection ◽  
Gaussian Mixture Models ◽  
Gaussian Mixture ◽  
Mean Value ◽  
Major Drawback ◽  
Malicious Behavior ◽  
Cluster Data ◽  
The Mean ◽  
Single Data ◽  
Two Parameters

Intrusion detection is the investigation process of information about the system activities or its data to detect any malicious behavior or unauthorized activity. Most of the IDS implements K-means clustering technique due to its linear complexity and fast computing ability. Nonetheless, it is Naïve use of the mean data value for the cluster core that presents a major drawback. The chances of two circular clusters having different radius and centering at the same mean the occur.  This condition cannot be addressed by the K-means algorithm because the mean value of the various clusters is very similar together. However, if the clusters are not spherical, it fails.  To overcome this issue, a new integrated hybrid model by integrating expectation maximizing (EM) clustering using Gaussian mixture model (GMM) and naïve Bays classifier have been proposed. In this model, GMM give more flexibility than K-Means in terms of cluster covariance. Also, they use probabilities function and soft clustering, that’s why they can have multiple cluster for a single data. In GMM, we can define the cluster form in GMM by two parameters: the mean and the standard deviation. This means that by using these two parameters, the cluster can take any kind of elliptical shape. EM-GMM will be used to cluster data based on data activity into the corresponding category.

scholarly journals Statistical properties of the telephone network

2019 ◽  
Keyword(s):  
Lognormal Distribution ◽  
Distribution Density ◽  
Dynamic Network ◽  
Mean Value ◽  
Statistical Properties ◽  
Telephone Network ◽  
Directed Network ◽  
The Subject ◽  
The Mean ◽  
Two Parameters

The directed network of telephone subscribers is considered in the article. It can be described as a dynamic network with vertices that correspond to the subscribers of the telephone network and emerging directional edges that correspond to the connections between the respective subscribers. The position of the edge and its direction is determined by the incoming and outgoing calls from the corresponding vertices. The subject of the article is the statistical properties of the connections of a certain subset of telephone network subscribers. Such connections are dynamic in nature due to their appearance and disappearance. The number of outgoing (or incoming) connections occurred during a day at a selected vertex is used as the main characteristic. The distribution density of the number of outgoing (or incoming) connections (or calls) of such a network has been analyzed using the experimental data. It has been shown that such a distribution density over the number of calls obeys the lognormal distribution density, which depends on the two parameters. The values of two parameters, namely the mean value and the variance, determining the lognormal distribution density are established. The reasons for the appearance of a lognormal distribution density over the number of incoming (or outgoing) connections have been discussed. The statistical properties of other groups of subscribers have been considered as well. In particular, the group that makes a large number of outgoing calls to various subscribers of the telephone network has been selected for a separate study. The members of this group, who create and distribute spam can be called spammers. It has been shown that these groups, spammers for example, also obeys the lognormal distribution density over the number of calls but they are characterized by the different mean value and variance.

Photo-electric Hβ and uvby photometry

1966 ◽  
Vol 24 ◽  
pp. 170-180
Author(s):  
D. L. Crawford
Keyword(s):  
Narrow Band ◽  
Line Strength ◽  
Interference Filter ◽  
B Stars ◽  
Relative Line ◽  
The Mean ◽  
F Stars ◽  
Two Parameters ◽  
Filter Photometry ◽  
The Continuum

Early in the 1950's Strömgren (1, 2, 3, 4, 5) introduced medium to narrow-band interference filter photometry at the McDonald Observatory. He used six interference filters to obtain two parameters of astrophysical interest. These parameters he calledlandc, for line and continuum hydrogen absorption. The first measured empirically the absorption line strength of Hβby means of a filter of half width 35Å centered on Hβand compared to the mean of two filters situated in the continuum near Hβ. The second index measured empirically the Balmer discontinuity by means of a filter situated below the Balmer discontinuity and two above it. He showed that these two indices could accurately predict the spectral type and luminosity of both B stars and A and F stars. He later derived (6) an indexmfrom the same filters. This index was a measure of the relative line blanketing near 4100Å compared to two filters above 4500Å. These three indices confirmed earlier work by many people, including Lindblad and Becker. References to this earlier work and to the systems discussed today can be found in Strömgren's article inBasic Astronomical Data(7).

Long-period modulated superstructures in Pd-12.5 at.%Ce and Pd-15 at.%Ce alloys

1990 ◽  
Vol 48 (4) ◽  
pp. 164-165
Author(s):  
Noriyuki Kuwano ◽  
Masaru Itakura ◽  
Kensuke Oki
Keyword(s):  
Electron Microscopy ◽  
Mean Value ◽  
Heavy Elements ◽  
Arc Furnace ◽  
X Ray ◽  
Long Period ◽  
Ultra High Purity ◽  
Heat Treated ◽  
Atomic Scattering ◽  
The Mean

Pd-Ce alloys exhibit various anomalies in physical properties due to mixed valences of Ce, and the anomalies are thought to be strongly related with the crystal structures. Since Pd and Ce are both heavy elements, relative magnitudes of (fcc-fpd) are so small compared with <f> that superlattice reflections, even if any, sometimes cannot be detected in conventional x-ray powder patterns, where fee and fpd are atomic scattering factors of Ce and Pd, and <f> the mean value in the crystal. However, superlattices in Pd-Ce alloys can be analyzed by electron microscopy, thanks to the high detectability of electron diffraction. In this work, we investigated modulated superstructures in alloys with 12.5 and 15.0 at.%Ce.Ingots of Pd-Ce alloys were prepared in an arc furnace under atmosphere of ultra high purity argon. The disc specimens cut out from the ingots were heat-treated in vacuum and electrothinned to electron transparency by a jet method.

Partition Coefficient Ratios and Tumour Perfusion Studied with 85mKr and 133Xe

1987 ◽  
Vol 26 (06) ◽  
pp. 253-257
Author(s):  
M. Mäntylä ◽  
J. Perkkiö ◽  
J. Heikkonen
Keyword(s):  
Partition Coefficient ◽  
Partition Coefficients ◽  
Regional Blood Flow ◽  
Blood Perfusion ◽  
Compartmental Analysis ◽  
Malignant Tumour ◽  
Mean Value ◽  
Perfusion Rate ◽  
Biological Variables ◽  
The Mean

The relative partition coefficients of krypton and xenon, and the regional blood flow in 27 superficial malignant tumour nodules in 22 patients with diagnosed tumours were measured using the 85mKr- and 133Xe-clearance method. In order to minimize the effect of biological variables on the measurements the radionuclides were injected simultaneously into the tumour. The distribution of the radiotracers was assumed to be in equilibrium at the beginning of the experiment. The blood perfusion was calculated by fitting a two-exponential function to the measuring points. The mean value of the perfusion rate calculated from the xenon results was 13 ± 10 ml/(100 g-min) [range 3 to 38 ml/(100 g-min)] and from the krypton results 19 ± 11 ml/(100 g-min) [range 5 to 45 ml/(100 g-min)]. These values were obtained, if the partition coefficients are equal to one. The equations obtained by using compartmental analysis were used for the calculation of the relative partition coefficient of krypton and xenon. The partition coefficient of krypton was found to be slightly smaller than that of xenon, which may be due to its smaller molecular weight.

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