74 research outputs found
COVID-19 esimeses laines Tallinna ja Saaremaa näitel
Local government decision-making in a crisis: a retrospect to the initial phase of the COVID-19 crisis in EstoniaThe study aimed to describe the factors that influenced COVID-19 crisis units’ decision-making during the first wave in Estonia, on the example of the municipalities of Tallinn and Saaremaa. The studied factors were categorized as internal and external, of which the external were the predominant influencers. In the first wave, the main factors influencing local governments’ decision-making were time pressure, stress, pressure from media and the public, and pressure from central government or other organizations.The factors’ influence was felt greater in Saaremaa where the situation escalated to a severe crisis already in the issue phase. Interviews with the decision-makers revealed real-life examples of the implications of those factors – problems in the legal sphere, click-bait media as an influencer of decision-making processes, confusing guidelines from central government etc. Correlation analysis of the factors revealed 13 statistically relevant interactions, which indicates that the factors do not just influence decision-making but also each other.The research results provide a novel insight into the decision-making processes in the early phase of the pandemic crisis in VUCA environment at the local government level and serve as a baseline for follow-up studies in the latter phases of the COVID crisis. Additionally, the article finds that by choosing the factors to be mitigated wisely, crisis managers and experts that support them in crisis management can have significantly better control over the quality of decision-making as a process.Keywords: decision-making, COVID-19, VUCA, crisis management, factors, local governmentVõtmesõnad: otsustamine, COVID-19, VUCA, kriisijuhtimine, mõjutegurid, kohalik omavalitsu
Boundary drive induced formation of aggregate condensates in stochastic transport with short-range interactions
We discuss the effects of particle exchange through open boundaries and the
induced drive on the phase structure and condensation phenomena of a stochastic
transport process with tunable short-range interactions featuring
pair-factorized steady states (PFSS) in the closed system. In this model, the
steady state of the particle hopping process can be tuned to yield properties
from the zero-range process (ZRP) condensation model to those of models with
spa- tially extended condensates. By varying the particle exchange rates as
well as the presence of a global drift, we observe a phase transition from a
free particle gas to a phase with condensates aggregated to the boundaries.
While this transition is similar to previous results for the ZRP, we find that
the mechanism is different as the presence of the boundary actually influences
the interaction due to the non-zero interaction range.Comment: 6 pages, 7 figure
A simple non-equilibrium, statistical-physics toy model of thin-film growth
We present a simple non-equilibrium model of mass condensation with
Lennard-Jones interactions between particles and the substrate. We show that
when some number of particles is deposited onto the surface and the system is
left to equilibrate, particles condense into an island if the density of
particles becomes higher than some critical density. We illustrate this with
numerically obtained phase diagrams for three-dimensional systems. We also
solve a two-dimensional counterpart of this model analytically and show that
not only the phase diagram but also the shape of the cross-sections of
three-dimensional condensates qualitatively matches the two-dimensional
predictions. Lastly, we show that when particles are being deposited with a
constant rate, the system has two phases: a single condensate for low
deposition rates, and multiple condensates for fast deposition. The behaviour
of our model is thus similar to that of thin film growth processes, and in
particular to Stranski-Krastanov growth.Comment: 26 pages, 16 figure
Open boundary conditions in stochastic transport processes with pair-factorized steady states
Using numerical methods we discuss the effects of open boundary conditions on
condensation phenomena in the zero-range process (ZRP) and transport processes
with pair-factorized steady states (PFSS), an extended model of the ZRP with
nearest-neighbor interaction. For the zero-range process we compare to
analytical results in the literature with respect to criticality and
condensation. For the extended model we find a similar phase structure, but
observe supercritical phases with droplet formation for strong boundary drives.Comment: conference contribution for the 27th Annual CSP Workshop on "Recent
Developments in Computer Simulation Studies in Condensed Matter Physics", CSP
2014 5 pages, 5 figure
Coarse-Grained Modeling of Genetic Circuits as a Function of the Inherent Time Scales
From a coarse-grained perspective the motif of a self-activating species,
activating a second species which acts as its own repressor, is widely found in
biological systems, in particular in genetic systems with inherent oscillatory
behavior. Here we consider a specific realization of this motif as a genetic
circuit, in which genes are described as directly producing proteins, leaving
out the intermediate step of mRNA production. We focus on the effect that
inherent time scales on the underlying fine-grained scale can have on the
bifurcation patterns on a coarser scale in time. Time scales are set by the
binding and unbinding rates of the transcription factors to the promoter
regions of the genes. Depending on the ratio of these rates to the decay times
of the proteins, the appropriate averaging procedure for obtaining a
coarse-grained description changes and leads to sets of deterministic
equations, which differ in their bifurcation structure. In particular the
desired intermediate range of regular limit cycles fades away when the binding
rates of genes are of the same order or less than the decay time of at least
one of the proteins. Our analysis illustrates that the common topology of the
widely found motif alone does not necessarily imply universal features in the
dynamics.Comment: 29 pages, 16 figure
Stochastic Description of a Bistable Frustrated Unit
Mixed positive and negative feedback loops are often found in biological
systems which support oscillations. In this work we consider a prototype of
such systems, which has been recently found at the core of many genetic
circuits showing oscillatory behaviour. Our model consists of two interacting
species A and B, where A activates not only its own production, but also that
of its repressor B. While the self-activation of A leads already to a bistable
unit, the coupling with a negative feedback loop via B makes the unit
frustrated. In the deterministic limit of infinitely many molecules, such a
bistable frustrated unit is known to show excitable and oscillatory dynamics,
depending on the maximum production rate of A which acts as a control
parameter. We study this model in its fully stochastic version and we find
oscillations even for parameters which in the deterministic limit are deeply in
the fixed-point regime. The deeper we go into this regime, the more irregular
these oscillations are, becoming finally random excitations whenever
fluctuations allow the system to overcome the barrier for a large excursion in
phase space. The fluctuations can no longer be fully treated as a perturbation.
The smaller the system size (the number of molecules), the more frequent are
these excitations. Therefore, stochasticity caused by demographic noise makes
this unit even more flexible with respect to its oscillatory behaviour.Comment: 28 pages, 17 figure
Application of a steady states transport model to condensation of water droplets on a substrate
Quantitative performance and optimal regularization parameter in block sequential regularized expectation maximization reconstructions in clinical 68Ga-PSMA PET/MR.
BACKGROUND: In contrast to ordered subset expectation maximization (OSEM), block sequential regularized expectation maximization (BSREM) positron emission tomography (PET) reconstruction algorithms can run until full convergence while controlling image quality and noise. Recent studies with BSREM and F-FDG PET reported higher signal-to-noise ratios and higher standardized uptake values (SUV). In this study, we investigate the optimal regularization parameter (β) for clinical Ga-PSMA PET/MR reconstructions in the pelvic region applying time-of-flight (TOF) BSREM in comparison to TOF OSEM. Two-minute emission data from the pelvic region of 25 patients who underwent Ga-PSMA PET/MR were retrospectively reconstructed. Reference OSEM reconstructions had 28 subsets and 2 iterations. BSREM reconstructions were performed with 15 β values between 150 and 1200. Regions of interest (ROIs) were drawn around lesions and in uniform background. Background SUVmean (average) and SUVstd (standard deviation), and lesion SUVmax (average of 5 hottest voxels) were calculated. Differences were analyzed using the Wilcoxon matched pairs signed-rank test.
RESULTS: A total of 40 lesions were identified in the pelvic region. Background noise (SUVstd) and lesions SUVmax decreased with increasing β. Image reconstructions with β values lower than 400 have higher (p < 0.01) background noise, compared to the reference OSEM reconstructions, and are therefore less useful. Lesions with low activity on images reconstructed with β values higher than 600 have a lower (p < 0.05) SUVmax compared to the reference. These reconstructions are likely visually appealing due to the lower background noise, but the lower SUVmax could possibly render small low-uptake lesions invisible.
CONCLUSIONS: In our study, we showed that PET images reconstructed with TOF BSREM in combination with the Ga-PSMA tracer result in lower background noise and higher SUVmax values in lesions compared to TOF OSEM. Our study indicates that a β value between 400 and 550 might be the optimal compromise between high SUVmax and low background noise
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