scholarly journals Estimating activity cycles with probabilistic methods

2018 ◽  
Vol 615 ◽  
pp. A111 ◽  
Author(s):  
N. Olspert ◽  
J. Pelt ◽  
M. J. Käpylä ◽  
J. Lehtinen
Keyword(s):  
Linear Trend ◽  
Synthetic Data ◽  
Probabilistic Methods ◽  
Data Sampling ◽  
Constant Variance ◽  
Noise Type ◽  
Periodic Model ◽  
Activity Cycles ◽  
Magnetic Cycles

Context. Period estimation is one of the central topics in astronomical time series analysis, in which data is often unevenly sampled. Studies of stellar magnetic cycles are especially challenging, as the periods expected in those cases are approximately the same length as the datasets themselves. The datasets often contain trends, the origin of which is either a real long-term cycle or an instrumental effect. But these effects cannot be reliably separated, while they can lead to erroneous period determinations if not properly handled. Aims. In this study we aim at developing a method that can handle the trends properly. By performing an extensive set of testing, we show that this is the optimal procedure when contrasted with methods that do not include the trend directly in the model. The effect of the form of the noise (whether constant or heteroscedastic) on the results is also investigated. Methods. We introduced a Bayesian generalised Lomb-Scargle periodogram with trend (BGLST), which is a probabilistic linear regression model using Gaussian priors for the coefficients of the fit and a uniform prior for the frequency parameter. Results. We show, using synthetic data, that when there is no prior information on whether and to what extent the true model of the data contains a linear trend, the introduced BGLST method is preferable to the methods that either detrend the data or opt not to detrend the data before fitting the periodic model. Whether to use noise with other than constant variance in the model depends on the density of the data sampling and on the true noise type of the process.

Long-term stellar magnetic field study at the Crimean Astrophysical Observatory

2018 ◽  
Vol 13 (S340) ◽  
pp. 35-38
Author(s):  
Varvara Butkovskaya ◽  
Sergei Plachinda ◽  
Dilyara Baklanova
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Field Study ◽  
Crimean Astrophysical Observatory ◽  
Activity Cycles ◽  
Magnetic Cycles ◽  
Long Term Monitoring ◽  
The Magnetic Field ◽  
Term Monitoring

AbstractThe long-term monitoring of magnetic cycles is a key diagnostic in understanding how dynamo generation and amplification of magnetic fields occur in solar-like stars. One of the current key problems is the establishment of the magnetic field behavior during the activity cycles for stars of different ages and evolutionary statuses. We present the experience of using own long-term datasets for study of activity cycles in selected stars at the Crimean Astrophysical Observatory.

scholarly journals By Slow Degrees: Two Centuries of Social Reproduction and Mobility in Britain

2007 ◽  
Vol 12 (1) ◽  
pp. 37-62 ◽  
Author(s):  
Paul Lambert ◽  
Kenneth Prandy ◽  
Wendy Bottero
Keyword(s):  
Social Mobility ◽  
Social Reproduction ◽  
Linear Trend ◽  
Time Frame ◽  
Quality Of Data ◽  
Term Change ◽  
Parental Background ◽  
Long Term Trends

This paper discusses long term trends in patterns of intergenerational social mobility in Britain. We argue that there is convincing empirical evidence of a small but steady linear trend towards increasing social mobility throughout the period 1800-2004. Our conclusions are based upon the construction and analysis of an extended micro-social dataset, which combines records from an historical genealogical study, with responses from 31 sample surveys conducted over the period 1963-2004. There has been much previous study of trends in social mobility, and little consensus on their nature. We argue that this dissension partly results from the very slow pace of change in mobility rates, which makes the time-frame of any comparison crucial, and raises important methodological questions about how long-term change in mobility is best measured. We highlight three methodological difficulties which arise when trying to draw conclusions over mobility trends - concerning the extent of controls for life course effects; the quality of data resources; and the measurement of stratification positions. After constructing a longitudinal dataset which attempts to confront these difficulties, our analyses provide robust evidence which challenges hitherto more popular, politicised claims of declining or unchanging mobility. By contrast, our findings suggest that Britain has moved, and continues to move, steadily towards increasing equality in the relationship between occupational attainment and parental background.

scholarly journals Learning about Stellar Dynamos from Long–term Photometry of Starspots

1991 ◽  
Vol 130 ◽  
pp. 353-369 ◽  
Author(s):  
Douglas S. Hall
Keyword(s):  
Differential Rotation ◽  
Rotation Period ◽  
Turnover Time ◽  
Rotating Stars ◽  
Photometric Variability ◽  
Solar Type ◽  
Magnetic Cycles ◽  
The Many ◽  
Rapidly Rotating Stars

AbstractSpottedness, as evidenced by photometric variability in 277 late-type binary and single stars, is found to occur when the Rossby number is less than about 2/3. This holds true when the convective turnover time versus B–V relation of Gilliland is used for dwarfs and also for subgiants and giants if their turnover times are twice and four times longer, respectively, than for dwarfs. Differential rotation is found correlated with rotation period (rapidly rotating stars approaching solid-body rotation) and also with lobe-filling factor (the differential rotation coefficient k is 2.5 times larger for F = 0 than F = 1). Also reviewed are latitude extent of spottedness, latitude drift during a solar-type cycle, sector structure and preferential longitudes, starspot lifetimes, and the many observational manifestations of magnetic cycles.

The Trans-Asian Pathways of ‘Oriental Products’: Navigating the prohibition of narcotics between Turkey, China, and Japan, 1918–1938

2021 ◽  
pp. 1-43
Author(s):  
DANIEL-JOSEPH MACARTHUR-SEAL
Keyword(s):  
Twentieth Century ◽  
Linear Trend ◽  
League Of Nations ◽  
Turkish Government ◽  
Medical Market ◽  
Opium Production ◽  
Production And Distribution ◽  
Historic Significance ◽  
Drug Prohibition

Abstract Patterns of opium production and distribution shifted immensely over the course of the twentieth century, with output falling by three-quarters, almost nine-tenths of which now takes place in Afghanistan. Supporters of drug prohibition trumpet the success of this long-term decline and hail the withdrawal of the four largest opium producers—India, China, Iran, and the Ottoman empire—from the non-medical market, but this seemingly linear trend conceals numerous deviations of historic significance. Among the most notable and little known is Turkey's prolonged resistance to international restrictions on the narcotics trade and the efforts of state and non-state networks to substitute Turkish opium for the diminishing supply of once-dominant Indian exports to a still opium-hungry China in the first half of the twentieth century. This article uses neglected League of Nations and Turkish government sources alongside international newspapers and diplomatic reports to demonstrate the extent of connections forged by state and non-state actors between Turkey and East Asia, expanding on recent research on trans-Asian connections in commerce and political thought.

scholarly journals Analysis of full disc Ca II K spectroheliograms

2018 ◽  
Vol 609 ◽  
pp. A92 ◽  
Author(s):  
Theodosios Chatzistergos ◽  
Ilaria Ermolli ◽  
Sami K. Solanki ◽  
Natalie A. Krivova
Keyword(s):  
Synthetic Data ◽  
Calibration Method ◽  
Poor Quality ◽  
Average Error ◽  
Photometric Calibration ◽  
Solar Observations ◽  
Relative Errors ◽  
Long Term Variations ◽  
The Ideal

Context. Historical Ca II K spectroheliograms (SHG) are unique in representing long-term variations of the solar chromospheric magnetic field. They usually suffer from numerous problems and lack photometric calibration. Thus accurate processing of these data is required to get meaningful results from their analysis. Aims. In this paper we aim at developing an automatic processing and photometric calibration method that provides precise and consistent results when applied to historical SHG. Methods. The proposed method is based on the assumption that the centre-to-limb variation of the intensity in quiet Sun regions does not vary with time. We tested the accuracy of the proposed method on various sets of synthetic images that mimic problems encountered in historical observations. We also tested our approach on a large sample of images randomly extracted from seven different SHG archives. Results. The tests carried out on the synthetic data show that the maximum relative errors of the method are generally <6.5%, while the average error is <1%, even if rather poor quality observations are considered. In the absence of strong artefacts the method returns images that differ from the ideal ones by <2% in any pixel. The method gives consistent values for both plage and network areas. We also show that our method returns consistent results for images from different SHG archives. Conclusions. Our tests show that the proposed method is more accurate than other methods presented in the literature. Our method can also be applied to process images from photographic archives of solar observations at other wavelengths than Ca II K.

scholarly journals Flexible approach for quantifying average long-term changes and seasonal cycles of tropospheric trace species

2019 ◽  
Author(s):  
David D. Parrish ◽  
Richard G. Derwent ◽  
Simon O'Doherty ◽  
Peter G. Simmonds
Keyword(s):  
Time Series ◽  
Seasonal Cycle ◽  
Linear Trend ◽  
Power Series Expansion ◽  
Mathematical Representation ◽  
Seasonal Cycles ◽  
Data Sets ◽  
Significant Information ◽  
Long Term Changes

Abstract. We present an approach to derive a systematic mathematical representation of the statistically significant features of the average long-term changes and seasonal cycle of concentrations of trace tropospheric species. The results for two illustrative data sets (time series of baseline concentrations of ozone and N2O at Mace Head, Ireland) indicate that a limited set of seven or eight parameter values provides this mathematical representation for both example species. This method utilizes a power series expansion to extract more information regarding the long-term changes than can be provided by oft-employed linear trend analyses. In contrast, the quantification of average seasonal cycles utilizes a Fourier series analysis that provides less detailed seasonal cycles than are sometimes represented as twelve monthly means; including that many parameters in the seasonal cycle representation is not usually statistically justified, and thereby adds unnecessary noise to the representation and prevents a clear analysis of the statistical uncertainty of the results. The approach presented here is intended to maximize the statistically significant information extracted from analyses of time series of concentrations of tropospheric species regarding their mean long-term changes and seasonal cycles, including non-linear aspects of the long-term trends. Additional implications, advantages and limitations of this approach are discussed.

scholarly journals Probability Calibration Of Load Duration Modification Factor For Timber Roofs In The Polish Mountain Zones

2014 ◽  
Vol 60 (2) ◽  
pp. 195-208
Author(s):  
T. Domański
Keyword(s):  
Limit State ◽  
High Stress ◽  
Life Time ◽  
Probabilistic Methods ◽  
Limit States ◽  
Term Limit ◽  
Load Duration ◽  
Maximum Likelihood Methods ◽  
Short And Long Term

Abstract The resistance parameters of timber structures decrease with time. It depends on the type of load and timber classes. Strength reduction effects, referred to as creep-rupture effects, due to long term loading at high stress ratio levels are known for many materials. Timber materials are highly affected by this reduction in strength with duration of load. Characteristic values of load duration and load duration factors are calibrated by means of using probabilistic methods. Three damage accumulation models are considered, that is Gerhard [1] model, Barret, Foschi[2] and Foshi Yao [3] models. The reliability is estimated by means of using representative short- and long-term limit states. Time variant reliability aspects are taken into account using a simple representative limit state with time variant strength and simulation of whole life time load processes. The parameters in these models are fitted by the Maximum Likelihood Methods using the data relevant for Polish structural timber. Based on Polish snow data over 45 years from mountain zone in: Zakopane – Tatra, Świeradów – Karkonosze, Lesko – Bieszczady, the snow load process parameters have been estimated. The reliability is evaluated using representative short – and long –term limit states, load duration factor kmod is obtained using the probabilistic model.

scholarly journals Magnetic Cycles and Rotation in Active Late–Type Stars

2004 ◽  
Vol 215 ◽  
pp. 289-291
Author(s):  
Ilkka Tuominen ◽  
Svetlana V. Berdyugina ◽  
Maarit J. Korpi
Keyword(s):  
Mean Field ◽  
Point Of View ◽  
Doppler Imaging ◽  
Late Type ◽  
Dynamo Theory ◽  
Flip Flop ◽  
Cyclic Behaviour ◽  
Magnetic Cycles ◽  
Mean Field Dynamo

Observational evidence, based both on spectroscopic Doppler imaging and long-term photometry, of strongly nonaxisymmetric spot distributions in magnetically very active late-type stars, with a special cyclic behaviour (the “flip-flop” effect), is presented. Theoretical implications of these results are discussed from the point of view of nonlinear mean-field dynamo theory.

scholarly journals Adjustable sockets may improve residual limb fluid volume retention in transtibial prosthesis users

2019 ◽  
Vol 43 (3) ◽  
pp. 250-256 ◽  
Author(s):  
Jacob T Brzostowski ◽  
Brian G Larsen ◽  
Robert T Youngblood ◽  
Marcia A Ciol ◽  
Brian J Hafner ◽  
...  
Keyword(s):  
Repeated Measures ◽  
Fluid Volume ◽  
Residual Limb ◽  
Short Term ◽  
Transtibial Prosthesis ◽  
Activity Cycles ◽  
Long Term Retention ◽  
Volume Retention ◽  
Intervention Condition

Background: Loss of residual limb volume degrades socket fit and may require accommodation. Objectives: To examine if either of two accommodation strategies executed during resting, socket release with full socket size return and socket release with partial socket size return, enhanced limb fluid volume retention during subsequent activity. Study design: Two repeated-measures experiments were conducted to assess the effects of socket release on limb fluid volume retention. Methods: Limb fluid volume was monitored while participants wore a socket with a single adjustable panel. Participants performed eight activity cycles that each included 10 min of sitting and 2 min of walking. The socket’s posterior panel and pin lock were released during the fifth cycle while participants were sitting. In one experiment (Full Return), the socket was returned to its pre-release size; in a second experiment (Partial Return), it was returned to 102% of its pre-release size. Short-term and long-term limb fluid volume retention were calculated and compared to a projected, No Intervention condition. Results: Partial Return and Full Return short-term retentions and Partial Return long-term retention were greater than those projected under the control condition ( p < 0.05). Conclusion: Socket release during resting after activity, particularly when the socket is returned to a slightly larger size, may be an effective accommodation strategy to reduce fluid volume loss in transtibial prosthesis users. Clinical relevance This study suggests that existing prosthetic technologies’ adjustable sockets and locking pin tethers can be used in novel ways to help maintain residual limb fluid volume in active prosthesis users.

scholarly journals Water Balance Backward: Estimation of Annual Watershed Precipitation and Its Long-Term Trend with the Help of the Calibration-Free Generalized Complementary Relationship of Evaporation

Water ◽  
2020 ◽  
Vol 12 (6) ◽  
pp. 1775
Author(s):  
Jozsef Szilagyi
Keyword(s):  
Water Balance ◽  
Mean Squared Error ◽  
Linear Trend ◽  
Free Water ◽  
The United States ◽  
Discharge Data ◽  
Complementary Relationship ◽  
Stream Discharge ◽  
Calibration Free

Watershed-scale annual evapotranspiration (ET) is routinely estimated by a simplified water balance as the difference in catchment precipitation (P) and stream discharge (Q). With recent developments in ET estimation by the calibration-free generalized complementary relationship, the water balance equation is employed to estimate watershed/basin P at an annual scale as ET + Q on the United States (US) Geological Survey’s Hydrologic Unit Code (HUC) 2- and 6-level watersheds over the 1979–2015 period. On the HUC2 level, mean annual PRISM P was estimated with a correlation coefficient (R) of 0.99, relative bias (RB) of zero, root-mean-squared-error (RMSE) of 54 mm yr−1, ratio of standard deviations (RS) of 1.08, and Nash–Sutcliffe efficiency (NSE) of 0.98. On the HUC6 level, R, RS, and NSE hardly changed, RB remained zero, while RMSE increased to 90 mm yr−1. Even the long-term linear trend values were found to be fairly consistent between observed and estimated values with R = 0.97 (0.81), RMSE = 0.63 (1.63) mm yr−1, RS = 0.99 (1.05), NSE = 0.92 (0.59) on the HUC2 and HUC6 (in parentheses) levels. This calibration-free water-balance method demonstrates that annual watershed precipitation can be estimated with an acceptable accuracy from standard atmospheric/radiation and stream discharge data.

Sign in / Sign up

Export Citation Format

Share Document