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Aging and memory of transitional turbulence
No full textThe recent classification of the onset of turbulence as a directed percolation (DP) phase transition has been applied to all major shear flows including pipe, channel, Couette and boundary layer flows. A cornerstone of the DP analogy is the memoryless (Poisson) property of turbulent sites. We here show that, for the classic case of channel flow, neither the decay nor the proliferation of turbulent stripes is memoryless. As demonstrated by a standard analysis of the respective survival curves, isolated channel stripes, in the immediate vicinity of the critical point, age. Consequently, the one to one mapping between turbulent stripes and active DP-sites is not fulfilled in this low Reynolds number regime. In addition, the interpretation of turbulence as a chaotic saddle with supertransient properties, the basis of recent theoretical progress, does not apply to individual localized stripes. The discrepancy between channel flow and the transition models established for pipe and Couette flow, illustrates that seemingly minor geometrical differences between flows can give rise to instabilities and growth mechanisms that fundamentally alter the nature of the transition to turbulence
Sex chromosome evolution in action in fourspine sticklebacks
No full textThe suppression of recombination between young X and Y chromosomes is a crucial step in their evolution, but why it occurs is not known. The detailed characterization of the polymorphic sex chromosomes of the fourspine stickleback by Liu et al. promises to shed new light on this longstanding question
The configuration of the vacuole is driven by clathrin-mediated trafficking in root cells of Arabidopsis thaliana
No full textThe central vacuole is a multifunctional organelle with the most significant occupancy in a differentiated plant cell. Plants depend on the function of the vacuole for critical development, growth, and environmental responses. As the cell expands, the vacuole changes shape and size, increasing its membrane and luminal content. The set of these events is called the vacuolar configuration process, which has not been well described. Our research highlights the impact of plasma membrane internalization on vacuole morphology during the vacuolar configuration process. We observed a direct correlation between differential endocytosis rates and the enrichment of vacuolar membranous structures. Chemical and genetic interference with clathrin-mediated endocytosis (CME) revealed that it is required for the vacuolar configuration of growing root cells. The contribution of CME to the vacuole configuration process co-occurs with the induction of post-trans-Golgi network (TGN)/early endosome (EE) trafficking with the participation of the Rab GTPases ARA6 and ARA7. Our results show that the CME plays an active role during vacuole configuration, most probably carrying the material that allows the establishment of the vacuole in elongating cells. Since membrane trafficking through the EE/TGN is required to reach the vacuole, additional players must be defined
Prospects of nanoscience with nanocrystals: 2025 edition
No full textNanocrystals (NCs) of various compositions have made important contributions to science and technology, with their impact recognized by the 2023 Nobel Prize in Chemistry for the discovery and synthesis of semiconductor quantum dots (QDs). Over four decades of research into NCs has led to numerous advancements in diverse fields, such as optoelectronics, catalysis, energy, medicine, and recently, quantum information and computing. The last 10 years since the predecessor perspective “Prospect of Nanoscience with Nanocrystals” was published in ACS Nano have seen NC research continuously evolve, yielding critical advances in fundamental understanding and practical applications. Mechanistic insights into NC formation have translated into precision control over NC size, shape, and composition. Emerging synthesis techniques have broadened the landscape of compounds obtainable in colloidal NC form. Sophistication in surface chemistry, jointly bolstered by theoretical models and experimental findings, has facilitated refined control over NC properties and represents a trusted gateway to enhanced NC stability and processability. The assembly of NCs into superlattices, along with two-dimensional (2D) photolithography and three-dimensional (3D) printing, has expanded their utility in creating materials with tailored properties. Applications of NCs are also flourishing, consolidating progress in fields targeted early on, such as optoelectronics and catalysis, and extending into areas ranging from quantum technology to phase-change memories. In this perspective, we review the extensive progress in research on NCs over the past decade and highlight key areas where future research may bring further breakthroughs
Beyond the pseudoforest strong Nine Dragon Tree theorem
No full textThe pseudoforest version of the Strong Nine Dragon Tree Conjecture states that if a graph G has maximum average degree mad(G) = 2 maxH⊆G e(H)/v(H) at most 2(k + d/d+k+1), then it has a decomposition into k + 1 pseudoforests where in one pseudoforest F the components of F have at most d edges. This was proven in 2020 in Grout and Moore (2020). We strengthen this
theorem by showing that we can find such a decomposition where additionally F is acyclic, the diameter of the components of F is at most 2ℓ + 2, where ℓ =⌊d−1/k+1⌋, and at most 2ℓ + 1 if
d ≡ 1 mod (k + 1). Furthermore, for any component K of F and any z ∈ N, we have diam(K) ≤ 2z if e(K) ≥ d − z(k − 1) + 1. We also show that both diameter bounds are best possible as an
extension for both the Strong Nine Dragon Tree Conjecture for pseudoforests and its original conjecture for forests. In fact, they are still optimal even if we only enforce F to have any constant maximum degree, instead of enforcing every component of F to have at most d edges
ISTA Thesis
No full textQuantitative properties offer a framework for specifying and verifying system behaviors beyond the traditional boolean perspective. For example, while a boolean property may specify whether a server eventually grants every request it receives, a quantitative one may map each server execution to its average response time. This quantitative view is relatively well-studied in the context of static verification. However, although such properties often appear in practice as performance or robustness measures in a dynamic verification context, a general theoretical framework for their analysis and classification from a monitoring perspective is still missing.
In this thesis, we aim to develop such a framework that takes resource-precision tradeoffs of monitors as a central consideration. We present the first theory of monitorability for quantitative properties where monitors can be naturally approximate and compared regarding their precision and resource use. In particular, we show that additional monitor resources such as registers or states lead to strictly better approximations for some properties. To enable such analyses in a machine-model independent way, we describe an abstract notion of monitors that can be instantiated with concrete models of monitors. Within this framework, we study how abstract monitors behave and identify classes of properties amenable to approximate monitoring with resource-precision considerations. We then extend the boolean safety-liveness dichotomy and safety-progress hierarchy to the quantitative setting with a monitoring perspective. In particular, we prove that every property is the pointwise minimum of a safety property and a liveness property, and properties that are both safe and co-safe can be approximately monitored arbitrarily precisely using only finitely many states. We also study the classes of quantitative properties definable by finite-state quantitative automata and provide algorithms for deciding their safety or liveness as well as their safety-liveness decompositions. Finally, we present the first general-purpose tool for automating the analysis, verification, and monitoring of quantitative automata.
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Reaction precursor-mediated formation of stable supercrystals in colloidal nanocrystal synthesis: PbTe case
No full textSupercrystals represent three-dimensional orderings of colloidal nanocrystals (NCs), showcasing collective properties in photonics, phononics, and electronics applications.1,2 Recent studies have shown that such assemblies are directly produced during nanocrystal reactions.3–6 However, a fundamental understanding of in situ formed supercrystals that withstand typical NC purification processes remains underexplored, which is important for further use. Herein, we report the reaction precursor-mediated formation of stable PbTe supercrystals. Rationalizing the formation of these assemblies through small-angle x-ray scattering (SAXS) measurements, we unveil their formation mechanism. Our findings reveal that the supercrystal formation occurs in the presence of an excess of lead oleates in the crude solution. It should be noted that the formed supercrystals can be stabilized under specific conditions determined by the lead oleate cluster concentration, content of trioctylphosphine telluride (TOP-Te), NC size and the need of an annealing step at mild conditions. Furthermore, this approach allows for the continuous growth of a secondary phase within the supercrystal; for example in the case of PbTe supercrystals, a PbS shell can be grown on each PbTe NC constituent, resulting in core-shell PbTe-PbS supercrystals. Our work elucidates that reaction precursors play an important role in in situ SC formation and stabilization, implying the possibility of applying this knowledge to other NC reactions
PMLR
No full textWe study the problem of predictive runtime monitoring of black-box dynamical systems with quantitative safety properties. The black-box setting stipulates that the exact semantics of the dynamical system and the controller are unknown, and that we are only able to observe the state of the controlled (aka, closed-loop) system at finitely many time points. We present a novel framework for predicting future states of the system based on the states observed in the past. The numbers of past states and of predicted future states are parameters provided by the user. Our method is based on a combination of Taylor’s expansion and the backward difference operator for numerical differentiation. We also derive an upper bound on the prediction error under the assumption that the system dynamics and the controller are smooth. The predicted states are then used to predict safety violations ahead in time. Our experiments demonstrate practical applicability of our method for complex black-box systems, showing that it is computationally lightweight and yet significantly more accurate than the state-of-the-art predictive safety monitoring techniques
PMLR
No full textIn this paper, we study the problem of estimating the unknown mean θ of a unit variance Gaussian distribution in a locally differentially private (LDP) way. In the high-privacy regime (ϵ≤1
), we identify an optimal privacy mechanism that minimizes the variance of the estimator asymptotically. Our main technical contribution is the maximization of the Fisher-Information of the sanitized data with respect to the local privacy mechanism Q. We find that the exact solution Qθ,ϵ of this maximization is the sign mechanism that applies randomized response to the sign of Xi−θ, where X1,…,Xn are the confidential iid original samples. However, since this optimal local mechanism depends on the unknown mean θ, we employ a two-stage LDP parameter estimation procedure which requires splitting agents into two groups. The first n1 observations are used to consistently but not necessarily efficiently estimate the parameter θ by θn1~
. Then this estimate is updated by applying the sign mechanism with θ~n1 instead of θ
to the remaining n−n1 observations, to obtain an LDP and efficient estimator of the unknown mean
ISTA Thesis
No full textCooperation, that is, one person paying a cost for another's benefit, is a fundamental principle without which no form of society could exist. The extent to which humans cooperate with each other is also an essential feature that differentiates them from other animals. Cooperation occurs even in the absence of altruistic motivations, when it is selfishly incentivised by the expectation of a future reward. For example, many economic interactions are well described that way. This kind of cooperation requires that people exhibit reciprocal behaviour that acts as a mechanism that rewards cooperation.
With game-theoretic models, it is possible to formally study potential such mechanisms and under what conditions they can exist. This thesis contributes to this effort by analysing recently introduced models of cooperation that advance on previous work by taking into account the potential for pre-existing inequality among cooperating individuals as well as the different forms that reciprocity can take.
Individuals may differ both intrinsically, in their abilities, as well as extrinsically, in the amount of resources they have available. Allowing for such differences in a model of cooperation helps to understand how inequality affects the potential for, and outcomes of, cooperation among unequals. In this thesis, it is shown that in the presence of intrinsic inequality, a similar unequal distribution of resources can increase the potential for cooperation. This effect is stronger the smaller the group is in which cooperation takes place. It is also shown that under particular assumptions, if the unequal members of a group vary the size of their contributions to a cooperative effort over time, they can thereby increase their efficiency and improve the collective outcome.
Cooperative behaviour in a two-person interaction can be rewarded either by direct reciprocation whenever the same two people interact again, or indirectly by a third party who observed the interaction. In the latter case of indirect reciprocity, individuals are proximally rewarded by a good reputation, which ultimately translates to being rewarded with cooperative behaviour by others. This mechanism can enable selfishly motivated cooperation even in circumstances where individuals are unlikely to meet again, akin to how money facilitates trade. While these two forms of reciprocity have mostly been studied in isolation, this thesis analyses both direct and indirect reciprocity in a general model in order to compare their relative effectiveness under different circumstances. The contribution of this thesis is an extension of previous work regarding a specific kind of interaction, whose parameters allow for convenient mathematical analysis, to the most general set of possible interactions