Signatures of self-organized dynamics in rapidly driven critical sandpiles.

We study two prototypical models of self-organized criticality, namely sandpile automata with deterministic (Bak-Tang-Wiesenfeld) and probabilistic (Manna model) dynamical rules, focusing on the nature of stress fluctuations induced by driving-adding grains during avalanche propagation, and dissipation through avalanches that hit the system boundary. Our analysis of stress evolution time series reveals robust cyclical trends modulated by collective fluctuations with dissipative avalanches. These modulated cycles attain higher harmonics, characterized by multifractal measures within a broad range of timescales.

Comparing prediction efficiency in the BTW and Manna sandpiles.

The state-of-the-art in the theory of self-organized criticality reveals that a certain inactivity precedes extreme events, which are located on the tail of the event probability distribution with respect to their sizes. The existence of the inactivity allows for the prediction of these events in advance. In this work, we explore the predictability of the Bak-Tang-Wiesenfeld (BTW) and Manna models on the square lattice as a function of the lattice length.

Explanation of flicker noise with the Bak-Tang-Wiesenfeld model of self-organized criticality.

With the original Bak-Tang-Wisenefeld (BTW) sandpile we uncover the 1/φ noise in the mechanism maintaining self-organized criticality (SOC)-the question raised together with the concept of SOC. The BTW sandpile and the phenomenon of SOC in general are built on the slow time scale at which the system is loaded and the fast time scale at which the stress is transported outward from overloaded locations. Exploring the dynamics of stress in the slow time in the BTW sandpile, we posit that it follows cycles of gradual stress accumulation that end up with an abrupt stress release and the drop of the system to subcritical state.

Uptake and Persistent Use of HIV Preexposure Prophylaxis Among Key Populations: Results From Ukraine's Scaled National Preexposure Prophylaxis Program.

Background: Ukraine has implemented ambitious HIV-prevention programs since 1999 and began offering preexposure prophylaxis (PrEP) in 2017. Little is known about PrEP uptake and persistence in this setting.

Setting: We analyzed data from 40 facilities providing PrEP in 11 oblasts (regions) of Ukraine between October 2020 and February 2022.

Impact of war on HIV-related healthcare services and health workers in eastern Ukraine: a qualitative study.

The 2022 Russian invasion of Ukraine has caused serious challenges for healthcare workers (HCWs) and HIV-related healthcare services. This study assessed the effects of the invasion on HCWs wellbeing and on continuity of HIV services, using in-depth interviews with HCWs from facilities offering HIV antiretroviral therapy (ART) and pre-exposure prophylaxis (PrEP) services in the Donetsk region of Eastern Ukraine. A directed content analysis, with both inductive and deductive approaches, was conducted.