Intrinsic leakage and adsorption currents associated with the electrocaloric effect in multilayer capacitors

During the last few years, the increasing demand of energy for refrigeration applications has relived the interest of the scientific community in the study of alternative methods to the traditional gas-based refrigeration. Within this framework, the use of solid state refrigeration based on the electrocaloric effect reveals itself as one of the most promising technologies. In this work, we analyze how the temperature change associated with the electrocaloric effect shows a correlation with the electrical properties of a commercial multilayer capacitor. In that sense we established a clear relation between the adsorption currents and the temperature change produced by the electrocaloric effect. Additionally, intrinsic leakage currents are responsible for the sample heating due to the Joule effect. These well distinguished contributions can be useful during the design of solid state refrigeration devices based on the electrocaloric effect.Comment: Acepted to be published in Applied Physics Letter

Energy Flow Puzzle of Soliton Ratchets

We study the mechanism of directed energy transport for soliton ratchets. The energy flow appears due to the progressive motion of a soliton (kink) which is an energy carrier. However, the energy current formed by internal system deformations (the total field momentum) is zero. We solve the underlying puzzle by showing that the energy flow is realized via an {\it inhomogeneous} energy exchange between the system and the external ac driving. Internal kink modes are unambiguously shown to be crucial for that transport process to take place. We also discuss effects of spatial discretization and combination of ac and dc external drivings.Comment: 4 pages, 3 figures, submitted to PR

When Does Output Feedback Enlarge the Capacity of the Interference Channel?

In this paper, the benefits of channel-output feedback in the Gaussian interference channel (G-IC) are studied under the effect of additive Gaussian noise. Using a linear deterministic (LD) model, the signal to noise ratios (SNRs) in the feedback links beyond which feedback plays a significant role in terms of increasing the individual rates or the sum-rate are approximated. The relevance of this work lies on the fact that it identifies the feedback SNRs for which in any G-IC one of the following statements is true: (a) feedback does not enlarge the capacity region; (b) feedback enlarges the capacity region and the sum-rate is greater than the largest sum-rate without feedback; and (c) feedback enlarges the capacity region but no significant improvement is observed in the sum-rate

Soliton ratchets

The mechanism underlying the soliton ratchet, both in absence and in presence of noise, is investigated. We show the existence of an asymmetric internal mode on the soliton profile which couples, trough the damping in the system, to the soliton translational mode. Effective soliton transport is achieved when the internal mode and the external force are phase locked. We use as working model a generalized double sine-Gordon equation. The phenomenon is expected to be valid for generic soliton systems.Comment: 4 pages, 4 figure

Nonlinear Schr\"odinger Equation with Spatio-Temporal Perturbations

We investigate the dynamics of solitons of the cubic Nonlinear Schr\"odinger Equation (NLSE) with the following perturbations: non-parametric spatio-temporal driving of the form $f(x,t) = a \exp[i K(t) x]$, damping, and a linear term which serves to stabilize the driven soliton. Using the time evolution of norm, momentum and energy, or, alternatively, a Lagrangian approach, we develop a Collective-Coordinate-Theory which yields a set of ODEs for our four collective coordinates. These ODEs are solved analytically and numerically for the case of a constant, spatially periodic force $f(x)$. The soliton position exhibits oscillations around a mean trajectory with constant velocity. This means that the soliton performs, on the average, a unidirectional motion although the spatial average of the force vanishes. The amplitude of the oscillations is much smaller than the period of $f(x)$. In order to find out for which regions the above solutions are stable, we calculate the time evolution of the soliton momentum $P(t)$ and soliton velocity $V(t)$: This is a parameter representation of a curve $P(V)$ which is visited by the soliton while time evolves. Our conjecture is that the soliton becomes unstable, if this curve has a branch with negative slope. This conjecture is fully confirmed by our simulations for the perturbed NLSE. Moreover, this curve also yields a good estimate for the soliton lifetime: the soliton lives longer, the shorter the branch with negative slope is.Comment: 21 figure

Afectación ósea severa en reticulohistiosis multicéntrica, una enfermedad infrecuente: A propósito de un caso

La reticulohistiocitosis multicéntrica es una enfermedad muy infrecuente que afecta preferentemente a individuos de una edad media, y que se caracteriza por la aparición de nódulos diseminados en piel, mucosas, tejido subcutáneo y sinovial, xantomas, y afectación de pequeñas articulaciones de los dedos de las manos de apariencia similar a la artritis reumatoide, además de articulaciones de gran tamaño, principalmente hombros, caderas y rodillas, sobre las que sobreviene una artritis deformante y mutilante. Se presenta el caso de un varón de 55 años con afectación severa de hombros y caderas al que fue preciso recambiarle ambas articulaciones coxofemorales.Multicentric reticulohystiocytoses is a rare systemic disease which affects middle age patients, manifested by gradual development of nodules in the skin, mucosa, subcutaneous tissues and synovia, xantomas, and arthritis of the small joints of the hands, similar to reumathoid arthritis. Involvement of large joints as shoulders, hips and knee resulting in deforming and erosive arthritis. A case of a 55 year-old patient is presented, with severe destruction of shoulder and hips requiring bilateral total hip arthroplasty

Artefacts and <A2> power corrections : revisiting the MOM Z_psi and Z_V

We extract the power corrections due to the A^2 condensate in the overlap quark propagator (vector part of the inverse propagator Z_psi). The results are consistent with the previous gluon analysis. The role of artefacts is extensively discussed.Comment: 33 pages, 5 figure

Equilibrium tuned by a magnetic field in phase separated manganite

We present magnetic and transport measurements on La5/8-yPryCa3/8MnO3 with y = 0.3, a manganite compound exhibiting intrinsic multiphase coexistence of sub-micrometric ferromagnetic and antiferromagnetic charge ordered regions. Time relaxation effects between 60 and 120K, and the obtained magnetic and resistive viscosities, unveils the dynamic nature of the phase separated state. An experimental procedure based on the derivative of the time relaxation after the application and removal of a magnetic field enables the determination of the otherwise unreachable equilibrium state of the phase separated system. With this procedure the equilibrium phase fraction for zero field as a function of temperature is obtained. The presented results allow a correlation between the distance of the system to the equilibrium state and its relaxation behavior.Comment: 13 pages, 5 figures. Submited to Journal of Physics: Condensed Matte

Desenvolupament de models experimentals murins per a l'avaluació de la virulència i patogenicitat de soques d'Escherichia coli

Les infeccions urinàries constitueixen una de les infeccions bacterianes més freqüents tant en la comunitat com en l'àmbit hospitalari, que afecten dones sanes i pacients amb factors predisponents. Escherichia coli és sens dubte l'agent causal més freqüent d'aquestes infeccions. El qual també, s'ha constatat com a causant d'altres infeccions extraintestinals com ara colecistitis, peritonitis, meningitis i sèpsia. Paradoxalment, E. coli és el principal component de la flora facultativa comensal de l'intestí humà i altres animals. Basant-se en tècniques moleculars s'ha demostrat que aquesta espècie pot dividir-se principalment en quatre grups filogenètics principals: A, B1, B2 i D. S'ha pogut comprovar que les infeccions extraintestinals estan causades majoritàriament per soques del filogrup B2 i en menor proporció del D. D'altra banda s'ha pogut demostrar en diversos estudis experimentals i de correlació estadística, que les soques d'aquests filogrups associades a infecció porten amb més freqüència un conjunt de factors de virulència als que s'atribueixen les funcions patogèniques; com són les adhesines, els quelants de ferro, les toxines, les càpsules i d'altres. No obstant això, hi ha observacions que posen en qüestió aquestes troballes, com és el fet que amb certa freqüència soques dels filogrups A i B1, portadores d'escassos factors de virulència, causin infeccions urinàries i sèpsia en persones sanes. Això, i estudis específics per a cadascun d'aquest factors han qüestionat el seu valor patogènic; considerats de forma aïllada o col·lectivament. La forta correlació entre el filogrup i l'acció patògena podria indicar la presència de factors de virulència desconeguts i la importància de la seva associació. En aquest context, l'única manera de conèixer si una soca és capaç de fer infeccions extraintestinals i en particular infeccions urinàries, és avaluar-les en models experimentals, amb aquesta finalitat s'han descrit dos models in vivo. El primer d'ells, valora la capacitat de causar infecció generalitzada una vegada s'han sobrepassat les barreres naturals de l'hoste, i de permetre la disseminació del patogen al sistema circulatori i causant bacterièmia o septicèmia. Mentre que el segon model, d'infecció urinària ascendent, avalua el potencial virulent i patogen en el sistema urinari. I la capacitat del bacteri per ascendir des de la bufeta fins als ronyons quan no s'apliquen pautes terapèutiques per a contenir la infecció urinària de les vies baixes. Per tant, els principals objectius d'aquesta tesi doctoral han estat: i) determinar el grup filogenètic, els factors de virulència i altres característiques biològiques d'un grup de soques d'E. coli d'origen urinari i intestinal; amb la finalitat de seleccionar les soques utilitzades per als estudis amb els models experimentals in vivo; ii) estandarditzar dos models murins d'experimentació animal per a l'avaluació d'infeccions extraintestinals causades per E. coli i iii) avaluar el potencial virulent i patogen en els dos models murins de les soques d'E. coli prèviament seleccionades. El treball realitzat han permès incorporar en el grup de Microbiologia de l'Institut de Recerca Vall d'Hebron, dins del Servei de Microbiologia del Hospital Universitari Vall d'Hebron; dos models experimentals murins per a l'avaluació de la virulència i patogenicitat de soques d'E. coli. Així mateix, també ha permès la caracterització in vitro d'un grup de soques heterogènies, aportant les primeres proves de conceptes dels models. Els dos models murins estandarditzats i les dades aportades per aquesta tesi obren futures vies de treball com són: i) estudis de virulència de microorganismes causants de sèpsies o infecció urinària, ii) monitorització d'infeccions extraintestinals per a la determinació de la implicació específica de determinants de virulència mitjançant tecnologies d'expressió in vivo o assajos de competició de mutants, iii) avaluació de la eficàcia, la farmacocinètica i la farmacodinàmica de nous antimicrobianes, entre altres.Urinary tract infections are one of the most common bacterial infections in the community and in hospitals, affecting healthy women and patients with predisposing factors. Escherichia coli is certainly the most common casual agent of these infections, which also is the cause of other extraintestinal infections such as cholecystitis, peritonitis, meningitis and sepsis. Paradoxically, E. coli is the main component of facultative commensal flora of the human intestine and other animals. Using molecular techniques it has been proven that this specie can be divided into four main phylogenetic groups, named A, B1, B2 and D. The majority of the extraintestinal infections are caused by strains from phylogenetic group B2 and in a less extent by group D strains. Moreover, several experimental studies and statistical correlations have demonstrated that the strains associated to infections, present more often a set of virulence factors attributed to features such as pathogenic adhesins, iron chelates, toxins, and capsules, among others. However, some observations are calling into question these results; such as the fact that frequently strains from phylogenetic groups A and B1 (carriers of fewer virulence factors) cause urinary tract infections and sepsis in healthy people. Because of this result and other studies carried out for each of the virulence factors, the pathogenic value of the factors, singly and collectively, has been questioned. The strong correlation among the pathogenic action of phylogenetic groups may indicate the presence of unknown virulence factors and the importance of their relationship with extraintestinal infections. Taking into account the background, the only way to know if a strain is capable of producing extraintestinal infection and particularly urinary tract infection, is evaluating them using experimental models. For this purpose, two in vivo models were described. The first one recognizes the worth of the ability to cause widespread infection once the natural barriers of the host have been exceeded, allowing the spread of the pathogen into the circulatory system causing bacteremia or septicemia. Meanwhile, the ascending urinary infection model assesses the pathogenicity and the virulent potential of the strains in the urinary system, besides the capability of the bacteria to ascend from the bladder to the kidneys without any treatment to contain the lower urinary tract infection Therefore, the main objectives of this thesis were: i) to determine the phylogenetic group, virulence factors, and other biological characteristics of urinary and intestinal E. coli strains, in order to select the strains to be used for in vivo experimental studies ii) to standardize two murine models for the evaluation of extraintestinal infections caused by E. coli, and iii) to evaluate the pathogenicity and the virulent potential of previously selected E. coli strains in murins models. The work has allowed the incorporation of two experimental murine models for the evaluation of the virulence and the pathogenicity of Escherichia coli strains into the Microbiology group of Vall d'Hebron Institut de Recerca in the Microbiology department of Hospital Universitari Vall d'Hebron. Likewise, it has allowed the in vitro characterization of a heterogeneous group of strains, providing the first evidence of concepts of those models. The two standardized murine models and the data provided by this thesis open several lines for future work, such as: i) studying the virulence of microorganisms causing sepsis or urinary tract infection, ii) monitoring of extraintestinal infections to determine the specific involvement of certain virulence factors by means of in vivo expression technologies or mutants competition assays, and iii) evaluating the efficacy, pharmacokinetics and pharmacodynamics of new antimicrobials, among other studies

The No-Pole Condition in Landau gauge: Properties of the Gribov Ghost Form-Factor and a Constraint on the 2d Gluon Propagator

We study the Landau-gauge Gribov ghost form-factor sigma(p^2) for SU(N) Yang-Mills theories in the d-dimensional case. We find a qualitatively different behavior for d=3,4 w.r.t. d=2. In particular, considering any (sufficiently regular) gluon propagator D(p^2) and the one-loop-corrected ghost propagator G(p^2), we prove in the 2d case that sigma(p^2) blows up in the infrared limit p -> 0 as -D(0)\ln(p^2). Thus, for d=2, the no-pole condition \sigma(p^2) 0) can be satisfied only if D(0) = 0. On the contrary, in d=3 and 4, sigma(p^2) is finite also if D(0) > 0. The same results are obtained by evaluating G(p^2) explicitly at one loop, using fitting forms for D(p^2) that describe well the numerical data of D(p^2) in d=2,3,4 in the SU(2) case. These evaluations also show that, if one considers the coupling constant g^2 as a free parameter, G(p^2) admits a one-parameter family of behaviors (labelled by g^2), in agreement with Boucaud et al. In this case the condition sigma(0) <= 1 implies g^2 <= g^2_c, where g^2_c is a 'critical' value. Moreover, a free-like G(p^2) in the infrared limit is obtained for any value of g^2 < g^2_c, while for g^2 = g^2_c one finds an infrared-enhanced G(p^2). Finally, we analyze the Dyson-Schwinger equation (DSE) for sigma(p^2) and show that, for infrared-finite ghost-gluon vertices, one can bound sigma(p^2). Using these bounds we find again that only in the d=2 case does one need to impose D(0) = 0 in order to satisfy the no-pole condition. The d=2 result is also supported by an analysis of the DSE using a spectral representation for G(p^2). Thus, if the no-pole condition is imposed, solving the d=2 DSE cannot lead to a massive behavior for D(p^2). These results apply to any Gribov copy inside the so-called first Gribov horizon, i.e. the 2d result D(0) = 0 is not affected by Gribov noise. These findings are also in agreement with lattice data.Comment: 40 pages, 2 .eps figure