scholarly journals Period Changes of W Ursae Majoris Stars

1977 ◽  
Vol 42 ◽  
pp. 393-397 ◽  
Author(s):  
J.M. Kreiner
Keyword(s):  
Astronomical Observatory ◽  
List Type ◽  
Type Number ◽  
Mass Ratio ◽  
Absolute Change ◽  
Versus Parameter ◽  
The Mean ◽  
Short Time

About 6000 times of minima for 120 W Ursae Majoris stars were collected by Mrs. Z. Frasińska and the writer in the Cracow Astronomical Observatory. From this material 15 O - C diagrams (fig. 1) with large number of minima were taken into consideration. Each of them covered more than 30,000 epochs. The analysis of O - C curves leads to the following conclusions: 1. The periods of all well-observed W UMa stars are variable.2. There are no “pure” parabolae in well-observed O - C curves.3. The periods change in a rather short time and then remain constant for 5,000 - 25,000 E (fig. 2).4. The number of increases and decreases of periods is approximately the same. The mean absolute change of period of 15 investigated stars amounts to 0.d00000365 = 0.P0000105. (The mean increase of period = 0.d00000386 = 0.P0000109, the mean decrease of period = 0.d00000349 = 0.P0000102).5. The mean absolute change of period for 15 investigated stars was plotted versus parameter q (mass ratio = m2/m1) (fig. 3). Systems with almost equal masses of stars have a tendency to show violent changes of period.

On random genetic drift in a subdivided population

1968 ◽  
Vol 5 (02) ◽  
pp. 314-333
Author(s):  
Edward Pollak
Keyword(s):  
Random Sampling ◽  
Joint Distribution ◽  
The Other ◽  
Small Positive Number ◽  
List Type ◽  
Type Number ◽  
Random Genetic Drift ◽  
Subdivided Population ◽  
Haploid Population ◽  
The Mean

Summary Generations are assumed to be non-overlapping. We consider a haploid population divided into K parts, each of which contain N adults in any generation. These are obtained by a random sampling of the offspring of the previous generation. We assume that the probability of an adult offspring of an individual in one subpopulation being in some other subpopulation is the same small positive number, no matter what two subpopulations are considered. If the population initially has individuals of two types, A and a, it is of interest to study approximations, if n is large, to (1) the rate at which A or a is lost between generations n-1 and n, (2) the probability that A and a are still present in generation n, (3) the joint distribution of frequencies of A in the subpopulations. A solution is given for the first problem. It is found that if the mean number of migrants per generation from one subpopulation to another is at least as large as 1, the population behaves almost as if it were not subdivided. But if this number is considerably less that 1, then the rate at which one or the other gene is lost is slower than in an undivided population. The other two problems are discussed for K = 2.

On random genetic drift in a subdivided population

1968 ◽  
Vol 5 (2) ◽  
pp. 314-333 ◽  
Author(s):  
Edward Pollak
Keyword(s):  
Random Sampling ◽  
Joint Distribution ◽  
The Other ◽  
Small Positive Number ◽  
List Type ◽  
Type Number ◽  
Random Genetic Drift ◽  
Subdivided Population ◽  
Haploid Population ◽  
The Mean

SummaryGenerations are assumed to be non-overlapping. We consider a haploid population divided into K parts, each of which contain N adults in any generation. These are obtained by a random sampling of the offspring of the previous generation. We assume that the probability of an adult offspring of an individual in one subpopulation being in some other subpopulation is the same small positive number, no matter what two subpopulations are considered.If the population initially has individuals of two types, A and a, it is of interest to study approximations, if n is large, to (1)the rate at which A or a is lost between generations n-1 and n,(2)the probability that A and a are still present in generation n,(3)the joint distribution of frequencies of A in the subpopulations.A solution is given for the first problem. It is found that if the mean number of migrants per generation from one subpopulation to another is at least as large as 1, the population behaves almost as if it were not subdivided. But if this number is considerably less that 1, then the rate at which one or the other gene is lost is slower than in an undivided population. The other two problems are discussed for K = 2.

The general N server finite queue

1971 ◽  
Vol 8 (04) ◽  
pp. 828-834 ◽  
Author(s):  
Asha Seth Kapadia
Keyword(s):  
Waiting Time ◽  
Busy Period ◽  
Queueing System ◽  
List Type ◽  
Type Number ◽  
Stochastic Nature ◽  
Mean Waiting Time ◽  
Queue Discipline ◽  
Mean And Variance ◽  
The Mean

Kingman (1962) studied the effect of queue discipline on the mean and variance of the waiting time. He made no assumptions regarding the stochastic nature of the input and the service distributions, except that the input and service processes are independent of each other. When the following two conditions hold: (a) no server sits idle while there are customers waiting to be served; (b) the busy period is finite with probability one (i.e., the queue empties infinitely often with probability one); he has shown that the mean waiting time is independent of the queue discipline and the variance of the waiting time is a minimum when the customers are served in order of their arrival. Conditions (a) and (b) will henceforward be called Kingman conditions and a queueing system satisfying Kingman conditions will be referred to in the text as a Kingman queue.

Survey for Duplicity Frequencies: Status and Prospects

1992 ◽  
Vol 135 ◽  
pp. 266-272
Author(s):  
Paul Couteau
Keyword(s):  
Stellar Evolution ◽  
List Type ◽  
Type Number ◽  
Complete Set ◽  
The Mean ◽  
Large Telescopes

I.We recall the main surveys: J. Herschel (1826), W. Struve (1825), A.W. Burnham and G.W. Hough (1880), R.G. Aitken and W.J. Hussey (1910), R. Jonckeere and T.E. Espin (1910), W.H. van den Bos (1925), R.A. Rossiter (1950). Presently the classical surveys are continuing with P. Muller, W.D. Heintz, and P. Couteau. The interferometric survey with large telescopes is carried out at CHARA.II.The results of old surveys, up to 1950, amount to 700 known orbits out of more than 35000 found binaries. The new surveys since 1965, both visual and interferometric, had checked 4000 new binaries giving already about 30 orbits. The periods are shorter and shorter: the mean period is 200 years for Struve (1825) binaries, 75 years for Aitken’s (1910), 25 years for Couteau and Muller’s (1970), and 7 years for CHARA’s. The number of known orbits increases exponentially with time.III.The “classical” surveys will have to be performed again within fifty years with refractors.The interferometric and aperture syntheses surveys will be able to observe every binary, even those in contact with each other. With HIPPARCOS’ results, astronomers will dispose of a complete set of data for new theories of stellar evolution.

Structural Glaciology of an Ice Layer in a Firn Fold, Ross Ice Shelf, Antarctica: Ice Grain Analysis

1964 ◽  
Vol 5 (38) ◽  
pp. 191-206
Author(s):  
John R. Reid
Keyword(s):  
Shear Stress ◽  
Maximum Shear Stress ◽  
Large Diameter ◽  
List Type ◽  
Type Number ◽  
Ice Shelf ◽  
Air Bubble ◽  
Ross Ice Shelf ◽  
The Mean ◽  
Circle Diameter

AbstractA highly deformed area in the Ross Ice Shelf near the Bay of Whales was studied during the 1958–59 Antarctic summer season. A series of snow-firn folds up to 8 m. high and with a wavelength of approximately 100 m. occurs here. Along one of these folds, a unique ice layer formed during the 1952–53 season through refreezing of melt water. From sites along this layer approximately 2,300 ice grains were measured using the root mean square method with the least circle diameter. The data obtained indicate the following:The mean diameter of the ice grains ranges from 4.5 mm. in the ice from the crest of the anticline to 2.5 mm. in the zone of maximum shear stress and/or in sections having a high air bubble content.The large diameter of the ice grains at the crest is attributed to greater solar radiation resulting from their proximity to the 1958–59 snow surface, and because they are near the surface of the exposed crevasse wall.The area of maximum shear stress, which is represented by small ice grains and the presence of secondary folds, is located almost halfway between the crest and the trough.Grains in the trough are larger than those in the shear zone because of less stress, and smaller than those at the crest because of deeper burial and the presence of a crevasse bridge which eliminates all direct radiation here.The growth of the ice grains is therefore controlled by temperature, stress and impurities.

scholarly journals Photometry of CH Cygni During 1991-1994

1995 ◽  
Vol 151 ◽  
pp. 260-261
Author(s):  
K.P. Panov ◽  
J.S.W. Stegert ◽  
G. Hildebrandt
Keyword(s):  
Mass Transfer ◽  
Time Scales ◽  
Time Variation ◽  
Dead Time ◽  
Astronomical Observatory ◽  
Balmer Lines ◽  
The Mean ◽  
Computer Controlled ◽  
Short Time ◽  
Interesting System

CH Cygni has been observed since about one decade at the Bulgarian National Astronomical Observatory Rozhen. UBV photometry was obtained with the 60 cm telescope. The computer controlled photometer is equipped with an EMI 9789 QB multiplier, a set of u,b,v filters and a diaphragm of 28". The reduction includes corrections for dead-time and background, differential extinction and transformation to the standard UBV system.Observations between 1991 and 1994 are displayed in Fig. 1 and show the new outburst, which is still going on. The previous major outburst lasted until 1984, and CH Cyg declined slowly between 1985 and 1988. In 1988, it reached its minimum in brightness and activity. The cause for the activity is probably mass transfer from the M giant component onto the hot companion. In this model, only the M star is seen during activity minimum. In July 1988, the mean brightness was V = 8.50, B - V = 1.39 and U - B = 1.48. Since 1989, some erratic activities appeared, including a hot variable continuum, broad and variable emissions in the Balmer lines and rapid light variations (Leedjarv 1990, Tomov and Mikolajewski 1992, Kuczawska et al. 1992, Panov and Ivanova 1992). Since 1991, a trend of increasing activity is observed, which persisted also in 1994. The brightening of CH Cyg of about 5m in U in 1994 with respect to 1991 shows that it undergoes another major outburst. Moreover, it exhibits light variations with different other time scales, minutes (flickering), days and weeks, probably resulting from the mass-transfer. Fig. 2 showns an example of a short time variation on October 1, 1994. The flickering of CH Cyg was very pronounced in the U, B and V filters and the amplitudes reached several 0m.1 in about half an hour. More observations of this interesting system are planned.

The general N server finite queue

1971 ◽  
Vol 8 (4) ◽  
pp. 828-834 ◽  
Author(s):  
Asha Seth Kapadia
Keyword(s):  
Waiting Time ◽  
Busy Period ◽  
Queueing System ◽  
List Type ◽  
Type Number ◽  
Stochastic Nature ◽  
Mean Waiting Time ◽  
Queue Discipline ◽  
Mean And Variance ◽  
The Mean

Kingman (1962) studied the effect of queue discipline on the mean and variance of the waiting time. He made no assumptions regarding the stochastic nature of the input and the service distributions, except that the input and service processes are independent of each other. When the following two conditions hold: (a)no server sits idle while there are customers waiting to be served;(b)the busy period is finite with probability one (i.e., the queue empties infinitely often with probability one); he has shown that the mean waiting time is independent of the queue discipline and the variance of the waiting time is a minimum when the customers are served in order of their arrival. Conditions (a) and (b) will henceforward be called Kingman conditions and a queueing system satisfying Kingman conditions will be referred to in the text as a Kingman queue.

scholarly journals Modelling Feedback Effects on the Production of Short Time Intervals

2021 ◽  
Vol 10 (1) ◽  
pp. 56-74
Author(s):  
John H. Wearden ◽  
Jordan Wehrman
Keyword(s):  
Standard Deviation ◽  
Coefficient Of Variation ◽  
Time Intervals ◽  
Average Deviation ◽  
Feedback Effects ◽  
Absolute Change ◽  
Target Time ◽  
The Mean ◽  
Short Time ◽  
Relative Variability

Abstract People produced time intervals of 500 to 1250 ms, with accurate feedback in ms provided after each production. The mean times produced tracked the target times closely, and the coefficient of variation (standard deviation/mean) declined with increasing target time. The mean absolute change from one trial to another, and its standard deviation, measures of trial-by-trial change, also increased with target time. A model of feedback was fitted to all four measures. It assumed that the time produced resulted from a combination of a scalar timing process and a non-timing process. Although the non-timing process was on average invariant with target time, the timing process was assumed to be sensitive to feedback, in two different ways. If the previous production was close to the target the model repeated it (a repeat process), but if it was further away the next production was adjusted by an amount related to the discrepancy between the previous production and the target (an adjust process). The balance between the two was governed by a threshold, which was on average constant, and it was further assumed that the relative variability of the repeat process was lower than that of the adjust process. The model produced output which fitted three of the four measures well (average deviation of 3 or 4%) but fitted the standard deviation of change less well. Reducing the magnitude of the non-timing process produced output which conformed approximately to scalar timing, and the model could also mimic data resulting from the provision of inaccurate feedback.

scholarly journals Structural Glaciology of an Ice Layer in a Firn Fold, Ross Ice Shelf, Antarctica: Ice Grain Analysis

1964 ◽  
Vol 5 (38) ◽  
pp. 191-206
Author(s):  
John R. Reid
Keyword(s):  
Shear Stress ◽  
Maximum Shear Stress ◽  
Large Diameter ◽  
List Type ◽  
Type Number ◽  
Ice Shelf ◽  
Air Bubble ◽  
Ross Ice Shelf ◽  
The Mean ◽  
Circle Diameter

AbstractA highly deformed area in the Ross Ice Shelf near the Bay of Whales was studied during the 1958–59 Antarctic summer season. A series of snow-firn folds up to 8 m. high and with a wavelength of approximately 100 m. occurs here. Along one of these folds, a unique ice layer formed during the 1952–53 season through refreezing of melt water. From sites along this layer approximately 2,300 ice grains were measured using the root mean square method with the least circle diameter. The data obtained indicate the following: The mean diameter of the ice grains ranges from 4.5 mm. in the ice from the crest of the anticline to 2.5 mm. in the zone of maximum shear stress and/or in sections having a high air bubble content.The large diameter of the ice grains at the crest is attributed to greater solar radiation resulting from their proximity to the 1958–59 snow surface, and because they are near the surface of the exposed crevasse wall.The area of maximum shear stress, which is represented by small ice grains and the presence of secondary folds, is located almost halfway between the crest and the trough.Grains in the trough are larger than those in the shear zone because of less stress, and smaller than those at the crest because of deeper burial and the presence of a crevasse bridge which eliminates all direct radiation here.The growth of the ice grains is therefore controlled by temperature, stress and impurities.

scholarly journals Periodic Orbits and Gas Flow in Barred Spiral Galaxies

1983 ◽  
Vol 100 ◽  
pp. 221-224
Author(s):  
R. H. Sanders ◽  
P. J. Teuben ◽  
G. D. van Albada
Keyword(s):  
Gas Flow ◽  
Rotation Curve ◽  
Spiral Galaxies ◽  
Radial Force ◽  
List Type ◽  
Type Number ◽  
Lagrange Points ◽  
Barred Galaxies ◽  
The Mean ◽  
Barred Spiral Galaxies

One purpose for studying the gas flow in barred spiral galaxies is to use the observed distribution and kinematics of the gas as a tracer of the underlying gravitational field. By comparing model hydrodynamical calculations with observations of actual systems, one would like to define three basic properties of barred galaxies: 1)The bar strength. How significant is the deviation from axial symmetry in the region of the bar, measured by some parameter such as qt, maximum aximuthal force in terms of the mean radial force (Sanders and Tubbs, 1980).2)The mean radial distribution of matter. Clearly in a system with large deviations from circular motion, the “rotation curve” gives no direct information on the radial mass distribution.3)The angular velocity of the bar. Where is the co-rotation radius (or Lagrange points) with respect to the bar axes? Are other principal resonances present?

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