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Dive into the research topics where Francisco Montero de Espinosa is active.

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Featured researches published by Francisco Montero de Espinosa.


Applied Physics Letters | 2015

Direct fabrication of thin layer MoS2 field-effect nanoscale transistors by oxidation scanning probe lithography

Francisco Montero de Espinosa; Y. K. Ryu; Kolyo Marinov; Dumitru Dumcenco; Andras Kis; Ricardo Garcia

Thin layer MoS2-based field effect transistors (FET) are emerging candidates to fabricate very fast and sensitive devices. Here, we demonstrate a method to fabricate very narrow transistor channel widths on a single layer MoS2 flake connected to gold electrodes. Oxidation scanning probe lithography is applied to pattern insulating barriers on the flake. The process narrows the electron path to about 200 nm. The output and transfer characteristics of the fabricated FET show a behavior that is consistent with the minimum channel width of the device. The method relies on the direct and local chemical modification of MoS2. The straightforward character and the lack of specific requirements envisage the controlled patterning of sub-100 nm electron channels in MoS2 FETs.


Bioprocess and Biosystems Engineering | 2009

On-line ultrasonic velocity monitoring of alcoholic fermentation kinetics

Pablo Resa; Luis Elvira; Francisco Montero de Espinosa; Ramón González; José María Barcenilla

In this work, fundamental aspects on the ultrasonic velocity monitoring of alcoholic fermentations in synthetic broths (glucose, fructose and sucrose) and natural media (must and wort) are reported. Results are explained in terms of monosaccharide catabolism, polysaccharide hydrolysis, gas production and microorganism growth. The effect of each one of these subprocesses upon ultrasonic velocity has been independently studied. It is shown that, regarding the sound propagation, the simplest systems behave as ternary dissolutions of sugar and ethanol in water, where, in the course of time, substrates are transformed into metabolites according to the fermentation reaction. A semi-empirical approach, based on the excess volume concept and the density and velocity measurements of binary mixtures, has been used to calculate these magnitudes in the ternary mixtures and to obtain the concentrations of the main solutes throughout the fermentations, reaching a good correlation (especially for the media of simplest composition). In all the processes analyzed, the data obtained from the ultrasonic measurements followed the changes caused by the yeast metabolism, asserting the potential of mechanical waves to monitor fermentations and, in general, biotechnological processes.


IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control | 2011

Shear resonance mode decoupling to determine the characteristic matrix of piezoceramics for 3-D modeling

L. Pardo; Álvaro López García; Francisco Montero de Espinosa; Klaus Brebøl

The determination of the characteristic frequencies of an electromechanical resonance does not provide enough data to obtain the material properties of piezoceramics, including all losses, from complex impedance measurements. Values of impedance around resonance and antiresonance frequencies are also required to calculate the material losses. Uncoupled resonances are needed for this purpose. The shear plates used for the material characterization present unavoidable mode coupling of the shear mode and other modes of the plate. A study of the evolution of the complex material coefficients as the coupling of modes evolves with the change in the aspect ratio (lateral dimension/thickness) of the plate is presented here. These are obtained using software. A soft commercial PZT ceramic was used in this study and several shear plates amenable to material characterization were obtained in the range of aspect ratios below 15. The validity of the material properties for 3-D modeling of piezoceramics is assessed by means of finite element analysis, which shows that uncoupled resonances are virtually pure thickness-driven shear modes.


IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control | 2010

Damage characterization using guided- wave linear arrays and image compounding techniques

Ricardo Tokio Higuti; Óscar Martínez-Graullera; Carlos J. Martín; A. Octavio; Luis Elvira; Francisco Montero de Espinosa

In this work, a high-resolution imaging method for the inspection of isotropic plate-like structures using linear arrays and Lamb waves is proposed. The evaluation of these components is limited by the low dynamic range resulting from main lobe and side lobe field patterns, and from the narrowband nature of the Lamb waves. Based on a full matrix array, synthetic aperture technique using all emitter-receiver combinations, different images from the same object are obtained by using different apodization coefficients, which are related to a trade-off between main lobe width and relative side lobe level. Several image compounding strategies have been tested and a new algorithm, based on apodization and polarity diversities between signals, is proposed. However, some effects, such as the dead zone close to the array and reverberations caused by interactions of the wavefront and defects, still limit the quality of the images. The use of spatial diversity, obtained by an additional array, introduces complementary information about the defects and improves the results of the proposed algorithm, producing high-resolution, high-contrast images. Experimental results are shown for a 1-mm-thick isotropic aluminum plate with artificial defects using linear arrays formed by 30 piezoelectric elements, with the low dispersion symmetric mode S0 at the frequency of 330 kHz.


Journal of Rheology | 2014

Two-step yielding in magnetorheology

J. C. Fernández-Toledano; Jaime Rodríguez-López; Keshvad Shahrivar; R. Hidalgo-Álvarez; Luis Elvira; Francisco Montero de Espinosa; Juan de Vicente

We use particle level dynamic simulations, ultrasonic characterization, and rheomicroscopy to investigate the yielding behavior of magnetorheological (MR) fluids under oscillatory shear in both dilute and concentrated regimes. Dilute suspensions exhibit a single peak in the elastic stress that is associated to the breaking of the field-induced structures at the flow point (G′ = G″). On the other hand, more concentrated suspensions demonstrate a two-step yielding that is associated to the existence of short-ranged attractions between the particles, possibly coming from remnant magnetization or van der Waals forces. This two-step yielding is demonstrated by introducing additives in the formulation of the MR fluids and performing particle level simulations that include R-shifted Lennard-Jones potentials of interaction.


Applied Physics Letters | 2015

Non-contact optoacoustic imaging with focused air-coupled transducers

X. Luís Deán-Ben; Genny A. Pang; Francisco Montero de Espinosa; Daniel Razansky

Non-contact optoacoustic imaging employing raster-scanning of a spherically focused air-coupled ultrasound transducer is showcased herein. Optoacoustic excitation with laser fluence within the maximal permissible human exposure limits in the visible and near-infrared spectra is applied to objects with characteristic dimensions smaller than 1 mm and absorption properties representative of the whole blood at near-infrared wavelengths, and these signals are shown to be detectable without contact to the sample using an air-coupled transducer with reasonable signal averaging. Optoacoustic images of vessel-mimicking tubes embedded in an agar phantom captured with this non-contact sensing technique are also showcased. These initial results indicate that an air-coupled ultrasound detection approach can be suitable for non-contact biomedical imaging with optoacoustics.


Journal of the Acoustical Society of America | 1997

Characterization of porous piezoelectric ceramics: The length expander case

Tomás Gómez Álvarez-Arenas; Francisco Montero de Espinosa

Porous piezoelectric ceramics and 0–3/3–3 connectivity piezoelectric composites are normally characterized following the Standards on Piezoelectricity. Nevertheless, these materials are not homogeneous and losses are significant. New constitutive and wave equations have been obtained recently for these kind of materials. The objective of this paper is to derive new definitions for the electromechanical coupling coefficients and a suitable characterization procedure according to the new constitutive and wave equations previously mentioned. In particular, the case of the length expander bar mode is analyzed in detail. The study of resonant elements requires the use of suitable boundary conditions. In this case the boundary conditions are borrowed from the theory of poroelasticity and extended for a piezoelectric material. Finally the procedure is applied to characterize a commercial porous piezoelectric ceramic.


Analytical Biochemistry | 2009

Ultrasonic velocity assay of extracellular invertase in living yeasts.

Pablo Resa; Luis Elvira; Carlos Sierra; Francisco Montero de Espinosa

The use of a low-intensity ultrasonic technique (noninvasive, nondestructive, on-line, and able to assess opaque samples) to monitor the kinetics of invertase hydrolysis is presented. Adiabatic compressibility has been shown to be sensitive to sugar species: ultrasonic velocity increasing as saccharose is transformed into glucose and fructose. The influence of initial sucrose mass concentration (2-60%), temperature (25-55 degrees C), pH (3.5-6.5), and number of microorganisms (10(5)-10(9) yeasts/ml) on the reaction rate, catalyzed by the extracellular invertases of intact Saccharomyces cerevisiae cells, has been measured. The results were proven to be in strict agreement with the optimal kinetic parameters of the enzyme. Ultrasonic velocity variations are explained in terms of changes of the solute concentrations in the mixture water-saccharose-glucose/fructose and calculated from the velocity of ultrasound in the corresponding pure sugar solutions. A linear relationship between the initial rate of ultrasonic velocity and the number of yeasts (enzymes) is pointed out.


Ultrasonics | 2012

Air-coupled MUMPs capacitive micromachined ultrasonic transducers with resonant cavities.

Alberto Octavio Manzanares; Francisco Montero de Espinosa

This work reports performance improvements of air-coupled capacitive micromachined ultrasonic transducers (CMUTs) using resonant cavities. In order to perform this work, we have designed and manufactured a CMUT employing multi-user microelectromechanical systems (MEMS) processes (MUMPs). The transducer was designed using Helmholtz resonator principles. This was characterised by the dimensions of the cavity and several acoustic ports, which had the form of holes in the CMUT plate. The MUMPs process has the advantage of being low cost which allows the manufacture of economic prototypes. In this paper we show the effects of the resonant cavities and acoustic ports in CMUTs using laser Doppler vibrometry and acoustical measurements. We also use Finite Element (FE) simulations in order to support experimental measurements. The results show that it is possible to enhance the output pressure and bandwidth in air by tuning the resonance frequency of the plate (f(p)) with that of the Helmholtz resonator (f(H)). The experimental measurements show the plate resonance along with an additional resonance in the output pressure spectrum. This appears due to the effect of the new resonant cavities in the transducer. FE simulations show an increase of 11 dB in the output pressure with respect to that of a theoretical vacuum-sealed cavity MUMPs CMUT by properly tuning the transducer. The bandwidth has been also analyzed by calculating the mechanical Q factor of the tuned CMUT. This has been estimated as 4.5 compared with 7.75 for the vacuum-sealed cavity MUMPs CMUT.


Cells Tissues Organs | 1980

New contribution on the oesophageal mucous innervation in certain monkeys (Cercopithecidae)

José A. Rodrigo; Elías M. Robles Chillida; Francisco Montero de Espinosa; Javier De Felipe; Carlos J. Hernandez; Antonio Arnedo; Isabel Mayo

Spindle-shaped, barrel-like, or bush-like corpuscular neural structures situated in the mucous epithelium of the upper third of the oesophagus are described. These structures are not homogeneously distributed in this area. Some are very close to the pharyngooesophageal sphincter, spanning the thickness of the epithelium and communicating with the basal membrane by means of a thin pedicle and with the lumen by a small hilus or pore, their morphology being that of a taste bud. The others are situated deeper in the mucous epithelium of the upper third, communicating with the basal membrane only by means of either a thin pedicle or a thicker one, and separated from the lumen by a thick layer of epithelial cells. The bush-like apparatuses lie closely adjacent to the basal membrane of the epithelium.

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Luis Elvira

Spanish National Research Council

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Jaime Rodríguez-López

Spanish National Research Council

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Pablo Resa

Spanish National Research Council

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Elvira Iglesias

Spanish National Research Council

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Juan Ramón Maestre

Spanish National Research Council

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L. Gomez-Ullate

Spanish National Research Council

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O. Martinez

Spanish National Research Council

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Pedro Castro

Spanish National Research Council

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