scholarly journals 3.6. AGN variability studies: an agenda for the next millenium?

1998 ◽  
Vol 184 ◽  
pp. 99-101
Author(s):  
M.-H. Ulrich
Keyword(s):  
Data Base ◽  
Accretion Disk ◽  
Time Scales ◽  
Large Amplitude ◽  
Rare Events ◽  
The Future ◽  
Optical Flux ◽  
Factor 20

Data which are obtained today can be re-acquired better and faster in the future. Their only enduring value, after they have been interpreted, is as historical markers. With electronic archiving one can envision archives covering decades, centuries and even longer periods of observations of selected objects or classes of objects. Such a data base would allow the study of phenomena with low temporal frequencies, and of rare events.First hints of such phenomena in AGN have been discovered recently: 1) The Seyfert 1s, the best studied AGN at present, exhibit flux variations on time scales ranging from hours to several years (see Ulrich et al. 1997). The faster variations (up to months) have been extensively observed, and they are best understood as being caused by magnetic flares in the corona above the central part of the accretion disk (Blandford and Payne 1982). The origin of the long term and large amplitude UV/optical flux variations (factor 20 in several years as observed in NGC4151 and F9), however, remain essentially unknown.

scholarly journals Conserving evolutionary history does not result in greater diversity over geological time scales

2019 ◽  
Vol 286 (1904) ◽  
pp. 20182896 ◽  
Author(s):  
J. L. Cantalapiedra ◽  
T. Aze ◽  
M. W. Cadotte ◽  
G. V. Dalla Riva ◽  
D. Huang ◽  
...  
Keyword(s):  
Time Scales ◽  
Phylogenetic Trees ◽  
Evolutionary History ◽  
Phylogenetic Diversity ◽  
Random Sets ◽  
Geological Time ◽  
The Future ◽  
Species Production

Alternative prioritization strategies have been proposed to safeguard biodiversity over macroevolutionary time scales. The first prioritizes the most distantly related species—maximizing phylogenetic diversity (PD)—in the hopes of capturing at least some lineages that will successfully diversify into the future. The second prioritizes lineages that are currently speciating, in the hopes that successful lineages will continue to generate species into the future. These contrasting schemes also map onto contrasting predictions about the role of slow diversifiers in the production of biodiversity over palaeontological time scales. We consider the performance of the two schemes across 10 dated species-level palaeo-phylogenetic trees ranging from Foraminifera to dinosaurs. We find that prioritizing PD for conservation generally led to fewer subsequent lineages, while prioritizing diversifiers led to modestly more subsequent diversity, compared with random sets of lineages. Importantly for conservation, the tree shape when decisions are made cannot predict which scheme will be most successful. These patterns are inconsistent with the notion that long-lived lineages are the source of new species. While there may be sound reasons for prioritizing PD for conservation, long-term species production might not be one of them.

scholarly journals Long-Term Brightness Changes in Cool Pulsating Variables

1993 ◽  
Vol 139 ◽  
pp. 425-427
Author(s):  
John R. Percy
Keyword(s):  
Time Scales ◽  
Large Amplitude ◽  
Variable Star ◽  
American Association ◽  
Long Term Changes ◽  
Long Time ◽  
Red Giant

AbstractSeveral types of cool pulsating variables show unexplained long-term changes in brightness, typically on time scales of 10 to 20 times the basic (pulsational) period. The visual and photoelectric programs of the American Association of Variable Star Observers (AAVSO) are well-suited for detecting and studying these changes. Some examples are given here, including yellow hypergiants, RV Tauri stars, small- and large-amplitude red giant and super giant variables. The study of pulsating variables on long time scales provides “new perspectives” on their behavior.

scholarly journals Characterization of optical light curves of extreme variability quasars over a ∼16-yr baseline

2020 ◽  
Vol 494 (3) ◽  
pp. 3686-3698 ◽  
Author(s):  
Yuanze Luo ◽  
Yue Shen ◽  
Qian Yang
Keyword(s):  
Time Scales ◽  
Dynamic Range ◽  
Accretion Disc ◽  
Light Curves ◽  
Short Term ◽  
Public Data ◽  
Extreme Variability ◽  
Average Flux ◽  
Optical Flux

ABSTRACT We study the optical light curves – primarily probing the variable emission from the accretion disc – of ∼900 extreme variability quasars (EVQs, with maximum flux variations more than 1 mag) over an observed-frame baseline of ∼16 yr using public data from the SDSS Stripe 82, PanSTARRS-1 and the Dark Energy Survey. We classify the multiyear long-term light curves of EVQs into three categories roughly in the order of decreasing smoothness: monotonic decreasing or increasing (3.7 per cent), single broad peak and dip (56.8 per cent), and more complex patterns (39.5 per cent). The rareness of monotonic cases suggests that the major mechanisms driving the extreme optical variability do not operate over time-scales much longer than a few years. Simulated light curves with a damped random walk model generally under-predict the first two categories with smoother long-term trends. Despite the different long-term behaviours of these EVQs, there is little dependence of the long-term trend on the physical properties of quasars, such as their luminosity, BH mass, and Eddington ratio. The large dynamic range of optical flux variability over multiyear time-scales of these EVQs allows us to explore the ensemble correlation between the short-term (≲6 months) variability and the seasonal-average flux across the decade-long baseline (the rms-mean flux relation). We find that unlike the results for X-ray variability studies, the linear short-term flux variations do not scale with the seasonal-average flux, indicating different mechanisms that drive the short-term flickering and long-term extreme variability of accretion disc emission. Finally, we present a sample of 16 EVQs, where the approximately bell-shaped large amplitude variation in the light curve can be reasonably well fit by a simple microlensing model.

scholarly journals MULTIWAVELENGTH OBSERVATIONS OF PKS 0528+134 IN QUIESCENCE

2012 ◽  
Vol 08 ◽  
pp. 311-314
Author(s):  
MARKUS BÖTTCHER ◽  
NORMAN PALMA
Keyword(s):  
Accretion Disk ◽  
Time Scales ◽  
Thermal Emission ◽  
High Energy ◽  
Degree Of Polarization ◽  
Acceleration Process ◽  
Quiescent State ◽  
Bolometric Luminosity ◽  
Optical Flux ◽  
Multiwavelength Observations

We present results of multiwavelength observations of the ultraluminous radio-loud quasar PKS 0528+134 in quiescence in the Fall of 2009. Significant flux variability on a time-scale of several hours was found in the optical regime, accompanied by a weak trend of spectral softening with increasing flux. The optical flux is weakly polarized with rapid variations of the degree and direction of polarization. Optical spectropolarimetry suggests a trend of increasing degree of polarization with increasing wavelength. Together with the spectral variability, this provides evidence for an unpolarized, slowly variable emission component, possibly thermal emission from the accretion disk, contributing towards the blue end of the optical spectrum. We find that even in the quiescent state, the bolometric luminosity of PKS 0528+134 is dominated by its γ-ray emission. A leptonic single-zone jet model produced acceptable fits to the SEDs with contributions to the high-energy emission from both synchrotron self-Compton radiation and Comptonization of direct accretion disk emission. The moderate variability on long time scales, compared to the expected radiative cooling time scales, implies the existence of on-going particle acceleration, while the observed optical polarization variability seems to point towards a turbulent acceleration process.

DIGITALIZATION OF LABOR MIGRATION PROCESSES IN UZBEKISTAN. WORLD EXPERIENCE

2020 ◽  
Vol 4 (3) ◽  
pp. 29-39
Author(s):  
Sulkhiya Gazieva ◽  
Keyword(s):  
Labor Market ◽  
Technological Change ◽  
Labor Migration ◽  
Smart Phone ◽  
Logic Circuits ◽  
Digital Logic ◽  
The Internet ◽  
The Future

The future of labor market depends upon several factors, long-term innovation and the demographic developments. However, one of the main drivers of technological change in the future is digitalization and central to this development is the production and use of digital logic circuits and its derived technologies, including the computer,the smart phone and the Internet. Especially, smart automation will perhaps not cause e.g.regarding industries, occupations, skills, tasks and duties

Der Wald-Wild-Konflikt – was kann die Forstökonomie zur Lösung beitragen? (Essay)

2017 ◽  
Vol 168 (4) ◽  
pp. 181-185
Author(s):  
Marc Hanewinkel
Keyword(s):  
Forest Economics ◽  
Production Risk ◽  
Damage Compensation ◽  
Land Expectation Value ◽  
Compensation Methods ◽  
The Future ◽  
Single Tree Selection ◽  
Simplifying Assumptions ◽  
Forest Enterprises

The forest-game conflict – how can forest economics contribute to solve it? (Essay) Core parameters of forest economics such as land expectation value or highest revenue show that damage caused by wild ungulates can critically influence the economic success of forest enterprises. When assessing and evaluating the damage in order to calculate damage compensation, methods are applied in Germany that look either into the past (“cost value methods”) or into the future (“expected value methods”). The manifold uncertainties related to this evaluation over long-term production periods are taken into account within a framework of conventions through strongly simplifying assumptions. Only lately, the increased production risk due to game-induced loss of species diversity is also considered. Additional aspects that should be taken into account in the future are the loss of climate-adapted species, the change of the insurance values of forest ecosystems and the impossibility of specific management systems such as single-tree selection forestry due to the influence of game. Because of high transaction costs when assessing the damage, financial compensation should only be the “ultimate measure” and a meditation between stakeholder groups with the goal to find a cooperative solution before the damage occurs should be preferred.

The Future of Muslim Education in the United States: An Agenda for Research

2003 ◽  
Vol 20 (3-4) ◽  
pp. 46-82
Author(s):  
Fathi Malkawi
Keyword(s):  
United States ◽  
The United States ◽  
American Education ◽  
Future Trends ◽  
Muslim Community ◽  
Short Term ◽  
The Future ◽  
Muslim Education ◽  
Future Plans

This paper addresses some of the Muslim community’s concerns regarding its children’s education and reflects upon how education has shaped the position of other communities in American history. It argues that the future of Muslim education will be influenced directly by the present realities and future trends within American education in general, and, more importantly, by the well-calculated and informed short-term and long-term decisions and future plans taken by the Muslim community. The paper identifies some areas in which a wellestablished knowledge base is critical to making decisions, and calls for serious research to be undertaken to furnish this base.

The Spread of Pollutants from Harbour Sludge Depots

1984 ◽  
Vol 16 (3-4) ◽  
pp. 623-633
Author(s):  
M Loxham ◽  
F Weststrate
Keyword(s):  
Time Scales ◽  
Molecular Diffusion ◽  
Near Field ◽  
Parameter Analysis ◽  
Migration Patterns ◽  
Long Time ◽  
Dilution Effects ◽  
Short Time ◽  
Harbour Sludge

It is generally agreed that both the landfill option, or the civil techniques option for the final disposal of contaminated harbour sludge involves the isolation of the sludge from the environment. For short time scales, engineered barriers such as a bentonite screen, plastic sheets, pumping strategies etc. can be used. However for long time scales the effectiveness of such measures cannot be counted upon. It is thus necessary to be able to predict the long term environmenttal spread of contaminants from a mature landfill. A model is presented that considers diffusion and adsorption in the landfill site and convection and adsorption in the underlaying aquifer. From a parameter analysis starting form practical values it is shown that the adsorption behaviour and the molecular diffusion coefficient of the sludge, are the key parameters involved in the near field. The dilution effects of the far field migration patterns are also illustrated.

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