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Spin Hamiltonian as Matrix-Free Linear Map
Authors:
Aditya Dev
Abstract:
We present an algorithm that computes the action of a generic spin Hamiltonian on a state vector on the fly, entirely avoiding explicit matrix assembly. This is achieved through mixed-radix indexing of the full tensor-product basis, which translates local spin operations into simple integer offsets. The result is an explicit framework for evaluating single- and two-site terms across arbitrary spin…
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We present an algorithm that computes the action of a generic spin Hamiltonian on a state vector on the fly, entirely avoiding explicit matrix assembly. This is achieved through mixed-radix indexing of the full tensor-product basis, which translates local spin operations into simple integer offsets. The result is an explicit framework for evaluating single- and two-site terms across arbitrary spin lattices, including mixed-spin systems. Our construction bridges the basis-indexing logic familiar from exact diagonalization with the matrix-free state-update philosophy of address-based frameworks. By writing the indexing logic in closed form, a single uniform loop applies to every site regardless of its local Hilbert-space dimension. The method is parallelizable and memory-conserving, and can be extended to restricted basis or truncated bosonic levels.
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Submitted 1 June, 2026;
originally announced June 2026.
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Lubrication-Induced Newtonianization Enables Passive Transport of Non-Newtonian materials
Authors:
Arvind Arun Dev,
Paszkal Papp,
Thomas M. Hermans,
Bernard Doudin
Abstract:
Non Newtonian flows are typically governed by intrinsic bulk rheology, which imposes strong constraints on transport through confined geometries. Here, we show that stable boundary lubrication can fundamentally alter this behavior by localizing shear within a thin, low-viscosity interfacial layer. As a result, the nonlinear rheological response of a broad class of complex materials, including yiel…
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Non Newtonian flows are typically governed by intrinsic bulk rheology, which imposes strong constraints on transport through confined geometries. Here, we show that stable boundary lubrication can fundamentally alter this behavior by localizing shear within a thin, low-viscosity interfacial layer. As a result, the nonlinear rheological response of a broad class of complex materials, including yield-stress, shear-dependent, and thixotropic materials, is strongly suppressed during flow. Using analytical solutions of Stokes flow and numerical simulations, we demonstrate that lubrication-induced shear localization leads to an apparent Newtonianization of transport, in which the macroscopic flow response becomes primarily controlled by the lubricating layer and geometric confinement rather than the intrinsic material properties. In this regime, materials that would otherwise require large pressure gradients can be transported at substantially lower driving forces. Notably, this boundary-dominated transport enables gravity-driven passive flow with orders-of-magnitude enhancement in throughput compared to rigid-wall conduits. These results establish lubrication as a powerful mechanism for tuning and simplifying complex fluid transport, with implications for biological systems, soft and jammed materials, and energy-efficient fluids.
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Submitted 9 May, 2026;
originally announced May 2026.
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Ultra-soft liquid-ferrofluid interfaces
Authors:
Arvind Arun Dev,
Thomas Hermans,
Bernard Doudin
Abstract:
Soft interfaces are ubiquitous in nature, governing quintessential hydrodynamics functions, like lubrication, stability and cargo transport. It is shown here how a magnetic force field at a magnetic-nonmagnetic fluid interface results in an ultra-soft interface with nonlinear elasticity and tunable viscous shear properties. The balance between magnetic pressure, viscous stress and Laplace pressure…
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Soft interfaces are ubiquitous in nature, governing quintessential hydrodynamics functions, like lubrication, stability and cargo transport. It is shown here how a magnetic force field at a magnetic-nonmagnetic fluid interface results in an ultra-soft interface with nonlinear elasticity and tunable viscous shear properties. The balance between magnetic pressure, viscous stress and Laplace pressure results in a deformed and stable liquid-in-liquid tube with apparent elasticity in the range 2 kPa -10 kPa, possibly extended by a proper choice of liquid properties. Such highly deformable liquid-liquid interfaces of arbitrary shape with vanishing viscous shear open doors to unique microfluidic phenomena, biomaterial flows and complex biosystems mimicking.
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Submitted 6 August, 2024;
originally announced August 2024.
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Scaling and flow profiles in magnetically confined liquid-in-liquid channels
Authors:
Arvind Arun Dev,
Florencia Sacarelli,
G Bagheri,
Aleena Joseph,
Anna Oleshkevych,
E Bodenschatz,
Peter Dunne,
Thomas Hermans,
Bernard Doudin
Abstract:
Ferrofluids kept in place by permanent magnet quadrupoles can act as liquid walls to surround a second non-magnetic inside, resulting in a liquid fluidic channel with diameter size ranging from mm down to less than 10 micrometer. Micro particle tracking velocimetry (micro PTV) experiments and modeling show that near ideal plug flow is possible in such liquid-in-liquid channels due to the reduced f…
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Ferrofluids kept in place by permanent magnet quadrupoles can act as liquid walls to surround a second non-magnetic inside, resulting in a liquid fluidic channel with diameter size ranging from mm down to less than 10 micrometer. Micro particle tracking velocimetry (micro PTV) experiments and modeling show that near ideal plug flow is possible in such liquid-in-liquid channels due to the reduced friction at the walls. The measured fluids velocity profiles agree with the predictions of a hydrodynamic model of cylindrical symmetry with a minimal set of hypotheses. By introducing symmetry breaking elements in the system, we show how unique velocity and flow properties can be obtained. Our liquid-in-liquid confinement opens new possibilities for < 10 micrometer-sized microfluidics with low pressures and low shear, with flow characteristics not attainable in comparable solid-wall devices.
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Submitted 26 February, 2024;
originally announced February 2024.
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Suppressing Rayleigh-Plateau Instability with a Magnetic Force Field for Deformable Interfaces Engineering
Authors:
Arvind Arun Dev,
Thomas Hermans,
Bernard Doudin
Abstract:
The Rayleigh-Plateau instability (RPI) is a classical hydrodynamics phenomenon that prevents a jet of liquid to flow indefinitely within air or another liquid. Here, we show how adding a magnetic force field makes possible its suppression. Enclosing the jet in a ferrofluid held by magnetic forces allows flow focusing without sheath flow, which completely avoids dripping failure at small flow rates…
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The Rayleigh-Plateau instability (RPI) is a classical hydrodynamics phenomenon that prevents a jet of liquid to flow indefinitely within air or another liquid. Here, we show how adding a magnetic force field makes possible its suppression. Enclosing the jet in a ferrofluid held by magnetic forces allows flow focusing without sheath flow, which completely avoids dripping failure at small flow rates and provides conditional stability for a continuous fluid jet. Highly deformable liquid interfaces withstanding spatial and time varying flow conditions within a large parameter space can be realized.
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Submitted 22 October, 2023;
originally announced October 2023.
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Searching for a Fifth Force with Atomic and Nuclear Clocks
Authors:
Dawid Brzeminski,
Zackaria Chacko,
Abhish Dev,
Ina Flood,
Anson Hook
Abstract:
We consider the general class of theories in which there is a new ultralight scalar field that mediates an equivalence principle violating, long-range force. In such a framework, the sun and the earth act as sources of the scalar field, leading to potentially observable location dependent effects on atomic and nuclear spectra. We determine the sensitivity of current and next-generation atomic and…
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We consider the general class of theories in which there is a new ultralight scalar field that mediates an equivalence principle violating, long-range force. In such a framework, the sun and the earth act as sources of the scalar field, leading to potentially observable location dependent effects on atomic and nuclear spectra. We determine the sensitivity of current and next-generation atomic and nuclear clocks to these effects and compare the results against the existing laboratory and astrophysical constraints on equivalence principle violating fifth forces. We show that in the future, the annual modulation in the frequencies of atomic and nuclear clocks in the laboratory caused by the eccentricity of the earth's orbit around the sun may offer the most sensitive probe of this general class of equivalence principle violating theories. Even greater sensitivity can be obtained by placing a precision clock in an eccentric orbit around the earth and searching for time variation in the frequency, as is done in anomalous redshift experiments. In particular, an anomalous redshift experiment based on current clock technology would already have a sensitivity to fifth forces that couple primarily to electrons at about the same level as the existing limits. Our study provides well-defined sensitivity targets to aim for when designing future versions of these experiments.
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Submitted 2 September, 2022; v1 submitted 28 July, 2022;
originally announced July 2022.
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MeMC: A package for monte-carlo simulations of spherical shells
Authors:
Vipin Agrawal,
Vikash Pandey,
Hanna Kylhammar,
Apurba Dev,
Dhrubaditya Mitra
Abstract:
The MeMC is an open-source software package for monte-carlo simulation of elastic shells. It is designed as a tool to interpret the force-distance data generated by indentation of biological nano-vesicles by atomic force microscopes. The code is written in c++ and python. The code is customizable -- new modules can be added in a straightforward manner.
The MeMC is an open-source software package for monte-carlo simulation of elastic shells. It is designed as a tool to interpret the force-distance data generated by indentation of biological nano-vesicles by atomic force microscopes. The code is written in c++ and python. The code is customizable -- new modules can be added in a straightforward manner.
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Submitted 25 April, 2022; v1 submitted 28 March, 2022;
originally announced March 2022.
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Fluid drag reduction by magnetic confinement
Authors:
Arvind Arun Dev,
Peter Dunne,
Thomas M. Hermans,
Bernard Doudin
Abstract:
The frictional forces of a viscous liquid flow are a major energy loss issue and severely limit microfluidics practical use. Reducing this drag by more than a few tens of percent remain illusive. Here, we show how cylindrical liquid-in-liquid flow leads to drag reduction of 60-99% for sub mm and mm sized channels, irrespective of whether the viscosity of the transported liquid is larger or smaller…
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The frictional forces of a viscous liquid flow are a major energy loss issue and severely limit microfluidics practical use. Reducing this drag by more than a few tens of percent remain illusive. Here, we show how cylindrical liquid-in-liquid flow leads to drag reduction of 60-99% for sub mm and mm sized channels, irrespective of whether the viscosity of the transported liquid is larger or smaller than that of the encapsulating one. In contrast to lubrication or sheath flow, we do not require the continuous flow of the encapsulating lubricant, here made up of a ferrofluid held in place by magnetic forces. In a laminar flow model with appropriate boundary conditions, we introduce a modified Reynolds number with a scaling that depends on geometrical factors and viscosity ratio of the two liquids. It explains our whole range of data and reveal the key design parameters for optimizing the drag reduction values. Our results therefore open the route to microfluidics designs with pressure gradients possibly reduced by orders of magnitudes.
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Submitted 1 October, 2021; v1 submitted 26 June, 2020;
originally announced June 2020.
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Behaviour of flexible superhydrophobic striped surfaces during (electro-)wetting of a sessile drop
Authors:
Arvind Arun Dev,
Ranabir Dey,
Frieder Mugele
Abstract:
We study here the microscopic deformations of elastic lamellae constituting a superhydrophobic substrate under different wetting conditions of a sessile droplet using electrowetting. The deformation profiles of the lamellae are experimentally evaluated using confocal microscopy. These experimental results are then explained using a variational principle formalism within the framework of linear ela…
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We study here the microscopic deformations of elastic lamellae constituting a superhydrophobic substrate under different wetting conditions of a sessile droplet using electrowetting. The deformation profiles of the lamellae are experimentally evaluated using confocal microscopy. These experimental results are then explained using a variational principle formalism within the framework of linear elasticity. We show that the local deformation profile of a lamella is mainly controlled by the net horizontal component of the capillary forces acting on its top due to the pinned droplet contact line. We also discuss the indirect role of electrowetting in dictating the deformation characteristics of the elastic lamellae. One important conclusion is that the small deflection assumption, which is frequently used in the literature, fails to provide a quantitative description of the experimental results; a full solution of the non-linear governing equation is necessary to describe the experimentally obtained deflection profiles.
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Submitted 12 August, 2019;
originally announced August 2019.
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Characteristics of solitary waves in a relativistic degenerate ion beam driven magneto plasma
Authors:
M. K. Deka,
A. N. Dev,
A. P. Misra,
N. C. Adhikary
Abstract:
The nonlinear propagation of small amplitude ion acoustic solitary wave in relativistic degenerate magneto plasma in presence of ion beam is investigated in detail. The nonlinear equations describing the evolution of solitary wave in presence of relativistic non-degenerate magnetized positive ions and ion beams including magnetized degenerate relativistic electrons are derived in terms of Zakharov…
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The nonlinear propagation of small amplitude ion acoustic solitary wave in relativistic degenerate magneto plasma in presence of ion beam is investigated in detail. The nonlinear equations describing the evolution of solitary wave in presence of relativistic non-degenerate magnetized positive ions and ion beams including magnetized degenerate relativistic electrons are derived in terms of Zakharov-Kuznetsov (Z-K) equation for such plasma systems. The ion beams which are ubiquitous ingredient in such plasma systems, are found to have a decisive role in the propagation of solitary wave in such highly dense plasma system. The conditions of wave, propagating with typical solitonic characteristics are examined and discussed in detail under suitable conditions of different physical parameter. Both subsonic and supersonic wave can propagate in such plasmas bearing different characteristics under different physical situations. A detailed analysis of waves propagating in subsonic and/or supersonic regime is carried out. The ion beam concentrations, magnetic field as well as ion beam streaming velocity is found to play a momentous role on the control of the amplitude and width of small amplitude perturbation both in weakly(or non-relativistic) and relativistic plasmas.
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Submitted 8 January, 2018;
originally announced January 2018.
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Nonlinear dust-acoustic solitary waves and shocks in dusty plasmas with a pair of trapped ions
Authors:
N. C. Adhikary,
A. P. Misra,
M. K. Deka,
A. N. Dev
Abstract:
The propagation characteristics of small-amplitude dust-acoustic (DA) solitary waves (SWs) and shocks are studied in an unmagnetized dusty plasma with a pair of trapped positive and negative ions. Using the standard reductive perturbation technique with two different scaling of stretched coordinates, the evolution equations for DA SWs and shocks are derived in the forms of complex Korteweg-de Vrie…
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The propagation characteristics of small-amplitude dust-acoustic (DA) solitary waves (SWs) and shocks are studied in an unmagnetized dusty plasma with a pair of trapped positive and negative ions. Using the standard reductive perturbation technique with two different scaling of stretched coordinates, the evolution equations for DA SWs and shocks are derived in the forms of complex Korteweg-de Vries (KdV) and complex Burgers' equations. The effects of dust charge variation, the dust thermal pressure, and the ratios of positive to negative ion number densities as well as the free to trapped ion temperatures on the profiles of SWs and shocks are analysed and discussed.
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Submitted 1 July, 2017; v1 submitted 16 February, 2017;
originally announced February 2017.
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Improving the hierarchy sensitivity of ICAL using neural network
Authors:
Ali Ajmi,
Abhish Dev,
Mohammad Nizam,
Nitish Nayak,
S. Uma Sankar
Abstract:
Atmospheric neutrino experiments can determine the neutrino mass hierarchy for any value of $δ_{CP}$. The Iron Calorimeter (ICAL) detector at the India-based Neutrino Observatory can distinguish between the charged current interactions of $ν_μ$ and $\barν_μ$ by determining the charge of the produced muon. Hence it is particularly well suited to determine the hierarchy. The hierarchy signature is m…
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Atmospheric neutrino experiments can determine the neutrino mass hierarchy for any value of $δ_{CP}$. The Iron Calorimeter (ICAL) detector at the India-based Neutrino Observatory can distinguish between the charged current interactions of $ν_μ$ and $\barν_μ$ by determining the charge of the produced muon. Hence it is particularly well suited to determine the hierarchy. The hierarchy signature is more prominent in neutrinos with energy of a few GeV and with pathlength of a few thousand kilometers, $\textit{i.e.}$ neutrinos whose direction is not close to horizontal. We use adaptive neural networks to identify such events with good efficiency and good purity. The hierarchy sensitivity, calculated from these selected events, reaches a $3 σ$ level, with a $Δχ^2$ of 9.
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Submitted 1 November, 2015; v1 submitted 7 October, 2015;
originally announced October 2015.
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Kadomtsev-Petviashvili (KP) Burgers equation in dusty negative ion plasmas: Evolution of dust-ion acoustic shocks
Authors:
A. N. Dev,
J. Sarmah,
M. K. Deka,
A. P. Misra,
N. C. Adhikary
Abstract:
We study the nonlinear propagation of dust-ion acoustic (DIA) solitary waves in an unmagnetized dusty plasma which consists of electrons, both positive and negative ions and negatively charged immobile dust grains. Starting from a set of hydrodynamic equations with the ion thermal pressures and ion kinematic viscosities included, and using a standard reductive perturbation method, the Kadomtsev-Pe…
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We study the nonlinear propagation of dust-ion acoustic (DIA) solitary waves in an unmagnetized dusty plasma which consists of electrons, both positive and negative ions and negatively charged immobile dust grains. Starting from a set of hydrodynamic equations with the ion thermal pressures and ion kinematic viscosities included, and using a standard reductive perturbation method, the Kadomtsev-Petviashivili Burgers (KPB) equation is derived, which governs the evolution of DIA shocks. A stationary solution of the KPB equation is obtained and its properties are analysed with different plasma number densities, ion temperatures and masses. It is shown that a transition from shocks with negative potential to positive one occurs depending on the negative ion concentration in the plasma and the obliqueness of propagation of DIA waves.
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Submitted 20 November, 2014;
originally announced November 2014.