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The effect of oriented external electric fields (OEEF) on chemical reactivity has been studied theoretically and computationally in the last decades. A central goal in this research area is to predict the orientation and the smallest amplitude electric field that renders a barrierless chemical process with the smallest possible strength. Recently, a model to find the optimal electric field has been proposed and described (Bofill JM et al., J. Chem. Theory Comput. 18:935, 2022). We here proof that this model is based on catastrophe and optimum control theories. Based on both theories a technical treatment of the model is given and applied to a two-dimensional generic example that provides insight into its nature and capability. Finally, the model is applied to determine the optimal OEEF for the trans-to-cis isomerization of a [3]cumulene derivative.

The ability to control the chemical conformation of a system via external stimuli is a promising route for developing molecular switches. For eventual deployment as viable sub-nanoscale components that are compatible with current electronic device technology, conformational switching should be controllable by a local electric field (i.e. E-field gateable) and accompanied by a rapid and significant change in conductivity. In organic chemical systems the degree of π-conjugation is linked to the degree of electronic delocalisation, and thus largely determines the conductivity. Here, by means of accurate first principles calculations, we study the prototypical biphenyl based molecular system in which the dihedral angle between the two rings determines the degree of conjugation. In order to make this an E-field gateable system we create a net dipole by asymmetrically functionalising one ring with: (i) electron withdrawing (F, Br and CN), (ii) electron donating (NH2), and (iii) mixed (NH2/NO2) substituents. In this way, the application of an E-field interacts with the dipolar system to influence the dihedral angle, thus controlling the conjugation. For all considered substituents we consider a range of E-fields, and in each case extract conformational energy profiles. Using this data we obtain the minimum E-field required to induce a barrierless switching event for each system. We further extract the estimated switching speeds, the conformational probabilities at finite temperatures, and the effect of applied E-field on electronic structure. Consideration of these data allow us to assess which factors are most important in the design of efficient gateable electrical molecular switches.

The use of oriented external electric fields (OEEF) as a tool to accelerate chemical reactions has recently attracted much interest. A new model to calculate the optimal OEEF of the least intensity to induce a barrierless chemical reaction path is presented. A suitable ansatz is provided by defining an effective potential energy surface (PES), which considers the unperturbed or original PES of the molecular reactive system and the action of a constant OEEF on the overall dipole moment of system. Based on a generalization of the Newton Trajectories (NT) method, it is demonstrated that the optimal OEEF can be determined upon locating a special point of the potential energy surface (PES), the so-called “optimal bond-breaking point” (optimal BBP), for which two different algorithms are proposed. At this point, the gradient of the original or unperturbed PES is an eigenvector of zero eigenvalue of the Hessian matrix of the effective PES. A thorough discussion of the geometrical aspects of the optimal BBP and the optimal OEEF is provided using a two-dimensional model, and numerical calculations of the optimal OEEF for a SN2 reaction and the 1,3-dipolar retrocycloaddition of isoxazole to fulminic acid plus acetylene reaction serve as a proof of concept. The knowledge of the orientation of optimal OEEF provides a practical way to reduce the effective barrier of a given chemical process.

Made available in DSpace on 2022-04-28T19:40:57Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-06-01 Electromechanical and dielectric properties of PMN-PT ferroelectric ceramics are investigated. In particular, dielectric response studies focus on the investigation of the influence of the DC applied electric field on the dielectric permittivity as a function of temperature and frequency. Results reveal an electric field driven dielectric anomaly in the dielectric permittivity curves, (E), which in turn prevails in the whole ferroelectric phase region and continuously vanishes for temperatures near the paraelectric-ferroelectric phase transition temperature. A schematic model for the domains dynamics of the studied material is proposed taking into account the simultaneous contribution of both 90° and 180° domains walls. Grupo de Ferroelétricos e Materiais Multifuncionais Instituto de Física Universidade Federal de Uberlândia, Uberlândia Universidade Federal Do Tocantins, Porto Nacional Departamento de Física e Química Universidade Estadual Paulista Department of Physics Universitat Politècnica de Catalunya - BarcelonaTech Departamento de Física e Química Universidade Estadual Paulista

External electric fields (EEFs) have proven to be very efficient in catalysing chemical reactions, even those inaccessible via wet-chemical synthesis. At the single-molecule level, oriented EEFs have been successfully used to promote in situ single-molecule reactions in the absence of chemical catalysts. Here, we elucidate the effect of an EEFs on the structure and conductance of a molecular junction. Employing scanning tunnelling microscopy break junction (STM-BJ) experiments, we form and electrically characterize single-molecule junctions of two tetramethyl carotene isomers. Two discrete conductance signatures show up more prominently at low and high applied voltages which are univocally ascribed to the trans and cis isomers of the carotenoid, respectively. The difference in conductance between both cis-/trans- isomers is in concordance with previous predictions considering π-quantum interference due to the presence of a single gauche defect in the trans isomer. Electronic structure calculations suggest that the electric field polarizes the molecule and mixes the excited states. The mixed states have a (spectroscopically) allowed transition and, therefore, can both promote the cis-isomerization of the molecule and participate in electron transport. Our work opens new routes for the in situ control of isomerisation reactions in single-molecule contacts.

We assess results of corona pulses detected under high background electric field in the laboratory and in the field in two different experimental sites. The first location is on the roof of a regular building, and the second is on a flat area. Due to the enhancement of the E-field caused by lightning strikes in the vicinity of a grounded rod with a sharp tip, we observed positive and negative pulses before or after the strikes. When lightning activity is far from the structure, but the electric field remains high, pulses are still observed.

Treballs Finals de Grau de Química, Facultat de Química, Universitat de Barcelona, Any: 2020, Tutor: Josep Maria Bofill Villà, The catalysis is one of the most important areas for the reaction synthesis and mechanists. Actually, there are thousand types of different catalysts. As we all know, a catalyst is a substance that increases the reaction rate but without reacting with the reagents and without modifying the course of the reaction. According to this definition, there is a new type of catalyst that we will probably use in the future: an Oriented External Electric Field (OEEF). In this research we study the general effects of an OEEF on the reactions and applied to different types of bonds. From this first application of the OEEF we extracted the Shaik rules, which are general rules about the OEEF effects in all type of bonds we know about. Secondly, we look at the Valance Bond (VB) diagrams, what they are and how to build them. This is a really good tool to understand which are all the structures involved in a reaction, plus the reagents and products, how intermediates appear and how we obtain the energy profile of any reaction (which we all know and have studied). Furthermore, we study the effect of the dipole moment in the opposite direction to the OEEF. The VB diagram model is the basic model to understand the Shaik rules for OEEF. We applied all this knowledge in four reactions: Diels-Alder reaction, Menshutkin reaction (SN2), benzene nucleophilic aromatic substitution (SNAr) and cyclobutene ring opening reaction by conrotatory rotation. We study the effects of the OEEF and how the reagents substituents can affect on this reactions, resulting in catalysis or inhibition. With all the initial knowledge and the new one acquired we study the cyclobutene ring opening reaction by disrotatory rotation and how the OEEF affects this reaction. We propose how to apply them so that the reaction goes from forbidden to allowed, something that no one has done before. Finally, we can say that we study the OEEF and its applications, a new type of catalyst that has many possibilities despite its possible negative effects.

Parametric amplification of attosecond coherent pulses around 100 eV at the single– atom level is demonstrated for the first time by using the 3D time–dependent Schrödinger equation in high–harmonic generation processes from excited states of He+. We present the attosecond dynamics of the amplification process far from the ionization threshold and resolve the physics behind it. The amplification of a particular central photon energy requires the seed XUV pulses to be perfectly synchronized in time with the driving laser field for stimulated recombination to the He+ ground state and is only produced in a few specific laser cycles in agreement with the experimental measurements. Our simulations show that the amplified photon energy region can be controlled by varying the peak intensity of the laser field. Our results pave the way to the realization of compact attosecond pulse intense XUV lasers with broad applications. Japan Society for the Promotion of Science (JP17H02813); Ministerio de Economía y Competitividad (FIS2017-85526-R)

Changes in membrane deformation and compressibility, induced by an external electric field, are investigated using coarse-grained martini force field simulations in a salt-free environment. We observe changes in the area of the membrane above a critical electric field. Below this value, the membrane compressibility modulus is found to decrease monotonically. For higher electric fields, the membrane projected area remains constant while the net interfacial area increases, with the corresponding compressibility moduli, show the opposite behavior. We find that the mechanical parameters, surface tension and bending modulus, of a freely floating membrane in the absence of explicit ions, are unaffected by the presence of the electric field. We believe these results have a bearing on our understanding of the electroformation of uncharged lipids in a salt-free environment.

Nowadays in aviation lightning safety efforts are focused on limiting the damage done to an aircraft when struck, and very little research on the reduction of lightning strikes has been carried out. Studies show that modifying the net electrical charge of an aircraft modifies its electrical interaction with the atmosphere and thus affecting the possibility of an aircraft triggering lightning.The Lightning Research Groupat the Universitat Politècnica de Catalunya is currently conducting tests on an aircraft prototype with which the control of the net electrical charge in an aircraft via corona discharge is attempted. The tool to measure the amount of acquired charge is the electric field mill, and this thesis aims to design and build an electric field mill for this specific reason

Treballs Finals de Grau de Química, Facultat de Química, Universitat de Barcelona, Any: 2019, Tutors: Jordi Ribas Ariño, Stefan Thomas Bromley, In this work we use computational chemistry to evaluate how an applied electric field can affect the conformation of a π-conjugated linker in 2D materials. To do this we use a model molecular system with different variations on its substituents and evaluate how an electric field can affect the energetic relative stability of their conformations through DFT calculations. Also, it will be explored in these model systems the validity of the first order approximation of the energy of a molecular system with an E-field applied. These analyses on model systems are done in order to be representative at a small scale of the rotation of a linker in a dimer representation of a 2D-CORF (2D-CORFs are a relative new material). The knowledge acquired on the study of the model system will be used later to analyze the dimer of the 2D-CORF building block which it represents. It has been found by the model system analysis that as higher is the dipole moment of the molecule is more susceptible to be changed its conformation. On other hand, the results reveal that the first order approximation works better as lower is the polarizability of the substituents, Fluorine is found to be the substituent with less error and because of this, it will be the substituent used in the following step of the study. Finally, we designed a dimer of a 2D-CORF building block and carried out DFT calculations about the energy related to the rotation of the linker in the singlet and triplet states of the dimer. Moreover, it has been analyzed the strength of the magnetic interactions at all the possible conformations of the linker, related to the calculated energy gap of the multiplicity states. It has been found that the strength of the magnetic interactions changes at different conformations. In addition, has been used the first order approximation to predict the behavior of the dimer in an electric field and it has been targeted the conformation with highest magnetic interactions. Finally, it has been proved that magnetic properties in the material studied can be tuned by an applied electric field.

A variational approach is used in order to study the stationary states of Hall devices. Charge accumulation, electric potentials and electric currents are investigated on the basis of the Kirchhoff-Helmholtz principle of least heat dissipation. A simple expression for the state of minimum power dissipated -- that corresponds to zero transverse current and harmonic chemical potential -- is derived. It is shown that a longitudinal surface current proportional to the charge accumulation is flowing near the edges of the device. Charge accumulation and surface currents define a boundary layer over a distance of the order of the Debye-Fermi length., Comment: 9 pages, 2 figures

Recent longitudinal neuroimaging studies in patients with electroconvulsive therapy (ECT) suggest local effects of electric stimulation (lateralized) occur in tandem with global seizure activity (generalized). We used electric field (EF) modeling in 151 ECT treated patients with depression to determine the regional relationships between EF, unbiased longitudinal volume change, and antidepressant response across 85 brain regions. The majority of regional volumes increased significantly, and volumetric changes correlated with regional electric field (t = 3.77, df = 83, r = 0.38, p=0.0003). After controlling for nuisance variables (age, treatment number, and study site), we identified two regions (left amygdala and left hippocampus) with a strong relationship between EF and volume change (FDR corrected p, eLife digest Electroconvulsive therapy, or ECT for short, can be an effective treatment for severe depression. Many patients who do not respond to medication find that their symptoms improve after ECT. During an ECT session, the patient is placed under general anesthesia and two electrodes are attached to the scalp to produce an electric field that generates currents within the brain. These currents activate neurons and make them fire, causing a seizure, but it remains unclear how this reduces symptoms of depression. For many years, researchers thought that the induced seizure must be key to the beneficial effects of ECT, but recent studies have cast doubt on this idea. They show that increasing the strength of the electric field alters the clinical effects of ECT, without affecting the seizure. This suggests that the benefits of ECT depend on the electric field itself. Argyelan et al. now show that electric fields affect the brain by making a part of the brain known as the gray matter expand. In a large multinational study, 151 patients with severe depression underwent brain scans before and after a course of ECT. The scans revealed that the gray matter of the patients’ brains expanded during the treatment. The patients who experienced the strongest electric fields showed the largest increase in brain volume, and individual brain areas expanded if the electric field within them exceeded a certain threshold. This effect was particularly striking in two areas, the hippocampus and the amygdala. Both of these areas are critical for mood and memory. Further studies are needed to determine why the brain expands after ECT, and how long the effect lasts. Another puzzle is why the improvements in depression that the patients reported after their treatment did not correlate with changes in brain volume. Disentangling the relationships between ECT, brain volume and depression will ultimately help develop more robust treatments for this disabling condition.

The discretization by the method of moments (MoM) of integral equations in the electromagnetic scattering analysis most often relies on divergence-conforming basis functions, such as the Rao–Wilton–Glisson (RWG) set, which preserve the normal continuity of the expanded currents across the edges arising from the discretization of the target boundary. Although for such schemes the boundary integrals become free from hypersingular kernel-contributions, which is numerically advantageous, their practical implementation in real-life scenarios becomes particularly cumbersome. Indeed, the application of the normal continuity condition on composite objects becomes elaborate and convoluted at junction-edges, where several regions intersect. Also, such edge-based schemes cannot even be applied to nonconformal meshes, where adjacent facets may not share single matching edges. In this paper, we present nonconforming schemes of discretization for the scattering analysis of complex objects based on the expansion of the boundary unknowns, electric or magnetic currents, with the facet-based monopolar-RWG set. We show with examples how these schemes exhibit great flexibility when handling composite piecewise homogeneous objects with junctions or targets modeled with nonconformal meshes. Furthermore, these schemes offer improved near- and far-field accuracy in the scattering analysis of electrically small single sharp-edged dielectric targets with moderate or high dielectric contrasts.

Moderate intensity pulse electric fields were applied in plum with the aim to increase bioactive compounds content of the fruit, while high-hydrostatic pressure was applied to preserve the purées. High-hydrostatic pressure treatment was compared with an equivalent thermal treatment. The addition of ascorbic acid during purée manufacture was also evaluated. The main objective of this study was to assess the effects on microorganisms, polyphenoloxidase, color and bioactive compounds of high-hydrostatic pressure, or thermal-processed plum purées made of moderate intensity pulse electric field-treated or no-moderate intensity pulse electric field-treated plums, after processing during storage. The application of moderate intensity pulse electric field to plums slightly increased the levels of anthocyanins and the antioxidant activity of purées. The application of Hydrostatic-high pressure (HHP) increased the levels of bioactive compounds in purées, while the thermal treatment preserved better the color during storage. The addition of ascorbic acid during the manufacture of plum purée was an important factor for the final quality of purées. The color and the bioactive compounds content were better preserved in purées with ascorbic acid. The no inactivation of polyphenoloxidase enzyme with treatments applied in this study affected the stability purées. Probably more intense treatments conditions (high-hydrostatic pressure and thermal treatment) would be necessary to reach better quality and shelf life during storage. The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: The authors wish to acknowledge the financial support by the project INIA RTA2010-00079-C02.

© 2015 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. The volumetric monopolar-RWG discretization of the electric-field integral equation (EFIE) imposes no continuity constraint across edges in the surface discretization around a closed conductor. The current is expanded with the monopolar-RWG set and the electric field is tested over a set of tetrahedral elements attached to the boundary surface. This scheme is facet-oriented and therefore, well suited for the scattering analysis of nonconformal meshes or composite objects. The observed accuracy, though, is only competitive with respect to the RWG-discretization for a restricted range of heights of the tetrahedral elements. In this communication, we introduce a novel implementation of the volumetric monopolar-RWG discretization of the EFIE with testing over a set of wedges. We show with RCS and near-field results that this scheme offers improved accuracy for a wider range of heights than the approach with tetrahedral testing. The application of the wedge testing to the even-surface odd-volumetric monopolar-RWG discretization of the EFIE, edge-oriented and therefore less versatile, shows similar accuracy as with tetrahedral testing, which is a sign of robustness.

This paper presents a model, which we have designed to get insight into the development of electro- induced instability of a thin toluene emulsion film in contact with the saline aqueous phase. Molecular dynamics (MD) simulations demonstrate the role of charge accumulation in the toluene-film rupture induced by a DC electric field. Two ensembles¿NVT and NPT ¿are used to determine the critical value of the external field at which the film ruptures, the charge distribution and capacitance of the thin film, number densities, and the film structure. The rupture mechanism as seen from this model is the following: in both NVT and NPT ensembles, condenser plates, where the charge density is maximal, are situated at the very border between the bulk aqueous (water) phase and the mixed layer. No ion penetration is observed within the toluene core, thus leaving all the distribution of charges within the mixed zone and the bulk phase that could be attributed to the formation of hydration shells. When the critical electric field is reached within a certain time after the field application, electric discharge occurs indicating the beginning of the rupturing process. The MD simulations indicate that the NPT ensemble predicts a value of the critical field that is closer to the experimental finding. Published by AIP Publishing. [http://dx.doi.org/10.1063/1.4983163

Current theories and mechanisms of nerve impulse propagation inside neurons do not give a satisfactory explanation to the nanoscale processes that occur inside the membrane. Propagation at the dendritic zones, and at the myelinated and unmyelinated axons, presents effects and events that, despite numerical calculations of current models fit with biological results obtained with macroscopic measurements, are far from giving an explanation to the real operation of biological mechanisms and to the effects and behaviors that the involved biological elements support. Current biological knowledge on the structure and behavior of biological membranes, as well as on the structure and function of voltage-regulated ion channels, allows us to consider alternatives to existing propagation mechanisms, giving explanation to the effects and behavior from both nanoscale and macroscopic level. This theoretical study proposes intra-membrane electric field propagation as a feasible propagation mechanism capable to explain both macroscopic and nanometric effects. With current theories and mechanisms, generation, propagation and regeneration of the nerve impulse is based on the action potential propagation effect. The action potential can be defined as the temporal imbalance that affects the membrane potential during nerve impulse propagation, as a consequence of ion channel opening. Progress on the neural membrane biological structure knowledge has allowed to propose a new hypothesis on the action potential operation. Besides the membrane potential variation, the electric charge that crosses the membrane generates an electric field that propagates inside the cell membrane, activating the closer ionic channels. This mechanism gives an explanation compatible with existing biological components and with other effects hard to explain with the standard current mechanisms. In addition, the proposed intra-membrane electric field propagation mechanism allows for a different explanation of the action potential evolution, as well as ion traffic level more in line with the capabilities of the biological reality, both on the ion traffic level and energy consumption. The proposed mechanism allows to explain the so-called saltatory action potential propagation on myelinated axons, and to apply the saltatory propagation to unmyelinated axons. In the latter, as short-distance steps; in the former, as long-distance jumps, also giving a coherent answer to the constant-time propagation independent of the distance between nodes of Ranvier. The proposed mechanism suggests that the effects the action potential presents are more the result of a charge displacement inside sodium and potassium channels than a current that crosses ion channels. An important factor to consider in this mechanism is the energy consumption minimization, a fundamental biological premise for maximum optimization of process operation., Les actuals teories i mecanismes de propagació de l'impuls nerviós per l'interior de les neurones no donen una explicació suficientment satisfactòria ni als principis físics als quals estan subjectes, ni als processos nanomètrics que es produeixen al seu interior. La propagació a les zones dendrítiques i als axons mielinitzats i no mielinitzats presenten efectes i esdeveniments que si bé el càlcul numèric dels actuals models concorda amb els resultats biològics obtinguts amb mesures macroscòpiques, estan lluny de donar una explicació al funcionament real dels mecanismes biològics i als efectes i comportaments que presenten la resta d'elements biològics participants que hi donen suport. Els actuals coneixements sobre l'estructura i comportament de les membranes biològiques, així com el coneixement sobre l'estructura i el funcionament dels canals iònics regulats per voltatge, ens permet plantejar una opció alternativa als mecanismes existents de propagació, donant explicació als efectes i comportaments tant des d'una escala nanomètrica com des d'una escala macroscòpica. En aquest treball teòric es proposa la propagació de camps elèctrics intra-membrana com un mecanisme possible de propagació amb la capacitat de donar explicació tant als efectes macroscòpics com als nanomètrics. Amb les teories i mecanismes actuals, la generació, la propagació i la reemissió de l'impuls nerviós es fonamenta en un efecte anomenat potencial d'acció. El potencial d'acció el podem definir com el desequilibri temporal que pateix el potencial de membrana, durant la propagació de l'impuls nerviós, i que és conseqüència de l'obertura dels canals iònics. El progrés en el coneixement sobre les estructures biològiques existents a les membranes neuronals ha permès plantejar una nova hipòtesi sobre el funcionament del potencial d'acció. A més de la variació del potencial de membrana, la càrrega elèctrica que travessa la membrana genera un camp elèctric que es propaga per l'interior de la membrana cel·lular, activant els canals iònics propers. Aquest mecanisme aporta una explicació consistent, compatible amb els components biològics existents i amb altres efectes difícilment explicables amb els mecanismes estàndard actuals. A més, el mecanisme de propagació per camp elèctric intra-membrana proposat permet donar una explicació diferent de l'evolució dels potencials d'acció, així com un nivell de tràfic iònic més en consonància amb les capacitats de la realitat biològica, tant en el nivell de tràfic existent com en el consum energètic. El mecanisme proposat permet explicar l'anomenada propagació saltatòria del potencial d'acció dels axons mielinitzats, i també aplicar la propagació saltatòria als axons no mielinitzats. En aquest cas com una propagació saltatòria de salts curts; per als axons mielinitzats, com una propagació saltatòria de salts llargs, donant també una resposta coherent a la propagació en temps constant independent de la distància entre nodes de Ranvier. El mecanisme proposat permet plantejar que els efectes que presenta el potencial d'acció són més el resultat d'un desplaçament de càrrega a l'interior dels canals de sodi i de potassi, que d'un corrent que realment travessa els canals iònics. Un factor important a tenir en compte en el mecanisme proposat és la minimització del cost energètic, premissa fonamental de la biologia per a la màxima optimització en el funcionament de processos.

High pressure/high temperature (HP/HT) and pulsed electric field (PEF) treatment of food are among the novel processing techniques considered as alternatives to conventional thermal food processing. Introduction of new processing techniques with fast and gentle processing steps may reveal new possibilities for preservation of healthy bioactive compounds in processed food. However, effects on various food components due to autolysis and fast reactions prior to the applied HP/HT or PEF need to be considered as the total contribution of processing steps affects the obtained food quality. The present experiments were performed on broccoli (Brassica oleracea var. Italica) florets, puree and juice. Specific focus was given to effects of HP/HT and PEF processing on the content of glucosinolates and activities of myrosinase isoenzymes (EC.3.2.1.147) in the broccoli preparations. Certain conditions applied in HP/HT processing of broccoli florets were able to maintain a high level of intact glucosinolates. Treatment at 700 MPa and 20 degrees C for 10 min was found to inactivate myrosinase activity, but also pressure treatments at 300 MPa and 20 degrees C were able to maintain a high level of intact glucosinolates present in the untreated broccoli florets. PEF processing of broccoli puree and juice showed that the myrosinase activities resulted in nearly total glucosinolate transformations as result of autolysis during pureeing and juice making prior to the PEF processing. These data demonstrated that insight into potential effects on myrosinase activities from application of PEF processing implies specific focus on the sample steps preceding the PEF processing

Devising new tools that expand our capabilities to sense and manipulate the world enables much of the scientific and technological progress around us. For example, light is increasingly more important as a tool for humanity. Not all light is equal, however - the light that we normally interact on a daily basis (e.g. the sun), despite its serene and directional appearance, exists in a state of ever changing disorder. What one would perceive as a smooth beam of white light is actually an ever changing pattern of colours. However, As the scale over which the colour changes is spatially too small and temporarily too rapid to be resolved by the human eye we perceive it as a smooth white beam. This lack of a clear spatio-temporal structure in naturally occurring light - coherence - limits what can be done with it. If one were to overlap all the frequencies in a temporally coherent beam of light, one could generate an extremely short and powerful pulse. For example, by compressing in time all the colours in sunlight one would generate a light pulse with just a few femtoseconds duration. If such pulse would have a very modest energy (e.g., a Joule), it would have a peak power approaching the PetaWatt - several orders of magnitude more than the total energy production on earth at a given time. When focused on a minuscule spot, the electric field oscillations of this wave would have amplitudes greatly surpassing the electric fields that bind electrons to atoms, or even atoms together in molecules. This implies that by focusing these pulses into matter one can destroy chemical bonds, free the electrons from the influence of the atom's nucleus and even further accelerate these particles away from the interaction region. It follows that with the correct electric field shape, one could control and manipulate matter in new and interesting ways.In this thesis we have dedicated ourselves to the creation and characterisation of intense, few-cycle pulsed sources of light, using several different approaches. In this thesis a light source with more than 3 octaves (450-4500 nm) has been developed through filamentation of intense mid-IR pulses in solids. This source has high repetition rate (100 kHz), high spectral density and absolute carrier-envelope phase stability. Additionally, numerical simulations suggest that the nonlinear propagation dynamics induce self-compression, possibly leading to single-cycle pulses. The scaling of strong field processes such as electron acceleration highly depends on the period or wavelength of the driving electrical field. This has implications for High harmonic generation (HHG) - the longer the wavelength of this field, the higher the energy of the generated photons. In this thesis we have built a high energy pulsed parametric light source at 2100 nm, a wavelength that enables one to generate soft-x-ray photons with energies exceeding 300 eV through phase-matched HHG ¿ and further demonstrated HHG cutoff extension up to 190 eV in Argon, when compared to HHG from 800 nm pulses.When doing HHG, in order to restrict the soft-X-ray emission to a single isolated attosecond pulse one needs to employ a gating technique. In this thesis we have extended the attosecond lighthouse technique up to the Water window (284-543 eV) which is of fundamental interest to study biological processes with unprecendent spatio-temporal resolution and elemental specificity. The routine generation and characterisation of pulses in the single-cycle regime has historically been a challenge. As such sources invariably require extreme nonlinear spectral broadening, the optimisation of the output pulse has always been a limitation. In this thesis we extend the dispersion-scan technique to the single-cycle regime and demonstrate its use as a straightforward way to compress, characterise and phase-stabilise 3.2 fs pulses with >50 GW peak power. We illustrate the steps done to optimise this source to reach the single-cycle regime., Concebir nuevas herramientas que expandan nuestras capacidades para medir y manipular el mundo habilita gran parte del progreso cientifico y tecnologico que nos rodea. Por ejemplo, la luz es cada vez más importante como herramienta para la humanidad. Sin embargo, no toda la luz es igual - la luz con la cual normalmente interactuamos a diario (por ejemplo, la luz del sol), a pesar de su aspecto sereno y direccional, existe en un estado de constante cambio y disorden. Lo que se podria percibir como un rayo homogeneo de luz blanca es en realidad un patron en constante cambio de color e forma. Sin embargo, como la escala de los cambios de color es espacialmente demasiado pequeña y temporalmente demasiado rapida para ser resuelta por el ojo humano lo percibimos como un rayo blanco homogeneo. Esta falta de una estructura espacio-temporal en la luz natural - coherencia - limita lo que se puede hacer con ella. Si uno superpone todas las frecuencias en un rayo temporalmente coherente de luz, uno genera un pulso de luz extremadamente corto y potente. Por ejemplo, mediante la superposicio¿n en el tiempo de todos los colores en la luz del sol se generaria un pulso de luz con una duracion de pocos femtosegundos. Si tal pulso tiene una energia muy modesta (por ejemplo, un Julio), tendria una potencia de pico alrededor del Petawatt - ordenes de magnitud mas grande que la produccio¿n de energia en la Tierra en un determinado momento. Cuando enfocadas en un punto minusculo, las oscilaciones del campo electrico de esta onda tendran amplitudes superando los campos electricos que unen los electrones a los atomos, o incluso los atomos unos a los otros en moleculas. Esto implica que enfocando estos pulsos en la materia uno puede destruir enlaces quimicos, liberar los electrones de la influencia del nucleo del atomo y acelerar estas particulas. En consecuencia, con la forma de campo electrico correcta, se podria controlar y manipular la materia en formas nuevas e interesantes. En esta tesis nos hemos dedicado a la creacion y caracterizacion de fuentes de pulsos de luz intensos de pocos ciclos, utilizando diversas tecnicas. En esta tesis una fuente de luz con mas de 3 octavas (450-4500 nm) ha sido desarrollada a traves de filamentacion en solidos de impulsos mid-IR intensos. Esta fuente tiene una alta tasa de repeticion (100 kHz), alta densidad espectral y estabilidad de fase. Ademas, simulaciones numericas sugieren que la dinamica de propagacion no lineal induce auto-compresion temporal. El escalamiento de los procesos de campo fuerte, como la aceleracion de electrones, depende en gran medida de la longitud de onda del campo electrico interveniente. Esto tiene grandes implicaciones para la generacion de harmonicos altos (HHG) - mas larga sea la longitud de onda del campo, mayor es la energia de los fotones generados. En esta tesis hemos construido una fuente de luz de alta energia a 2100nm, una longitud de onda que nos permite generar fotones con energi¿as superiores a 300 eV a traves de HHG con phase-matching - y ademas demostrado extension de corte HHG hasta 190 eV en argon, en comparacion con HHG a partir de pulsos a 800 nm. Al hacer HHG, para limitar la emision de rayos-X blandos a un solo pulso de attosegundos aislado, uno necesita emplear una tecnica de gating. En esta tesis hemos extendido la te¿cnica del faro de attosegundos hasta la ventana de la agua (284-543 eV) lo cual posee interes fundamental para estudiar procesos biologicos con resolucio¿n espacio-temporal y especificidad elemental. Como esas fuentes invariablemente requieren un ensanchamiento espectral no lineal extremo, la optimizacion del pulso siempre presenta un problema. En esta tesis hemos extendido la tecnica de dispersion-scan, hasta el regimen de un solo ciclo optico y demostramos su uso como una forma de comprimir, caracterizar y estabilizar la fase de pulsos de 3.2 fs.

©2016 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. Nonconforming implementations of the electric-field integral equation (EFIE), based on the facet-oriented monopolar-RWG set, impose no continuity constraints in the expansion of the current between adjacent facets. These schemes become more versatile than the traditional edge-oriented schemes, based on the RWG set, because they simplify the management of junctions in composite objects and allow the analysis of nonconformal triangulations. Moreover, for closed moderately small conductors with edges and corners, they show improved accuracy with respect to the conventional RWG-discretization. However, they lead to elaborate numerical schemes because the fields are tested inside the body, near the boundary surface, over volumetric subdomains attached to the surface meshing. In this letter, we present a new nonconforming discretization of the EFIE that results from testing with RWG functions over pairs of triangles such that one triangle matches one facet of the surface triangulation and the other one is oriented perpendicularly, inside the body. This “tangential-normal” testing scheme, based on surface integrals, simplifies considerably the matrix generation when compared to the volumetrically tested approaches.

Pulsed electric fields have the potential to be used as alternative to other conventional techniques of food production. In the last few years, several studies have demonstrated the ability of intense treatments to obtain safe and shelf-stable liquid foods. On the other hand, novel applications such as improvement of mass transfer processes or generation of bioactive compounds by using moderate field strengths are under current development. However, the effects of pulsed electric field treatments on minor constituents of foods, namely on bioactive compounds, have not been always considered. This review aims at updating the state of the art regarding the impact of pulsed electric field processing conditions on the stability of bioactive compounds in food systems.

A response surface methodology was used to determine the combined effect of HIPEF critical processing conditions on vitamin C, anthocyanins and antioxidant capacity of strawberry juice. Keeping constant the electric field strength at 35 kV/cm and the treatment time at 1000 μs, the treatments were set at frequencies from 50 to 250 Hz, pulse width from 1 to 7 μs using monopolar or bipolar mode. A second order response function covering the whole range of experimental conditions was obtained for each health-related compound. Strawberry juice antioxidant potential was affected linearly by frequency, pulse width and pulse polarity. The quadratic term of frequency and the combined effect of frequency and pulse width were also significant. HIPEF treatments conducted at 232 Hz with bipolar pulses of 1 μs led to strawberry juices with the greatest presence of health-related compounds. The evaluation of the HIPEF critical parameters influence on health-related compounds can contribute to achieve optimal processing conditions to obtain strawberry juices with high antioxidant potential.

Apple juice, extracted from golden delicious fruits, was pasteurized using a pulsed electric field (PEF) treatment and compared with a conventional high temperature-short time (HTST) method. The PEF treatment was carried out using a PEF laboratory unit, set with a bipolar pulse (4 μs wide), an intensity of 35 kV/cm, and a frequency of 1200 pulses per second (pps). The thermal pasteurization was performed at 90 °C for 30 s with an adapted laboratory set-up. Effects of variables of both treatments on pH, total acidity, phenolics content, and volatile compounds were investigated. While minimal variability was observed in pH and no significant changes were detected in acidity, phenolics content and volatile compounds concentration showed statistical significant differences between treatments. In general, these measured variables were less affected by the PEF treatment than by the thermal pasteurization.

Recent attention has been devoted to the development of nonconforming method-of-moment (MoM) implementations of the Electric-Field Integral Equation (EFIE), which provide current solutions with no continuity constraints between neighboring facets. These schemes rely on the testing of the fields over small volumetric domains attached to the surface triangulation, inside the body under analysis. In the scattering analysis of closed conductors with edges and corners, improved accuracy is observed when compared with the conventional RWG-discretization of the EFIE. Similarly, in these cases, the Galerkin MoM-implementation of the Magnetic-Field Integral Equation (MFIE) with the monopolar-RWG basis functions, a low-order example of nonconforming set, shows improved accuracy with respect to the poorly accurate RWG-discretization of the MFIE. In this paper, we show RCS-results for the monopolar-RWG MoM-implementation of the Combined-Field Integral Equation (CFIE), which arises from the linear combination of the EFIE and the MFIE. As expected, it offers improved accuracy for the sharp-edged conductor tested with respect to the conventional RWG-discretization of the CFIE.

The Method-of-Moment (MoM) discretization of the Electric-Field Integral Equation (EFIE) for a transversal electric (TE) illuminating plane wave impinging on an infinitely long cylinder (2D-object) traditionally requires continuous piecewise linear basis functions. These basis functions are particularly convenient in the numerical implementation because they reduce the degree of the Kernel singularity. Recently, a nonconforming implementation of the TE-EFIE discretized with discontinuous piecewise linear basis functions has been successfully developed with the testing procedure done over small surface entities attached to the boundary of the object, inside the body under analysis. In this paper we present a novel nonconforming discretization of the TE-EFIE based on discontinuous piecewise linear basis functions with a testing procedure that relies only on line integrals. This allows for an easier and more efficient computation of the impedance matrix elements while preserving the improved far-field accuracy observed for sharp edged objects in the previous surface-tested TE-EFIE implementation.

Pores can be generated in lipid membranes by the application of an external electric field or by the addition of particular chemicals such as dimethyl sulfoxide (DMSO). Molecular dynamics (MD) has been shown to be a useful tool for unveiling many aspects of pore formation in lipid membranes in both situations. By means of MD simulations, we address the formation of electropores in cholesterol-containing lipid bilayers under the influence of DMSO. We show how a combination of physical and chemical mechanisms leads to more favorable conditions for generating membrane pores and, in particular, how the addition of DMSO to the medium significantly reduces the minimum electric field required to electroporate a lipid membrane. The strong alteration of membrane transversal properties and the energetic stabilization of the hydrophobic pore stage by DMSO provide the physicochemical mechanisms that explain this effect. Fil: Fernández, María Laura. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. Instituto Tecnológico de Buenos Aires; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Reigada, Ramón. Universidad de Barcelona; España