arXiv subjects

Frank P. Pijpers

Publications and source records attributed to Frank P. Pijpers.

15 recordsLinked to original sources

arXiv2026

Analysis of a maximum-entropy based estimator for dynamic random graph models

We study dynamic random graphs in which the set of nodes is fixed, but edges evolve over time according to an underlying stochastic mechanism. Using a maximum-entropy approach, we define a probability distribution on graph trajectories that is consistent with observed constraints, capturing the inherent uncertainty in partially observed networks. We introduce a moment-based estimator for the parameters of this distribution and establish its statistical properties, such as consistency and asymptotic normality, with explicit formulas for the covariance structure. Numerical experiments demonstrate the estimator's accuracy and robustness across various dynamic network scenarios. Our framework bridges probabilistic modeling and statistical inference in time-varying networks, providing practical tools for understanding and predicting complex edge dynamics.

math.ST↗

arXiv2026

The effect of a toroidal opinion space on opinion bi-polarisation

Many models of opinion dynamics include measures of distance between opinions. Such models are susceptible to boundary effects where the choice of the topology of the opinion space may influence the dynamics. In this paper we study an opinion dynamics model following the seminal model by Axelrod, with the goal of understanding the effect of a toroidal opinion space. To do this we systematically compare two versions of the model: one with toroidal opinion space and one with cubic opinion space. In their most basic form the two versions of our model result in similar dynamics (consensus is attained eventually). However, as we include bounded confidence and eventually per agent weighting of opinion elements the dynamics become quite contrasting. The toroidal opinion space consistently allows for a greater number of groups in steady state than the cubic opinion space model. Furthermore, the outcome of the dynamics in the toroidal opinion space model are more sensitive to the inclusion of extensions than in the cubic opinion space model.

physics.soc-ph↗

arXiv2025

Critical fragility in socio-technical systems

Socio-technical systems, where technological and human elements interact in a goal-oriented manner, provide important functional support to our societies. Here we draw attention to the underappreciated concept of timeliness -- i.e., system elements being available at the right place at the right time -- that has been ubiquitously and integrally adopted as a quality standard in the \textit{modus operandi\/} of socio-technical systems. We point out that a variety of incentives, often reinforced by competitive pressures, prompt system operators to myopically optimize for efficiencies, running the risk of inadvertently taking timeliness to the limit of its operational performance, correspondingly making the system critically fragile to perturbations by pushing the entire system towards the proverbial `edge of a cliff'. Invoking a stylized model for operational delays, we identify the limiting operational performance of timeliness, as a true critical point, where the smallest of perturbations can lead to a systemic collapse. Specifically for firm-to-firm production networks, we suggest that the proximity to \textit{critical fragility\/} is an important ingredient for understanding the fundamental ``excess volatility puzzle'' in economics. Further, in generality for optimizing socio-technical systems, we propose that critical fragility is a crucial aspect in managing the trade-off between efficiency and robustness.

physics.soc-ph↗

arXiv2024

Timeliness criticality in complex systems

In complex systems, external parameters often determine the phase in which the system operates, i.e., its macroscopic behavior. For nearly a century, statistical physics has extensively studied systems' transitions across phases, (universal) critical exponents, and related dynamical properties. Here we consider the functionality of systems, notably operations in socio-technical ones, production in economic ones and, more generally, any schedule-based system, where timing is of crucial importance. We introduce a stylized model of delay propagation on temporal networks, where the magnitude of delay-mitigating buffer acts as a control parameter. The model exhibits {\it timeliness criticality}, a novel form of critical behavior. We characterize fluctuations near criticality, commonly referred to as ``avalanches'', and identify the corresponding critical exponents. The model exhibits timeliness criticality also when run on real-world temporal systems such as production networks. Additionally, we explore potential connections with the Mode-Coupling Theory of glasses, the depinning transition and the directed polymer problem.

physics.soc-ph↗

arXiv2024

Commodity-specific triads in the Dutch inter-industry production network

Triadic motifs are the smallest building blocks of higher-order interactions in complex networks and can be detected as over-occurrences with respect to null models with only pair-wise interactions. Recently, the motif structure of production networks has attracted attention in light of its possible role in the propagation of economic shocks. However, its characterization at the level of individual commodities is still poorly understood. Here we analyze both binary and weighted triadic motifs in the Dutch inter-industry production network disaggregated at the level of 187 commodity groups, which Statistics Netherlands reconstructed from National Accounts registers, surveys and known empirical data. We introduce appropriate null models that filter out node heterogeneity and the strong effects of link reciprocity and find that, while the aggregate network that overlays all products is characterized by a multitude of triadic motifs, most single-product layers feature no significant motif, and roughly $85\%$ of the layers feature only two motifs or less. This result paves the way for identifying a simple `triadic fingerprint' of each commodity and for reconstructing most product-specific networks from partial information in a pairwise fashion by controlling for their reciprocity structure. We discuss how these results can help statistical bureaus identify fine-grained information in structural analyses of interest for policymakers.

physics.soc-ph↗

arXiv2023

Reducing societal impacts of SARS-CoV-2 interventions through subnational implementation

To curb the initial spread of SARS-CoV-2, many countries relied on nation-wide implementation of non-pharmaceutical intervention measures, resulting in substantial socio-economic impacts. Potentially, subnational implementations might have had less of a societal impact, but comparable epidemiological impact. Here, using the first COVID-19 wave in the Netherlands as a case in point, we address this issue by developing a high-resolution analysis framework that uses a demographically-stratified population and a spatially-explicit, dynamic, individual contact-pattern based epidemiology, calibrated to hospital admissions data and mobility trends extracted from mobile phone signals and Google. We demonstrate how a subnational approach could achieve similar level of epidemiological control in terms of hospital admissions, while some parts of the country could stay open for a longer period. Our framework is exportable to other countries and settings, and may be used to develop policies on subnational approach as a better strategic choice for controlling future epidemics.

physics.soc-ph↗

arXiv2021

Observational daily and regional photovoltaic solar energy production for the Netherlands

This paper presents a classical estimation problem for calculating the energy generated by photovoltaic solar energy systems in the Netherlands, on a daily, annual and regional basis. We identify two data sources to construct our methodology: pvoutput, an online portal with solar energy yield measurements, and modelled irradiance data, from the Royal Netherlands Meteorological Institute. Combining these, we obtain probability functions of observing energy yields, given the irradiance, which we then apply to our PV systems database, allowing us to calculate daily and annual solar energy yields. We examine the variation in our daily and annual estimates as a result of taking different subsets of pvoutput systems with certain specifications such as orientation, tilt and inverter to PV capacity ratio. Hence we obtain specific annual energy yields in the range of 877-946 kWh/kWp and 838-899 kWh/kWp for 2016 and 2017 respectively. The current method used at Statistics Netherlands assumes this to be 875 kWh/kWp, meaning the yields were underestimated and overestimated for 2016 and 2017 respectively. Finally, we translate our national estimates into solar energy yields per municipality. This research demonstrates that an irradiance based measure of solar energy generation is necessary to obtain more accurate energy yields on both a national and regional level.

stat.AP↗

arXiv2007

Solar-like oscillations in the G2 subgiant beta Hydri from dual-site observations

We have observed oscillations in the nearby G2 subgiant star beta Hyi using high-precision velocity observations obtained over more than a week with the HARPS and UCLES spectrographs. The oscillation frequencies show a regular comb structure, as expected for solar-like oscillations, but with several l=1 modes being strongly affected by avoided crossings. The data, combined with those we obtained five years earlier, allow us to identify 28 oscillation modes. By scaling the large frequency separation from the Sun, we measure the mean density of beta Hyi to an accuracy of 0.6%. The amplitudes of the oscillations are about 2.5 times solar and the mode lifetime is 2.3 d. A detailed comparison of the mixed l=1 modes with theoretical models should allow a precise estimate of the age of the star.

astro-ph↗

arXiv2006

The spectral resolving power of irregularly sampled time series

A method is presented for investigating the periodic signal content of time series in which a number of signals is present, such as arising from the observation of multiperiodic oscillating stars in observational asteroseismology. Standard Fourier analysis tends only to be effective in cases when the data are perfectly regularly sampled. During normal telescope operation it is often the case that there are large, diurnal, gaps in the data, that data are missing, or that the data are not regularly sampled at all. For this reason it is advantageous to perform the analysis as much as possible in the time domain. Furthermore, for quantitative analyses of the frequency content and power of all real signals, it is of importance to have good estimates of the errors on these parameters. This is easiest to perform if one can use linear combinations of the measurements. Here such a linear method is described. The method is based in part on well-known techniques in radio technology used in every FM radio receiver, and in part on the SOLA inverse method

astro-ph↗

arXiv2005

The gamma-ray giant flare from SGR1806-20: Evidence for crustal cracking via initial timescales

We report here on serendipitous observations of the intense gamma-ray flare from SGR 1806-20 that occured on 27 December 2004. Unique data from the Cluster and Double Star-2 satellites, designed to study the Earth's magnetosphere, provide the first observational evidence of three separate timescales within the early (first 100ms) phases of this class of events. These observations reveal that, in addition to the initial very steep (<0.25ms) X-ray onset, there is firstly a 4.9ms exponential rise timescale followed by a continued exponential rise in intensity on a timescale of 70ms. These three timescales are a prominent feature of current theoretical models including the timescale (several ms) for fracture propagation in the crust of the neutron star.

astro-ph↗

arXiv2003

Selection criteria for targets of asteroseismic campaigns

Various dedicated satellite projects are underway or in advanced stages of planning to perform high-precision, long duration time series photometry of stars, with the purpose of using the frequencies of stellar oscillations to put new constraints on the internal structure of stars. It is known (cf. Brown, et al. 1994) that the effectiveness of oscillation frequencies in constraining stellar model parameters is significantly higher if classical parameters such as effective temperature, and luminosity are known with high precision. In order to optimize asteroseismic campaigns it is therefore useful to select targets from among candidates for which good spectroscopic and astrometric data already exists. This paper presents selection criteria, as well as redeterminations of stellar luminosity and reddening for stars satisfying these criteria.

astro-ph↗

arXiv2002

The time delay of the quadruple quasar RX J0911.4+0551

We present optical lightcurves of the gravitationally lensed components A (=A1+A2+A3) and B of the quadruple quasar RX J0911.4+0551 (z = 2.80). The observations were primarily obtained at the Nordic Optical Telescope between 1997 March and 2001 April and consist of 74 I-band data points for each component. The data allow the measurement of a time delay of 146 +- 8 days (2 sigma) between A and B, with B as the leading component. This value is significantly shorter than that predicted from simple models and indicates a very large external shear. Mass models including the main lens galaxy and the surrounding massive cluster of galaxies at z = 0.77, responsible for the external shear, yield H_0 = 71 +- 4 (random, 2 sigma) +- 8 (systematic) km/s/Mpc. The systematic model uncertainty is governed by the surface-mass density (convergence) at the location of the multiple images.

astro-ph↗

arXiv1997

Solar rotation inversions and the relationship between a-coefficients and mode splittings

From the observing campaigns of a number of helioseismic telescope networks such as the Global Oscillation Network Group (GONG) and also from the Solar Heliospheric Observatory satellite (SoHO), helioseismologists now have data on in excess of 20000 oscillation frequencies of the modes known collectively as the 5 minute oscillations. Depending on the order and degree of the modes these data are available either as individual frequencies of modes with known radial order n, spherical harmonic degree l, and order m, or as so-called `a-coefficients' which are obtained by fitting polynomials to ridges of power in the (l,ν) diagram. Although there is a one-to-one relationship between these two types of data, the conversion between them is not straightforward which complicates comparison of helioseismic inference between the two types of data. Their relationship with each other and with the solar rotation rate is clarified in this paper.

astro-ph↗

arXiv1996

The determination of time lags using SOLA

A common problem in astronomy is the determination of the time shift between two otherwise identical time series of measured flux from a variable source, in short the determination of a time lag. Two examples of where this problem occurs are in the determination of the Hubble constant from multiple images of gravitationally lensed variable quasars and also in the determination of distances to OH/IR stars. It is shown here that this problem can be seen as a restricted inversion problem. It therefore can be solved using the subtractive optimally localized averages (SOLA) method for inversion which has been described elsewhere (Pijpers & Thompson 1992, 1994 ; Pijpers & Wanders 1994).

astro-ph↗

arXiv1994

Reverberation mapping of active galactic nuclei : The SOLA method for time-series inversion

In this paper a new method is presented to find the transfer function of the broad-line region in active galactic nuclei. The subtractive optimally localized averages (SOLA) method is a modified version of the Backus-Gilbert method and is presented as an alternative to the more often used maximum-entropy method. The SOLA method has been developed for use in helioseismology. It has been applied to the solar oscillation frequency splitting data currently available to deduce the internal rotation rate of the sun. The original SOLA method is reformulated in the present paper to cope with the slightly different problem of inverting time series. We use simulations to test the viability of the method and apply the SOLA method to the real data of the Seyfert-1 galaxy NGC 5548. We investigate the effects of measurement errors and how the resolution of the TF critically depends upon both the sampling rate and the photometric accuracy of the data. A uuencoded compressed postscript file of the paper which includes the figures is available by anonymous ftp at ftp://solaris.astro.uu.se/pub/articles/atmos/frank/PijWan.uue

astro-ph↗