scholarly journals Statistical inference of prehistoric demography from frequency distributions of radiocarbon dates: a review and a guide for the perplexed

2021 ◽  
Author(s):  
Enrico R. Crema
Keyword(s):  
Frequency Data ◽  
Statistical Nature ◽  
Radiocarbon Dates ◽  
Frequency Distributions ◽  
Practical Applications ◽  
Time Frequency ◽  
Comparative Demography ◽  
Frequency Changes ◽  
Past Population

The last decade saw a rapid increase in the number of applications where time-frequency changes of radiocarbon dates have been used as a proxy for inferring past population dynamics. Although its simple and universal premise is appealing and undoubtedly offers some unique opportunities for research on long-term comparative demography, practical applications are far from trivial and riddled by challenges. Here I review: 1) the most common criticisms concerning the nature of radiocarbon time-frequency data as a demographic proxy; 2) the statistical nature of the problem; and 3) three classes of inferential approaches proposed so far in the literature.

scholarly journals Ecology of the collapse of Rapa Nui society

2020 ◽  
Vol 287 (1929) ◽  
pp. 20200662 ◽  
Author(s):  
M. Lima ◽  
E. M. Gayo ◽  
C. Latorre ◽  
C. M. Santoro ◽  
S. A. Estay ◽  
...  
Keyword(s):  
Recurrent Events ◽  
Dynamic Models ◽  
Ecological Factors ◽  
Long Term Effects ◽  
Rapa Nui ◽  
Radiocarbon Dates ◽  
Underlying Causes ◽  
Capita Food ◽  
Past Population

Collapses of food producer societies are recurrent events in prehistory and have triggered a growing concern for identifying the underlying causes of convergences/divergences across cultures around the world. One of the most studied and used as a paradigmatic case is the population collapse of the Rapa Nui society. Here, we test different hypotheses about it by developing explicit population dynamic models that integrate feedbacks between climatic, demographic and ecological factors that underpinned the socio-cultural trajectory of these people. We evaluate our model outputs against a reconstruction of past population size based on archaeological radiocarbon dates from the island. The resulting estimated demographic declines of the Rapa Nui people are linked to the long-term effects of climate change on the island's carrying capacity and, in turn, on the ‘per-capita food supply’.

scholarly journals Time-Frequency Analysis of Clinical Percussion Signals Using Matrix Pencil Method

2015 ◽  
Vol 2015 ◽  
pp. 1-10 ◽  
Author(s):  
Moinuddin Bhuiyan ◽  
Eugene V. Malyarenko ◽  
Mircea A. Pantea ◽  
Dante Capaldi ◽  
Alfred E. Baylor ◽  
...  
Keyword(s):  
Frequency Analysis ◽  
Matrix Pencil ◽  
Time Frequency Analysis ◽  
Frequency Distributions ◽  
Practical Applications ◽  
Time Frequency ◽  
Matrix Pencil Method ◽  
Oscillation Modes ◽  
Cross Terms ◽  
Time Frequency Localization

This paper discusses time-frequency analysis of clinical percussion signals produced by tapping over human chest or abdomen with a neurological hammer and recorded with an air microphone. The analysis of short, highly damped percussion signals using conventional time-frequency distributions (TFDs) meets certain difficulties, such as poor time-frequency localization, cross terms, and masking of the lower energy features by the higher energy ones. The above shortcomings lead to inaccurate and ambiguous representation of the signal behavior in the time-frequency plane. This work describes an attempt to construct a TF representation specifically tailored to clinical percussion signals to achieve better resolution of individual components corresponding to physical oscillation modes. Matrix Pencil Method (MPM) is used to decompose the signal into a set of exponentially damped sinusoids, which are then plotted in the time-frequency plane. Such representation provides better visualization of the signal structure than the commonly used frequency-amplitude plots and facilitates tracking subtle changes in the signal for diagnostic purposes. The performance of our approach has been verified on both ideal and real percussion signals. The MPM-based time-frequency analysis appears to be a better choice for clinical percussion signals than conventional TFDs, while its ability to visualize damping has immediate practical applications.

scholarly journals DOA Estimation and Self-Calibration under Unknown Mutual Coupling

Sensors ◽  
2019 ◽  
Vol 19 (4) ◽  
pp. 978
Author(s):  
Dong Qi ◽  
Min Tang ◽  
Shiwen Chen ◽  
Zhixin Liu ◽  
Yongjun Zhao
Keyword(s):  
Mutual Coupling ◽  
Linear Equations ◽  
Least Square Method ◽  
Calibration Method ◽  
Least Square ◽  
Frequency Distributions ◽  
Steering Vector ◽  
Practical Applications ◽  
Time Frequency ◽  
Self Calibration

In practical applications, the assumption of omnidirectional elements is not effective in general, which leads to the direction-dependent mutual coupling (MC). Under this condition, the performance of traditional calibration algorithms suffers. This paper proposes a new self-calibration method based on the time-frequency distributions (TFDs) in the presence of direction-dependent MC. Firstly, the time-frequency (TF) transformation is used to calculate the space-time-frequency distributions (STFDs) matrix of received signals. After that, the estimated steering vector and corresponding noise subspace are estimated by the steps of noise removing, single-source TF points extracting and clustering. Then according to the transformation relationship between the MC coefficients, steering vector and MC matrix, we deduce a set of linear equations. Finally, with two-step alternating iteration, the equations are solved by least square method in order to estimate DOA and MC coefficients. Simulations results show that the proposed algorithm can achieve direction-dependent MC self-calibration and outperforms the existing algorithms.

Optimization of multicomponent signals entered to the system using estimation of instantaneous frequency

2021 ◽  
pp. 107754632098638
Author(s):  
Milad Daneshvar ◽  
Pouria Salehi
Keyword(s):  
Instantaneous Frequency ◽  
Energy Concentration ◽  
Signal Frequency ◽  
Signal Phase ◽  
Frequency Distributions ◽  
Time Frequency ◽  
Multicomponent Signals ◽  
Frequency Changes ◽  
Changes Over Time ◽  
Zero Points

The frequency signal displays are not efficient for analyzing nonstationary signals because of their inability to represent frequency changes over time. In fact, because most of the signals are real, nonstationary, and time varying, analyzing the signals in the time–frequency domain to estimate the instantaneous frequency of a signal is inevitable. The methods of estimating the instantaneous frequency of the multicomponent signals are divided into three groups, which include the methods using signal phase derivatives that are sensitive to noise, methods that calculate the number of zero points of the signal and consider the signal frequency equal to half the frequency of the zero points and are suitable for signals that can be imagined as stationary, and methods based on time–frequency distributions and distributions such as Wigner for instantaneous frequency calculations and more for instantaneous frequency calculations on nonstationary noise signals that exhibit varied time–frequency distributions. In this article, a new hybrid algorithm is used to evaluate different distribution criteria and comparing their performance in investigating one or more features of time–frequency distributions, such as resolution and energy concentration.

scholarly journals Linking population size structure, heat stress and bleaching responses in a subtropical endemic coral

Coral Reefs ◽  
2021 ◽  
Author(s):  
Liam Lachs ◽  
Brigitte Sommer ◽  
James Cant ◽  
Jessica M. Hodge ◽  
Hamish A. Malcolm ◽  
...  
Keyword(s):  
Heat Stress ◽  
Size Structure ◽  
Temporal Trends ◽  
Early Recovery ◽  
Size Frequency Distribution ◽  
Frequency Distributions ◽  
Community Organisation ◽  
Size Frequency ◽  
Eastern Australia

AbstractAnthropocene coral reefs are faced with increasingly severe marine heatwaves and mass coral bleaching mortality events. The ensuing demographic changes to coral assemblages can have long-term impacts on reef community organisation. Thus, understanding the dynamics of subtropical scleractinian coral populations is essential to predict their recovery or extinction post-disturbance. Here we present a 10-yr demographic assessment of a subtropical endemic coral, Pocillopora aliciae (Schmidt-Roach et al. in Zootaxa 3626:576–582, 2013) from the Solitary Islands Marine Park, eastern Australia, paired with long-term temperature records. These coral populations are regularly affected by storms, undergo seasonal thermal variability, and are increasingly impacted by severe marine heatwaves. We examined the demographic processes governing the persistence of these populations using inference from size-frequency distributions based on log-transformed planar area measurements of 7196 coral colonies. Specifically, the size-frequency distribution mean, coefficient of variation, skewness, kurtosis, and coral density were applied to describe population dynamics. Generalised Linear Mixed Effects Models were used to determine temporal trends and test demographic responses to heat stress. Temporal variation in size-frequency distributions revealed various population processes, from recruitment pulses and cohort growth, to bleaching impacts and temperature dependencies. Sporadic recruitment pulses likely support population persistence, illustrated in 2010 by strong positively skewed size-frequency distributions and the highest density of juvenile corals measured during the study. Increasing mean colony size over the following 6 yr indicates further cohort growth of these recruits. Severe heat stress in 2016 resulted in mass bleaching mortality and a 51% decline in coral density. Moderate heat stress in the following years was associated with suppressed P. aliciae recruitment and a lack of early recovery, marked by an exponential decrease of juvenile density (i.e. recruitment) with increasing heat stress. Here, population reliance on sporadic recruitment and susceptibility to heat stress underpin the vulnerability of subtropical coral assemblages to climate change.

scholarly journals Issues Related to Late-Life Sexuality: Sex in Long-Term Care

2020 ◽  
Vol 4 (Supplement_1) ◽  
pp. 602-602
Author(s):  
Rachael Spalding ◽  
Peter Lichtenberg
Keyword(s):  
Best Practice ◽  
Long Term Care ◽  
Social Stigma ◽  
Late Life ◽  
Assessment Tools ◽  
Geographical Differences ◽  
Term Care ◽  
Practical Applications ◽  
Ethical And Legal Issues

Abstract Despite surrounding social stigma and stereotypes of the “asexual older adult,” older adults, including those residing in long-term care facilities, indicate that expressing their sexuality continues to be important to them (Doll, 2013). This presentation will feature presentations regarding recent research and perspectives relevant to late-life sexuality with a focus on how issues of sexual expression may particularly emerge in long-term care settings. Dr. Maggie Syme will present findings from mixed-methods, consumer-based approaches that elucidate how current and future long-term care residents view late-life sexuality, with a focus on the practical applications of these findings to inform facility administration and policies. Ethical and legal issues surrounding sexuality in long-term care will be discussed by Dr. Pamela Teaster, who will present ethical models that can translate into potential best-practice recommendations and strategies. Rachael Spalding will discuss the paucity of psychometrically sound assessment tools for measuring attitudes towards late-life sexuality and discuss their development of such a measure. Finally, Dr. Lilanta Bradley and Dr. Pamela Payne-Foster will present a framework for sexual agency in late-life and identify relevant gaps in the literature regarding gender, ethnicity/race, and geographical differences. Ultimately, this presentation will offer a forum for lively discussion among attendees regarding these pertinent topics.

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