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Identifying Pd9OX as the optimum catalyst for the direct synthesis of H2O2 through microkinetic modeling with coverage effects
No full textIdentifying efficient active sites for the direct synthesis of hydrogen peroxide over Pd-based catalysts has been a subject of considerable debate. In this study, we employ particle swarm optimization method and density functional theory to explore the H2O2 synthesis mechanism on Pd, PdO, and the partially oxidized surface (Pd9OX). A comprehensive mechanism for Pd9OX is elucidated, and subsequent coverage-dependent kinetic analysis allows for a quantitative assessment of catalytic performance at the interphase. Our findings conclusively establish that the interphase between Pd and PdO represents the optimal active site. Phase diagram analysis further aids in determining stable structures under reaction conditions. At 298.15 K and under oxygen balance, the Pd9O6 surface remains stable throughout the reaction, demonstrating high activity and selectivity. This work underscores the significance of the interphase in comprehending catalytic performance and unveils promising avenues for optimizing catalyst performance by controlling reaction conditions and surface composition
ISTA Master's Thesis
No full textEpilepsy affects about 50 to 65 million people globally. It summarizes a spectrum of neurological
disorders that have in common a hyperactivity of the neuronal network resulting in seizures. A common
assumption is that an imbalance between neuronal excitation and inhibition is a key mechanism in
seizure generation and epileptogeneisis. In at least one-third of the patients, current therapies have
proven unsuccessful in treating seizure progression. One potential reason could be that the therapies
only focus on neurons. Recent studies suggest that neuronal hyperactivity causes a microglial
response, which reinstates brain homeostasis. Additionally, interactions between microglia and neurons
have been shown to inhibit neuronal firing and dampen seizure activity. However, the exact relationship
between microglia and seizure progression in epilepsy is yet to be elucidated. A main bottleneck is that
several studies investigate microglia dynamics in ex vivo slice models, which can severely affect the
microglia dynamics due to their rapid response to environmental changes. On the other hand, in vivo
studies focus mostly on behavior characterization of the epileptic seizure phenotype and their long-term
consequences on microglia activity leaving out the direct consequences of acute seizure activity on
microglia dynamics.
Here, we perform a pilot study to combine electroencephalography (EEG) and in vivo live imaging to
directly monitor and correlate the onset of seizure activity with microglia response. To induce seizures,
we take advantage of the kainic acid (KA) model, which represents similar neuropathological and
electroencephalographic features seen in human patients with temporal lobe epilepsy (TLE). After
confirmation of induction of the seizure and microglia activity in the hippocampus as a focal point, we
investigated whether these changes also reached the primary visual cortex (V1) as a secondary
generalized seizure activity. Indeed, we found that microglia changed their morphology at high doses
of KA in the V1. Next, we optimized each of the two methodological components: for the EEG recording,
our initial attempts under the microscope suffered from extensive electrical noise, which overlaid the
actual signal. Thus, we built a customized Faraday-cage and confirmed that the signal-to-noise ratio
was sufficiently reduced to be able to record brain oscillatory activity. For the in vivo live imaging of
microglia, we had to optimize the imaging parameters, so that we would be able to detect microglial
processes in a sufficient resolution to track their process changes. Finally, we combined both
methodologies with the KA model. We confirmed that KA induced seizure activity and found first
indication that those correlate with microglia volume changes.
Overall, we have developed a first methodological approach, which allows the analysis of the acute
effects of seizure onset on microglia. Future studies will have to continue to optimize the drift during
imaging recording and the post-image analysis
Optical Shubnikov-de Haas oscillations in two-dimensional electron systems
No full textWe report on dynamic Shubnikov–de Haas (SdH) oscillations that are measured in the optical response, subterahertz transmittance of two-dimensional systems, and reveal two distinct types of oscillation nodes: “universal” nodes at integer ratios of radiation and cyclotron frequencies and “tunable” nodes at positions sensitive to all parameters of the structure. The nodes in both real and imaginary parts of the measured complex transmittance are analyzed using a dynamic version of the static Lifshitz-Kosevich formula. These results demonstrate that the node structure of the dynamic SdH oscillations provides an all-optical access to quantization- and interaction-induced renormalization effects, in addition to parameters one can obtain from the static SdH oscillations
LNCS
No full textMemory-hard functions (MHF) are functions whose evaluation provably requires
a lot of memory. While MHFs are an unkeyed primitive, it is natural to consider the
notion of trapdoor MHFs (TMHFs). A TMHF is like an MHF, but when sampling
the public parameters one also samples a trapdoor which allows evaluating the
function much cheaper.
Biryukov and Perrin (Asiacrypt’17) were the first to consider TMHFs and put
forth a candidate TMHF construction called Diodon that is based on the Scrypt
MHF (Percival, BSDCan’09). To allow for a trapdoor, Scrypt’s initial hash chain
is replaced by a sequence of squares in a group of unknown order where the order of
the group is the trapdoor. For a length n sequence of squares and a group of order
N, Diodon’s cumulative memory complexity (CMC) is O(n2log N) without the
trapdoor and O(n log(n) log(N)2) with knowledge of it.
While Scrypt is proven to be optimally memory-hard in the random oracle
model (Alwen et al., Eurocrypt’17), Diodon’s memory-hardness has not been
proven so far. In this work, we fill this gap by rigorously analyzing a specific
instantiation of Diodon. We show that its CMC is lower bounded by Ω( n2log nlog N)
which almost matches the upper bound. Our proof is based Alwen et al.’s lower
bound on Scrypt’s CMC but requires non-trivial modifications due to the algebraic
structure of Diodon. Most importantly, our analysis involves a more elaborate
compression argument and a solvability criterion for certain systems of Diophantine
equations
Majority dynamics and internal partitions of random regular graphs: Experimental results
No full textThis paper focuses on Majority Dynamics in sparse graphs, in particular, as a
tool to study internal cuts. It is known that, in Majority Dynamics on a finite
graph, each vertex eventually either comes to a fixed state, or oscillates with
period two. The empirical evidence acquired by simulations suggests that for
random odd-regular graphs, approximately half of the vertices end up
oscillating with high probability. We notice a local symmetry between
oscillating and non-oscillating vertices, that potentially can explain why the
fraction of the oscillating vertices is concentrated around . In
our simulations, we observe that the parts of random odd-regular graph under
Majority Dynamics with high probability do not contain -cores at any timestep, and thus, one cannot use Majority Dynamics to
prove that internal cuts exist in odd-regular graphs almost surely. However, we
suggest a modification of Majority Dynamics, that yields parts with desired
cores with high probability
ISTA Thesis
No full textThis dissertation is the summary of the author’s work, concerning the relations between
cohomology rings of algebraic varieties and rings of functions on zero schemes and fixed
point schemes. For most of the thesis, the focus is on smooth complex varieties with
an action of a principally paired group, e.g. a parabolic subgroup of a reductive group.
The fundamental theorem 5.2.11 from co-authored article [66] says that if the principal
nilpotent has a unique zero, then the zero scheme over the Kostant section is isomorphic
to the spectrum of the equivariant cohomology ring, remembering the grading in terms of
a C^* action. A similar statement is proved also for the G-invariant functions on the total
zero scheme over the whole Lie algebra. Additionally, we are able to prove an analogous
result for the GKM spaces, which poses the question on a joint generalisation.
We also tackle the situation of a singular variety. As long as it is embedded in a smooth
variety with regular action, we are able to study its cohomology as well by means of
the zero scheme. In case of e.g. Schubert varieties this determines the cohomology ring
completely. In largest generality, this allows us to see a significant part of the cohomology
ring.
We also show (Theorem 6.2.1) that the cohomology ring of spherical varieties appears as
the ring of functions on the zero scheme. The computational aspect is not easy, but one
can hope that this can bring some concrete information about such cohomology rings.
Lastly, the K-theory conjecture 6.3.1 is studied, with some results attained for GKM
spaces.
The thesis includes also an introduction to group actions on algebraic varieties. In
particular, the vector fields associated to the actions are extensively studied. We also
provide a version of the Kostant section for arbitrary principally paired group, which
parametrises the regular orbits in the Lie algebra of an algebraic group. Before proving
the main theorem, we also include a historical overview of the field. In particular we bring
together the results of Akyildiz, Carrell and Lieberman on non-equivariant cohomology
rings
New fluorescent auxin derivatives: Anti-auxin activity and accumulation patterns in Arabidopsis thaliana
No full textAuxin belongs among major phytohormones and governs multiple aspects of plant growth and development. The establishment of auxin concentration gradients, determines, among other processes, plant organ positioning and growth responses to environmental stimuli.
Herein we report the synthesis of new NBD- or DNS-labelled IAA derivatives and the elucidation of their biological activity, fluorescence properties and subcellular accumulation patterns in planta. These novel compounds did not show auxin-like activity, but instead antagonized physiological auxin effects. The DNS-labelled derivatives FL5 and FL6 showed strong anti-auxin activity in roots and hypocotyls, which also occurred at the level of gene transcription as confirmed by quantitative PCR analysis. The auxin antagonism of our derivatives was further demonstrated in vitro using an SPR-based binding assay. The NBD-labelled compound FL4 with the best fluorescence properties proved to be unsuitable to study auxin accumulation patterns in planta. On the other hand, the strongest anti-auxin activity possessing compounds FL5 and FL6 could be useful to study binding mechanisms to auxin receptors and for manipulations of auxin-regulated processes
Multi-objective reward generalization: Improving performance of Deep Reinforcement Learning for applications in single-asset trading
No full textWe investigate the potential of Multi-Objective, Deep Reinforcement Learning for stock and cryptocurrency single-asset trading: in particular, we consider a Multi-Objective algorithm which generalizes the reward functions and discount factor (i.e., these components are not specified a priori, but incorporated in the learning process). Firstly, using several important assets (BTCUSD, ETHUSDT, XRPUSDT, AAPL, SPY, NIFTY50), we verify the reward generalization property of the proposed Multi-Objective algorithm, and provide preliminary statistical evidence showing increased predictive stability over the corresponding Single-Objective strategy. Secondly, we show that the Multi-Objective algorithm has a clear edge over the corresponding Single-Objective strategy when the reward mechanism is sparse (i.e., when non-null feedback is infrequent over time). Finally, we discuss the generalization properties with respect to the discount factor. The entirety of our code is provided in open-source format
Dynamic and selective engrams emerge with memory consolidation
No full textEpisodic memories are encoded by experience-activated neuronal ensembles that remain necessary and sufficient for recall. However, the temporal evolution of memory engrams after initial encoding is unclear. In this study, we employed computational and experimental approaches to examine how the neural composition and selectivity of engrams change with memory consolidation. Our spiking neural network model yielded testable predictions: memories transition from unselective to selective as neurons drop out of and drop into engrams; inhibitory activity during recall is essential for memory selectivity; and inhibitory synaptic plasticity during memory consolidation is critical for engrams to become selective. Using activity-dependent labeling, longitudinal calcium imaging and a combination of optogenetic and chemogenetic manipulations in mouse dentate gyrus, we conducted contextual fear conditioning experiments that supported our model’s predictions. Our results reveal that memory engrams are dynamic and that changes in engram composition mediated by inhibitory plasticity are crucial for the emergence of memory selectivity
The stochastic primitive equations with transport noise and turbulent pressure
No full textIn this paper we consider the stochastic primitive equation for geophysical flows subject to transport noise and turbulent pressure. Admitting very rough noise terms, the global existence and uniqueness of solutions to this stochastic partial differential equation are proven using stochastic maximal L² regularity, the theory of critical spaces for stochastic evolution equations, and global a priori bounds. Compared to other results in this direction, we do not need any smallness assumption on the transport noise which acts directly on the velocity field and we also allow rougher noise terms. The adaptation to Stratonovich type noise and, more generally, to variable viscosity and/or conductivity are discussed as well