Papers by Monica Vélez Tobarias
In this paper we study semilinear sets over arbitrary ordered flelds. In particular we show that ... more In this paper we study semilinear sets over arbitrary ordered flelds. In particular we show that open (resp. closed) semilinear sets are convex if and only if they are basic, that is, a flnite intersection of open (resp. closed) halfspaces. As a corollary we get that any bounded convex closed semilinear set is the convex hull of a flnite family
Convex polytopes over ordered fields
ACM SIGSAM Bulletin, 1999
... tional power series with exponents lying in strongly convex polyhedral cones given by admissi... more ... tional power series with exponents lying in strongly convex polyhedral cones given by admissible edges of the Newton polyhedron of ... WV Vasconcelos vas conce~math, rutgers, edu Department of Mathematics, Rutgers University Hill Center for the Mathematical Sciences 110 ...
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures Processing, Measurement, and Phenomena, 1998
Silicon oxynitride thin films have been deposited using remote plasma chemical vapor deposition f... more Silicon oxynitride thin films have been deposited using remote plasma chemical vapor deposition from SiCl4+NH3+O2 gas mixtures. The stoichiometry of the deposited films varies from that corresponding to the silicon oxide to a stoichiometry very close to silicon nitride when the NH3/O2 gas ratio is changed in the plasma. The approximate compositions of the films were determined by Rutherford backscattering spectroscopy and nuclear reaction analysis, and the local bonding arrangements were determined by infrared spectroscopy. Analysis of metal–insulator–semiconductor devices under the effect of and external sinusoidal electric field (dielectric spectrometry) indicates the presence of traps centers in the Si–SiO2 interface. Correlations between the local bonded structures in the oxynitride and the conduction and polarization processes detected in the films are also discussed.
2010 IEEE International Symposium on Broadband Multimedia Systems and Broadcasting (BMSB), 2010
This paper presents the design of a DVB-T2 modulator algorithm supporting multiple PLP and auxili... more This paper presents the design of a DVB-T2 modulator algorithm supporting multiple PLP and auxiliary streams. The algorithm works over an asynchronous modulator design, presenting per stream scheduling policies, T2 Frames capacity management, and DFL computation. A software tool was developed in order to create system configurations, validate input parameters, and manage per stream capacity distribution, according to proposed scheduling policies.
Sky wave interfering signals evaluation for digital local broadcasting services in the 11 meter band
A characterization of the potential long distance sky wave interferences between DRM local servic... more A characterization of the potential long distance sky wave interferences between DRM local services in the 26 MHz band is presented in this paper. To do this, a statistical analysis of the ionospheric conditions that cause such electromagnetical impairments has been done in order to contribute to the ITU-R Question 127/6 concerning the use of digital modulation in the 26
2010 IEEE International Instrumentation & Measurement Technology Conference - I2MTC 2010, 2010
This paper presents a methodology for efficient measurement of digital broadcasting signals, both... more This paper presents a methodology for efficient measurement of digital broadcasting signals, both with field trials or at the laboratory. The study is focused on measuring the C/N requirement for achieving a threshold BER. A comparison between the traditional techniques and the proposed methodology is analyzed in this work. The key of the methodology presented in this paper is the use of general purpose equipment such as a vector signal analyzer for recording baseband IQ samples.
HDTV field trials using DVB-T and DVB-T2 broadcasting systems
2010 IEEE International Symposium on Broadband Multimedia Systems and Broadcasting (BMSB 2010), 2010
AbstractThis paper presents the first field trials carried out in Spain to test HDTV reception u... more AbstractThis paper presents the first field trials carried out in Spain to test HDTV reception using DVB-T and DVB-T2 systems. High definition and standard definition digital television contents and services were multiplexed and broadcasted from a terrestrial transmitter. The aim of ...
Journal of Applied Physics, 2004
The mechanisms controlling the growth rate and composition of epitaxial CdTe and Cd 1-x Zn x Te f... more The mechanisms controlling the growth rate and composition of epitaxial CdTe and Cd 1-x Zn x Te films were studied. The films were grown by isothermal closed space configuration technique. A GaAs(100) substrate was exposed sequentially to the elemental sources (Zn, Te, and Cd) in isothermal conditions. While growth of ZnTe followed an atomic layer epitaxy (ALE) regime [self-regulated at one monolayer (ML) per cycle]; the CdTe films revealed different growth rates in dependence of the growth parameters (exposure and purge times). Combination of short purge times and larger Cd exposure times led to not self-regulated growth regime for CdTe. This is ascribed to large Cd coverages that were dependent on Cd exposure times (following a Brunauer-Emmett and Teller-type adsorption). However, for longer purge times and/or short Cd exposure times, an ALE self-regulated regime was achieved with 2 ML/ cycle. In this sense, the self-regulation of the growth is limited by desorption, instead of absorption, as in the traditional growth technique. Cd atoms substitution by Zn atoms and subsequent evaporation of surface Cd atoms during Zn exposure has been proved. The influence of these facts on the growth and composition of the alloy is discussed.
Néel wall pinning on amorphous CoxSi1−x and CoyZr1−y films with arrays of antidots in the diluted regime
Journal of Applied Physics, 2006
The magnetization reversal process has been studied in amorphous magnetic films patterned with or... more The magnetization reversal process has been studied in amorphous magnetic films patterned with ordered arrays of antidots in the diluted limit (i.e., with small enough antidot density so that the original film anisotropy is maintained and the flux closure structures around each dot are independent from each other). The role of the material parameters in the final behavior has been analyzed comparing the results on films made of two different Co-based amorphous alloys, CoxSi1−x and CoyZr1−y, that present a similar intrinsic uniaxial anisotropy but have a different saturation magnetization. The patterned holes are found to act as weak pinning centers for the motion of the Néel walls involved in the reversal process which results in an enhancement of coercivity in certain angular ranges. However, they are only effective in the material with the lower saturation magnetization (CoxSi1−x) which can be related with the different relative sizes of the patterned holes and the Néel walls in e...
Journal of Applied Physics, 2000
Amorphous FexSi1−x films have been prepared on Si substrates in order to fabricate submicrometric... more Amorphous FexSi1−x films have been prepared on Si substrates in order to fabricate submicrometric magnetic structures with soft magnetic behavior. The magnetic properties compositional dependence of the unpatterned samples has been analyzed to select the Fe content (x=0.7) with the lowest coercive and anisotropy fields values. Arrays of Fe0.7Si0.3 lines have been fabricated by electron beam lithography combined with a liftoff technique, with typical dimensions of 200 nm linewidth and 1 μm line spacing. These arrays present coercive fields parallel to the line direction as small as 9 Oe.
Journal of Applied Physics, 2007
Nanohole arrays in Ni films have been prepared by a replica/antireplica method based on anodic al... more Nanohole arrays in Ni films have been prepared by a replica/antireplica method based on anodic alumina membranes. The nanohole arrays exhibited long range ordering with hexagonal symmetry, the hole distance was kept constant (105nm), and the hole diameter and the film thickness were varied between 50 and 70nm and 55 and 600nm, respectively. The magnetic domain structures of such samples have been studied by analyzing magnetic force microscopy images at remanent state. Different domain structures have been observed depending on the geometrical characteristics of the films. The experimental results have been interpreted with the help of micromagnetic simulations.
Journal of Applied Physics, 2012
Nd-Co amorphous magnetic films with perpendicular magnetic anisotropy have been grown on nanostru... more Nd-Co amorphous magnetic films with perpendicular magnetic anisotropy have been grown on nanostructured templates prepared with self-organized di-block poly(styrene)-block-poly(4-vinylpyridine) copolymer layers with a periodic structure of 60 nm spaced pores. These templates modify both the magnetic film topography and mechanical strain on a local scale. The effect of these structural changes is particularly noticeable in the low thickness range of the magnetic films where the transition from in-plane to out-of plane magnetization takes place. The Nd-Co films grown on the copolymer template present lower perpendicular magnetic anisotropy and, also, stronger stripe domain pinning effects in comparison with reference films grown on flat Si substrates.
Journal of Applied Physics, 2009
Shifted hysteresis loops characteristic of the exchange bias effect between a ferromagnet and an ... more Shifted hysteresis loops characteristic of the exchange bias effect between a ferromagnet and an antiferromagnet are demonstrated in structures formed by a 2.5 nm Cr layer deposited on top of an array of Fe nanoislands (Cr/Fe-nanoislands). This effect evidences the persistence of antiferromagnetic (AF) order for Cr layers much thinner than the thickness reported in the literature. The field shift measured is found to increase for the smallest island sizes, which can be related with the enhancement of the Fe-nanoisland surface to volume ratio. The comparative study between superconducting proximity effects in Nb/Cr/Fe-nanoislands and Nb/normal metal/Fe-nanoisland hybrids (where the normal metals used are Al and Pt) confirms the presence of AF order in the 2.5 nm Cr spacer layer. A much shorter penetration depth of the Cooper pairs into the AF Cr layers than in the normal metal Pt and Al spacer layers is deduced.
Electronics Letters, 2011
This letter presents the C/N requirements for DVB-T2 fixed reception. Results have been obtained ... more This letter presents the C/N requirements for DVB-T2 fixed reception. Results have been obtained from field trials carried out to test DVB-T2 performance, considering outdoor rooftop antenna scenario. Two commercial receivers have been used to obtain C/N threshold values for image error-free condition. The tested configuration modes are the ones recommended for this scenario: 32K FFT and 64 and 256 QAM constellations. DVB-T has also been measured in order to obtain direct comparison between both systems. Introduction: In 2009 a new standard for Digital Terrestrial Television (DTT), named DVB-T2, was published by the ETSI [1]. The use of DVB-T2 to carry out HDTV services for rooftop reception is suggested in DVB-T2 Implementation Guidelines [2], so this scenario was chosen to be tested during the field trials. The aim of this study is to provide broadcasters with real C/N threshold values that can be used for the first network developments and to help choosing the correct system configuration options that provide the required data rate with the lowest C/N requirement. This study could be very useful, as no field trial results have been published until now and at this moment some countries have just adopted this new standard and many others are deciding what DTT standard they adopt, so having values for real reception conditions could be a key factor when taking the decision. At the time of the measurement campaign (June and July, 2010) no professional receivers with BER measurement capabilities were available. Two commercial DVB-T2 receivers were used instead; a TV Set and a Set-Top Box (STB).
Critical currents and pinning forces in a-axis oriented EuBa2Cu3O7/PrBa2Cu3O7 superlattices
Applied Physics Letters, 1995
a-axis oriented EuBa2Cu3O7/PrBa2Cu3O7 (EBCO/PBCO) superlattices have been grown by dc sputtering.... more a-axis oriented EuBa2Cu3O7/PrBa2Cu3O7 (EBCO/PBCO) superlattices have been grown by dc sputtering. The critical current (JC) behavior is modified by the pinning force arising from the insulating PrBa2Cu3O7 layers, which in a-axis oriented superlattices are perpendicular to the Cu–O planes. Depending on the EBCO and PBCO layer thicknesses the pinning forces deviate from the usual scaling laws as a function of temperature observed in single films. When B is perpendicular to the sample, an exponential dependence of JC(B) appears as the PBCO thickness is increased (coupling is reduced), and also as the thickness of the EBCO layer is reduced.
Applied Physics Letters, 2007
Ni nanohole arrays are prepared by a replication process involving sputtering, polymer molding pr... more Ni nanohole arrays are prepared by a replication process involving sputtering, polymer molding pressing, and electroplating techniques, using anodic alumina membranes as templates. Nanohole diameter to interhole distance ratio is engineered by suitable template processing. From the analysis of the magnetization curves for increasing nanohole diameter, it is concluded that coercivity increases due to the pinning of domain walls to nanoholes, while in-plane anisotropy decreases owing to local shape anisotropy effects.
Applied Physics Letters, 2009
A coexistence of lateral and in-depth domain walls in antiferromagnet/ferromagnet (AF/FM) thin fi... more A coexistence of lateral and in-depth domain walls in antiferromagnet/ferromagnet (AF/FM) thin films exhibiting double hysteresis loops (DHLs) is demonstrated. Comparison of single and DHLs together with local and global measurements confirms the formation of two oppositely oriented domains in the AF that imprint a lateral domain structure into the FM layer. Most significantly, the magnetization reversal mechanism within each opposite domain takes place by incoherent rotation of spring-like domain walls extending through the Ni thickness. Therefore, complex three-dimensional domain walls are created perpendicular and parallel to the AF/FM interface in exchange biased systems.
Applied Physics Letters, 2009
Experimental and theoretical evidence of plasmon-enhanced Kerr rotation in purely ferromagnetic m... more Experimental and theoretical evidence of plasmon-enhanced Kerr rotation in purely ferromagnetic membranes with sufficiently small dimensions to be out of extraordinary optical transmission conditions (45 nm pore diameter, 90nm lattice constant), is reported in this work. It is shown that the spectral location of the enhanced Kerr rotation region varies as the refractive index of the material inside the pore is modified. A similar behavior is obtained if the pore radius changes while keeping the pore concentration unchanged. Those are clear signatures indicating that localized surface plasmon resonances propagating along the pores govern the magneto-optical response of the membrane.
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Papers by Monica Vélez Tobarias