Spectral identification of networks using sparse measurements

We propose a new method to recover global information about a network of interconnected dynamical systems based on observations made at a small number (possibly one) of its nodes. In contrast to classical identification of full graph topology, we focus on the identification of the spectral graph-theoretic properties of the network, a framework that we call spectral network identification. The main theoretical results connect the spectral properties of the network to the spectral properties of the dynamics, which are well-defined in the context of the so-called Koopman operator and can be extracted from data through the Dynamic Mode Decomposition algorithm. These results are obtained for networks of diffusively-coupled units that admit a stable equilibrium state. For large networks, a statistical approach is considered, which focuses on spectral moments of the network and is well-suited to the case of heterogeneous populations. Our framework provides efficient numerical methods to infer global information on the network from sparse local measurements at a few nodes. Numerical simulations show for instance the possibility of detecting the mean number of connections or the addition of a new vertex using measurements made at one single node, that need not be representative of the other nodes' properties.Comment: 3

Relative derived functors

AbstractThe Gabriel-Popescu Theorem states essentially that every Grothendieck category is (up to equivalence) of the form (R,σ)-mod, i.e., the quotient category of some left module category R-mod, by some Serre subcategory Tσ associated to an idempotent kernel functor σ. It follows that every Grothendieck category is a Giraud suncategory of a left module category.In this paper, we study the relationship between derived functors in a Grothendieck category C and a Giraud subcategory D. With C=R-mod, the foregoing thus yields methods to study derived functors in arbitrary Grothendieck categories from knowledge about derived functors in R-mod

News packaging during a pandemic:A computational analysis of news diffusion via Facebook

Facebook remains the most important platform where social media editors package and try to ‘sell’ media outlets’ online news articles to audiences. In one of the first studies of its kind, we assess how this practice was effectuated during the first year of the COVID-19 pandemic. We use computational analysis to determine the polarity, subjectivity and use of some linguistics features in the status messages of 140,359 Facebook posts of 17 mainstream and alternative news titles from Flanders (Belgium) between March 2020 and 2021. Among other things, we find that status messages score considerably higher than headlines in terms of polarity and subjectivity, and that they, along with the use of question and interrogation marks, peaked in the first months of the pandemic. We contextualise our findings within existing scholarship and wider trends in increasingly digitised and globalised media societies

Impact of g-factors and valleys on spin qubits in a silicon double quantum dot

We define single electron spin qubits in a silicon MOS double quantum dot system. By mapping the qubit resonance frequency as a function of gate-induced electric field, the spectrum reveals an anticrossing that is consistent with an inter-valley spin-orbit coupling. We fit the data from which we extract an inter-valley coupling strength of 43 MHz. In addition, we observe a narrow resonance near the primary qubit resonance when we operate the device in the (1,1) charge configuration. The experimental data is consistent with a simulation involving two weakly exchanged-coupled spins with a g-factor difference of 1 MHz, of the same order as the Rabi frequency. We conclude that the narrow resonance is the result of driven transitions between the T- and T+ triplet states, using an ESR signal of frequency located halfway between the resonance frequencies of the two individual spins. The findings presented here offer an alternative method of implementing two-qubit gates, of relevance to the operation of larger scale spin qubit systems

Substantiating displacement

The Phd by project ‘Substantiating displacement’ looks at a generic topic through a specific lens: it looks at architecture’s potential to trigger physical en mental (inter)action through the lens of my personal spatial artistic practice. This practice is situated on four levels (architecture, art, education and research) and was gradually transformed by engaging with architecture in three different environments (educational, professional, academic). The environment that was set-up to grind this lens is the OPAK research project ‘Art as Vacancy’. This environment opened up a space for the creation new works in trans-disciplinary collaborations with different artists selected for their specific and often complementary approach towards architectural topics. In that sense a reflection on my architectural practice was triggered by consciously displacing this practice into the overlapping field of architecture and art. As such ‘Substantiating displacement’ can best be described as an evidence based case study that aims at revealing and questioning the frameworks I work with(in), by actively engaging with mediators (a.o. art & artists) in the design and creation of new work, in order to explore the transitional space between subject and object. It presents evidence that suggests different models of how a spatial artistic practice bridges the object subject gap, a method to reveal and question the conceptual frameworks a creative practitioner works with/in and the potential of engaging with mediators in the creative practice