Tesis Doctorals - Departament - Física de la Matèria Condensada

URI permanent per a aquesta col·leccióhttps://hdl.handle.net/2445/106688

Estadístiques

Examinar

Mostrant 1 - 19 de 19

Functional connectivity at multiple scales: From neuronal cultures to human brain
(Universitat de Barcelona, 2024-03-20) Montalà Flaquer, Marc; Guàrdia-Olmos, Joan, 1958-; Soriano i Fradera, Jordi; Universitat de Barcelona. Departament de Psicologia Social i Psicologia Quantitativa
[eng] One of the greatest challenges in the field of neuroscience is to obtain an accurate functional description of the brain that allows us to understand the functioning of higher complexity cognitive processes such as memory or consciousness. Many techniques are used to fit in the various experimental paradigms, among which the functional magnetic resonance (fMRI) imaging stands out. Another standard procedure is the calcium fluorescence imaging, a technique that allows the monitoring of neuronal activations over time thanks to the changes in calcium concentration in the synaptic cleft. This thesis aims to study the functional connectivity of a complex multiscale system, the brain, in a healthy aging paradigm. To achieve this objective, two complementary lines of research have been followed: a mesoscopic approach with primary rat neuronal cultures and a whole–brain study, i.e., at a large scale, using brain spontaneous activity from healthy participants. Throughout the first line of research, neuronal cultures have been developed on surfaces with a certain topography —track and square obstacles— that enabled to characterize the functional features and the dynamical richness of the emerging spontaneous activity. The second line of research has addressed the analysis of the fMRI signal from healthy participants as well as the characterization of the functional networks that derive from connectivity matrices. As a secondary objective, we analysed how the filtering methods affected these functional indicators extracted from the connectivity matrices. In neuronal cultures, and regarding the track’s configuration, we have observed that the activation dynamics was substantially different from the one observed in standard, flat surface cultures. The parallel lines completely break the isotropy of the surface creating a privileged direction in the connections with neighbouring neurons. However, there is a certain possibility that neurons connect transversely, which originate activations throughout the entire neuronal culture. We note that in this paradigm it is no longer possible to assume that the propagation takes place following a circular wave front. Indeed, we found a rapid propagation velocity along the track and a slower speed of propagation in the transverse direction. Finally, local and global measures of segregation and integration such as global efficiency, aggregation coefficient or degree of connectivity have been analysed. This study has allowed us to better understand communication throughout the culture and the dynamic changes of spontaneous activity. Thanks to transfer entropy algorithms to unveil information flow, we have found that cultures with square and track configurations show an effective modular organization, while homogeneous cultures on a flat surface show a more random organization. Effective connectivity analyses have revealed the emergence of spatially compact functional modules that can be associated with topographical features and spatiotemporal activity fronts. All these results support the assumption that the introduction of patterns as physical perturbation modifies the functional dynamics of neuronal cultures and endows them with greater dynamical richness. Regarding the analysis of fMRI signal, the results seem to indicate that the analysis methods fALFF (fractional Amplitude of low-frequency fluctuations) and ReHo (Region Homogeneity) correctly describe the aging process of a healthy population, that is, without decline of cognitive performance, and highlight two interesting facts. On the one hand, fALFF shows that there is a significant difference in low–intensity fluctuations as aging occurs. Other studies have reported a loss of functional connectivity without the manifestation of a decline in neuropsychological measurements or participant performance. On the other hand, ReHo indicates an increase in regional synchrony when comparing the oldest group with the other age groups. This increase in synchronization has been described in other studies as a compensatory mechanism, in which certain regions need greater coherence to continue operating without any decline in neuropsychological performance indicators. We therefore believe that ReHo could be describing the process of healthy aging. In relation to the exploration of filtering methods, we have been able to verify that the most stable technique is TMFG (Triangulated Maximally Filtered Graph). It is also the technique that is furthest away from the null model, i.e., the random distribution of signal correlation, throughout all the connectivity indicators studied. In addition, the advantage of this technique is that it preserves the maximum information stored in the connectivity matrix by eliminating redundant or spurious connections.
Colloidal dynamics in artificial particle ice systems
(Universitat de Barcelona, 2024-03-22) Rodríguez Gallo, Carolina; Tierno, Pietro; Ortiz Ambriz, Antonio; Universitat de Barcelona. Departament de Física de la Matèria Condensada
[eng] Geometrical frustration is a general phenomenon inﬂuencing the behavior of diverse natural systems across diﬀerent length scales. Geometrical frustration arises when the symmetry of the interaction among building blocks and the system geometry do not match. This incompatibility generates a system with competing interactions that are the in charge of generating a rich phenomenology. In systems where geometrical frustration is present, we may have a degenerate ground state at zero temperature, a rich phase diagram or intrinsic disorder. Nowadays, with the technological advances, scientists can construct artiﬁcial frustrated systems. Those present the potential to become materials with engineered properties or be used as a tool to further comprehend the nature of this exotic phenomena. In this thesis, I used an Artiﬁcial Colloidal Ice (ACI) as a model system to study the geometric frustration in systems with a spin degree of freedom. Colloidal particles are the interacting units of an ACI and present the advantage of having accessible time and length scales. In addition, colloidal particles have demonstrated the capability to behave as model system for atoms or molecules, both systems at length scales that are more diﬃcult to observe. To complete this investigation, I used numerical simulations using the LAMMPS molecular dynamics simulator and experimental realizations. For the experimental realizations, I used video optical microscopy, state-of-art lithography techniques and holographic optical tweezers. This thesis presents the result of four projects that study the ACI system under diﬀerent conditions, under the form of four publications accompanied by an introductory part. In the ﬁrst one, I studied the eﬀects on an ACI if the boundaries of the system are ﬁxed. We observed that the boundaries can inﬂuence the bulk behavior; and in particular that, antiferromagnetic boundaries can reach a full ground state of the system, not possible with other types of boundaries. In the second project, I computed the colloidal and latice parameters to achieve an extensive degeneracy in a square ACI. In here, I observed a reentrant behavior: the system starting from a disordered conﬁguration reaches a low-energy state to then achieve disorder again. The third project, studied the eﬀects of changing the geometry of an ACI without altering its topology. I observed that excitations of the ground state with opposite topological charges can be accumulated in a certain sublatice of a mixed coordination latice or be balanced. Filling the gap among ACI and natural systems. Finally, In the fourth project, I investigated the low-energy states of a Cairo ACI, a latice made of irregular pentagons. The Cairo ACI presents a high degree of degeneracy, exhibiting a disordered ensemble at low-energy states that corresponds with a frustrated antiferrotoroid.
Non-Equilibrium Dynamics of Driven and Confined Colloidal Systems
(Universitat de Barcelona, 2023-07-14) Cereceda López, Eric; Tierno, Pietro; Ortiz Ambriz, Antonio; Universitat de Barcelona. Departament de Física de la Matèria Condensada
[eng] In this thesis, I study the behavior of confined colloidal particles in aqueous suspension driven through an optical potential. For this purpose, I use micro-meter polystyrene particles, which I confine in the optical potential created with a system of optical tweezers. With the help of an Acousto Optical Deflector (AOD), which varies the laser position at a high frequency, I can create multiple quasi-simultaneous optical traps. This way, I can easily manipulate the particles and define the desired experimental conditions for the potential. I record videos of the particles' dynamics using optical microscopy. Thus, I obtain position information over time, which allows me to extract the necessary data to analyze the mechanisms that develop during forced transport. The results presented in this thesis expose the importance of Hydrodynamic Interactions (HI) when the transport of particles occurs due to a fluid drag. In addition, different situations are compared, including the change in the relative particle size concerning the separation between potential wells. In addition, I present a study on the emergence of solitons propagating in the opposite direction to the drag force. This situation, which appears when the experimental system is overcrowded, presents a mechanism where the transport dynamics accelerate, increasing the systems' efficiency.
Modelling the dynamics of cellular membranes
(Universitat de Barcelona, 2022-07-08) Fernández i Gallén, Andreu; Hernández Machado, Aurora; Universitat de Barcelona. Departament de Física de la Matèria Condensada
[eng] Membranes are present in all cells, in some viruses, and are involved in all kinds of biological functions. The goal of this thesis is to expand our knowledge of this element, in hope that this -on top of all the other knowledge of biology and physics- can help someday improve people's life. With this aim, what I tried to do was to understand how cells react when things happen to them. This is the drive behind the two different research paths written in this thesis: membranes inside a fluid flow, and membranes during topological transitions and fluctuations. For the first research path -on membranes inside a flow- while this is not a new topic we wanted to start by making it more approachable. That has been achieved by introducing a new methodology to couple membranes and flows by using the stream function and the vorticity to solve the Navier Stokes equation. This approach creates a model derived straight from the hydrodynamic equations and grounded on the physics of the system rather than other more complex approaches. With this model we tried to study the effects of confinement for membranes inside a Poiseuille flow. We mainly tried to replicate red blood cell shapes as it is a very researched case and there is plenty of experimental data on them. First starting with cells inside channels slightly bigger than their diameter, which is known to give a set of shapes named parachutes and slippers. We use this knowledge to prove the validity of our model. For very wide channels, the low confinement Poiseuille flows have shown a different meta-stable shape which we named anti-parachute. Moreover, tumbling can be produced by introducing a different viscosity for the cell fluid, higher than the surrounding fluid. In very narrow super-confined channels we have a Poiseuille flow where the cell is much bigger than the channel and gives very different shapes. However, the model is capable of studying other flows rather than Poiseuille. Couette flow has been studied, where one can see a lift perpendicular to the flow that depends on the reduced volume of the cell as well as the viscosity contrast. The most important thing has been leaving behind a methodology ready for expansion to time-dependent flows, inertial flows, or to generalize to 3 dimensions. For the second research path --on topological transitions-- we have implemented the Gaussian curvature energy term to the membrane model, to allow study of fission and fusion. With this methodology we study fission of tubes with the use of the spontaneous curvature, which deforms a membrane tube into a pearled tube. This pearled tube formed by an array of spheres connected through membrane tethers undergoes fission if the Gaussian rigidity is negative and high enough. A phase diagram of what happens depending on the values of Gaussian and bending rigidity is obtained. Then we expand to study geometries less helpful for fission, such as a flat planar membrane. It will not matter how big is the spontaneous curvature of the Gaussian rigidity, as a perfectly flat membrane is a meta-stable shape. This is due the fact that to start the fission process we need an area with enough curvature so that the spontaneous curvature can kick-off the membrane budding process. To solve this, we added a white noise to mimic temperature. This noise makes each point of the membrane position to fluctuate. There is a phase transition between a flat membrane that is not undergoing fission and one that does.
Nonlinear and spatial dynamics for multicellular organisms
(Universitat de Barcelona, 2022-06-16) Mercadal Melià, Josep; Ibañes Miguez, Marta; Sancho, José M.; Universitat de Barcelona. Departament de Física de la Matèria Condensada
[eng] The development of living systems, from their conception to their death, involves a very tight coordination between gene expression in time and space. The processes involved in such an unfolding do not solely depend on the interactions between genes, but also on the environment the organism is embedded in, partly random and unpredictable, partly constructed by the organism itself. Indeed, no embryo grows without a warm womb or a protected egg. Understanding development is understanding how diverse functions or phenotypic traits arise from these relationships. In this thesis we have studied some of these biological processes mainly in plants. The approach we take to these problems is that of systems biology, the theoretical framework that studies the interactions between the constituent parts of organisms, be they molecules, genes or cells, and how these relations lead to emergent behaviours which cannot be understood through the study of the parts alone. The main goal is to understand, through this theoretical approach, the biological processes involved in cellular decision-making, whether they are related to the division, differentiation, or generation of molecular signals. The first part of the thesis focuses on the regulatory interactions between BRAVO and WOX5, two transcription factors involved in the regulation of quiescent cells in the stem cell niche of the Arabidopsis thaliana root. By combining theoretical modelling with experimental evidence, we find that these two factors interplay both at the transcriptional and post-transcriptional level, and they involve the formation of a complex. Owing to the convergence of the two transcription factors at the quiescent center, we propose a simple mechanism for regulating cell division and find that the formation of the BRAVO-WOX5 complex can be relevant. We also consider the effect of space in the regulations between BRAVO and WOX5, finding that the movement of WOX5 can be relavant to explain the expression patterns observed experimentally. The second part has focused on the role of genetic circuits operating in coupled cellular lattices by the diffusion of one of the molecules, and how these interactions can generate spatial patterns of different cell types. We first apply this approach to the formation of rhizoid precursor cell patterns in the epidermis of the Marchantia polymorpha plant. Rhizoids are thin outgrowths which appear at the interface between the plant main body and the substrate, and extend distally into the soil effectively increasing the total surface area for water and nutrient absorption. The formation of rhizoids in the epidermis of Marchantia is known to be regulated by several factors, but how the specific spatial distribution emerges from a field of epidermal cells is poorly understood. Building on recent experiments, we propose that rhizoid patterns appear from the interactions between the microRNA FRH1 and the rhizoid-promoting transcription factor RSL1, in a feedback circuit of activator-inhibitor type, where RSL1 activates FRH1, and FRH1 diffuses and represses the activity of RSL1. We find that our theoretical predictions precisely match those of the experiments, underscoring the capabilities of the model. We then study the spatiotemporal behaviours of a small genetic circuit capable of displaying diverse spatiotemporal behaviours, including bistability, oscillations and pattern formation. The circuit is based on the mixed feedback loop, a genetic circuit overrepresented in statistical analyses of gene and protein interaction databases. It consists of the transcriptional repression of a gene by another, plus the formation of a reversible complex between the proteins coded by the two genes. Through dynamical systems theory and bifurcation analysis, we find the conditions for each regime to appear and emphasize the multi-functional nature of the circuit, a feature embodying an increasingly common theme in developmental and evolutionary systems biology, namely the importance of small circuits capable of performing multiple, qualitatively different functions, which arise from the circuit’s topology but depend on the specific external context of which the circuit is embedded. The ultimate goal of systems biology is to understand life at its most basic level. As complex systems par excellence, living organisms have characteristics that cannot be reduced only to the behaviors of their parts. Instead, it is the nature of its systems that characterizes its most iconic idiosyncrasies, from the internal functioning of a cell to the complicated structure of the nervous system.
Giant caloric and multicaloric effects in magnetic alloys
(Universitat de Barcelona, 2022-04-21) Gràcia Condal, Adrià; Mañosa, Lluís; Universitat de Barcelona. Departament de Física de la Matèria Condensada
[eng] The urgent need to reduce our footprint on the earth environment is leading to ever more stringent commitments to decrease greenhouse gases emissions, which entails one of the greatest challenges that mankind has to tackle. As a direct consequence, it is of utmost importance to develop novel, energy-efficient and environmentally-friendly refrigeration technologies that do not require the use of climate-damaging substances. In this regard, solid-state refrigerants based on the large thermal response exhibited by a variety of materials when field-inducing a ferroic phase transition are among the best alternatives. Specifically, materials undergoing a first-order phase transition are of particular interest as the latent heat associated with the phase transition contributes on enhancing the magnitude of the thermal response. Depending on the nature of the external field that drives the phase transition one distinguishes between magnetocaloric, electrocaloric, elastocaloric or barocaloric effects. In spite of all the intensive research devoted to the study of the diverse caloric effects, there are still a series of bottlenecks to overcome. Firstly, they require the application of strong external fields in order to induce a large thermal response. Secondly, the hysteresis associated with the phase transition can drastically reduce the efficiency and compromises its reversibility. A way out of such issues can be provided by materials exhibiting a strong coupling between the structural, magnetic or electronic degrees of freedom, denoted as multicaloric materials, which allow to drive their phase transition by the combination of diverse external fields, giving rise to multicaloric effects. Despite the high potential they exhibit, the research on multicaloric materials is germinal as it requires the use of non-commercial experimental systems. In this dissertation, we have focused on the study of materials displaying a magnetostructural first- order phase transition with a strong coupling between the structural and magnetic degrees of freedom. For such purpose, we have used distinct purpose-built calorimetric and adiabatic thermometry systems to investigate their caloric and multicaloric effects by direct methods. We have concentrated on two distinct families of multicaloric materials: Fe-Rh and Ni-Mn-based Heusler alloys. Our research is aimed at thoroughly characterizing the diverse advantages of multicaloric effects: showing that lower driving fields are required, that the operating temperature windows of the materials can be enlarged and discussing how their inherent hysteresis can be mastered or even exploited.
Out-of-equilibrium dynamics in driven and active magnetic colloids
(Universitat de Barcelona, 2019-12-11) Massana-Cid, Helena; Tierno, Pietro; Universitat de Barcelona. Departament de Física de la Matèria Condensada
[eng] In this thesis we investigate the structure formation and the out-of-equilibrium dynamics of driven and active magnetic colloids. The interactions in our system were tuned in situ by using external fields, with the aim of finding novel approaches to drive and engineer these microparticles into a rich variety of microstructures. The colloids formed chains and clusters able to transport cargos, space-filling gels and self-healing crystals. Moreover, we demonstrated the bidirectional transport of paramagnetic particles on top of a structured magnetic substrate. Because of their associated length-scale, colloids are experimentally accessible with traditional optical microscope techniques. We analysed the data extracted from digital video microscopy and used such information to infer the particle dynamics. Colloids have been proven to be excellent model systems for structures across different length scales that are more difficult to observe, such as collections of atoms and molecules. Furthermore, they are helpful test-beds to investigate fluid dynamics at low Reynolds number and can form artificial micromachines that are essential for the realization of disparate functional tasks at the microscale.
Dynamics and Effective Connectivity in Bi- and Three–dimensional Neuronal Cultures: from Self–organization to Engineering
(Universitat de Barcelona, 2019-11-22) Estévez Priego, Estefanía; Soriano i Fradera, Jordi; Tornero, Daniel; Universitat de Barcelona. Departament de Física de la Matèria Condensada
[eng] This thesis was part of the European consortium MESOBRAIN, a team of 5 organizations that joined efforts in nanofabrication, cell culturing, imaging and data analysis to build tailored human 3D networks. The thesis timing was limited to 3 years, and several of the resources needed for its development were built from scratch. The main objective of this Ph.D. thesis was to explore complex characteristics of cortical neuronal cultures in terms of effective connectivity and exhaustive network analyses. This objective comprised four research lines: (i) The evaluation of neuronal network resilience and emerging plasticity mechanisms, (ii) the characterization of functional development to underline crucial timepoints in healthy neuronal networks, (iii) the study of 3D network interactions of neurons embedded inside an ECM--like environment, and (iv) the design, construction and viability inspection of neurons seeded on tiny 3D nanoprinted solid scaffold structures as a first step towards recreating cortical columns in vitro. For these multiple lines, we used either primary rat cultures (i,iii,iv) or human--derived neurons (ii). The former group corresponds to cultures with long established protocols that have been thoroughly studied in the field. The latter group corresponds to human neurons derived from iPSCs, a relatively novel model with promising and thrilling applications in regenerative medicine. Despite the increasing use of stem cells in neuroscience, complex systems and medicine, they still lack a thorough exploration in terms of neuronal and circuit formation as well as the properties of the emergent activity patterns. With either primary or stem cells, we explored the formation of neuronal circuits in 2D and 3D, characterized the effective connectivity and rendered a number of network traits. This Thesis combines experiments of highly difficult implementation with detailed data analysis. It was necessary to develop brand new protocols for culturing 3D neuronal networks and for human-derived neurons, the use of different microscopy setups the programming of object detection and tracking software and advance the analysis toolbox of calcium fluorescence data. First, resilience experiments on primary clustered neuronal cultures consisted on progressive perturbations through chemical receptor antagonists. This study represents an inspiring numerical--experimental model to comprehend the impact of plasticity mechanisms in the spontaneous activity of neuronal circuits. The results showed that, upon progressive connectivity blockade through chemical receptors' antagonists, only--excitatory neuronal networks displayed a surprising hyper--efficiency (HE) state for early--onset doses. As plasticity mechanisms influence the response of effective connectivity in the presence of perturbations, these compensatory mechanisms, usually disregarded, must be included in biological modeling as accurately as possible. Otherwise, episodes of functional rewiring and synaptic strengthening could mask important phenomena during experiments that alter channel communication. A simple algorithm that hypothesized an effective synaptic scaling was able to capture the hyper--efficiency state seen in experimental data, while percolation models wrongly predicted a progressive decay. The second research line was a sum of engineering efforts within the MESOBRAIN consortium, the European adventure to build 3D neuronal cultures embedded in hydrogels and with the presence of scaffolds. After several months of biomaterials testing, the candidate D--Clear resulted suitable for the construction of scaffolds, both with primary rat cells and hiPSCs, due to its good optical properties, manageability and biocompatibility. To our knowledge, D--Clear was never used before outside the orthodontic field and could provide a new catalogue of interesting designs for support and guidance of neuronal assemblies. Using this material, we developed a series of designs to offer support and guidance to cortical neurons in a 3D platform. The third research line focused on the study of neuronal development and cell-to-cell interactions in a semi-synthetic hydrogel that resembles the extracellular matrix of the brain. These hydrogel cultures keep the advantages of in vitro models while achieving an effective connectivity and architecture closer to in vivo. Finally, the fourth line of research applied cortical neurons from human-derived pluripotent stem cells to study key developmental stages and characterize the healthy maturation of these cells in vitro. As this technology has tremendous potential for regenerative medicine and to model neuronal diseases, it is urgent to consolidate the capacity of these human neuronal networks to reproduce efficient activity patterns of healthy patients, and explore the differences against the results obtained with animal models.
Revealing DNA dynamics from atomistic to genomic level by multiscale computational approaches
(Universitat de Barcelona, 2019-10-04) Walther, Jürgen; Orozco López, Modesto; Universitat de Barcelona. Departament de Física de la Matèria Condensada
[eng] The study of DNA from atomistic to mesoscopic level and connecting different resolution levels constitutes a major challenge since the new millennium. In the early 2000s, experiments could resolve for the first time the structure of the nucleosome in high detail or capture physical contacts in the genome of segments far apart in sequence. At around the same time, the force field development for atomistic nucleic acid simulations reached a peak with parmbsc0 in 2007 and coarse grain nucleosome fiber models emerged. The first decade ended with a remarkable experimental advance in visualizing the whole genome, Hi-C. In the current decade, almost ten years after Hi-C was invented, the structure of the cell nucleus is still a very hot topic. We can now harvest the fruits of the pioneers in the first decade of multi-scale investigation of DNA and connect the different resolution levels to obtain a complete picture of DNA from electron orbitals to genome folding. In this work, we use computational approaches to dissect the different resolution levels, from atomistic MD simulations to mesoscopic secondary chromatin structure modeling. We developed a force-field (parmbsc1) for the accurate description of atomistic DNA dynamics based on quantum mechanical simulations. With the accuracy of parmbsc1, sequence-dependent effects of B-DNA flexibility beyond the base pair level were described and used as a starting point to parametrize a novel helical coarse grain model which shows similar accuracy to the DNA dynamics obtained by atomistic MD, but at much lower computational cost. In a newly developed nucleosome fiber model the coarse grain DNA algorithm is used for the linker DNA description and alongside with a simple mesoscopic characterization of the nucleosome chromatin dynamics can be probed at kilobase scale with a DNA model whose roots lie in the quantum mechanical regime. On top of that, to meet current standards of accessibility and usability of tools, the developed coarse grain DNA and nucleosome fiber model are freely available as stand-alone versions or integrated in a single webserver or large-scale online research environment platform.
Free energy and information-content measurements in thermodynamic and molecular ensembles
(Universitat de Barcelona, 2019-05-28) Martínez Monge, Álvaro; Ritort Farran, Fèlix; Mañosas Castejón, María; Universitat de Barcelona. Departament de Física de la Matèria Condensada
[eng] Single-molecule experiments have emerged as a powerful tool that allow researchers to investigate the physical behavior of individual molecules with unprecedented resolution. The feasibility exerting forces at the piconewton scale (10^-12 N) and measuring nanometric displacements in the sub-millisecond scale, offer a widespread range of exciting possibilities. The major part of this thesis is devoted to address fundamental topics of statistical physics using single-molecule experiments. In particular, in the first part of the thesis, we aimed to study one of the eldest questions in statistical mechanics: the issue of ensemble inequivalence. By performing single- molecule experiments on a well-known molecule (the CD4 DNA hairpin), we have been able of exploring two conjugate ensembles: the fixed-extension and the force-fixed ensemble. Both ensembles are conjugate with respect to energy since the product force times extension equals has energy dimensions. We carried out experiments in the fixed-force ensemble using both optical tweezers and magnetic tweezers, and in the fixed-extension using optical tweezers. We have found that these two conjugate ensembles are not equivalent at the level of thermodynamics nor in kinetics. Moreover, we showed that the often-neglected boundary terms in the definition of the thermodynamic work are essential to the validity of the fluctuation theorem. The second part of this thesis is also merely theoretical. Recent single-molecule assays confirmed the connection between information theory and statistical physics. Single- molecule experiments have turned out to be the perfect playground to explore the thermodynamic implications of having —or lacking— information. It is worthwhile to mention the experimental realization of the Szilard engine and the experimental verification of Landauer’s limit. With the current existing results, the information-to- energy connection is well established. We have been able to experimentally demonstrate, for the first time, the reversed implication. We have been able to quantify the information-content of neutral molecular ensembles by means of thermodynamic measurements. That is, we experimentally demonstrated the energy- to-information conversion. Our works are built on what we call ensemble force spectroscopy, a systematic procedure capable of obtaining a robust characterization of molecular ensembles in the best tradition of statistical physics, by measuring few tens of molecules. In the final part of the thesis we aimed to measure the specific binding energy of a metallic ion to the tertiary structure of a three-way RNA junction belonging to the central domain of the 16S ribosomal RNA (rRNA). From the physics perspective, to the best of our knowledge, first time we have been able to discern the free energy contribution due to the specific binding of magnesium ions to an RNA substrate by means of single-molecule assays. On the other hand, such molecule is able to form, besides its native conformation, a force-induced misfolded state. Despite this fact was already pointed out in previous single-molecule studies, there was a lack of knowledge regarding the molecular kinetics and the folding pathway. Aiming to fill this gap, we performed a thorough study of the three-helix RNA junction using dynamic force spectroscopy. As a result, we have characterized the full folding pathway of the molecule, including both the native and the misfolded structure. Furthermore, we have experimentally confirmed the fact that the presence of magnesium promotes the stabilization of the native structure and we have measured this contribution. We have found that magnesium is able to rescue the native structure from the misfolded structure via electrostatic interactions due to magnesium binding. This fact is biologically relevant, since we have been able to characterize the conditions in which a misfolded molecule is able to recover its native conformation.
Activity Mediated Interactions in Soft Matter. Structure, Interactions, and Phase Transitions
(Universitat de Barcelona, 2018-10-09) Codina Sala, Joan; Pagonabarraga Mora, Ignacio; Universitat de Barcelona. Departament de Física de la Matèria Condensada
[eng] In this thesis we asses the phenomena of arising interactions in soft matter in coexistence with soft active matter. As a non-equilibrium bath we introduce ensembles of self-propelled particles, granular shaken beds, and photo active catalytic particles. We start the thesis with a detailed study of the widely used Active Brownian Particle (ABP) model. This model exhibits a non-equilibrium phase transition which has been intensively studied in recent years, we have finally reported that this transition satisfies all features of equilibrium first order phase transitions. Then, we introduce aligning interactions in ABP and characterize the emergent collective phenomena. In parallel, we explore the emergent forces, from mechanical contact forces, in probe particles in suspensions of aligning active particles and horizontally shaken granular beds. We characterize the forces and identify the emergence of long range interactions in both systems, in aligning active particles long range attractive interactions appear as alignment is increased, and in granular shaken media when the pair of particles align in the shaking direction. Finally, we conclude this thesis with the study of emergent interactions in spherically symmetric systems of catalytic active particles. Symmetry does not permit such particles to propell but the symmetry is broken with the addition of neighboring particles. We model the pair interaction in terms of the relative velocity between particles, and proceed to explore the emergent structures in mixtures of catalytic magnetic particles, and passive particles. We have unveiled the formation of clusters of passive particles. The addition of magnetic interactions between active particles leads to the formation of ramified gel-like structures for dense configurations of active particles. In this case, experimentalists have checked the formation of structures with the same morphologies in experiments in the laboratory.
Nanofabrication, simulation and optical characterization of plasmonic nanostructures
(Universitat de Barcelona, 2018-09-13) Conde Rubio, Ana; Batlle Gelabert, Xavier; Labarta, Amílcar; Universitat de Barcelona. Departament de Física de la Matèria Condensada
[eng] This thesis is devoted to the nanofabrication, simulation and optical characterization of different plasmonic nanostructures. When an electromagnetic wave reaches a metallic nanostructure, it can give rise to collective oscillations of the free electrons in the metal. These oscillations reach a maximum at the so-called surface plasmon resonance, whose intensity and frequency depend in the material, geometry, embedding medium, interparticle interactions, etc. Based on the tunability of core-shell nanoparticles, hollow cylindrical gold nanostructures (nanocups) have been fabricating using a combination of nanoimprint lithography (NIL) and non-directional metallization. Besides, to overcome the high-aspect ratio limitations of NIL, a trilayer stack (resist-oxideresist) has been used in such a way that the bottom resist layer, which controls the height of the nanostructure, is not affected by the lithography, which takes place only in the top resist layer. Also, the fabrication method allows for easy changes in the geometry: the height can be changed by changing the thickness of the bottom resist layer, the thickness by modifying the amount of deposited material and the diameter by changing the etching time. By hanging the geometric parameters of the nanostructures, the plasmonic properties can be easily tuned. Besides, for certain dimensions (400 nm in diameter and height and 30 nm of Wall and base thickness), these structures present a peak in the extinction spectra in the visible range that corresponds to a concentration of the electric field within the cavity. This excitation mode has also been reported for other nanostructures with semispherical symmetry. However, the fact of being cylindrical enables a homogeneous enhancement of the electric field along the cavity while in the other case this is not possible due to the lack of symmetry. Also, based on geometrically frustrated magnetic systems, three particular cases of hexagonal lattices of plasmonic nanoelements have been studied. All of them have been designed so that the pitch is of the order of the resonance wavelength and the gaps between elements small enough to enable near-field coupling. Besides, a metal-insulator-metal configuration has been implemented, designed to have constructive interference, which leads to high absorption peaks. The samples have been fabricated by electron beam lithography to be able to change easily the design and study the optical response as a function of the geometries. Both simulation and spectroscopy results show that all these systems present high absorption peaks in the visible and/or near infrared. Also, they present a broad absorption peak in the NIR due to the dipolar excitation of the gaps between neighboring elements and sharper peaks in the visible that are assigned to collective modes. Moreover, these systems present an extended time response where the system fluctuates between collective and localized modes. This behavior, characteristic from magnetic frustrated systems, is induced by the frustration of the dipolar excitation of the gaps due to the geometry of the lattice. Besides, the collective modes give rise to enhancements of the electric field in large areas, making these systems of interest for enhanced spectroscopies.
Forces and flows in cells and tissues. Blebs, active gels, and collective cell migration
(Universitat de Barcelona, 2018-01-12) Alert Zenón, Ricard; Casademunt i Viader, Jaume; Universitat de Barcelona. Departament de Física de la Matèria Condensada
[eng] In this thesis, we have studied mechanical aspects of some biological processes in cells and tissues, which we addressed by developing theoretical models based on the physics of soft active matter. The thesis contains three parts that focus on different biological systems. In Part I, we study the adhesion between the plasma membrane and the actin cortex of eukaryotic cells. We propose a continuum model for membrane-cortex adhesion that couples the mechanics and hydrodynamics of the membrane to the force-dependent binding kinetics of the linker proteins. We predict the critical pressure difference that causes membrane-cortex detachment, and we discuss how cortical tension can be inferred from micropipette suction experiments. Then, we study the fluctuations of an adhered membrane, and suggest ways in which our predictions could allow probing membrane-cortex adhesion in fluctuation spectroscopy experiments. Then, we employ the proposed model to study the nucleation of blebs, which are balloon-like membrane protrusions arising from a local membrane-cortex detachment. We show that bleb nucleation is governed by membrane peeling, the fracture propagation process whereby adjacent membrane-cortex bonds break sequentially. Through this mechanism, bleb nucleation is not determined by the energy of a local detachment like in the classical nucleation picture, but rather by the kinetics of membrane-cortex linkers. We predict the critical radius for bleb nucleation through membrane peeling and the corresponding effective energy barrier. Finally, we simulate a fluctuating adhered membrane to obtain the probability distribution of bleb nucleation times. In Part II, we study the dynamics of active polar gels, which are soft materials, usually transiently-crosslinked polymeric networks, that are maintained out of equilibrium by internal processes that continuously transduce energy. We derive the constitutive equations of an active polar gel from a mesoscopic model for the dynamics of the molecules that crosslink the polar elements of the system. This way, we establish a connection between the molecular properties and the macroscopic behaviour of active polar gels. Specifically, we explicitly obtain the transport coefficients in terms of molecular parameters, showing that all transport coefficients have an active contribution that stems from breaking detailed balance for the crosslinker binding kinetics. In Part III, we study cell colonies and tissues, focusing in collective cell migration and tissue morphology. First, we propose a particle-based description of cell colonies to study how the different organizations of cells in tissues emerge from intercellular interactions. The model intends to capture generic cellular behaviours such as cell migration, adhesion, and cell-cell overlapping. In addition, it models the so-called contact inhibition of locomotion (CIL), which repolarizes cell migration away from cell-cell contacts, as a torque on the migration direction. We show how CIL yields an effective repulsion between cells, which allows to predict transitions between non-cohesive, cohesive, and 3D tissues. We conclude that, at low cell-cell adhesion, CIL hinders the formation of cohesive tissues. Yet, in continuous cell monolayers, CIL gives rise to self-organized collective motion, ensures tensile stresses in the monolayer, and opposes cell extrusion, thereby hindering the collapse of the monolayer into a 3D aggregate. Then, we focus on the spreading of epithelial monolayers, which we address by means of a continuum model based on the theory of active polar gels. First, we concentrate on the wetting transition of epithelial tissues, which separates monolayer spreading from retraction towards a 3D aggregate — namely the equivalent of a fluid droplet. We show that a critical radius exists for the wetting transition, which does not exist in the classical wetting picture. Thus, we show how the wetting properties of tissues emerge from active cellular forces, evidencing that the wetting transition has an active nature. Finally, we study the morphological stability of the front of a spreading monolayer. The model predicts that traction forces cause a long-wavelength instability of the monolayer front, whereas tissue contractility has a stabilizing effect. The predicted instability can explain the formation of finger-like multicellular protrusions observed during epithelial spreading. It can also explain the symmetry breaking of tissue shape observed during monolayer dewetting. By fitting the predictions to experimental data, we infer the monolayer viscosity and the noise intensity of tissue shape fluctuations, which we suggest to have an active origin.
Linear and nonlinear approaches to unravel dynamics and connectivity in neuronal cultures
(Universitat de Barcelona, 2017-09-15) Tibau Martorell, Elisenda; Soriano i Fradera, Jordi; Universitat de Barcelona. Departament de Física de la Matèria Condensada
[eng] In the present thesis, we propose to explore neuronal circuits at the mesoscale, an approach in which one monitors small populations of few thousand neurons and concentrates in the emergence of collective behavior. In our case, we carried out such an exploration both experimentally and numerically, and by adopting an analysis perspective centered on time series analysis and dynamical systems. Experimentally, we used neuronal cultures and prepared more than 200 of them, which were monitored using fluorescence calcium imaging. By adjusting the experimental conditions, we could set two basic arrangements of neurons, namely homogeneous and aggregated. In the experiments, we carried out two major explorations, namely development and disintegration. In the former we investigated changes in network behavior as it matured; in the latter we applied a drug that reduced neuronal interconnectivity. All the subsequent analyses and modeling along the thesis are based on these experimental data. Numerically, the thesis comprised two aspects. The first one was oriented towards a simulation of neuronal connectivity and dynamics. The second one was oriented towards the development of linear and nonlinear analysis tools to unravel dynamic and connectivity aspects of the measured experimental networks. For the first aspect, we developed a sophisticated software package to simulate single neuronal dynamics using a quadratic integrate–and–fire model with adaptation and depression. This model was plug into a synthetic graph in which the nodes of the network are neurons, and the edges connections. The graph was created using spatial embedding and realistic biology. We carried out hundreds of simulations in which we tuned the density of neurons, their spatial arrangement and the characteristics of the fluorescence signal. As a key result, we observed that homogeneous networks required a substantial number of neurons to fire and exhibit collective dynamics, and that the presence of aggregation significantly reduced the number of required neurons. For the second aspect, data analysis, we analyzed experiments and simulations to tackle three major aspects: network dynamics reconstruction using linear descriptions, dynamics reconstruction using nonlinear descriptors, and the assessment of neuronal connectivity from solely activity data. For the linear study, we analyzed all experiments using the power spectrum density (PSD), and observed that it was sufficiently good to describe the development of the network or its disintegration. PSD also allowed us to distinguish between healthy and unhealthy networks, and revealed dynamical heterogeneities across the network. For the nonlinear study, we used techniques in the context of recurrence plots. We first characterized the embedding dimension m and the time delay δ for each experiment, built the respective recurrence plots, and extracted key information of the dynamics of the system through different descriptors. Experimental results were contrasted with numerical simulations. After analyzing about 400 time series, we concluded that the degree of dynamical complexity in neuronal cultures changes both during development and disintegration. We also observed that the healthier the culture, the higher its dynamic complexity. Finally, for the reconstruction study, we first used numerical simulations to determine the best measure of ‘statistical interdependence’ among any two neurons, and took Generalized Transfer Entropy. We then analyzed the experimental data. We concluded that young cultures have a weak connectivity that increases along maturation. Aggregation increases average connectivity, and more interesting, also the assortativity, i.e. the tendency of highly connected nodes to connect with other highly connected node. In turn, this assortativity may delineates important aspects of the dynamics of the network. Overall, the results show that spatial arrangement and neuronal dynamics are able to shape a very rich repertoire of dynamical states of varying complexity.
Prospects of microwave spectrometry for vascular stent monitoring. Towards a non-invasive and non-ionizing follow-up alternative
(Universitat de Barcelona, 2017-06-13) Arauz-Garofalo, Gianluca; Tejada Palacios, Javier; García Santiago, Antoni; Universitat de Barcelona. Departament de Física de la Matèria Condensada
[eng] Throughout this thesis we have assessed the prospects of microwave spectrometry (MWS) as a non-ionizing non-invasive monitoring alternative for stented patients in a very early proof-of-concept stage. In Chapter 1 we have provided a generalist retrospective medical background along with a state-of-the-art summary of existing microwave-based stent monitoring approaches. First, we have introduced cardiovascular diseases in general, and ischemic heart disease in particular. Next we have reviewed how percutaneous coronary interventions addressed the medical problem represented by atherosclerosis, giving a special emphasis to balloon angioplasty, bare-metal stenting and drug-eluting stenting. We have further exposed how the outcomes of such revolutionary strategies were compromised by the high rates of post-procedural complications, making unavoidable the invasive and ionizing follow-up of stented patients. Finally, we have summarized existing non-invasive and non-ionizing stent monitoring alternatives based in microwave techniques. In Chapter 2 we have introduced the working principle of our MWS setup. We have first presented how this arrangement can obtain the absorbance of a stent as a function of the frequency and the incidence angle of the microwave fields. We have also shown how these data are combined in a single two-dimensional chart, and how we recognize therein the characteristic resonance frequencies of stents at a glance. As an example, we have presented a typical absorbance diagram to illustrate the general features of such resonances. In particular we have highlighted that these resonances are discrete and have multi-lobed angular patterns. In Chapter 3 we have characterized many stents having a wide variety of nominal sizes to better understand their characteristic resonances in terms of microwave scattering. First, we have found that the resonance frequency obeys a reciprocal dependence on the stent length. This has allowed us to obtain an empirical expression for such relationship just by adjusting two fitting parameters. However, we have not been able to find an analogous expression for the dependence on the stent diameter. In any case, while investigating the latter, we have unexpectedly uncovered how the particular stent architecture influences the corresponding resonance frequencies. By gathering all these individual results we have finally suggested a straightforward half-theoretical half-empirical model linking the resonance frequencies of stents with their structural integrity (through their length), with their particular architecture (through the scaling factor), as well as with their surrounding medium (through the dielectric permittivity and the magnetic permeability). We have also theoretically estimated the resonance frequencies of implanted stents from their corresponding values in free space conditions, showing that in vivo resonance frequencies should be around one order of magnitude smaller than their free space counterparts. Finally, in Chapters 4 and 5 we have explored the potential diagnostic capabilities of MWS in two possible scenarios: stent fracture (SF) and in-stent neoatherosclerosis (ISNA). We have started both chapters reviewing the incidence, the medical implications, and the mechanism of these two stent-related complications. SF has been evaluated in Chapter 4 by means of two “fracture tests” consisting in a successive series of strut cuts. We have shown that MWS provides qualitative indicators for single and multiple strut fractures (downshift of the fundamental resonance frequency), and also quantitative indicators for single or multiple complete transverse linear SFs (split and upshift of that frequency). ISNA has been evaluated in Chapter 6 by means of four ``cholesterol tests'' consisting in a gradual process of increasing cholesterol deposition. We have shown that MWS provides an indicator for a growing presence of cholesterol around a stent (downshift of the fundamental resonance frequency). We have concluded this chapter calculating the theoretical evolution of the resonance frequencies along a cholesterol deposition process, estimating the upper limit for the resonance frequency displacement. Taking together the results we have reported in Chapters 5 and 6, we have shown that MWS could potentially warn about SF and ISNA.
Giant caloric effects in the vicinity of first-order phase transitions
(Universitat de Barcelona, 2017-04-07) Stern Taulats, Enric; Mañosa, Lluís; Universitat de Barcelona. Departament d'Àlgebra i Geometria
[eng] Solid state materials are candidates to exhibit a large field-driven thermal response in the vicinity of first-order transitions. The strong sensitivity of the transition temperature with the applied field and the latent heat associated with the change of phase can give rise to the giant magneto-, electro-, baro-, and elastocaloric effects. Furthermore, the coupling between structural, magnetic and electronic degrees of freedom at the transition regime enables the thermal response to be driven by multiple fields and, thus, giving rise to the multicaloric effect. In the last years, the interest in understanding and tailoring novel caloric materials has exceptionally grown in view of their potential application to alternative cooling technologies for large scale industry. The present thesis reports the giant caloric effects encompassing the Fe49Rh51 magnetovolumic transition, the magnetostructural martensitic transformation in Ni-Mn based Heusler alloys, and the ferroelectric perovskites BaTiO3 and Pb(Sc0.5Ta0.5)O3. The physical conditions for the optimization of the thermal response which yield to an enlarged magnitude and operation range are explored, as well as the corresponding reproducibility upon field cycling and the potential multicaloric character. This evaluation is achieved by means of a complete caloric characterization in which the calorimetric experimental techniques which have been developed in purpose are crucial.
Spatio-temporal dynamics of intercellular Notch signaling: a modeling approach
(Universitat de Barcelona, 2016-10-14) Luna Escalante, Juan Camilo; Ibañes Miguez, Marta; Sancho, José M.; Universitat de Barcelona. Departament de Física de la Matèria Condensada
[eng] Intercellular signalling is a mechanism by which cells communicate and mediate coordinated responses. In this Thesis we perform theoretical and computational analyses to evaluate spatio-temporal organizations that can arise in developing embryos through juxtacrine signalling mediated by Notch receptor. Juxtacrine signalling is a type of intercellular communication in which adjacent cells mutually interact through membrane-attached proteins (receptors and ligands). In the case of Notch signalling, the ligands are regulated by the signalling, establishing a feedback loop on the activation of the signal between adjacent cells. Our study focused on the following open questions: 1. What coordinated responses arise when Notch signalling is activated by two (or more) co-expressing ligands? 2. What is the effect on the response mediated by Notch signalling when considering a gene involved in cell differentiation that promotes it on transcription, but in turn is repressed by the signal? 3. Which processes can modulate the signalling efficiency of a ligand? These questions encompass aspects occurring at different levels, ranging from the type of response that arises in a tissue (salt-and-pepper patterning, homogeneous states or propagation of a cell fate in an expansive wave), the signalling state of cells (sending, receiver, among others), up to the dynamics of the intracellular processing of Notch. We used a modelling and computational approach for their study and compared, when possible, with previously reported phenotypes in developing embryos.
Anomalous transport and diffusion of Brownian particles on disordered landscapes
(Universitat de Barcelona, 2016-11-25) Suñé Simon, Marc; Sancho, José M.; Universitat de Barcelona. Departament de Física de la Matèria Condensada
[eng] Brownian motion refers to the random movement that undergo mesosized particles suspended in a simple sol- vent. Einstein’s probabilistic approach to the Brownian motion is founded on the principal that it is on account of the molecular motions of heat; it can be summarized in three postulates: particles do not to interact with each other, the motion is memoryless at long times, and the distribution of displacements possesses at least two lower moments. According to the Einstein’s theory, the displacements of Brownian particles ought to exhibit a Gaussian distribution whose variance is proportional to time through the diffusion coefficient, that involves the temperature and the friction coefficient. May a constant external force be applied, the mean displacement scales linearly with time. This scenario is referred to as normal transport and diffusion. The thesis aims at exploring the deviations of normal transport and diffusion to exhibit Brownian particles in a disordered medium. The method of choice are numerical simulations of the classical Langevin equation, a generalization of Newtonian equations so as to account for the Brownian trajectories. To grasp the influence of the disorder’s attributes on Brownian motion is the main focus of the thesis. Further, the outcome sheds light into the physical foundations of the anomalous transport and diffusion. Complementarily, some refinements are made on the algorithms employed to simulate the stochastic differential equations. First, it is reviewed the Brownian motion in a periodic potential. According to the attained outcome, some hypothesis are conjectured for the subsequent explorations in disordered media: transport anomalies—if any— would be only of subtransport type when the disorder is static, enhanced diffusion and superdiffusion are likely to be reached, and anomalous transport and diffusion regimes might be transient in dynamic landscapes. For overdamped Brownian particles in a disordered static potential, the anomalous regimes are characterized by the time exponents that exhibit the statistical moments of the ensemble of particle trajectories, as well as by the particle displacement distributions and the clouds of particles. This case of study bears out that the length scale of the roughness of the potential is an essential parameter in the understanding of the effect of disorder. Besides, the shape of the particle density histograms and the particle clouds have been proved to be related to the anomalies. The analogous scenario in the underdamped limit leads to the instantaneous velocity distributions, that disclose appealing properties of the system. This case of study proves that the anomalous transport and diffusion regimes occur no matter the damping, yet they come about at higher forces for high friction conditions. Overdamped Brownian motion of particles in random landscapes of moving deformable obstacles is also studied. It is settled an effective set of quantities to portray the transport and diffusion properties. The characteristic time scale constrains the time span of anomalies, and thus the subsequent steady transport and diffusion coefficients. For a given density of obstacles, both trafficking and diffusion are favored by wider and therefore fewer obstacles. To end, a high density of obstacles hinders both transport and dispersion. Algorithms to carry out the numerical simulations are discussed. A novel method to build Gaussian potential landscapes with arbitrary spatial correlation functions and the only requirement of isotropy is developed. It has the particularity that, although it uses the Fourier space, its constraints are in real space. A refreshing architec- ture for simulating random dynamic obstacles is also covered. Finally, two supplementary physical systems are addressed; the physics of particles undergoing changing viscosi- ties and confinement to quasi 2 d layers, and the transport of the motor KIF1A in a two–dimensional ratchet model that mimics a microtubule.
Statistical thermodynamics of long-range interacting systems and near-field thermal radiation
(Universitat de Barcelona, 2016-06-27) Latella, Ivan; Pérez Madrid, Agustín; Franzese, Giancarlo; Universitat de Barcelona. Departament de Física de la Matèria Condensada
[eng] Two main topics are examined in this thesis: classical systems with long-range interactions and thermal radiation in the near-field regime. In the first part, we present a thermodynamic approach describing systems with long-range interactions which takes into account the intrinsic nonadditivity in these systems. The basic concept behind this approach is to consider a large ensemble of replicas of the system where the standard formulation of thermodynamics can be naturally applied and the properties of a single system can be consequently inferred. The formulation of the thermodynamic for these systems is in close connection with Hill's thermodynamics of systems with small number of particles. It is shown that systems with long-range interactions can attain equilibrium configurations in the unconstrained ensemble. In this statistical ensemble, the control parameters are the temperature, pressure, and chemical potential, while the energy, volume, and number of particles fluctuate. We consider a solvable model as a concrete example of a system that achieves stable equilibria in this ensemble. We also give a complete description of the phase-diagram of the Thirring model in both the microcanonical and the canonical ensemble, highlighting the main features of ensemble inequivalence. I the second part, we study energy and entropy fluxes of near-field thermal radiation in many-body systems, with application to energy-conversion processes. It is shown that the maximum work that can be obtained from the thermal radiation emitted by two planar sources in the near-field regime is much larger than that corresponding to the blackbody limit. This quantity as well as an upper bound for the efficiency of the process are computed from the formulation of thermodynamics in the near-field regime. The case when the difference of temperatures of the hot source and the environment is small, relevant for energy harvesting, is studied in detail. We also show that thermal radiation energy conversion can be more efficient in the near-field regime. Moreover, by analyzing the thermodynamic performance of three-body near-field heat engines, we demonstrate that the power they supply can be substantially larger than that of two-body systems, showing their strong potential for energy harvesting. Theoretical limits for energy and entropy fluxes in three-body systems are discussed and compared with their corresponding two-body counterparts. Such considerations confirm that the thermodynamic availability in energy-conversion processes driven by three-body photon tunneling can exceed the thermodynamic availability in two-body systems.

Examinar

Enviaments recents