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📰 "The Quantum Memory Matrix: A Unified Framework for the Black Hole Information Paradox"
arxiv.org/abs/2504.00039 #Physics.Gen-Ph #Mechanics #Matrix

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arXiv.orgThe Quantum Memory Matrix: A Unified Framework for the Black Hole Information ParadoxWe present the Quantum Memory Matrix (QMM) hypothesis, which addresses the longstanding Black Hole Information Paradox rooted in the apparent conflict between Quantum Mechanics (QM) and General Relativity (GR). This paradox raises the question of how information is preserved during black hole formation and evaporation, given that Hawking radiation appears to result in information loss, challenging unitarity in quantum mechanics. The QMM hypothesis proposes that space-time itself acts as a dynamic quantum information reservoir, with quantum imprints encoding information about quantum states and interactions directly into the fabric of space-time at the Planck scale. By defining a quantized model of space-time and mechanisms for information encoding and retrieval, QMM aims to conserve information in a manner consistent with unitarity during black hole processes. We develop a mathematical framework that includes space-time quantization, definitions of quantum imprints, and interactions that modify quantum state evolution within this structure. Explicit expressions for the interaction Hamiltonians are provided, demonstrating unitarity preservation in the combined system of quantum fields and the QMM. This hypothesis is compared with existing theories, including the holographic principle, black hole complementarity, and loop quantum gravity, noting its distinctions and examining its limitations. Finally, we discuss observable implications of QMM, suggesting pathways for experimental evaluation, such as potential deviations from thermality in Hawking radiation and their effects on gravitational wave signals. The QMM hypothesis aims to provide a pathway towards resolving the Black Hole Information Paradox while contributing to broader discussions in quantum gravity and cosmology.

📰 "PRC1 resists microtubule sliding in two distinct resistive modes due to variations in the separation between overlapping microtubules"
doi.org/doi:10.1101/2024.12.31
pubmed.ncbi.nlm.nih.gov/401662
#Cytoskeletal #Microtubule #Mechanics

bioRxiv · PRC1 resists microtubule sliding in two distinct resistive modes due to variations in the separation between overlapping microtubulesCrosslinked cytoskeletal filament networks provide cells with a mechanism to regulate cellular mechanics and force transmission. An example in the microtubule cytoskeleton is mitotic spindle elongation. The three-dimensional geometry of these networks, such as the degree of overlap length or lateral microtubule spacing, likely controls how forces can be regulated, but how these parameters evolve during filament sliding is unknown. Recent evidence suggests that PRC1, a non-motor crosslinking protein of the MAP65 family, can resist microtubule sliding by two distinct modes: a braking mode in which microtubule sliding is significantly impeded and a less resistive coasting mode. To explore how molecular-scale mechanisms influence three-dimensional network geometry in this system, we developed a computational model of sliding microtubule pairs crosslinked by PRC1 that reproduces the experimentally observed braking and coasting modes. Surprisingly, we found that the braking mode was associated with a substantially smaller lateral separation between the crosslinked microtubules than the coasting mode. This closer separation aligns the PRC1-mediated forces against sliding, increasing the resistive PRC1 force and dramatically reducing sliding speed. The model also finds an emergent similar average sliding speed due to PRC1 resistance, because higher initial sliding speed favors the transition to braking. Together, our results highlight the importance of the three-dimensional geometric relationships between crosslinkers and microtubules, which likely extends to other cytoskeletal architectures such as cilia. ### Competing Interest Statement The authors have declared no competing interest.

📰 "Fully GPU-Accelerated Immersed Boundary Method for Fluid-Structure Interaction in Complex Cardiac Models"
arxiv.org/abs/2503.22695 #Physics.Comp-Ph #Mechanics #Matrix

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arXiv.orgFully GPU-Accelerated Immersed Boundary Method for Fluid-Structure Interaction in Complex Cardiac ModelsFluid-structure interaction (FSI) plays a crucial role in cardiac mechanics, where the strong coupling between fluid flow and deformable structures presents significant computational challenges. The immersed boundary (IB) method efficiently handles large deformations and contact without requiring mesh regeneration. However, solving complex FSI problems demands high computational efficiency, making GPU acceleration essential to leverage massive parallelism, high throughput, and memory bandwidth. We present a fully GPU-accelerated algorithm for the IB method to solve FSI problems in complex cardiac models. The Navier-Stokes equations are discretized using the finite difference method, while the finite element method is employed for structural mechanics. Traditionally, IB methods are not GPU-friendly due to irregular memory access and limited parallelism. The novelty of this work lies in eliminating sparse matrix storage and operations entirely, significantly improving memory access efficiency and fully utilizing GPU computational capability. Additionally, the structural materials can be modeled using general hyperelastic constitutive laws, including fiber-reinforced anisotropic biological tissues such as the Holzapfel-Ogden (HO) model. Furthermore, a combined geometric multigrid solver is used to accelerate the convergence. The full FSI system, consisting of millions of degrees of freedom, achieves a per-timestep computation time of just 0.1 seconds. We conduct FSI simulations of the left ventricle, mitral valve, and aortic valve, achieving results with high consistency. Compared to single-core CPU computations, our fully GPU-accelerated approach delivers speedups exceeding 100 times.

📰 "Soft matter mechanics of immune cell aggregates"
arxiv.org/abs/2503.21402 #Physics.Bio-Ph #Mechanical #Mechanics #Cell

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arXiv.orgSoft matter mechanics of immune cell aggregatesT-cells are a crucial subset of white blood cells that play a central role in the immune system. When T-cells bind antigens, it leads to cell activation and the induction of an immune response. If T-cells are activated by antigens in vivo or artificially in vitro, they form multicellular aggregates. The mechanical properties of such clusters provide valuable information on different T-cell activation pathways. Furthermore, the aggregate mechanics capture how T-cells are affected by mechanical forces and interact within larger conglomerates, such as lymph nodes and tumours. However, an understanding of collective T-cell adhesion and mechanics following cell activation is currently lacking. Probing the mechanics of fragile and microscopically small living samples is experimentally challenging. Here, the micropipette force sensor technique was used to stretch T-cell aggregates and directly measure their Young's modulus and ultimate tensile strength. A mechanistic model was developed to correlate how the stiffness of the mesoscale multicellular aggregate emerges from the mechanical response of the individual microscopic cells within the cluster. We show how the aggregate elasticity is affected by different activators and relate this to different activation pathways in the cells. Our soft matter mechanics study of multicellular T-cell aggregates contributes to our understanding of the biology behind immune cell activation.

📰 "Theory of multiscale epithelial mechanics under stretch: from active gels to vertex models"
biorxiv.org/content/10.1101/20 #Cytoskeletal #Mechanical #Mechanics

bioRxiv · Theory of multiscale epithelial mechanics under stretch: from active gels to vertex modelsEpithelial monolayers perform a variety of mechanical functions, which include maintaining a cohesive barrier or developing 3D shapes, while undergoing stretches over a wide range of magnitudes and loading rates. To perform these functions, they rely on a hierarchical organization, which spans molecules, cytoskeletal networks, adhesion complexes and junctional networks up to the tissue scale. While the molecular understanding and ability to manipulate cytoskeletal components within cells is rapidly increasing, how these components integrate to control tissue mechanics is far less understood, partly due to the disconnect between theoretical models of sub-cellular dynamics and those at a tissue scale. To fill this gap, here we propose a formalism bridging active-gel models of the actomyosin cortex and 3D vertex-like models at a tissue scale. We show that this unified framework recapitulates a number of seemingly disconnected epithelial time-dependent phenomenologies, including stress relaxation following stretch/unstretch maneuvers, active flattening after buckling, or nonreciprocal and non-affine pulsatile contractions. We further analyze tissue dynamics probed by a novel experimental setup operating in a pressure-controlled ensemble. Overall, the proposed framework systematically connects sub-cellular cortical dynamics and tissue mechanics, and ties a variety of epithelial phenomenologies to a common sub-cellular origin. ### Competing Interest Statement The authors have declared no competing interest.
Continued thread

We had a customer in who insisted he had to talk to the owner about the issues with his bike.

So when my boss came back from his break, I told him and he got really annoyed. The customer came back a little later, and told my boss the issues. My boss got really annoyed and said couldn't the customer tell me that himself? And he mentioned an incident with his previous mechanic in the old place. The customer insisted on making the boss come up for a second opinion because he didn't trust the (female) mechanic's quote. So my boss told him the exact same thing the mechanic told him, and added a tenner to the quote for wasting his time! 😆

So now I know my boss has hired at least two female mechanics before me (one of them was the lady with us at the bike show. I do wish my boss would tell me how he knows a person when he introduces them!).

You know, I've experienced general bullying, racial abuse and religious abuse, but the only time I've experienced overt #sexism is in my current industry.

In my previous job, I'd frequently be ignored by male customers who would walk past me and look for a man. Once, both I and a female colleague asked a customer if he needed help, he blanked up both, went to a male colleague and was promptly told, "ask one of the two ladies there."

Once I had a customer completely ignore me, then actually walk into the back room. I ran after him and told him he can't just walk into staff areas. He said he needed help. I said I asked you twice if you need help, I could have helped you. When he did eventually get the male member of staff he so desired, he decided to shout at him as well. "Why are you asking be what's wrong with my bike! You're paid to do it! Why don't you tell me!"

I bet when he goes to the doctor, he just sits there refusing to tell the doctor what's wrong.

Later I told one of my homies and he gave him a lecture, and when I said" yes, actually I'm a technician and I could help you if you didn't ignore me", he basically talked over me. I told him, "You're literally ignoring me when I'm talking to you!" He didn't learn. I think women are just invisible to him.

Once I was helping a male customer choose accessories as he was planning on starting to cycle to work. There was another male customer looking towards us. He then asked the CUSTOMER if he can help him. I said, he isn't staff. The second customer ignored me and again asked my customer for help. When the customer said he doesn't work there and that I'm the staff member, he walked off to the till to my male colleague.

Once I was actually building a bike, and a lady came up to the till area asking if someone can help her choose a bike. The supervisor was busy doing admin stuff on the till, so I got up and said I can help. The lady then said, I mean I need someone who knows about bikes.

I WAS LITERALLY BUILDING A BIKE FFS.

Instead I said, yes I know about bikes and went on to show her our range and help her choose the best bike for her. At the end, she's like, you really know a lot about bikes... but of course you do, you work here!

I'm used to men patronising me, but it was a bit weird getting sexism from a female customer. She was fine at the end though. So at least I got a teachable moment out of that.

There was an interview in the trade magazine where a female mechanic had a customer who expressed surprise at seeing a female mechanic. And she thought, he was going to say something about how it's a pleasant surprise or something, instead he said she should do the repair for free since she's a woman.

Who Wants What Weapon Groups?

One of the design choices in the structure of 4th edition Dungeons & Dragons is the way that weapons are given categorical signifiers that let you treat them in shared, mechanically related ways. What did these groups do, and who needs help?

squarefireballs.invincible.ink

squarefireballs.invincible.inkWho Wants What Weapon Groups? – The Square Fireball
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