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Cell Deformation Signatures along the Apical-Basal Axis: A 3D Continuum Mechanics Shell Model
Authors:
Jairo M. Rojas,
Mayisha Z. Nakib,
Vivian W. Tang,
William M. Brieher,
Sascha Hilgenfeldt
Abstract:
Two-dimensional (2D) mechanical models of confluent tissues have related the mechanical state of a monolayer of cells to the average perimeter length of the cell cross sections, predicting floppiness or rigidity of the material. For the well-studied system of in-vitro MDCK epithelial cells, however, we find experimentally that cells in mechanically rigid tissues display long perimeters characteris…
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Two-dimensional (2D) mechanical models of confluent tissues have related the mechanical state of a monolayer of cells to the average perimeter length of the cell cross sections, predicting floppiness or rigidity of the material. For the well-studied system of in-vitro MDCK epithelial cells, however, we find experimentally that cells in mechanically rigid tissues display long perimeters characteristic of a floppy state in 2D models. We suggest that this discrepancy is due to mechanical effects in the third (apical-basal) dimension, including those caused by actin stress fibers near the basal membrane. To quantitatively understand cell deformations in 3D, we develop a continuum mechanics model of epithelial cells as elastic cylindrical shells, with appropriate boundary conditions reflecting both the passive confinement of neighboring cells and the active stress of actomyosin contractility. This formalism yields analytical solutions predicting cell cross sections along the entire cylinder axis. Deconvolution microscopy experimental data confirm the significant and systematic change in cell shape parameters in this apical-basal direction. In addition to providing a wealth of detailed information on deformation on the subcellular scale, the results of the approach alter our understanding of how active tissues balance requirements of their stiffness and integrity, suggesting they are more robust against loss of rigidity than previously inferred.
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Submitted 29 January, 2025;
originally announced January 2025.
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Mono-exponential Current Attenuation with Distance across 16 nm Thick Bacteriorhodopsin Multilayers
Authors:
Domenikos Chryssikos,
Jerry A. Fereiro,
Jonathan Rojas,
Sudipta Bera,
Defne Tüzün,
Evanthia Kounoupioti,
Rui N. Pereira,
Christian Pfeiffer,
Ali Khoshouei,
Hendrik Dietz,
Mordechai Sheves,
David Cahen,
Marc Tornow
Abstract:
The remarkable ability of natural proteins to conduct electricity in the dry state over long distances remains largely inexplicable despite intensive research. In some cases, a (weakly) exponential length-attenuation, as in off-resonant tunneling transport, extends to thicknesses even beyond 10 nm. This report deals with such charge transport characteristics observed in self-assembled multilayers…
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The remarkable ability of natural proteins to conduct electricity in the dry state over long distances remains largely inexplicable despite intensive research. In some cases, a (weakly) exponential length-attenuation, as in off-resonant tunneling transport, extends to thicknesses even beyond 10 nm. This report deals with such charge transport characteristics observed in self-assembled multilayers of the protein bacteriorhodopsin (bR). About 7.5 nm to 15.5 nm thick bR layers were prepared on conductive titanium nitride (TiN) substrates using aminohexylphosphonic acid and poly-diallyl-dimethylammonium electrostatic linkers. Using conical EGaIn top contacts, an intriguing, mono-exponential conductance attenuation as a function of the bR layer thickness with a small attenuation coefficient $β\approx 0.8 \space {\rm nm}^{-1}$ is measured at zero bias. Variable-temperature measurements using evaporated Ti/Au top contacts yield effective energy barriers of about 100 meV from fitting the data to tunneling, hopping, and carrier cascade transport models. The observed temperature-dependence is assigned to the protein-electrode interfaces. The transport length and temperature dependence of the current densities are consistent with tunneling through the protein-protein and protein-electrode interfaces, respectively. Importantly, our results call for new theoretical approaches to find the microscopic mechanism behind the remarkably efficient, long-range electron transport within bR.
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Submitted 17 August, 2024;
originally announced August 2024.
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Current rectification via Photosystem I monolayers induced by their orientation on hydrophilic self-assembled monolayers on titanium nitride
Authors:
Jonathan Rojas,
Zhe Wang,
Feng Liu,
Jerry A. Fereiro,
Domenikos Chryssikos,
Thomas Dittrich,
Dario Leister,
David Cahen,
Marc Tornow
Abstract:
Photosystem I (PSI) is a photosynthetic protein which evolved to efficiently transfer electrons through the thylakoid membrane. This remarkable process attracted the attention of the biomolecular electronics community, which aims to study and understand the underlying electronic transport through these proteins by contacting ensembles of PSI with solid-state metallic contacts. This paper extends p…
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Photosystem I (PSI) is a photosynthetic protein which evolved to efficiently transfer electrons through the thylakoid membrane. This remarkable process attracted the attention of the biomolecular electronics community, which aims to study and understand the underlying electronic transport through these proteins by contacting ensembles of PSI with solid-state metallic contacts. This paper extends published work of immobilizing monolayers of PSI with a specific orientation, by using organophosphonate self-assembled molecules with hydrophilic heads on ultra-flat titanium nitride. Electrical measurements carried out with eutectic GaIn top contacts showed current rectification ratios of up to ~200. The previously proposed rectification mechanism, relying on the protein's internal electric dipole, was inquired by measuring shifts in the work function. Our straightforward bottom-up fabrication method may allow for further experimental studies on PSI molecules, such as embedding them in solid-state, transparent top contact schemes for optoelectronic measurements.
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Submitted 17 August, 2024;
originally announced August 2024.
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Effect of X-Ray Irradiation on Magnetocaloric Material, (MnNiSi)1-x(Fe2Ge)x
Authors:
John Peter J. Nunez,
Vaibhav Sharma,
Jessika V. Rojas,
Radhika Barua,
Ravi L. Hadimani
Abstract:
(MnNiSi)1-(Fe2Ge)x composition (x=0.34) alloy was prepared by arc melting, crushed, and sieved to approximately <32 microns. They were utilized in examining the possible magnetic and structural changes when exposed to a dosage of a continuous sweeping rate of ~>120 Gy/min and an absorbed dose of 35 kGy of X-ray radiation. This study reports observable trends in X-ray diffraction and magnetic measu…
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(MnNiSi)1-(Fe2Ge)x composition (x=0.34) alloy was prepared by arc melting, crushed, and sieved to approximately <32 microns. They were utilized in examining the possible magnetic and structural changes when exposed to a dosage of a continuous sweeping rate of ~>120 Gy/min and an absorbed dose of 35 kGy of X-ray radiation. This study reports observable trends in X-ray diffraction and magnetic measurements. Magnetization in the magnetization vs. temperature (both heating and cooling) measurements showed an increase from 2.72 emu/g to 4.01 emu/g in the irradiated sample. The Magnetization vs. magnetic field loops exhibited irradiation-induced magnetic hysteresis. The irradiated sample also exhibited an observable change in its coercivity of ΔHc = 14.7% at 200 K. A maximum entropy change ΔSmag of ~ 11.139 J/kg*K and a Tave peak of 317.5 K was achieved for the pristine sample in comparison to ΔSmag of ~ 11.349 J/kg*K and a Tave peak of 312.5 K for the irradiated sample. These presented results provided deeper insights into tuning the effect of irradiation to the magnetic properties of (MnNiSi)1-(Fe2Ge)x for composition (x=0.34) that can be utilized in a wide range of magnetocaloric applications in high-energy radiation environments. The irradiation applied to the sample did not induce any structural or magnetic phase changes in the selected composition but modified the magnetic properties marginally.
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Submitted 15 March, 2023;
originally announced March 2023.
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Quantum dot molecule devices with optical control of charge status and electronic control of coupling
Authors:
Frederik Bopp,
Jonathan Rojas,
Natalia Revenga,
Hubert Riedl,
Friedrich Sbresny,
Katarina Boos,
Tobias Simmet,
Arash Ahmadi,
David Gershoni,
Jacek Kasprzak,
Arne Ludwig,
Stephan Reitzenstein,
Andreas Wieck,
Dirk Reuter,
Kai Muller,
Jonathan J. Finley
Abstract:
Tunnel-coupled pairs of optically active quantum dots - quantum dot molecules (QDMs) - offer the possibility to combine excellent optical properties such as strong light-matter coupling with two-spin singlet-triplet ($S-T_0$) qubits having extended coherence times. The $S-T_0$ basis formed using two spins is inherently protected against electric and magnetic field noise. However, since a single ga…
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Tunnel-coupled pairs of optically active quantum dots - quantum dot molecules (QDMs) - offer the possibility to combine excellent optical properties such as strong light-matter coupling with two-spin singlet-triplet ($S-T_0$) qubits having extended coherence times. The $S-T_0$ basis formed using two spins is inherently protected against electric and magnetic field noise. However, since a single gate voltage is typically used to stabilize the charge occupancy of the dots and control the inter-dot orbital couplings, operation of the $S-T_0$ qubits under optimal conditions remains challenging. Here, we present an electric field tunable QDM that can be optically charged with one (1h) or two holes (2h) on demand. We perform a four-phase optical and electric field control sequence that facilitates the sequential preparation of the 2h charge state and subsequently allows flexible control of the inter-dot coupling. Charges are loaded via optical pumping and electron tunnel ionization. We achieve one- and two-hole charging efficiencies of 93.5 $\pm$ 0.8 % and 80.5 $\pm$ 1.3 %, respectively. Combining efficient charge state preparation and precise setting of inter-dot coupling allows control of few-spin qubits, as would be required for on-demand generation of two-dimensional photonic cluster states or quantum transduction between microwaves and photons.
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Submitted 20 May, 2022;
originally announced May 2022.
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Parameter identification for a damage model using a physics informed neural network
Authors:
Carlos J. G. Rojas,
Marco L. Bitterncourt,
José L. Boldrini
Abstract:
This work applies concepts of artificial neural networks to identify the parameters of a mathematical model based on phase fields for damage and fracture. Damage mechanics is the part of the continuum mechanics that models the effects of the micro-defect formation using state variables at the macroscopic level. The equations that define the model are derived from fundamental laws of physics and pr…
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This work applies concepts of artificial neural networks to identify the parameters of a mathematical model based on phase fields for damage and fracture. Damage mechanics is the part of the continuum mechanics that models the effects of the micro-defect formation using state variables at the macroscopic level. The equations that define the model are derived from fundamental laws of physics and provide important relationships between state variables. Simulations using the model considered in this work produce good qualitative and quantitative results, but many parameters must be adjusted to reproduce a certain material behavior. The identification of model parameters is considered by solving an inverse problem that uses pseudo-experimental data to find the values that produce the best fit to the data. We apply a physics-informed neural network and combine some classical estimation methods to identify the material parameters that appear in the damage equation of the model. Our strategy consists of a neural network that acts as an approximating function of the damage evolution with its output regularized using the residue of the differential equation. Three stages of optimization seek the best possible values for the neural network and the material parameters. The training alternates between the fitting of only the pseudo-experimental data or the total loss that includes the regularizing terms. We test the robustness of the method to noisy data and its generalization capabilities using a simple physical case for the damage model. This procedure deals better with noisy data in comparison with a PDE-constrained optimization method, and it also provides good approximations of the material parameters and the evolution of damage.
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Submitted 25 June, 2021;
originally announced July 2021.
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Water Contribution to the Protein Folding and its Relevance in Protein Design and Protein Aggregation
Authors:
Giancarlo Franzese,
Joan Àguila Rojas,
Valentino Bianco,
Ivan Coluzza
Abstract:
Water plays a fundamental role in protein stability. However, the effect of the properties of water on the behaviour of proteins is only partially understood. Several theories have been proposed to give insight into the mechanisms of cold and pressure denaturation, or the limits of temperature and pressure above which no protein has a stable, functional state, or how unfolding and aggregation are…
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Water plays a fundamental role in protein stability. However, the effect of the properties of water on the behaviour of proteins is only partially understood. Several theories have been proposed to give insight into the mechanisms of cold and pressure denaturation, or the limits of temperature and pressure above which no protein has a stable, functional state, or how unfolding and aggregation are related. Here we review our results based on a theoretical approach that can rationalise the water contribution to protein solutions' free energy. We show, using Monte Carlo simulations, how we can rationalise experimental data with our recent results. We discuss how our findings can help develop new strategies for the design of novel synthetic biopolymers or possible approaches for mitigating neurodegenerative pathologies.
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Submitted 24 March, 2021;
originally announced March 2021.
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Reconstructing phase-resolved hysteresis loops from first-order reversal curves
Authors:
Dustin A. Gilbert,
Peyton D. Murray,
Julius De Rojas,
Randy K. Dumas,
Joseph E. Davies,
Kai Liu
Abstract:
The first order reversal curve (FORC) method is a magnetometry based technique used to capture nanoscale magnetic phase separation and interactions with macroscopic measurements using minor hysteresis loop analysis. This makes the FORC technique a powerful tool in the analysis of complex systems which cannot be effectively probed using localized techniques. However, recovering quantitative details…
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The first order reversal curve (FORC) method is a magnetometry based technique used to capture nanoscale magnetic phase separation and interactions with macroscopic measurements using minor hysteresis loop analysis. This makes the FORC technique a powerful tool in the analysis of complex systems which cannot be effectively probed using localized techniques. However, recovering quantitative details about the identified phases which can be compared to traditionally measured metrics remains an enigmatic challenge. We demonstrate a technique to reconstruct phase-resolved magnetic hysteresis loops by selectively integrating the measured FORC distribution. From these minor loops, the traditional metrics - including the coercivity and saturation field, and the remanent and saturation magnetization - can be determined. In order to perform this analysis, special consideration must be paid to the accurate quantitative management of the so-called reversible features. This technique is demonstrated on three representative materials systems, high anisotropy FeCuPt thin-films, Fe nanodots, and SmCo/Fe exchange spring magnet films, and shows excellent agreement with the direct measured major loop, as well as the phase separated loops.
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Submitted 20 December, 2020;
originally announced December 2020.
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Chiral symmetry restoration in RQED at finite temperature in the supercritical coupling regime
Authors:
Jean Báez,
Alfredo Raya,
J. C. Rojas
Abstract:
We explore the conditions for chiral symmetry breaking in reduced (or pseudo) quantum electrodynamics at finite temperature in connection with graphene and other 2D-materials with an underlying Dirac behavior of the charge carriers. By solving the corresponding Schwinger-Dyson equation in rainbow approximation, in a Landau-like gauge and neglecting wavefunction renormalization effects, we find the…
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We explore the conditions for chiral symmetry breaking in reduced (or pseudo) quantum electrodynamics at finite temperature in connection with graphene and other 2D-materials with an underlying Dirac behavior of the charge carriers. By solving the corresponding Schwinger-Dyson equation in rainbow approximation, in a Landau-like gauge and neglecting wavefunction renormalization effects, we find the need of the coupling to exceed a critical value $α_c$ in order for chiral symmetry to be broken, in agreement with known results from other groups. In this supercritical regime, we add the effects of a thermal bath at temperature $T$ and find the critical values of this parameter that leads to chiral symmetry restoration.
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Submitted 7 September, 2020; v1 submitted 10 July, 2020;
originally announced July 2020.
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Nitrogen magneto-ionics
Authors:
Julius de Rojas,
Alberto Quintana,
Aitor Lopeandía,
Joaquín Salguero,
Beatriz Muñiz,
Fatima Ibrahim,
Mairbek Chshiev,
Maciej O. Liedke,
Maik Butterling,
Andreas Wagner,
Veronica Sireus,
Llibertat Abad,
Christopher J. Jensen,
Kai Liu,
Josep Nogués,
José L. Costa-Krämer,
Enric Menéndez,
Jordi Sort
Abstract:
So far, magneto-ionics, understood as voltage-driven ion transport in magnetic materials, has largely relied on controlled migration of oxygen ion/vacancy and, to a lesser extent, lithium and hydrogen. Here, we demonstrate efficient, room-temperature, voltage-driven nitrogen transport (i.e., nitrogen magneto-ionics) by electrolyte-gating of a single CoN film (without an ion-reservoir layer). Nitro…
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So far, magneto-ionics, understood as voltage-driven ion transport in magnetic materials, has largely relied on controlled migration of oxygen ion/vacancy and, to a lesser extent, lithium and hydrogen. Here, we demonstrate efficient, room-temperature, voltage-driven nitrogen transport (i.e., nitrogen magneto-ionics) by electrolyte-gating of a single CoN film (without an ion-reservoir layer). Nitrogen magneto-ionics in CoN is compared to oxygen magneto-ionics in Co3O4, both layers showing a nanocrystalline face-centered-cubic structure and reversible voltage-driven ON-OFF ferromagnetism. In contrast to oxygen, nitrogen transport occurs uniformly creating a plane-wave-like migration front, without assistance of diffusion channels. Nitrogen magneto-ionics requires lower threshold voltages and exhibits enhanced rates and cyclability. This is due to the lower activation energy for ion diffusion and the lower electronegativity of nitrogen compared to oxygen. These results are appealing for the use of magneto-ionics in nitride semiconductor devices, in applications requiring endurance and moderate speeds of operation, such as brain-inspired computing.
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Submitted 24 March, 2020;
originally announced March 2020.
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Boosting room temperature magneto-ionics in Co3O4
Authors:
Julius de Rojas,
Alberto Quintana,
Aitor Lopeandía,
Joaquín Salguero,
José L. Costa-Krämer,
Llibertat Abad,
Maciej O. Liedke,
Maik Butterling,
Andreas Wagner,
Lowie Henderick,
Jolien Dendooven,
Christophe Detavernier,
Jordi Sort,
Enric Menéndez
Abstract:
Voltage control of magnetism through electric field-induced oxygen motion (magneto-ionics) could represent a significant breakthrough in the pursuit for new strategies to enhance energy efficiency in a large variety of magnetic devices, such as magnetic micro-electro-mechanical systems (MEMS), magnetic logics, spin electronics, or neuromorphic computing, i.e., envisaging ultra-low power emulation…
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Voltage control of magnetism through electric field-induced oxygen motion (magneto-ionics) could represent a significant breakthrough in the pursuit for new strategies to enhance energy efficiency in a large variety of magnetic devices, such as magnetic micro-electro-mechanical systems (MEMS), magnetic logics, spin electronics, or neuromorphic computing, i.e., envisaging ultra-low power emulation of the biological synapse. Boosting the induced changes in magnetization, magneto-ionic motion and cyclability (endurance) continue to be key challenges to turn magneto-ionic phenomena into real applications. Here, we demonstrate that, without degrading cyclability, room temperature magneto-ionic motion in electrolyte-gated paramagnetic and fairly thick (> 100 nm) Co3O4 films largely depends on the configuration used to apply the electric field. In particular, magneto-ionic effects are significantly increased both in terms of generated magnetization (6 times larger: from 118.5 to 699.2 emu cm-3) and speed (35 times faster: from 33.1 to 1170.8 emu cm-3 h-1) if the electric field is applied across a conducting buffer layer (grown underneath the Co3O4 films), instead of directly contacting Co3O4. This is attributed to a greater uniformity and strength of the applied electric field when using the conducting layer. These results may trigger the use of oxygen magneto-ionics into promising new technologies, such as magnetic MEMS or brain-inspired computing, which require endurance and moderate speeds of operation.
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Submitted 22 January, 2020;
originally announced January 2020.
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Very large domain wall velocities in Pt/Co/Gd trilayers with Dzyaloshinskii-Moriya interaction
Authors:
Thai Ha Pham,
J. Vogel,
J. Sampaio,
M. Vaňatka,
J. -C. Rojas,
M. Bonfim,
D. S. Chaves,
F. Choueikani,
P. Ohresser,
E. Otero,
A. Thiaville,
S. Pizzini
Abstract:
We carried out measurements of domain wall (DW) velocities driven by magnetic field pulses in symmetric Pt/Co/Pt and asymmetric Pt/Co/AlOx, Pt/Co/GdOx and Pt/Co/Gd trilayers with ultrathin Co layers and perpendicular magnetic anisotropy. In agreement with theoretical models, the maximum observed velocity is much larger in the asymmetric samples, where the interfacial Dzyaloshinskii-Moriya interact…
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We carried out measurements of domain wall (DW) velocities driven by magnetic field pulses in symmetric Pt/Co/Pt and asymmetric Pt/Co/AlOx, Pt/Co/GdOx and Pt/Co/Gd trilayers with ultrathin Co layers and perpendicular magnetic anisotropy. In agreement with theoretical models, the maximum observed velocity is much larger in the asymmetric samples, where the interfacial Dzyaloshinskii-Moriya interaction (DMI) stabilises chiral Néel walls, than in the symmetric stack. In addition, in Pt/Co/Gd very large DW speeds (up to 600 m/s) are obtained, 2.5 times larger than in samples with oxidised Gd. Magnetic measurements reveal that this may be explained by the anti-parallel coupling between the magnetic moments of Gd and Co at the Gd/Co interface, leading to a decrease of the total magnetisation. In quantitative agreement with analytical models, in all samples the maximum observed DW speed scales as D=Ms, where D is the strength of the DMI and Ms the spontaneous magnetisation.
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Submitted 12 February, 2016;
originally announced February 2016.
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Magnetic catalysis of a charged Bose-Einstein condensate
Authors:
Alejandro Ayala,
M. Loewe,
Juan Cristobal Rojas,
C. Villavicencio
Abstract:
We study the condensation phenomenon for a system of charged bosons in the presence of an external magnetic field. We show that condensation happens for a definite critical temperature instead of through a diffuse phase transition. The essential ingredient, overlooked in previous analyses and accounted for in this work, is the treatment of the plasma screening effects by means of resummation. We c…
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We study the condensation phenomenon for a system of charged bosons in the presence of an external magnetic field. We show that condensation happens for a definite critical temperature instead of through a diffuse phase transition. The essential ingredient, overlooked in previous analyses and accounted for in this work, is the treatment of the plasma screening effects by means of resummation. We compute the critical temperature, for the case in which the condensate is made of charged pions and for typical densities found in compact astrophysical objects, for small and large values of the magnetic field. We show that the magnetic field catalyzes the onset of condensation at very small and at large values of the magnetic field, and that for intermediate values, the critical temperature for condensation is lower than for the zero magnetic field case.
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Submitted 8 October, 2012; v1 submitted 1 August, 2012;
originally announced August 2012.
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Numerical Forecast of the Melting and Thermal Histories of Particles Injected in a Plasma Jet
Authors:
Jorge Romero Rojas,
Marcela A. Cruchaga,
Diego J. Celentano,
Mohamed El Ganaoui,
Bernard Pateyron
Abstract:
This work presents the numerical simulation of the melting process of a particle injected in a plasma jet. The plasma process is nowadays applied to produce thin coatings on metal mechanical components with the aim of improving the surface resistance to different phenomena such as corrosion, temperature or wear. In this work we studied the heat transfer including phase-change of a bi-layer parti…
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This work presents the numerical simulation of the melting process of a particle injected in a plasma jet. The plasma process is nowadays applied to produce thin coatings on metal mechanical components with the aim of improving the surface resistance to different phenomena such as corrosion, temperature or wear. In this work we studied the heat transfer including phase-change of a bi-layer particle composed of a metallic iron core coated with ceramic alumina, inside a plasma jet. The model accounted for the environmental conditions along the particle path. The numerical simulation of this problem was performed via a temperature-based phase-change finite element formulation. The results obtained with this methodology satisfactorily described the melting process of the particle. Particularly, the results of the present work illustrate the phase change evolution in a bi-layer particle during its motion in the plasma jet. Moreover, the numerical trends agreed with those previously reported in the literature and computed with a finite volume enthalpy based formulation.
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Submitted 11 February, 2010;
originally announced February 2010.
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Microcanonical Molecular Dynamic Simulations of Au Nanoclusters
Authors:
Karina L. D. Barturen H.,
F. A. R. Navarro,
Justo T Rojas
Abstract:
In this paper, we study nanoparticles with constituent atoms ranging from dozens to hundreds of them. These types of particles display structural and magnetic properties that strongly depend on the number of constituents N. The metal clusters are important due their interesting properties when compared to bulk materials; hence they have potential technological applications. Specifically, we stud…
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In this paper, we study nanoparticles with constituent atoms ranging from dozens to hundreds of them. These types of particles display structural and magnetic properties that strongly depend on the number of constituents N. The metal clusters are important due their interesting properties when compared to bulk materials; hence they have potential technological applications. Specifically, we study the Au nanoclusters through classical molecular dynamics simulations; we analyze the total and potential energy as a function of time. Likewise, we study the geometrical structures of Au Nanocluster corresponding to the lowest energy states at 0 K. We consider the method of microcanonical ensemble, and we carry out computer simulations by operating the XMD software package and the atomistic configuration viewer AtomEye.
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Submitted 5 February, 2010;
originally announced February 2010.
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The Cummings-Stell model of associative fluids: a general solution
Authors:
J. F. Rojas
Abstract:
In a series of publications the Cummings-Stell model (CSM), for a binary mixture of associative fluids with steric effects, has been solved analytically using the Percus-Yevick approximation (PYA). The solution consists in a square well potential of width w, whose center is placed into the hard sphere shell ($r < σ$): at $L = σ/ n$ (n = 1, ..., 4). This paper presents a general solution, for any…
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In a series of publications the Cummings-Stell model (CSM), for a binary mixture of associative fluids with steric effects, has been solved analytically using the Percus-Yevick approximation (PYA). The solution consists in a square well potential of width w, whose center is placed into the hard sphere shell ($r < σ$): at $L = σ/ n$ (n = 1, ..., 4). This paper presents a general solution, for any n, of the first order Difference Differential Equation (DDE), for the auxiliary Baxter's function that appears in the CSM, using recursive properties of these auxiliary functions and a matrix composed by differential and shift operators (MDSO). This problem is common in some other models of associative fluids such as the CSM for homogeneus and inhomogeneus mixtures of sticky shielded hard spheres including solvent effects under PYA, and in that of mean-spherical approximation (MSA), for chemical ion association and dipolar dumbbells and polymers. The sticky potential implies a discontinuity step at $L$ in the solution of auxiliary Baxter's functions so that, one side, $L$ now is arbitrary and, for some additional effects, it can be placed one or more sticky potentials at different positions into the hard shell.
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Submitted 22 March, 2009;
originally announced March 2009.
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Atomic and electronic structure transformations of silver nanoparticles under rapid cooling conditions
Authors:
I. Lobato,
J. Rojas,
C. V. Landauro,
J. Torres
Abstract:
The structural evolution and dynamics of silver nanodrops Ag${}_{2896}$ (4.4 nm in diameter) during rapid cooling conditions has been studied by means of molecular dynamics simulations and electronic density of state calculations. The interaction of silver atoms is modeled by a tight-binding semiempirical interatomic potential proposed by Cleri and Rosato. The pair correlation functions and the…
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The structural evolution and dynamics of silver nanodrops Ag${}_{2896}$ (4.4 nm in diameter) during rapid cooling conditions has been studied by means of molecular dynamics simulations and electronic density of state calculations. The interaction of silver atoms is modeled by a tight-binding semiempirical interatomic potential proposed by Cleri and Rosato. The pair correlation functions and the pair analysis technique is applied to reveal the structural transition in the process of solidification. It is shown that Ag nanoparticles evolve into different nanostructures under different cooling processes. At a cooling rate of $1.5625\times10^{13} Ks^{-1}$ the nanoparticles preserve an amorphous like structure containing a large amount of 1551 and 1541 pairs which correspond to the icosahedral symmetry. For a lower cooling rate ($1.5625\times10^{12} Ks^{-1}$), the nanoparticles transform into a crystal-like structure consisting mainly of 1421 and 1422 pairs which correspond to the fcc and hcp structures, respectively. The variations of the electronic density of states for the differently cooled nanoparticles are small but in correspondence with the structural changes.
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Submitted 22 January, 2009; v1 submitted 8 September, 2008;
originally announced September 2008.