-
Electron spin dynamics guide cell motility
Authors:
Kai Wang,
Gabrielle Gilmer,
Matheus Candia Arana,
Hirotaka Iijima,
Juliana Bergmann,
Antonio Woollard,
Boris Mesits,
Meghan McGraw,
Brian Zoltowski,
Paola Cappellaro,
Alex Ungar,
David Pekker,
David H. Waldeck,
Sunil Saxena,
Seth Lloyd,
Fabrisia Ambrosio
Abstract:
Diverse organisms exploit the geomagnetic field (GMF) for migration. Migrating birds employ an intrinsically quantum mechanical mechanism for detecting the geomagnetic field: absorption of a blue photon generates a radical pair whose two electrons precess at different rates in the magnetic field, thereby sensitizing cells to the direction of the GMF. In this work, using an in vitro injury model, w…
▽ More
Diverse organisms exploit the geomagnetic field (GMF) for migration. Migrating birds employ an intrinsically quantum mechanical mechanism for detecting the geomagnetic field: absorption of a blue photon generates a radical pair whose two electrons precess at different rates in the magnetic field, thereby sensitizing cells to the direction of the GMF. In this work, using an in vitro injury model, we discovered a quantum-based mechanism of cellular migration. Specifically, we show that migrating cells detect the GMF via an optically activated, electron spin-based mechanism. Cell injury provokes acute emission of blue photons, and these photons sensitize muscle progenitor cells to the magnetic field. We show that the magnetosensitivity of muscle progenitor cells is (a) activated by blue light, but not by green or red light, and (b) disrupted by the application of an oscillatory field at the frequency corresponding to the energy of the electron-spin/magnetic field interaction. A comprehensive analysis of protein expression reveals that the ability of blue photons to promote cell motility is mediated by activation of calmodulin calcium sensors. Collectively, these data suggest that cells possess a light-dependent magnetic compass driven by electron spin dynamics.
△ Less
Submitted 4 March, 2025;
originally announced March 2025.
-
Analysis of the Pressure-Velocity boundary conditions for the projection method solution of the incompressible Navier-Stokes Equations
Authors:
Leonid Pekker,
David Pekker
Abstract:
The projection method is the standard approach for numerically integrating the incompressible Navier-Stokes equation initial-boundary-value problem. Typical boundary conditions specify either the velocity or the gradient velocity on the boundary. Here, we consider the pressure-tangential-velocity boundary condition in which the tangential components of the velocity and the pressure at the boundary…
▽ More
The projection method is the standard approach for numerically integrating the incompressible Navier-Stokes equation initial-boundary-value problem. Typical boundary conditions specify either the velocity or the gradient velocity on the boundary. Here, we consider the pressure-tangential-velocity boundary condition in which the tangential components of the velocity and the pressure at the boundary are specified.
△ Less
Submitted 19 May, 2024;
originally announced May 2024.
-
Equilibrium Contact Angles and Dewetting in Capillaries
Authors:
Leonid Pekker,
David Pekker,
James Myrick
Abstract:
In this work, we extend the model of contact angles that we have previously developed for sessile drops on a wetted surface to the case of a meniscus in a capillary. The underlying physics of our model describe the intermolecular forces between the fluid and the surface of the capillary that result in the formation of a thin, non-removable fluid layer that coats the capillary wall. We describe the…
▽ More
In this work, we extend the model of contact angles that we have previously developed for sessile drops on a wetted surface to the case of a meniscus in a capillary. The underlying physics of our model describe the intermolecular forces between the fluid and the surface of the capillary that result in the formation of a thin, non-removable fluid layer that coats the capillary wall. We describe the shape of the meniscus using a Young-Laplace equation and an incompressible, two-phase, CFD calculation, both modified to take into account intermolecular forces using the disjoining pressure model. We find that our numerical solutions of the Young-Laplace equation and equilibrium meniscus shapes obtained by CFD agree well with each other. Furthermore, for capillaries that are sufficiently larger than the thickness of the non-removable film, our numerical solutions agree well with the effective contact angle model that we previously developed for sessile drops. Finally, we observe that it is possible to tune the disjoining pressure model parameters so that the intermolecular forces between the liquid and solid molecules becomes so strong compared to the surface tension that our formula for effective contact angle gives an imaginary solution. We analyze this situation using CFD and find that it corresponds to dewetting, where the bulk liquid detaches from the walls of the capillary leaving behind the non-removable thin liquid film.
△ Less
Submitted 18 December, 2023;
originally announced December 2023.
-
Machine Learning 1- and 2-electron reduced density matrices of polymeric molecules
Authors:
David Pekker,
Chungwen Liang,
Sankha Pattanayak,
Swagatam Mukhopadhyay
Abstract:
Encoding the electronic structure of molecules using 2-electron reduced density matrices (2RDMs) as opposed to many-body wave functions has been a decades-long quest as the 2RDM contains sufficient information to compute the exact molecular energy but requires only polynomial storage. We focus on linear polymers with varying conformations and numbers of monomers and show that we can use machine le…
▽ More
Encoding the electronic structure of molecules using 2-electron reduced density matrices (2RDMs) as opposed to many-body wave functions has been a decades-long quest as the 2RDM contains sufficient information to compute the exact molecular energy but requires only polynomial storage. We focus on linear polymers with varying conformations and numbers of monomers and show that we can use machine learning to predict both the 1-electron and the 2-electron reduced density matrices. Moreover, by applying the Hamiltonian operator to the predicted reduced density matrices we show that we can recover the molecular energy. Thus, we demonstrate the feasibility of a machine learning approach to predicting electronic structure that is generalizable both to new conformations as well as new molecules. At the same time our work circumvents the N-representability problem that has stymied the adaption of 2RDM methods, by directly machine-learning valid Reduced Density Matrices.
△ Less
Submitted 9 August, 2022;
originally announced August 2022.
-
An Improved Self-Consistent One-Dimensional Slender Jet Model
Authors:
Leonid Pekker,
David Pekker
Abstract:
In 1994, Eggers and Dupont suggested the slender jet model, a one-dimensional model that describes the motion of a thin axisymmetric column of viscous, incompressible fluid with a free surface. In their model, the momentum equation was derived in a manner that was not completely self-consistent. Consequently, the viscosity term was described with less accuracy than the surface tension term. In thi…
▽ More
In 1994, Eggers and Dupont suggested the slender jet model, a one-dimensional model that describes the motion of a thin axisymmetric column of viscous, incompressible fluid with a free surface. In their model, the momentum equation was derived in a manner that was not completely self-consistent. Consequently, the viscosity term was described with less accuracy than the surface tension term. In this paper, we derive a novel slender jet momentum equation in completely self-consistent manner that allows us to describe both the viscosity and the surface tension forces with the same accuracy as the surface tension term in the Eggers-Dupont model. Our derivation does not affect the volume conservation equation, which remains identical to the one in the Eggers-Dupont model. We show that our model predicts different Plateau-Rayleigh instability dynamics as compared to the Eggers-Dupont's model. The differences between the models are particularly large at small Reynolds numbers, where the viscosity plays a prominent role in development the Plateau-Rayleigh instability.
△ Less
Submitted 14 July, 2022;
originally announced July 2022.
-
Equilibrium Contact Angle at the Wetted Substrate
Authors:
Leonid Pekker,
David Pekker,
Nikolai Petviashvili
Abstract:
We construct a novel model for the steady-state contact angles of liquid droplets at the wetted substrate. The non-removable, thin liquid film covering the substrate is governed by the intermolecular forces between molecules of liquid and solid, which we describe using the standard disjoining pressure approximation. Balancing the disjoining pressure against the surface tension we find the smooth s…
▽ More
We construct a novel model for the steady-state contact angles of liquid droplets at the wetted substrate. The non-removable, thin liquid film covering the substrate is governed by the intermolecular forces between molecules of liquid and solid, which we describe using the standard disjoining pressure approximation. Balancing the disjoining pressure against the surface tension we find the smooth shape of the surface of the liquid. We show that we can extract an effective contact angle from the region where the film and the droplet meet. Crucially, we find that for large droplets the contact angle is independent of the droplet size. Instead, the contact angle is determined by the surface tension and the disjoining pressure parameters through a simple formula that works for both small and large contact angles. We suggest that comparing predictions of our model to experimentally measured contact angles will enable constraining the parameters of the disjoining pressure models.
△ Less
Submitted 14 July, 2022;
originally announced July 2022.