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Non-Thermal Pressure due to Gas Motions in the Intracluster Medium: Confronting XRISM/Resolve with TNG-Cluster Simulations
Erwin T. Lau, Naomi Ota, Daisuke Nagai
https://arxiv.org/abs/2608.04757 https://arxiv.org/pdf/2608.04757 https://arxiv.org/html/2608.04757
arXiv:2608.04757v1 Announce Type: new
Abstract: Intracluster medium (ICM) gas motions probe cluster assembly, feedback, and non-thermal pressure support, but recent XRISM observations reveal velocity dispersions and non-thermal pressure fractions systematically lower than simulations predict, with extreme systems such as Abell 2029 falling below nearly all simulated clusters. Using the TNG-Cluster simulations, we show that the non-thermal pressure fraction depends sensitively on cool-core state and formation history, and provide a two-scale fitting function capturing both the inner cool-core suppression and outer rise of the radial profile. By forward-modeling mock XRISM observations and comparing them with both projected and intrinsic three-dimensional quantities, we find that azimuthal variations and projection effects contribute to the deficit in the observed velocity dispersion and non-thermal pressure fraction. This bias increases with radius and partially offsets the intrinsic outward rise in the true three-dimensional non-thermal pressure fraction. However, these effects cannot explain the extremely low values of the non-thermal pressure fraction observed in Abell 2029, which fall below approximately the 0th - 6th percentiles of the simulated cool-core cluster distribution at every measured radius under both the turbulence-only and turbulence-plus-bulk definitions. The remaining tension points to rare dynamical conditions or missing physics affecting the amplitude of gas motions in current ICM models.
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I wanted to post mountain photos more regularly again! So here's one trail from last year where I started really early to avoid the heat.
It was a hike that I did alone and met just like ... 2 or 3 people. Oh and I was glad to have a water filter with me!
I spotted a spring on my way up and - knowing that I'd come pack to it later - I didn't have to use my water sparingly.
Enjoy!

Weather forecast was about rain and maybe lightning ... so we just biked to your lokal mountain and did a quick loop in high humidity.
#hiking #bayern #mountains

Solutocapillary instability in slipping falling films
Sanghasri Mukhopadhyay, S\'everine Millet, Bastien Di Pierro, Asim Mukhopadhyay
https://arxiv.org/abs/2605.17519 https://arxiv.org/pdf/2605.17519 https://arxiv.org/html/2605.17519
arXiv:2605.17519v1 Announce Type: new
Abstract: We present a comprehensive framework for gravity-driven, surfactant-laden thin films flowing over slippery substrates, elucidating how wall slip modifies the coupled hydrodynamics and interfacial transport. A long-wave model is formulated with a conservative bulk-surface mass balance and a Navier slip condition. The Orr-Sommerfeld eigenvalue problem governs the linear regime, while a weighted-residual model captures the nonlinear evolution over a range of equilibrium surfactant coverages, Marangoni strengths, and adsorption kinetics. The analysis predicts a non-monotonic variation of the critical Reynolds number with equilibrium coverage, exhibiting a maximum at intermediate $\Gamma_e$, and a slip-induced transition from single- to double-hump solitary structures with increasing Marangoni number, accompanied by attenuated capillary ripples. Under fast adsorption kinetics, the surface field homogenizes, preserving the mean film shape and flux while flattening both the surface concentration $\Gamma$ and the bulk inventory $\chi h\phi$. A spurious interfacial mass growth reported by Pascal et al.(PRF, 2019) and D'Alessio et al.(JFM, 2020) is resolved through a revised surface balance ensuring strict conservation. Wall slip thus emerges as a key control parameter, reducing viscous resistance and mitigating Marangoni back-stress. The slip parameter $\beta$ is a useful control knob for surfactant-laden films. Slip prevents fragile multi-hump bound states, promoting a single broad crest or an almost flat, uniform sheet by carefully bonding $\beta$ to wave selection, ripple damping, and the bulk-surface surfactant balance.
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Good morning! I replaced the morning walk with a morning ride. 😊 I tried to push a bit harder today for training. Next time should be lighter again. But it felt really good!
#cycling #goodmorning

Formal Verification of an Out-of-Order Multiprocessor against an In-Order Weak-Memory ISA
Janggun Lee, Jeehoon Kang
https://arxiv.org/abs/2607.18727 https://arxiv.org/pdf/2607.18727 https://arxiv.org/html/2607.18727
arXiv:2607.18727v1 Announce Type: new
Abstract: Out-of-order multiprocessor is a critical piece of modern hardware, and their verification must solve the following challenges. First, inter-core interleaving, in which the order their reads and writes reach shared memory is unrestricted. Second, intra-core out-of-order execution, in which instructions fire out of program order. The combination of the two yields weak outcomes, which no sequential execution explains, and modern ISA allows such behaviors to account for them. However, the microarchitecture even exhibits excess out-of-order executions, temporarily entering states forbidden by the ISA. While discarded later, such states complicate reasoning about the core in full-system verification. Prior works verify a range of processor designs, while none have performed unbounded verification for out-of-order multiprocessor exhibiting such weak outcomes.
We present the first formal verification of an out-of-order multiprocessor against an in-order, weak-memory ISA. Our key idea is a well-designed core specification, which captures the essence of excess executions in a single list of instructions. Building upon this, we decompose the proof into two steps. The first is a core refinement, proving a core implementation against this specification, abstracting away every microarchitectural state except those necessary to reason about excess executions and the core interface. The second is a system inclusion, serializing the out-of-order memory executions and inter-core interleaving into the ISA, easily removing excess executions thanks to the core specification. All of our proofs are mechanized in Rocq, heavily utilizing large language model (LLM) agents to write proofs automatically.
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