Física de la Materia Condensada

URI permanente para esta comunidadhttps://hdl.handle.net/11441/10868

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1,1,3,3-tetramethylguanidinium dihydrogenorthophosphate
(International Union of Crystallography, 2000) Criado Vega, Alberto; Diánez Millán, María Jesús; Pérez Garrido, Simeón; Fernandes, I. M L; Belsley, Michael Scott; Matos Gomes, Etelvina M. de; Universidad de Sevilla. Departamento de Física de la Materia Condensada; Comisión Interministerial de Ciencia y Tecnología (CICYT). España
In the title compound, C 5 H 14 N 3 + H 2 PO 4 ˇ , the cation has a central guanidinium fragment with a planar geometry, as expected for a central C sp 2 atom with a small charge delocalization along the three C–N bonds. The crystal packing is governed by hydrogen bonds so that the phosphate anions are linked head to tail, forming chains running parallel to the c direction. These chains in turn are interconnected by hydrogen bonds to intermediate tetramethylguanidinium cations forming hydrogen-bonded molecular layers stacked parallel to the bc crystal planes
(1E,3E)-4-(tetra-O-acetyl-D-arabino-tetritol-1-yl)-1-(4-tolyl)-1,2-diaza-1, 3-butadiene
(International Union of Crystallography, 2006) Diánez Millán, María Jesús; Estrada de Oya, María Dolores; Pérez Garrido, Simeón; Universidad de Sevilla. Departamento de Física de la Materia Condensada
n the title compound, C 21 H 26 N 2 O 8 , the configurations of the three chiral centres are known from the synthesis, corre- sponding to a d - arabino configuration. Both double bonds show the E configuration in the solid state. Packing of the molecules is governed by normal van der Waals contacts
A cellular automata model of a laser reproducing laser passive and active Q-Switching
(Elsevier, 2025-01) Jiménez-Morales, Francisco de Paula; Guisado Lizar, José Luis; Guerra, José Manuel; Universidad de Sevilla. Departamento de Física de la Materia Condensada; Universidad de Sevilla. Departamento de Arquitectura y Tecnología de Computadores; Ministerio de Ciencia, Innovación y Universidades (MICINN). España
The Q-switching (QS) phenomenon in lasers refers to the production of high intensity pulses by means of a saturable absorber (passive method) or by modifying the reflectivity or losses of the intracavity optics or mirrors (active method). Theoretically, the QS is studied through the laser rate equations which are useful to predict, at least qualitatively and roughly, the fundamental aspects of laser dynamics. However, specific details such as the spatial distribution of the intensity of the laser emission escape the simplicity of the rate equations. In this work we present a two dimensional cellular automata model (CA) to study the QS phenomenology for both the passive and the active method. To simulate the passive method we consider a spatial distribution of cells whose physical properties emulate those of the saturable adsorbers. And for the active method we introduce a periodic modulation of the lifetime of the photons inside the cavity. We have done numerous numerical simulations that show that despite the simplicity of the evolution rules, the AC model is capable of obtaining the main dynamics of operation of the laser by modifying the system parameters such as the pumping probability and the properties of the absorber.
A cellular automaton for the modeling of oscillations in a surface reaction
(AIP Publishing, 2004-08) Lemos Fernández, María del Carmen; Jiménez-Morales, Francisco de Paula; Universidad de Sevilla. Departamento de Física de la Materia Condensada; Ministerio de Ciencia y Tecnología (MCYT). España
The reaction of CO and O over a catalytic surface is studied with a cellular automata ~CA! model. We extend the CA model proposed by Mai and von Niessen @Phys. Rev. A 44 R6165 ~1991!# taking into account the variation of the temperature of the catalyst with the aim of analyzing the existence of oscillations in this reaction. The rate constants for different processes which govern the reaction are chosen in the Arrhenius form. Quasiperiodic, aperiodic, O-poisoned, and CO-poisoned regimes are observed depending on the temperature relaxation parameter. The results from the CA model presented are in agreement with several oscillatory behaviors which the catalyzed oxidation of CO exhibits.
A chronobiological evaluation of the risks of canceling Daylight Saving Time
(Taylor and Francis, 2022) Martín Olalla, José María; Universidad de Sevilla. Departamento de Física de la Materia Condensada; FQM-130
The long term impact of seasonal regulation of clocks (Daylight Saving Time) is analyzed showing that it helped to mitigate the advance of the phase of human activity during the 20th century and the exposition to the hours of the dawn winter. The increased risks induced by circadian misalignment around transition dates are balanced by a better alignment of social clocks to the natural day in summer and in winter. --- Se analiza el impacto a largo plazo de la regulación estacional de la hora mostrando que ayudó a minimizar el avance de la fase de la actividad humana durante el siglo XX y con ello la exposición a las horas de la madrugada en invierno. El mayores riesgos que induce el desalineamiento del ciclo circadiano alrededor de las fechas de los cambio de hora se ven compensados con una mejor alineación de los horarios sociales con el día invernal y estival.
A concise rebuttal on a concise proof of the equivalence of the Nernst theorem and the heat capacity statement of the third law of thermodynamics
(World Scientific Publishing, 2024-06-01) Martín Olalla, José María; Universidad de Sevilla. Departamento de Física de la Materia Condensada
The interplay between adiabatic cooling and isothermal ordering is analyzed to rebut the proof of the equivalence of the Nernst theorem and the heat capacity statement of the third law presented by Su and Chen.
A constant magnetocaloric response in FeMoCuB amorphous alloys with different FeB ratios
(AIP Publishing, 2007-05-04) Franco García, Victorino; Conde Amiano, Clara Francisca; Blázquez Gámez, Javier Sebastián; Conde Amiano, Alejandro; Švec, P.; Janičkovič, D.; Kiss, László Ferenc; Universidad de Sevilla. Departamento de Física de la Materia Condensada
The magnetocaloric effect of Fe91−xMo8Cu1Bx (x = 15 , 17 , 20) amorphous alloys has been studied. The temperature of the peak of magnetic entropy change can be tuned by altering the Fe / B ratio in pk pk the alloy, without changing its magnitude, ILlSM I. The average contribution of the Fe atoms to ILlSM I increases with increasing B content. This is correlated with the increase in the low temperature mean magnetic moment of Fe. A recently proposed master curve behavior for the magnetic entropy change is also followed by these alloys and is common for all of them.
A Corneal Biomechanical Study Measured with a Scheimpflug Dynamic Analyser in Soft Contact Lens Wearers
(MDPI, 2023) López Muñoz, Alfredo; López Castaño, Isabel; Torres Parejo, Úrsula; García Romera, Marta de la Concepción; Universidad de Sevilla. Departamento de Física de la Materia Condensada
The aim of this study was to evaluate the biomechanical changes in the cornea after wearing soft contact lenses (CLs) in healthy myopic patients measured with a Corvis ST® (CST, Oculus Optikgeräte GmbH, Wetzlar, Germany) analyser. This prospective, cross-sectional, single-centre study was performed on twenty-two Caucasian patients aged between 19 and 24 years (20.64 ± 1.21 years) range. Five device-specific biomechanical parameters, the central corneal thickness (CCT), and biomechanically corrected intraocular pressure (bIOP) were measured prior to fitting and one month after CL wear. Differences between the means of the deflection amplitude ratio (DA Ratio) and the standard deviation of the DA Ratio (SD DA Ratio) pre- and post-CL wear were found to be significant (p value = 0.002 in both cases). Significant differences were found between pre- and post-CL wear values in CCT (p value = 0.013). For all other biomechanical measures, no significant differences were observed before and after treatment. A significant association was found between changes in bIOP and classification according to changes in Int. Radius (p value = 0.047) and SSI (p value = 0.026) standard deviations. The corneal biomechanical indices provided by CST demonstrate that the fitting of soft CLs is a safe optical compensation method for the stability of corneal stiffness. No significant differences were found pre- and post-CL wear in the assessment of bIOP.
A Direct Extension of the Avrami Equation to Describe the Non-isothermal Crystallization of Al-base Alloys
(Elsevier, 2007) Blázquez Gámez, Javier Sebastián; Conde Amiano, Clara Francisca; Conde Amiano, Alejandro; Kulik, T.; Universidad de Sevilla. Departamento de Física de la Materia Condensada; European Commission (EC). Fondo Europeo de Desarrollo Regional (FEDER)
A direct extension of the Avrami equation considering the temperature dependence of the frequency factor is applied to describe the crystallization of a series of Al-Mm-Ni-Co amorphous alloys (Mm is a mischmetal). For high Al content, a nanocrystalline microstructure (fcc α-Al embedded in an amorphous matrix) is formed during the first crystallization process. However, for the alloy with 85 at.% of Al, the devitrification process consists of two strongly overlapped stages, which yield the formation of intermetallic metastable phase(s) without the detection of any amorphous residual matrix. Results are compared with those obtained using other kinetic approaches.
A Finemet-type alloy as a low-cost candidate for high-temperature magnetic refrigeration
(AIP Publishing, 2006) Franco García, Victorino; Blázquez Gámez, Javier Sebastián; Conde Amiano, Clara Francisca; Conde Amiano, Alejandro; Universidad de Sevilla. Departamento de Física de la Materia Condensada
The refrigerant capacity RC of Fe68.5Mo5Si13.5B9Cu1Nb3 alloy is studied. For the amorphous sample, RC=63 J kg−1 for an optimal reversible cycle with cold and hot ends at 328 K and 520 K, respectively, for a maximum applied field H=15 kOe. Nanocrystallization diminishes both the peak entropy change and RC of the material. Although the measured RC is smaller than for Gd5Ge1.9Si2Fe0.1 240 J kg−1 for H=50 kOe , the Mo-Finemet alloy is more than 20 times cheaper, the applied field employed is smaller, and the temperature span of the optimal cycle is increased. This makes this alloy a promising material for high-temperature refrigeration.
A first insight into the microstructure and crack propagation in novel boron nitride nanosheet/3YTZP composites
(Sociedad Española de Cerámica y Vidrio, 2021) Muñoz Ferreiro, Carmen; Morales Rodríguez, Ana; Gallardo López, Ángela María; Poyato Galán, Rosalía; Universidad de Sevilla. Departamento de Física de la Materia Condensada
In this work, novel 3mol% yttria tetragonal zirconia polycristalline (3YTZP) ceramic composites with boron nitride nanosheets (BNNS) are investigated for the first time. Highly densified composites with 1 and 4vol% BNNS were obtained by spark plasma sintering (SPS) after BNNS synthesis using a solution exfoliation method and BNNS dispersion into the ceramic powder by ultrasonication. The BNNS presented homogeneous distribution throughout the ceramic matrix and preferential alignment in the plane perpendicular to the pressing axis during SPS. The BNNS incorporation had practically no effect on the Vickers hardness of the material nor on the Young's modulus. Anisotropy in crack development was found in the composite with 4%vol BNNS, together with a mechanism of extensive microcracking. Several energy-absorbing mechanisms during crack propagation, such as crack deflection, crack bridging, crack branching, BNNS pull-out and BNNS debonding, were identified in the composites by a close observation of the indentation-induced fracture paths.
A Genetic Algorithm to Study a P3 Non-trivial Collective Task
(INSTICC, Institute for Systems and Technologies of Information Control and Communication, 2012) Jiménez-Morales, Francisco de Paula; Guisado Lizar, José Luis; Universidad de Sevilla. Departamento de Arquitectura y Tecnología de Computadores; Universidad de Sevilla. Departamento de Física de la Materia Condensada
Here we report new results of a genetic algorithm (GA) used to evolve one dimensional Cellular Automata (CA) to perform a P3 non-trivial collective behavior task. For this task the goal is to find a CA rule that reaches one final configuration in which the concentration of active cells oscillates among three different values. Though the majority of the best evolved rules belong to the II Wolfram’s class, the GA also finds rules of the III and IV classes. The different computational mechanisms used by each rule to synchronize the entire lattice are analyzed by means of the spatio-temporal patterns generated.
A Hh-driven gene network controls specification, pattern and size of the Drosophila simple eyes
(Company of Biologists Ltd, 2013) Aguilar Hidalgo, Daniel; Domínguez Cejudo, María Ángeles; Amore, Gabriele; Brockman, Anette; Lemos Fernández, María del Carmen; Córdoba Zurita, Antonio; Casares Fernández, Luis Fernando; Universidad de Sevilla. Departamento de Física de la Materia Condensada; Ministerio de Ciencia e Innovación (MICIN). España; Junta de Andalucía
During development, extracellular signaling molecules interact with intracellular gene networks to control the specification, pattern and size of organs. One such signaling molecule is Hedgehog (Hh). Hh is known to act as a morphogen, instructing different fates depending on the distance to its source. However, how Hh, when signaling across a cell field, impacts organ-specific transcriptional networks is still poorly understood. Here, we investigate this issue during the development of the Drosophila ocellar complex. The development of this sensory structure, which is composed of three simple eyes (or ocelli) located at the vertices of a triangular patch of cuticle on the dorsal head, depends on Hh signaling and on the definition of three domains: two areas of eya and so expression - the prospective anterior and posterior ocelli - and the intervening interocellar domain. Our results highlight the role of the homeodomain transcription factor engrailed (en) both as a target and as a transcriptional repressor of hh signaling in the prospective interocellar region. Furthermore, we identify a requirement for the Notch pathway in the establishment of en maintenance in a Hh-independent manner. Therefore, hh signals transiently during the specification of the interocellar domain, with en being required here for hh signaling attenuation. Computational analysis further suggests that this network design confers robustness to signaling noise and constrains phenotypic variation. In summary, using genetics and modeling we have expanded the ocellar gene network to explain how the interaction between the Hh gradient and this gene network results in the generation of stable mutually exclusive gene expression domains. In addition, we discuss some general implications our model may have in some Hh-driven gene networks.
A New Method for Determining the Curie Temperature From Magnetocaloric Measurements
(Institute of Electrical and Electronics Engineers, 2016) Moreno Ramírez, Luis Miguel; Blázquez Gámez, Javier Sebastián; Franco García, Victorino; Conde Amiano, Alejandro; Marsilius, Mie; Budinsky, Viktoria; Herzer, Giselher; Universidad de Sevilla. Departamento de Física de la Materia Condensada; Ministerio de Economía y Competitividad (MINECO). España
A new method is proposed for determining the Curie temperature from magnetocaloric measurements. It is based on the field dependence of the magnetic entropy change close to the Curie temperature. The main advantages over other methods are that the obtained temperature is field independent, and the process is noniterative and does not require a fitting procedure nor prior knowledge of the critical exponents of the transition. The reliability of the method is demonstrated using both simulated and experimental data for pure Ni and an Fe-based amorphous alloy.
A New Surgical Technique to Deliver Riboflavin Beneath Corneal Epithelium: The Corneal Cross-Linking Epi-Pocket
(Wolters Kluwer, 2021) Borroni, Davide; Bonzano, Chiara; Hristova, Rozaliya; Sánchez González, José María; Pennisi, Flavia; Rocha Bogas, Aurelio; Rocha de Lossada, Carlos; Universidad de Sevilla. Departamento de Física de la Materia Condensada
Purpose: To describe a new technique to deliver riboflavin into the corneal stroma during Corneal Cross-Linking (CXL) without the removal of corneal epithelium. Methods: Keratoconus patients underwent CXL for progressive keratoconus. Riboflavin was delivered by manually creating an epithelial pocket (CXL Epi-Pocket). Verbal rating scale was recorded postoperatively. Best-corrected visual acuity, keratometric indices, corneal thickness and corneal densitometry were recorded at baseline and at 12-month follow-up. Results: Eighteen eyes of 18 patients were included in the study. At a 12-month follow-up, best-corrected visual acuity, K1, K2 and densitometry values were stable. Maximum keratometry (Kmax) reduced from 55.31 ± 6.21 (SD) to 52.34d ± 4.12d (SD) (P value = 0.032). the thinnest point went from 441 ± 21.18 (SD) to 425.4 ± 19.02 (SD) um (P value = 0.041). The verbal rating scale at 1, 2 and 3 days postoperatively were 1.76 ± 0.19 (SD), 1.02 ± 0.51 (SD) and 0.28 ± 0.14 (SD). Conclusions: CXL Epi-Pocket is able to deliver riboflavin to halt the progression of keratoconus at a 12-month follow-up.
A phenomenological fitting curve for the magnetocaloric effect of materials with a second-order phase transition
(AIP Publishing, 2008-06-02) Dong, Q. Y.; Zhang, H. W.; Sun. J. R.; Shen, B. G.; Franco García, Victorino; Universidad de Sevilla. Departamento de Física de la Materia Condensada
The magnetic entropy change of polycrystalline samples Gd, La(Fe0.92Co0.08)11.83Al1.17, LaFe10.8Si2.2, Mn5Ge2.7Ga0.3, Nd2AlFe13Mn3, and TbCo2 with a second-order phase transition has been investigated. A uniform phenomenological function that describes the magnetic entropy change is found for these materials. This could be of great benefit for the design of magnetic refrigerators. The field dependence of the critical exponent for the variation in the maximum entropy change with field is studied. The critical exponent value of 2/3, which is predicted by the mean field theory, is only satisfied for moderate field values. The refrigerant capacity is analyzed and compared to the predictions of the fitting function.
A practical Analysis for Decelerated Growth Processes to Get Physically Meaningful Kinetic Parameters from Classical Nucleation and Growth Theory Despite of Overgrowth
(Elsevier, 2023) Blázquez Gámez, Javier Sebastián; Caballero Flores, Rafael; Manchón Gordón, A. F.; Borrego Moro, Josefa María; Conde Amiano, Clara Francisca; Universidad de Sevilla. Departamento de Física de la Materia Condensada; Junta de Andalucía
We have analyzed the overgrowth problem arising in decelerated growth processes of spherical crystals in the frame of classical nucleation and growth theory developed by Kolmogorov, Johnson and Mehl, and Avrami (KJMA). To do that, simulations of decelerated growth transformations with a constant nucleation rate have been performed, changing the linear growth rate of spherically shaped nuclei from null (instantaneous growth rate) to constant (characteristic of interface controlled growth processes). We propose the determination of the actual kinetic parameters through the analysis of the inflection point of time evolution of transformed fraction. The correlations found between the effective kinetic parameters from direct KJMA analysis and the actual ones make it possible obtaining physically meaningful parameters. The proposed analysis has been applied to the nanocrystallization of amorphous FINEMET-type compositions.
A procedure to extract the magnetocaloric parameters of the single phases from experimental data of a multiphase system.
(AIP Publishing, 2014) Ipus Bados, Jhon Jairo; Moreno Ramírez, Luis Miguel; Blázquez Gámez, Javier Sebastián; Franco García, Victorino; Conde Amiano, Alejandro; Universidad de Sevilla. Departamento de Física de la Materia Condensada
In this work, we propose a method to extract the individual parameters that describe the field dependence of magnetic entropy change of each phase in a multiphase system. This method makes use of the scaling laws of the magnetocaloric effect and can help us to determine the behavior of individual phases and to predict their critical exponents. The accuracy of the procedure is illustrated applying it to ball milled powders, in which an amorphous phase with T C around room temperature coexists with bcc-Fe type crystallites. The obtained values are in good agreement with those reported in the literature for single phase systems. The proposed method could be applied to other systems where single phase materials cannot be easily obtained in order to characterize the effect of impurities.
A procedure to obtain the parameters of Curie temperature distribution from thermomagnetic and magnetocaloric data
(Elsevier, 2019) Manchón Gordón, Alejandro F.; Moreno Ramírez, Luis Miguel; Ipus Bados, Jhon Jairo; Blázquez Gámez, Javier Sebastián; Conde Amiano, Clara Francisca; Franco García, Victorino; Conde Amiano, Alejandro; Universidad de Sevilla. Departamento de Física de la Materia Condensada; Agencia Estatal de Investigación. España; European Union (UE)
We propose a procedure for the determination of the parameters of the Curie temperature distribution (TCD)in a compositionally inhomogeneous ferromagnetic material. Assuming a Gaussian TCD and using a mean field approach based on the Brillouin function, we report that with respect to the average value of the distribution: a)both inflection point of magnetization, Tinf, and temperature at maximum magnetic entropy change curves, Tpk MCE, shift to lower temperatures and b)temperature at maximum paramagnetic susceptibility, Tpk χ, shifts to higher temperatures. Using these evolutions as a function of the TCD broadening and fitting them to a second order polynomial function, a self-consistent procedure to determine the parameters of the distribution is supplied. These predictions have been experimentally tested for a ball milled Fe70Zr30 amorphous alloy using thermomagnetic and magnetocaloric measurements. The obtained parameters using the proposed procedure agree with those directly measured using Mössbauer spectrometry.
A quantitative criterion for determining the order of magnetic phase transitions using the magnetocaloric effect
(Nature Publishing Group, 2018) Law, Jia Yan; Franco García, Victorino; Moreno Ramírez, Luis Miguel; Conde Amiano, Alejandro; Karpenkov, Dmitriy Y.; Radulov, Iliya; Skokov, Konstantin P.; Gutfleisch, Oliver; Universidad de Sevilla. Departamento de Física de la Materia Condensada; Ministerio de Economía y Competitividad (MINECO). España; European Commission (EC). Fondo Europeo de Desarrollo Regional (FEDER)
The ideal magnetocaloric material would lay at the borderline of a first-order and a second-order phase transition. Hence, it is crucial to unambiguously determine the order of phase transitions for both applied magnetocaloric research as well as the characterization of other phase change materials. Although Ehrenfest provided a conceptually simple definition of the order of a phase transition, the known techniques for its determination based on magnetic measurements either provide erroneous results for specific cases or require extensive data analysis that depends on subjective appreciations of qualitative features of the data. Here we report a quantitative fingerprint of first-order thermomagnetic phase transitions: the exponent n from field dependence of magnetic entropy change presents a maximum of n > 2 only for first-order thermomagnetic phase transitions. This model-independent parameter allows evaluating the order of phase transition without any subjective interpretations, as we show for different types of materials and for the Bean–Rodbell model.

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