The contribution of hydrogen bonding interactions to the formation of local density inhomogeneities in supercritical water at near-critical conditions has been extensively studied by means of molecular dynamics simulations. The results obtained have revealed the strong effect of water molecules forming one and two hydrogen bonds on the determination of the local density augmentation in the fluid. The local structural order has also been studied in terms of the trigonal and tetrahedral order parameters, revealing the correlation between local orientational order and hydrogen bonding. The dynamics of the structural order parameters exhibit similarities with local density ones. The local structural analysis performed in terms of nearest neighbors around the individual molecules provides additional significant evidence about the existence of a liquid-like to gas-like structural transition in supercritical water at the density range close to 0.2 ¿c, further supporting previous suggestions based on the interpretation of experimental thermodynamic data.
Romanini, M.; Del Barrio, M.; Macovez, R.; Ruiz, M.; Capaccioli, S.; Tamarit, J. Ll. Scientific reports Vol. 7, num. 1346, p. 1-11 DOI: 10.1038/s41598-017-01464-2 Data de publicació: 2017-12-01 Article en revista
We probe the temperature- and pressure-dependent specific volume (v) and dipolar dynamics of the amorphous phase (in both the supercooled liquid and glass states) of the ternidazole drug (TDZ). Three molecular dynamic processes are identified by means of dielectric spectroscopy, namely the a relaxation, which vitrifies at the glass transition, a Johari-Goldstein ßJG relaxation, and an intramolecular process associated with the relaxation motion of the propanol chain of the TDZ molecule. The lineshapes of dielectric spectra characterized by the same relaxation time (isochronal spectra) are virtually identical, within the studied temperature and pressure ranges, so that the time-temperature-pressure superposition principle holds for TDZ. The a and ßJG relaxation times fulfil the density-dependent thermodynamic scaling: master curves result when they are plotted against the thermodynamic quantity Tv¿, with thermodynamic exponent ¿ approximately equal to 2. These results show that the dynamics of TDZ, a system characterized by strong hydrogen bonding, is characterized by an isomorphism similar to that of van-der-Waals systems. The low value of ¿ can be rationalized in terms of the relatively weak density-dependence of the dynamics of hydrogen-bonded systems.
Linares, J.I.; Cantizano González, A.; Arenas, E.; Moratilla, B.; Martin, V.; Batet, L. Energy Vol. 140, num. Part 1, p. 307-317 DOI: 10.1016/j.energy.2017.08.105 Data de publicació: 2017-12-01 Article en revista
The EUROfusion research program is currently exploring alternative solutions for a future fusion power plant with DEMO (DEMOnstration Power Plant) prototype. One of the most important issues arising from a dual coolant lithium lead blanket-based reactor is the correct integration of the four thermal sources in order to achieve the highest electricity production. This study analyses the technical feasibility of supercritical CO2 Brayton power cycles. Starting with a classical re-compressed cycle, which is taken as the baseline case, two alternative proposals are investigated. On the one hand, a modified re-compressed layout with only one recuperator is studied, and is found to achieve the same electric efficiency as that of the baseline case (34.6%). On the other hand, an optimised recuperated layout is proposed, which achieves a 33.6% electric efficiency. A parametric study is conducted in order to optimise the heat exchanger size. When the re-compressed layout is optimised, a loss of efficiency (5%) is experienced. In the case of the recuperated layout optimisation the efficiency loss is reduced to 3%, achieving a reduction in heat exchanger size of 2/3.
L'objectiu d'aquesta tesi és la fabricació, aplicació i integració de sensors químics amb transducció electroquímica basats en nanomaterials funcionals per a la detecció de contaminants d'aigua.Aquest treball es divideix en 7 capítols, dels quals el Capítol 1 és la "Introducció", on es revisen qüestions generals amb la finalitat d'establir antecedents sobre els temes tractats en aquesta tesi, així com també l'estat de l'art dels mateixos.El segon capítol anomenat "Síntesi de Materials" descriu el procés de fabricació del transductor electroquímic basat en un material compost de nanotubs de carboni en una matriu de poliestirè utilitzat com a suport per al creixement de les nanopartícules Així mateix es detalla el procediment seguit per a l'electrodeposició de nanopartícules metàl·liques d'or, plata, coure i bismut, emprades com a element de reconeixement, la seva caracterització morfològica i química, així com el seu comportament electroquímic de cara a l'aplicació desitjada.Els Capítols 3, 4 i 5 descriuen l'aplicació dels sensors elaborats. Al Capítol 3 denominat "Or per a la detecció de formaldehid" es realitza un estudi comparatiu entre nanopartícules i clústers d'àtoms d'or, tots dos per a la detecció de formaldehid. El Capítol 4 "micropartícules de plata per a la detecció de sucralosa" mostra l'anàlisi de la interacció de la plata amb ions clorur com a base per a la posterior aplicació d'aquest sensor per a l'anàlisi de la molècula organoclorada sucralosa. El Capítol 5 "Bismut per a la detecció d¿ions de metalls pesants" tracta sobre la detecció de cadmi i plom emprant nanopartícules de bismut dipositades seguint dues metodologies diferents mitjançant voltamperometria de redissolució anòdica.En el Capítol 6, "Dispositius fluídics compactes", s'aborda la integració dels sensors en una plataforma fluídica compacta per tal de realitzar mesures automàtiques en continu. Es van elaborar dos tipus de famílies de dispositius, un denominat de primera generació que permetia realitzar mesures amb un sol sensor i un altre anomenat de segona generació que a causa del seu disseny admetia la integració de dos sensors diferents per realitzar mesures simultànies.Finalment, en el Capítol 7 de "Conclusions" s'engloben les conclusions de tots els capítols.
Aznar, A.; LLoveras, P.; Romanini, M.; Del Barrio, M.; Tamarit, J. Ll.; Cazorla, C.; Errandonea, D.; Mathur, N.; Planes, A.; Moya, X.; Mañosa Carrera, Lluis Nature communications num. 8, p. 1-6 DOI: 10.1038/s41467-017-01898-2 Data de publicació: 2017-11-29 Article en revista
Current interest in barocaloric effects has been stimulated by the discovery that these pressure-driven thermal changes can be giant near ferroic phase transitions in materials that display magnetic or electrical order. Here we demonstrate giant inverse barocaloric effects in the solid electrolyte AgI, near its superionic phase transition at ~420 K. Over a wide range of temperatures, hydrostatic pressure changes of 2.5 kbar yield large and reversible barocaloric effects, resulting in large values of refrigerant capacity. Moreover, the peak values of isothermal entropy change (60 J K-1 kg-1 or 0.34 J K-1 cm-3) and adiabatic temperature changes (18 K), which we identify for a starting temperature of 390 K, exceed all values previously recorded for barocaloric materials. Our work should therefore inspire the study of barocaloric effects in a wide range of solid electrolytes, as well as the parallel development of cooling devices.
The dynamics of a DC-AC self-oscillating LC resonant inverter with a zero current switching strategy is considered in this paper. A model that includes both the series and the parallel topologies and accounts for parasitic resistances in the energy storage components is used. It is found that only two reduced parameters are needed to unfold the bifurcation set of this extended system: one is related to the quality factor of the LC resonant tank, and the other accounts for the balance between serial and parallel losses. Through a rigorous mathematical study, a complete description of the bifurcation set is obtained and the parameter regions where the inverter can work properly is emphasized.
We propose an ultrafast femtosecond time scale trichromatic p-pulse illumination scheme for coherent excitation and manipulation of low-lying Rydberg states in rubidium. Selective population of nP3/2 levels with principal quantum numbers n¿12 using 75-fs laser pulses is achieved. The density-matrix equations of a four-level ladder system beyond the rotating-wave approximation have to be solved to clarify the balance between the principal quantum numbers, the duration of the laser pulses, and the associated ac-Stark effects for the fastest optimal excitation. The mechanism is robust for femtosecond control using different level configurations for applications in ultrafast quantum information processing and spectroscopy.
The temperature dependence of the dielectric response of ordinary ferroelectric materials exhibits a frequency-independent anomalous peak as a manifestation of the ferroelectric to paraelectric phase transition. A second anomaly in the permittivity has been reported in different ferroelectric perovskite-type systems at low temperatures, often at cryogenic temperatures. This anomaly manifests as a frequency-dependent local maximum, which exhibits similar characteristics to that observed in relaxor ferroelectrics around their phase transition. The origin of this unexpected behavior is still controversial. In order to clarify this phenomenon, a model-free route solution is developed in this work. Our findings reveal the same critical linear pattern/glass-like freezing behavior previously observed for glass-forming systems. Contrary to current thought, our results suggest that a critical-like dynamic parameterization could provide a more appropriate solution than the conventional Vogel–Fulcher–Tammann equation. The implemented methodology may open a new pathway for analyzing relaxation phenomena in other functional materials like relaxor ferroics.
Semiconductor lasers with time-delayed optical feedback display a wide range of dynamical regimes, which have found various practical applications. They also provide excellent testbeds for data analysis tools for characterizing complex signals. Recently, several of us have analyzed experimental intensity time-traces and quantitatively identified the onset of different dynamical regimes, as the laser current increases. Specifically, we identified the onset of low-frequency fluctuations (LFFs), where the laser intensity displays abrupt dropouts, and the onset of coherence collapse (CC), where the intensity fluctuations are highly irregular. Here we map these regimes when both, the laser current and the feedback strength vary. We show that the shape of the distribution of intensity fluctuations (characterized by the standard deviation, the skewness, and the kurtosis) allows to distinguish among noise, LFFs and CC, and to quantitatively determine (in spite of the gradual nature of the transitions) the boundaries of the three regimes. Ordinal analysis of the interdropout time intervals consistently identifies the three regimes occurring in the same parameter regions as the analysis of the intensity distribution. Simulations of the well-known time-delayed Lang-Kobayashi model are in good qualitative agreement with the observations.
For a few decades the local rainfall measurements are generally obtained by tipping bucket sensors, that allow to record each tipping time corresponding to a well-known rain depth. However, a considerable part of rainfall data to be used in the hydrological practice is available in aggregated form within constant time intervals. This can produce undesirable effects, like the underestimation of the annual maximum rainfall depth, Hd, associated with a given duration, d, that is the basic quantity in the development of rainfall depth-duration-frequency relationships. The errors in the evaluation of Hd from data characterized by a coarse temporal aggregation, ta, and a procedure to reduce the non-homogeneity of the Hd series are here investigated. Our results show that for ta¿=¿1¿min the underestimation is practically negligible, whereas for larger temporal aggregations with d¿=¿ta the error in a single Hd can reach values up to 50% and in a series of Hd in the average up to 17%. Relationships between the non-dimensional ratio ta/d and the average underestimation of Hd, derived through continuous rainfall data observed in many stations of Central Italy, are presented to overcome this issue. These equations allow to improve the Hd estimates and the associated depth-duration-frequency curves at least in areas with similar climatic conditions. The effect of the correction of the Hd series on the rainfall depth-duration-frequency curves is quantified. Our results indicate that the improvements obtained by the proposed procedure are of the order of 10%.
For a few decades the local rainfall measurements are generally obtained by tipping bucket sensors, that allow to record each tipping time corresponding to a well-known rain depth. However, a considerable part of rainfall data to be used in the hydrological practice is available in aggregated form within constant time intervals. This can produce undesirable effects, like the underestimation of the annual maximum rainfall depth, Hd, associated with a given duration, d, that is the basic quantity in the development of rainfall depth-duration-frequency relationships. The errors in the evaluation of Hd from data characterized by a coarse temporal aggregation, ta, and a procedure to reduce the non-homogeneity of the Hd series are here investigated. Our results show that for ta = 1 min the underestimation is practically negligible, whereas for larger temporal aggregations with d = ta the error in a single Hd can reach values up to 50% and in a series of Hd in the average up to 17%. Relationships between the non-dimensional ratio ta/d and the average underestimation of Hd, derived through continuous rainfall data observed in many stations of Central Italy, are presented to overcome this issue. These equations allow to improve the Hd estimates and the associated depth-duration-frequency curves at least in areas with similar climatic conditions. The effect of the correction of the Hd series on the rainfall depth-duration-frequency curves is quantified. Our results indicate that the improvements obtained by the proposed procedure are of the order of 10%.
A compromise solution to increase flight efficiency in cruise, but without penalising capacity (or even safety), would be perhaps to remove (or relax) the minimum rate of climb (ROC) constraint and/or to reduce the height of the step climbs in cruise. In this paper, the benefits (in terms of total operating costs) and the associated impact on the air traffic management (ATM) of such “relaxed cruise” operations are quantified for a representative medium-haul aircraft under different scenarios, by means of an in-house trajectory optimisation software. Results show that by reducing the minimum ROC from 500 to 300 ftmin-1, whilst keeping the step climb height according to current reduced vertical separation minima (RVSM) standard would give a good compromise between cost savings and impact on the ATM.
We present and discuss a solution to the growing demand for satellite telecommunication coverage in the high-latitude geographical regions (beyond 55°N), where the signal from geostationary satellites is limited or unavailable. We focus on the dynamical issues associated to the design, the coverage, the maintenance and the disposal of a set of orbits selected for the purpose. Specifically, we identify a group of highly inclined, moderately eccentric geosynchronous orbits derived from the Tundra orbit (geosynchronous, eccentric and critically inclined). Continuous coverage can be guaranteed by a constellation of three satellites in equally spaced planes and suitably phased. By means of a high-precision model of the terrestrial gravity field and the relevant environmental perturbations, we study the evolution of these orbits. The effects of the different perturbations on the ground track (which is more important for coverage than the orbital elements themselves) are isolated and analyzed. The physical model and the numerical setup are optimized with respect to computing time and accuracy. We show that, in order to maintain the ground track unchanged, the key parameters are the orbital period and the argument of perigee. Furthermore, corrections to the right ascension of the ascending node are needed in order to preserve the relative orientation of the orbital planes. A station-keeping strategy that minimizes propellant consumption is then devised, and comparisons are made between the cost of a solution based on impulsive maneuvers and one with continuous thrust. Finally, the issue of end-of-life disposal is discussed.
Rea, N.; de Martino, D.; Israel, G.; Bozzo, E.; Linares, M.; Hernanz, M.; Casares, J. Monthly notices of the Royal Astronomical Society Vol. 471, num. 3, p. 2902-2916 DOI: 10.1093/mnras/stx1560 Data de publicació: 2017-11-01 Article en revista
In a search for the counterpart to the Fermi-LAT source 3FGL J0838.8-2829, we performed a multiwavelength campaign: in the X-ray band with Swift and XMM-Newton; in the infrared and optical with OAGH, ESO-NTT and IAC80; and in the radio with ATCA observations. We also used archival hard X-ray data obtained by INTEGRAL. We report on three X-ray sources consistent with the position of the Fermi-LAT source.We confirm the identification of the brightest object, RX J0838-2827, as a magnetic cataclysmic variable that we recognize as an asynchronous system (not associated with the Fermi-LAT source). RX J0838-2827 is extremely variable in the X-ray and optical bands, and timing analysis reveals the presence of several periodicities modulating its X-ray and optical emission. The most evident modulations are interpreted as being caused by the binary system orbital period of ~1.64 h and the white dwarf spin period of ~1.47 h. A strong flux modulation at ~15 h is observed at all energy bands, consistent with the beat frequency between spin and orbital periods. Optical spectra show prominent Hß, He I and He II emission lines that are Doppler-modulated at the orbital period and at the beat period. Therefore, RX J0838-2827 accretes through a disc-less configuration and could be either a strongly asynchronous polar or a rare example of a pre-polar system on its way to reaching synchronism. Regarding the other two X-ray sources, XMM J083850.4-282759 showed a variable X-ray emission, with a powerful flare lasting for ~600 s, similar to what is observed in transitional millisecond pulsars during the subluminous disc state: this observation possibly means that this source can be associated with the Fermi-LAT source.
The largest eigenvalue of a network’s adjacency matrix and its associated principal eigenvector are key elements for determining the topological structure and the properties of dynamical processes mediated by it. We present a physically grounded expression relating the value of the largest eigenvalue of a given network to the largest eigenvalue of two network subgraphs, considered as isolated: the hub with its immediate neighbors and the densely connected set of nodes with maximum
-core index. We validate this formula by showing that it predicts, with good accuracy, the largest eigenvalue of a large set of synthetic and real-world topologies. We also present evidence of the consequences of these findings for broad classes of dynamics taking place on the networks. As a by-product, we reveal that the spectral properties of heterogeneous networks built according to the linear preferential attachment model are qualitatively different from those of their static counterparts.
Mobile impurity atoms immersed in Bose–Einstein condensates provide a new platform for exploring Bose polarons. Recent experimental advances in the field of ultracold atoms make it possible to realize such systems with highly tunable microscopic parameters and to explore equilibrium and dynamical properties of polarons using a rich toolbox of atomic physics. In this paper we present a detailed theoretical analysis of Bose polarons in one-dimensional systems of ultracold atoms. By combining a non-perturbative renormalization group approach with numerically exact diffusion Monte Carlo calculations we obtain not only detailed numerical results over a broad range of parameters but also qualitative understanding of different regimes of the system. We find that an accurate description of Bose polarons requires the inclusion of two-phonon scattering terms which go beyond the commonly used Fröhlich model. Furthermore we show that when the Bose gas is in the strongly interacting regime, one needs to include interactions between the phonon modes. We use several theoretical approaches to calculate the polaron energy and its effective mass. The former can be measured using radio-frequency spectroscopy and the latter can be studied experimentally using impurity oscillations in a harmonic trapping potential. We compare our theoretical results for the effective mass to the experiments by Catani et al (2012 Phys. Rev. A 85 023623). In the weak-to-intermediate coupling regimes we obtain excellent quantitative agreement between theory and experiment, without any free fitting parameter. We supplement our analysis by full dynamical simulations of polaron oscillations in a shallow trapping potential. We also use our renormalization group approach to analyze the full phase diagram and identify regions that support repulsive and attractive polarons, as well as multi-particle bound states.
Electromagnetic response of a PT dipole is studied both analytically and numerically. In the analytical approach, the dipole is represented by two point scatterers. Within the first Born approximation, the asymmetry of the scattering field with respect to the orientation of the dipole is proven. In numerical simulations, the dipole is represented by two infinitely long, parallel cylinders with opposite sign of the imaginary part of a refractive index. Numerical data confirm the validity of the Born approximation in the weak scattering limit, while significant deviations from the Born approximation were observed for stronger scatterers and in the near-field range.
Free energy surfaces associated to the adsorption of metal cations ((Formula presented.), (Formula presented.), (Formula presented.), and (Formula presented.)) in biological environments have been computed by metadynamics simulations. In all cases, the systems were modelled using the CHARMM36 force field. The free-energy landscapes unveil specific binding behaviour of metal cations. So, (Formula presented.) and (Formula presented.) are more likely to stay in the aqueous solution, and can easily bind to a few lipid oxygens by overcoming low free-energy barriers. Differently, (Formula presented.) is most stable when bound to four lipid oxygens of the membranes, rather than being hydrated in the aqueous solution. Finally, (Formula presented.) is tightly hydrated, and can hardly lose a hydration water and bind directly to the membranes. When cholesterol is included inside the membrane at concentration up to 50%, the resulting free-energy landscapes reveal the competition between binding of sodium to water and to lipid head groups, although the binding competitiveness of lipid head groups is diminished by cholesterol contents. When cholesterol concentration is greater than 30%, the ionic binding is significantly reduced, which coincides with the phase transition point of DMPC-cholesterol membranes from a liquid-disordered phase to a liquid-ordered phase.
We derive a convenient model for broad aperture micro-lasers, such as microchip lasers, broad area semiconductor lasers, or VCSELs, taking into account several longitudinal mode families. We provide linear stability analysis, and show characteristic spatio-temporal dynamics in such multi-longitudinal mode laser models. Moreover, we derive the coupled mode model in the presence of intracavity refraction index modulation (intracavity photonic crystal). Graphical abstract: [Figure not available: see fulltext.].
Golomedov, A.; Lozovik, Y.; Astrakharchik, G.; Boronat, J. Journal of low temperature physics Vol. 189, num. 5-6, p. 300-311 DOI: 10.1007/s10909-017-1814-y Data de publicació: 2017-10-13 Article en revista
Ground-state properties of a fermionic Coulomb gas are calculated using the fixed-node diffusion Monte Carlo method. The validity of the composite boson description is tested for different densities. We extract the exciton–exciton s-wave scattering length by solving the four-body problem in a harmonic trap and mapping the energy to that of two trapped bosons. The equation of state is consistent with the Bogoliubov theory for composite bosons interacting with the obtained s-wave scattering length. The perturbative expansion at low density has contributions physically coming from (a) exciton binding energy, (b) mean-field Gross–Pitaevskii interaction between excitons, and (c) quantum depletion of the excitonic condensate (Lee–Huang–Yang terms for composite bosons). In addition, for low densities we find a good agreement with the Bogoliubov bosonic theory for the condensate fraction of excitons. The equation of state in the opposite limit of large density is found to be well described by the perturbative theory including (a) mixture of two ideal Fermi gases and (b) exchange energy. We find that for low densities both energetic and coherent properties are correctly described by the picture of composite bosons (excitons).
The present study aims to propose basic recommendations to follow in the design of restaurants for them to be acoustically ideal. Complying with recommendations of good hotel practices and fire and acoustic regulation, we reproduced a restaurant in a class room at E.T.S.A.B. We performed the study with real occupation, variable in gender, number and distribution, and for different levels of background noise. We applied objective and subjective methods to measure and assess the intelligibility. Our results are contrasted with those we would obtain through simulation and theoretical study developed in previously validated models.
El estudio se desarrolla con el objetivo de proponer unas recomendaciones básicas a seguir en el diseño de restaurantes para que sean ideales acústicamente. Cumpliendo con las recomendaciones de buenas prácticas de Hostelería y normativas de incendios y Acústica, reproducimos un restaurante en un aula de la E.T.S.A.B. Practicamos el estudio con ocupación real, variable en género, número y disposición, y para diferentes niveles de ruido de fondo. Aplicamos métodos objetivos y subjetivos para la medición y valoración de la inteligibilidad. Los resultados obtenidos se contrastan con los que obtendríamos mediante simulación y estudio teórico desarrollados en modelos validados anteriormente.
We systematically investigate the phenomena of coherence resonance in time-delay coupled networks of FitzHugh-Nagumo elements in the excitable regime. Using numerical simulations, we examine the interplay of noise, time-delayed coupling, and network topology in the generation of coherence resonance. In the deterministic case, we show that the delay-induced dynamics is independent of the number of nearest neighbors and the system size. In the presence of noise, we demonstrate the possibility of controlling coherence resonance by varying the time-delay and the number of nearest neighbors. For a locally coupled ring, we show that the time-delay weakens coherence resonance. For nonlocal coupling with appropriate time-delays, both enhancement and weakening of coherence resonance are possible.
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Sadou, H.; Rietveld, I.; Del Barrio, M.; Secrétan, P.; Faucheron, A.; Karoui, M.; Tilleul, P.; Yagoubi, N.; Do, B. European journal of pharmaceutical sciences Vol. 107, p. 62-70 DOI: 10.1016/j.ejps.2017.06.031 Data de publicació: 2017-09-30 Article en revista
The mainstay treatment for patients with acute coronary syndrome is an oral route dual antiplatelet therapy with a P2Y12-receptor antagonist and Aspirin (ASA). To improve patient adherence to such treatments, combination therapies (polypill) are envisioned. Physicochemical solid-state studies have been carried out to develop a preformulation strategy of ASA with the P2Y12-receptor antagonist Ticagrelor (TIC). The investigations were carried out using differential scanning calorimetry, liquid chromatography-high resolution-multistage mass spectrometry (LC-HR-MSn) and as complementary techniques Fourier transform infrared measurements and thermogravimetric analysis. A simple eutectic transition at 98 °C with a mole fraction for the eutectic liquid of 0.457 has been observed and the mixing of ASA and TIC molecules in each other's crystal structures appears to be limited. No cocrystals of TIC and ASA have been found. The appearance of the eutectic liquid was linked with a clear onset of chemical instability of the two pharmaceuticals. The decomposition mechanism in the liquid phase involves prior decomposition of ASA, whose residues react with well-identified TIC interaction sites. Seven interaction products were observed by LC-HR-MSn linked to corresponding degradation products. The most important degradation pathway is N-dealkylation. In conclusion, polypills of ASA and TIC are a viable approach, but the decomposition of ASA should be avoided by eliminating high temperatures and high humidity.
L'objectiu principal d'aquesta tesi es l'estudi de propietats estàtiques i dinàmiques de diferents fluids quàntics utilitzant tècniques de Monte Carlo quàntiques, principalment emprant el formalisme de path integrals per obtenir results tan a temperatura zero com a temperatura finita. Primer de tot, presentem els mètodes de Monte Carlo quàntics més importants, i introduïm el mètode de Path Integral Monte Carlo (PIMC), que fem servir al llarg de tota la tesi, i el mètode de Path Integral Ground State (PIGS), que es una extensió del primer pero a temperatura zero. Després d'introduir el formalisme bàsic, comentem les diferents aproximacions necesaries i aportem una comparació entre elles. També expliquem un posible mètode de paral·lelització i tècniques de mostreig avançat.Els primers resultats que mostrem en aquesta tesi son pel diagrama de fases d'un gas de Coulomb unidimensional, que hem obtingut emprant PIMC. Hem construit el diagrama de fases mitjançant el càlcul de propietats energètiques i estructurals. Els nostres resultats amplien estudis previs que s'havien realitzat pel mateix sistema a temperatura zero. Els nostres resultats mostren l'existencia d'un règim de cristall de Wigner quàntic i un d'un gas de Fermi ideal a temperatures baixes. Incrementant la temperatura obtenim un cristall de Wigner clàssic i un gas clàssic.En el següent capítol ensenyem els resultats per un sistema quasi-unidimensional de parahidrogen. L'objectiu d'aquest estudi es veure si la quasi-unidimensionalitat afecta al paràmetre de Luttinger quan el comparem pel cas purament unidimensional. Això ho fem a temperatura zero utilitzant PIGS. Sent el parahidrogen un fort candidat a ser superfluid, la idea principal es veure si reduint la dimensionalitat del sistema podem alleugerir suficient la interacció intermolecular. Per fer-ho, provem diferents potentials externs per controlar l'obertura del sistema en dues de les dimensions. Tot i l'increment del paràmetre de Luttinger respecte al cas unidimensional, aquest no arriba als valors esperats per mostrar superfluidesa.El següents resultats són del nostre estudi sobre el factor d'estructura dinàmic per 4He. Utilitzant PIMC, calculem la funció de dispersió a diferents temperatures i fem una inversió per tal d'accedir a les propietats dinàmiques del sistema. Tot i la naturalesa de problema mal posat d'aquesta inversió, obtenim resultats qualitativament bons en comparació amb els experimentals, i provem que el nostre mètode d'inversió obté resultats superiors per 4He a temperatura finita que els obtinguts previament utilitzant altres mètodes. En aquest sentit, aportem una comparació amb el mètode de màxima entropia i amb resultats experimentals. L'estudi a diferents temperatures ens deixa veure la desaparició del pic del rotó quan creuem T=2.17K desde el règim superfluid al fluid normal. També observem una curvatura extranya en la distribució de moments en el règim de superfluidesa que desapareix a temperatures més elevades, i pel qual no existeix cap explicació teòrica.Finalment, mostrem un mètode per calcular funcions de correlació en temps complex, l'objectiu del qual es obtenir factors d'estructura dinàmic superiors als obtinguts en temps purament imaginari. Aquest model ha sigut provat amb èxit en sistemes d'una sola partícula. El nostre objectiu es veure si obtenim resultats bons en sistemes amb més partícules, i si el temps complex màxim al que podem accedir no es redueix amb aquest increment. Tot i el increment en la variança, obtenim bons resultats pel factor dinàmic i, comparant-los amb els obtinguts amb temps imaginari, podem veure com el temps complex ofereix resultats més pròxims als exactes.
Hernando, M.; Mora, M.; Pelayo, I. M.; Alcom, L.; Gonzalez, M.; Cañadas, J.C. Colourings, Independence and Domination: Workshop on Graph Theory p. 84 Data de presentació: 2017-09-20 Presentació treball a congrés
Liu, Q.; Romero, P.; Mantilla, P.; Colodrero, S.; Toudert, J.; Martorell, J. Advanced energy materials Vol. 7, num. 18, p. 1700356-1-1700356-8 DOI: 10.1002/aenm.201700356 Data de publicació: 2017-09-20 Article en revista
An optimal photon absorption in thin film photovoltaic technologies can only be reached by effectively trapping the light in the absorber layer provided a considerable portion of the photons is rejected or scattered out of such layer. Here, a new optical cavity is proposed that can be made to have a resonant character at two different nonharmonic frequencies when adjusting the materials or geometry configurations of the partially transmitting cavity layers. Specific configurations are found where a reminiscence of such two fundamental resonances coexists leading to a broadband light trapping. When a PTB7-Th:PC71BM organic cell is integrated within such cavity, a power conversion efficiency of 11.1% is measured. This study also demonstrates that when materials alternative to organics are used in the photoactive cell layer, a similar cavity can be implemented to also obtain the largest light absorption possible. Indeed, when it is applied to perovskite cells, an external quantum efficiency is predicted that closely matches its corresponding internal one for a broad wavelength range.
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One of the major contributions to aircraft operational costs corresponds to maintenance. This is a time consuming and expensive process, but necessary, for instance, to detect early formation of cracks, monitoring crack growth, and for removing or fixing parts with repairs to regain their original strength. Thus, repair technologies play an important role in minimizing the aircraft operational costs, and airlines pay careful attention to these technologies to improve their efficiency and revenue. Aircraft repair patches are usually made of aluminium or composites. Composites have very high strength to weight ratio compared to aluminium but, when riveted, they may lose nearly 60% of their total strength and carrying capacity. In spite of these drawbacks, the aviation industry still uses nowadays riveting of composites as common practice. This work analyses and compares the performance of several configurations of aircraft repair patches; particularly, riveted lap joints consisting of aluminium or composite substrates repaired with aluminium or composite doublers. Each of the studied joints consists of two substrate plates separated by a gap of 12.7 mm (simulating and induced crack or hole), repaired with two doublers riveted to the substrate plates, with a total of eight rivets. The performance is computed numerically using commercial Finite Element Analysis (FEA) code ABAQUS for the riveted joints with substrate-doubler configurations as follows: aluminium alloy (AA)-AA, AA-Carbon fibre reinforced polymer (CFRP), CFRP-CFRP and CFRP-AA. For the different configurations, the joints are loaded with their limit load (7.5 kN) and ultimate load (11.3 kN), as derived from experimental results, and the stresses at various locations on the substrates are compared. The experiments and simulations presented in this work are compliant with FAR 25.571 requirements.
The instability mechanisms for self-organized kilometer-scale shoreline sand waves have been extensively explored by modeling. However, while the assumed bathymetric perturbation associated with the sand wave controls the feedback between morphology and waves, its effect on the instability onset has not been explored. In addition, no systematic investigation of the effect of the physical parameters has been done yet. Using a linear stability model, we investigate the effect of wave conditions, cross-shore profile, closure depth, and two perturbation shapes (P1: cross-shore bathymetric profile shift, and P2: bed level perturbation linearly decreasing offshore). For a P1 perturbation, no instability occurs below an absolute critical angle ¿c0˜ 40-50°. For a P2 perturbation, there is no absolute critical angle: sand waves can develop also for low-angle waves. In fact, the bathymetric perturbation shape plays a key role in low-angle wave instability: such instability only develops if the curvature of the depth contours offshore the breaking zone is larger than the shoreline one. This can occur for the P2 perturbation but not for P1. The analysis of bathymetric data suggests that both curvature configurations could exist in nature. For both perturbation types, large wave angle, small wave period, and large closure depth strongly favor instability. The cross-shore profile has almost no effect with a P1 perturbation, whereas large surf zone slope and gently sloping shoreface strongly enhance instability under low-angle waves for a P2 perturbation. Finally, predictive statistical models are set up to identify sites prone to exhibit either a critical angle close to ¿c0 or low-angle wave instability.
Cojocaru, E.; Rebassa, A.; Torres, S.; Garcia-berro, E. Monthly notices of the Royal Astronomical Society Vol. 470, num. 2, p. 1442-1452 DOI: 10.1093/mnras/stx1326 Data de publicació: 2017-09-11 Article en revista
We present a Monte Carlo population synthesis study of white dwarf-main sequence (WD+MS) binaries in the Galactic disc aimed at reproducing the ensemble properties of the entire population observed by the Sloan Digital Sky Survey (SDSS) Data Release 12. Our simulations take into account all known observational biases and use the most up-to-date stellar evolutionary models. This allows us to perform a sound comparison between the simulations and the observational data. We find that the properties of the simulated and observed parameter distributions agree best when assuming low values of the common envelope efficiency (0.2-0.3), a result that is in agreement with previous findings obtained by observational and population synthesis studies of close SDSSWD+MS binaries.We also show that all synthetic populations that result from adopting an initial mass ratio distribution with a positive slope are excluded by observations. Finally, we confirm that the properties of the simulated WD+MS binary populations are nearly independent of the age adopted for the thin disc, on the contribution of WD+MS binaries from the thick disc (0-17 per cent of the total population) and on the assumed fraction of the internal energy that is used to eject the envelope during the common envelope phase (0.1-0.5).
In the heart, rapid pacing rates may induce alternations in the strength of cardiac contraction, termed pulsus alternans. Often, this is due to an instability in the dynamics of the intracellular calcium concentration, whose transients become larger and smaller at consecutive beats. This alternation has been linked experimentally and theoretically to two different mechanisms: an instability due to (1) a strong dependence of calcium release on sarcoplasmic reticulum (SR) load, together with a slow calcium reuptake into the SR or (2) to SR release refractoriness, due to a slow recovery of the ryanodine receptors (RyR2) from inactivation. The relationship between calcium alternans and refractoriness of the RyR2 has been more elusive than the corresponding SR Ca load mechanism. To study the former, we reduce a general calcium model, which mimics the deterministic evolution of a calcium release unit, to its most basic elements. We show that calcium alternans can be understood using a simple nonlinear equation for calcium concentration at the dyadic space, coupled to a relaxation equation for the number of recovered RyR2s. Depending on the number of RyR2s that are recovered at the beginning of a stimulation, the increase in calcium concentration may pass, or not, over an excitability threshold that limits the occurrence of a large calcium transient. When the recovery of the RyR2 is slow, this produces naturally a period doubling bifurcation, resulting in calcium alternans. We then study the effects of inactivation, calcium diffusion, and release conductance for the onset of alternans. We find that the development of alternans requires a well-defined value of diffusion while it is less sensitive to the values of inactivation or release conductance.
Astrakharchik, G.; Krutitsky, K.V.; Lewenstein, M.; Mazzanti, F.; Boronat, J. Physical Review A Vol. 96, num. 3, p. 1-13 DOI: 10.1103/PhysRevA.96.033606 Data de publicació: 2017-09-05 Article en revista
We study the superfluid response, the energetic and structural properties of a one-dimensional ultracold Bose gas in an optical lattice of arbitrary strength. We use the Bose-Fermi mapping in the limit of infinitely large repulsive interaction and the diffusion Monte Carlo method in the case of finite interaction. For slightly incommensurate fillings we find a superfluid behavior, which is discussed in terms of vacancies and interstitials. It is shown that both the excitation spectrum and static structure factor are different for the cases of microscopic and macroscopic fractions of defects. This system provides an extremely well-controlled model for studying defect-induced superfluidity.
Del Barrio, M.; Tamarit, J. Ll.; Céolin, R.; Robert, B.; Guechot, C.; Teulon, J.; Rietveld, I. Journal of chemical thermodynamics Vol. 112, p. 308-313 DOI: 10.1016/j.jct.2017.05.022 Data de publicació: 2017-09-01 Article en revista
The pressure-temperature phase diagram of morniflumate (niflumic acid ß-morpholinoethyl ester) has been obtained by high-pressure thermal analysis. In addition, calorimetric melting data (TI¿L = (348.1 ± 0.4) K and ¿HI¿L = (89 ± 2) J·g-1) and the specific volumes of the solid and the liquid state have been obtained under normal pressure. Comparison of the measured high-pressure melting data with the equilibrium curve obtained through the Clapeyron equation indicates that the initial slopes are the same (dP/dT = (2.96 ± 0.06) MPa·K-1) at the melting point under normal pressure. The fact that the Clapeyron equation can be used to construct topological phase diagrams may be of interest for the food and pharmaceutical industries.
la Cognata, M.; Pizzone, R.; Jose, J.; Hernanz, M.; Cherubini, S.; Gulino, M.; Rapisarda, G.; Spitaleri, C. Astrophysical journal Vol. 846, p. 65-1-65-6 DOI: 10.3847/1538-4357/aa845f Data de publicació: 2017-09-01 Article en revista
Crucial information on nova nucleosynthesis can be potentially inferred from ¿-ray signals powered by 18F decay. Therefore, the reaction network producing and destroying this radioactive isotope has been extensively studied in the last years. Among those reactions, the 18F(p, a)15O cross-section has been measured by means of several dedicated experiments, both using direct and indirect methods. The presence of interfering resonances in the energy region of astrophysical interest has been reported by many authors including the recent applications of the Trojan Horse Method. In this work, we evaluate what changes are introduced by the Trojan Horse data in the 18F(p, a)15O astrophysical factor recommended in a recent R-matrix analysis, accounting for existing direct and indirect measurements. Then the updated reaction rate is calculated and parameterized and implications of the new results on nova nucleosynthesis are thoroughly discussed.
Rubio-Marcos, F.; Fernández, J.F; Ochoa, D. A.; Garcia, J. E.; Rojas-Hernandez, R. E.; Castro, M.; Ramajo, L. Journal of the european ceramic society Vol. 37, num. 11, p. 3501-3509 DOI: 10.1016/j.jeurceramsoc.2017.04.045 Data de publicació: 2017-09 Article en revista
Lead zirconate titanate (PZT) based ceramics are currently enjoying a wide use in piezoelectric devices despite lead toxicity. Due to growing environmental concerns, the attention on piezoelectric ceramics has been moving to lead-free materials, in particular to (K,Na)NbO3-based ceramics. Here we report a systematic evaluation of the effects of the compositional modifications on [(K0.44Na0.52Li0.04)[(Nb0.86Ta0.10Sb0.04)1-xZr5x/4]O3 lead–free piezoceramics. We show that an interrelationship between the intrinsic and extrinsic factors is the linchpin for the development of good piezoelectric properties. Hence, the stabilization of the tetragonal symmetry on the orthorhombic-tetragonal polymorphic phase boundary facilities the poling process of the system, thereby enhancing the piezoelectric response. Additionally, the microstructure appears to be related to the piezoelectric properties; i.e., the improved piezoelectric properties correlate to the increase in grain size. The results of this work could help to understand the origin of piezoelectricity in potassium–sodium niobate-based ceramics.
Early molecular dynamics simulations discovered an important asymmetry in the speed of water solvation dynamics for charge extinction and charge creation for an immersed solute, a feature representing a first demonstration of the breakdown of linear response theory. The molecular level mechanism of this asymmetry is examined here via a novel energy flux theoretical approach coupled to geometric probes. The results identify the effect as arising from the translational motions of the solute-hydrating water molecules rather than their rotational/librational motions, even though the latter are more rapid and dominate the energy flow.
We combine a Ginzburg–Landau model for a ferroelastic transition with the theory of micromagnetism to study the magnetostructural behavior leading to multicaloric effects in ferromagnetic shape memory alloys. We analyze the ferroelastic transition under different conditions of temperature, stress and magnetic field and establish the corresponding phase diagram. On the one hand, our results show that the proper combination of both fields may be used to reduce the transition hysteresis and thus improve the reversibility of the related elastocaloric effects, superelasticity and stress-mediated magnetocaloric effects. On the other hand, the stress-free magnetic field-driven and thermally driven magnetostructural evolution provides physical insight into the low-temperature field-induced domain reorientation, from which we derive strategies to modify the operational temperature ranges and thus the corresponding (magnetic) shape-memory effect.
Vispa, A.; Monserrat, D.; Cuello, G. J.; Fernandez-Alonso, F.; Mukhopadhyay, S.; Demmel, F.; Tamarit, J. Ll.; Pardo, L. Physical chemistry chemical physics Vol. 19, num. 30, p. 20259-20266 DOI: 10.1039/c7cp03630b Data de publicació: 2017-08-14 Article en revista
Globular molecules of 1-chloroadamantane form a plastic phase in which the molecules rotate in a restrained way, but with their centers of mass forming a crystalline ordered lattice. Plastic phases can be regarded as test cases for the study of disordered phases since, contrary to what happens in the liquid phase, there is a lack of stochastic translational degrees of freedom. When the temperature is increased, a hump in the specific heat curve is observed indicating a change in the energetic footprint of the dynamics of the molecules. This change takes place without a change in the symmetry of the crystalline lattice, i.e. no first-order transition is observed between temperatures below and above the calorimetric hump. This implies that subtle changes in the dynamics of the disordered plastic phase concerning purely orientational degrees of freedom should appear at the thermodynamic anomaly. Accordingly, we describe, for the first time, the microscopic mechanisms behind a disorder–disorder transition through the analysis of neutron diffraction and QENS experiments. The results evince a change in the molecular rotational dynamics accompanied by a continuous change in density.
del Aguila , F.; Ametller, L.; Illana, J.I.; Santiago, J.; Talavera, P.; Vega-Morales, R. Journal of high energy physics Vol. 08, num. 028, p. 1-26 DOI: 10.1007/JHEP08(2017)028 Data de publicació: 2017-08-08 Article en revista
We calculate loop induced lepton flavor violating Higgs decays in the Littlest
Higgs model with T-parity. We find that a finite amplitude is obtained only when all
contributions from the T-odd lepton sector are included. This is in contrast to lepton fla-
vor violating processes mediated by gauge bosons where the partners of the right-handed
mirror leptons can be decoupled from the spectrum. These partners are necessary to can-
cel the divergence in the Higgs mass introduced by the mirror leptons but are otherwise
unnecessary and assumed to be decoupled in previous phenomenological studies. Further-
more, as we emphasize, including the partner leptons in the spectrum also introduces a
new source of lepton flavor violation via their couplings to the physical pseudo-Goldstone
electroweak triplet scalar. Although this extra source also affects lepton flavor changing
gauge transitions, it decouples from these amplitudes in the limit of heavy mass for the
partner leptons. We find that the corresponding Higgs branching ratio into taus and muons
can be as large as ~ 0.2 × 10 -6 for T-odd masses of the order a few TeV, a demanding
challenge even for the high luminosity LHC.
Ruiz, G.; Romanini, M.; Hauptmann, A.; Loerting, T.; Shalaev, E.; Tamarit, J. Ll.; Pardo, L.; Macovez, R. Scientific reports Vol. 7, p. 1-8 DOI: 10.1038/s41598-017-07643-5 Data de publicació: 2017-08-07 Article en revista
Water is the most important plasticizer of biological and organic hydrophilic materials, which generally exhibit enhanced mechanical softness and molecular mobility upon hydration. The enhancement of the molecular dynamics upon mixing with water, which in glass-forming systems implies a lower glass transition temperature (T g ), is considered a universal result of hydration. In fact, even in the cases where hydration or humidification of an organic glass-forming sample result in stiffer mechanical properties, the molecular mobility of the sample almost always increases with increasing water content, and its T g decreases correspondingly. Here, we present an experimental report of a genuine antiplasticizing effect of water on the molecular dynamics of a small-molecule glass former. In detail, we show that addition of water to prilocaine, an active pharmaceutical ingredient, has the same effect as that of an applied pressure, namely, a decrease in mobility and an increase of T g . We assign the antiplasticizing effect to the formation of prilocaine-H2O dimers or complexes with enhanced hydrogen bonding interactions.
Quantum crystals abound in the whole range of solid-state species. Below a certain threshold temperature the physical behavior of rare gases (4He and Ne), molecular solids (H2 and CH4), and some ionic (LiH), covalent (graphite), and metallic (Li) crystals can be explained only in terms of quantum nuclear effects (QNE). A detailed comprehension of the nature of quantum solids is critical for achieving progress in a number of fundamental and applied scientific fields such as planetary sciences, hydrogen storage, nuclear energy, quantum computing, and nanoelectronics. This review describes the current physical understanding of quantum crystals formed by atoms and small molecules, as well as the wide palette of simulation techniques that are used to investigate them. Relevant aspects in these materials such as phase transformations, structural properties, elasticity, crystalline defects, and the effects of reduced dimensionality are discussed thoroughly. An introduction to quantum Monte Carlo techniques, which in the present context are the simulation methods of choice, and other quantum simulation approaches (e.g., path-integral molecular dynamics and quantum thermal baths) is provided. The overarching objective of this article is twofold: first, to clarify in which crystals and physical situations the disregard of QNE may incur in important bias and erroneous interpretations. And second, to promote the study and appreciation of QNE, a topic that traditionally has been treated in the context of condensed matter physics, within the broad and interdisciplinary areas of materials science.
Gillespie, S.; Parikh, A.; Barton, C.; Faestermann, T.; Jose, J.; Hertenberger, R.; Wirth, H.; de Séréville, N.; Riley, J.; Williams, M. Physical Review C Vol. 96, num. 2, p. 1-8 DOI: 10.1103/PhysRevC.96.025801 Data de publicació: 2017-08-02 Article en revista
Sulphur isotopic ratio measurements may help to establish the astrophysical sites in which certain presolar grains were formed. Nova model predictions of the 34S/32S ratio are, however, unreliable due to the lack of an experimental 34S(p,¿)35Cl reaction rate. To this end, we have measured the 34S(3He,d)35Cl reaction at 20 MeV using a high resolution quadrupole-dipole-dipole-dipole magnetic spectrograph. Twenty-two levels over 6.2 MeV
This paper compares different optimization strategies for the minimization of flight and passenger delays at two levels: pre-tactical, with on-ground delay at origin, and tactical, with airborne delay close to the destination airport. The optimization model is based on the ground holding problem and uses various cost functions. The scenario considered takes place in a busy European airport and includes realistic values of traffic. A passenger assignment with connections at the hub is modeled. Statistical models are used for passenger and connecting passenger allocation, minimum time required for turnaround and tactical noise; whereas uncertainty is also introduced in the model for tactical noise. Performance of the various optimization processes is presented and compared to ration by schedule results.