87 research outputs found
Early warning signals for critical transitions in complex systems
In this review, we present the different measures of early warning signals
that can indicate the occurrence of critical transitions in complex systems. We
start with the mechanisms that trigger critical transitions, how they relate to
warning signals and the methods used to detect early warning signals (EWS) for
sudden transitions or tipping. We discuss briefly a few applications in real
systems in this context, like transitions in ecology, climate and environment,
medicine, epidemics, finance and engineering. Towards the end, we mention the
issues in detecting EWS in specific applications and our perspective on future
trends in this area, especially related to sudden transitions in the dynamics
of connected systems on complex networks.Comment: 35 pages, 11 figure
Evidence for dynamical changes in Betelgeuse using multi-wavelength data
The reasons behind the Great Dimming and subsequent rising in the brightness
of Betelgeuse between October 2019 and March 2020 still continue to baffle
astronomers. It has been shown by George et. al. (2020) that critical slowing
down preceded the dimming event. This suggested that the dimming was a result
of the change in the nature of the nonlinear dynamics of the star. In this work
we present additional evidence for dynamical changes in Betelgeuse prior to the
Great Dimming event, using nonlinear time series analysis. We study the
relations between the different bands in the photometry data collected from the
Wing photometry (IR/near-IR) and Wasatonic observatory (V-band). We also
analyse how the early warning signals studied previously changed during and
after the Great Dimming.Comment: 9 pages, 4 figures, Contribution to the Proceedings of the Sixteenth
Marcel Grossmann Meeting (MG16), July 5-10, 202
Early warning signals indicate a critical transition in Betelgeuse
Critical transitions occur in complex dynamical systems, when the system
dynamics undergoes a regime shift. These can often occur with little change in
the mean amplitude of system response prior to the actual time of transition.
The recent dimming and brightening event in Betelgeuse occured as a sudden
shift in the brightness and has been the subject of much debate. Internal
changes or an external dust cloud have been suggested as reasons for this
change in variability. We examine whether the dimming and brightening event of
2019-20 could be due to a critical transition in the pulsation dynamics of
Betelgeuse, by studying the characteristics of the light curve prior to
transition. We calculate the quantifiers hypothesised to rise prior to a
critical transition for the light curve of Betelgeuse upto the dimming event of
2019-20. These include the autocorrelation at lag-1, variance and the spectral
coefficient calculated from detrended fluctation analysis (DFA), apart from two
measures that quantify the recurrence properties of the light curve.
Significant rises are confirmed using the Mann-Kendall trend test. We see a
significant increase in all quantifiers (p < 0.05) prior to the dimming event
of 2019-20. This suggests that the event was a critical transition related to
the underlying nonlinear dynamics of the star. Together with results that
suggests minimal change in and infra-red flux, a critical transition
in the pulsation dynamics could be a possible reason for the unprecedented
dimming of Betelgeuse. The rise in the studied quantifiers prior to the dimming
event, supports this possibility.Comment: 8 pages, 8 figure
Suzaku observation of the transient X-ray pulsar GRO J1008-57
We report the timing and broad-band spectral properties of the Be transient
high mass X-ray binary pulsar GRO J1008-57 using a Suzaku observation in the
declining phase of its 2007 November-December outburst. Pulsations with a
period of 93.737 s were clearly detected in the light curves of the pulsar up
to the 80-100 keV energy band. The pulse profile was found to be strongly
energy dependent, a double peaked profile at soft X-ray energy bands (< 8 keV)
and a single peaked smooth profile at hard X-rays. The broad-band energy
spectrum of the pulsar, reported for the first instance in this paper, is well
described with three different continuum models viz. (i) a high energy cut-off
power-law, (ii) a Negative and Positive power-law with EXponential cut-off
(NPEX), and (iii) a partial covering power-law with high energy cut-off.
Inspite of large value of absorption column density in the direction of the
pulsar, a blackbody component of temperature ~0.17 keV for the soft excess was
required for the first two continuum models. A narrow iron K_\alpha emission
line was detected in the pulsar spectrum. The partial covering model, however,
is found to explain the phase averaged and phase resolved spectra well. The dip
like feature in the pulse profile can be explained by the presence of an
additional absorption component with high column density and covering fraction
at the same pulse phase. The details of the results are described in the paper.Comment: 9 pages, 7 figures, Accepted for publication in MNRA
Slumping in the Upper Jurassic Baisakhi Formation of the Jaisalmer Basin, western India : sign of synsedimentary tectonics?
A spectacularly exposed slump is described from a 120-m-long road cut between the villages of Kanod and Deva in the northeastern Jaisalmer Basin of Rajasthan, India. The Upper Jurassic part of the sediments at the outcrop was formed in a near-shore setting and belongs to the Ludharwa Member of the Baisakhi Formation. The 3-m-thick unit shows a number of asymmetric folds and thrust faults leading to an imbrication of partly lithified sandstone beds. The deformation structures allow the reconstruction of a movement towards the northwest. This agrees well with the basin configuration that shows a deepening into this direction. Although the determination of a specific trigger mechanism is difficult for soft-sediment deformation structures, an earthquake caused by synsedimentary tectonics in the basin seems to be the most likely explanation
Analyses of different parameters affecting household consumption in the United Kingdom
This research outlines the consumption behavior in United Kingdom. The previous recessions in UK marked a contraction in consumption expenditure which was boosted by high level of debt financing. The validation of conventional consumption theories in accordance with UK economy is questioned and new consumption model is developed. A model developed is based on all the consumption theories and the current economic trend. The trend of households’ behavior in specific economic periods is highlighted. The study then assess the impact of central bank’s monetary policy impact on the debt levels of the households. It also emphasize on the issues of rising household debt and problem debt and its impact on consumption. The paper then provides an empirical investigation of UK spending in relation to variables including interest rates, debt levels, income and savings of the households. Analysis is drawn based on the empirical evidence, consumption model and the current trends of these variables. The results suggest that the consumption theories are not completely in line with the current economic conditions in UK
Lumbar Intramedullary Epidermoid Following Repair of Sacral Myelomeningocele and Tethered Cord: A Case Report With a Review of the Relevant Literature and Operative Nuances
Bimodality and scaling in recurrence networks from ECG data
Human heart is a complex system that can be studied using its electrical activity recorded as Electrocardiogram (ECG). Any variations or anomalies in the ECG can indicate abnormalities in the cardiac dynamics. In this work, we present a detailed analysis of ECG data using the framework of recurrence networks (RNs). We show how the measures of the recurrence networks constructed from ECG data sets, can quantify the complexity and variability underlying the data. Our study shows for the first time that the RNs from ECG show the unique feature of bimodality in their degree distribution. We relate this to the complex dynamics underlying the cardiac system, with structures at two spatial scales. We also show that there is relevant information to be extracted from the scaling of measures with recurrence threshold ε. Thus we observe two scaling regions in the link density for ECG data which are compared with scaling in RNs from standard chaotic and hyperchaotic systems and noise. While both bimodality and scaling are common features of RNs from all types of ECG data, we find that disease specific variations in them can be quantified
Confounding features of ectopic craniopharyngioma: A differential for tumors showing diffusion restriction
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