Ciencias

URI permanente para esta comunidadhttps://hdl.handle.net/11441/10802

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0/1-Polytopes related to Latin squares autotopisms
(2008) Falcón Ganfornina, Raúl Manuel; Universidad de Sevilla. Departamento de Matemática Aplicada I (ETSII)
The set LS(n) of Latin squares of order n can be represented in Rn3 as a (n−1)3-dimensional 0/1-polytope. Given an autotopism Θ=(α,β,γ)∈An, we study in this paper the 0/1-polytope related to the subset of LS(n) having Θ in their autotopism group. Specifically, we prove that this polyhedral structure is generated by a polytope in R((nα−l1α)⋅n2+l1α⋅nβ⋅n)(l1α⋅l1β⋅(n−l1γ)+l1α⋅l1γ⋅(nβ−l1β)+l1β⋅l1γ⋅(nα−l1α)), where nα and nβ are the number of cycles of α and β, respectively, and l1δ is the number of fixed points of δ, for all δ∈{α,β,γ}. Moreover, we study the dimension of these two polytopes for Latin squares of order up to 9.
1 V CMOS subthreshold log domain PDM
(Springer, 2003) Serra Graells, Francesc; Huertas Díaz, José Luis; Comisión Interministerial de Ciencia y Tecnología (CICYT). España; European Union (UE)
A new CMOS circuit strategy for very low-voltage Pulse-Duration Modulators (PDM) is proposed. Optimization of voltage supply scaling below the sum of threshold voltages is based on Instantaneous Log Companding processing through the MOSFET operating in weak inversion. A 1 V VLSI PDM circuit for very low-voltage audio applications such as Hearing Aids is presented, showing good agreement between simulated and experimental data.
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
1,2,3-Triazoles from carbonyl azides and alkynes: filling the gap
(Royal Society of Chemistry, 2014) Haldón, Estela; Álvarez González, Eleuterio; Nicasio Jaramillo, María del Carmen; Pérez, Pedro J.; Universidad de Sevilla. Departamento de Química Inorgánica; Ministerio de Economía y Competitividad (MINECO). España; Junta de Andalucía
Electron deficient azides are challenging substrates in CuAAC reactions. Particularly, when N-carbonyl azides are applied the formation of N-carbonyl triazoles has not yet been observed. We report herein the first example of this class of reaction, with a copper-based system that efficiently enables the synthesis of N-carbamoyl 1,2,3-triazoles by [3+2] cycloaddition of N-carbamoyl azides and alkynes
1,4-Dideoxy-1,4-imino-d-arabinitol (DAB) Analogues Possessing a Hydrazide Imide Moiety as Potent and Selective α-Mannosidase Inhibitors
(American Chemical Society, 2020) Haarr, Marianne B.; López López, Óscar; Pejov, Ljupcho; Fernández-Bolaños Guzmán, José María; Lindbäck, Emil; Sydnes, Magne O.; Universidad de Sevilla. Departamento de Química orgánica
The synthesis of two polyhydroxylated pyrrolidines as 1,4-dideoxy-1,4-imino-d-arabinitol (DAB) analogues bearing a hydrazide moiety is described. The DAB analogues act as selective and potent inhibitors of α-mannosidase in the submicromolar concentration ranges (Ki values ranging from 0.23 to 1.4 μM).
1-Alquil-2-benciltio-4-imidazolcarbozaldehidos
(1967-10-31) Heredia Moreno, Antonia; Fernández Bolaños, José; Universidad de Sevilla. Departamento de Química orgánica
1.2V, 1.96mW @ 2.4GHz CMOS-90nm switched-transconductor mixer
(2010) Villegas Calvo, José Alberto; Vázquez García de la Vega, Diego; Rueda Rueda, Adoración; Universidad de Sevilla. Departamento de Electrónica y Electromagnetismo; Gobierno de España; Junta de Andalucía
This paper presents the design of a fully differential double balanced switched transconductor mixer for ZigBee applications in the 2.4GHz band. It provides programmable conversion gain by using an active load stage. The design includes RF and LO input matching networks. It has been implemented in a 90nm 1P9M CMOS process. Post-layout simulations show conversion gains of 12dB/20dB, NF of 18.9dB/18.1dB and power consumption of 4.1mW/4.4mW at high and low gain mode respectively from a 1.2V power supply. It also offers very good linearity performance.
1/f/sup y/ noise generation through a chaotic nonlinear switched-capacitor circuit
(Institute of Electrical and Electronics Engineers, 1992) Delgado Restituto, Manuel; Rodríguez Vázquez, Ángel Benito; Huertas Díaz, José Luis; Universidad de Sevilla. Departamento de Electrónica y Electromagnetismo
A programmable switched-capacitor circuit for the generation of 1/f/sup y/ noise is reported. The circuit is described by a chaotic first-order piecewise-linear finite-difference equation which yields a hopping transition between regions of chaotic motions and hence produces 1/f/sup y/ noise. Experimental results illustrating the circuit performance are included.
100 años de derechos : la primera mujer española doctora en física
(Unidad para la Igualdad, Universidad de Sevilla, 2010) Núñez Valdés, Juan; Carbonell Coronado, Carmen; Universidad de Sevilla. Departamento de Geometría y Topología
En este año en el que se celebra el II Congreso Universitario Nacional “Investigación y Género” en la Universidad de Sevilla, se cumple el centenario de la Real Orden del Ministerio de Instrucción Pública y Bellas Artes por la que se permitía la “admisión de mujeres en todos los establecimientos docentes”, publicada en la Gaceta de Madrid en 1910, siendo Ministro de la Gobernación el Excmo. Sr. D. Julio Burrel y Cuéllar, durante el reinado de Alfonso XIII. Esta orden permitía a las mujeres la entrada en la universidad, que hasta entonces sólo había sido posible en casos individuales y con permisos especiales, en igualdad legal con el varón. En este contexto, esta Ponencia nace con la intención de celebrar esta efemérides en el campo científico, glosando la historia personal y profesional de la guipuzcoana Felisa Martín Bravo (San Sebastián, 1898), primera mujer española doctora en Física en nuestro país (Universidad Central de Madrid, 1926). En la misma se muestran las numerosísimas dificultades que tuvo que superar Felisa para conseguir esa titulación, entre las que las de género ocupan un lugar preferencial.
10Be low-energy AMS with the passive absorber technique
(ScienceDirect, 2019-01) Scognamiglio, Grazia; Lachner, J.; Chamizo Calvo, Elena; López Gutiérrez, José María; Priller, A.; Universidad de Sevilla. Departamento de Física Aplicada I; Ministerio de Economía y Competitividad (MINECO). España
The passive absorber technique is one of the most common ways to suppress the 10B interference during 10Be measurements at facilities working with beam energies above 7 MeV. At lower energies, the range straggling complicates the application of absorbers, so that other suppression techniques are normally preferred. Several experiments were conducted at the SARA (hosted at Centro Nacional de Aceleradores, Seville, Spain) and VERA (Faculty of Physics, University of Vienna, Austria) AMS facilities to demonstrate the potential of the passive absorber technique also at and below 2.4 MeV. Two different absorber setups were installed and tested. For the detection of the rare isotopes both facilities used a gas ionization chamber optimized for light ions detection based on the same design. The absorber installed at the SARA facility was a combination of SiN foils and an isobutane gas volume, whereas VERA was equipped with an absorber constituted of a stack of SiN foils. In both cases, 10Be could be clearly separated from 10B and the use of a passive absorber at the entrance of the detector gave higher transmission compared to the degrader method. Depending on the absorber design, different background contributions could be identified: Rutherford scattering of 10B on the protons contained in the SiN foils and isobutane gas was responsible of a severe background at SARA, and fragments from 9Be1H molecules surviving the stripping process resulted in events partially overlapping the 10Be gate at VERA. The measured transmissions and background levels will be presented for the tested setups, as well as the advantages and disadvantages of each absorber design.
10mhz cmos ota-c voltage-controlled quadrature oscillator
(Institution of Engineering and Technology, 1989) Linares Barranco, Bernabé; Rodríguez Vázquez, Ángel Benito; Sánchez Sinencio, Edgar; Huertas Díaz, José Luis; Universidad de Sevilla. Departamento de Electrónica y Electromagnetismo
A quadrature-type voltage-controlled oscillator with operational transconductance amplifiers and capacitors (OTA-C) is presented. A monolithic integrated CMOS test circuit is introduced to verify theoretical results. The attainable frequency range of oscillation of the chip test circuit is 3-10.34 MHz. The total harmonic distortion (THD) is 0.201.87% for corresponding peak-to-peak amplitude voltages between 100 mV and IV. This amplitude can be controlled either by using a diode connection of two MOS transistors or a proposed nonlinear resistor.
11Li Breakup on 208Pb at Energies Around the Coulomb Barrier
(American Physical Society, 2013-04-05) Fernández García, Juan Pablo; Rodríguez Gallardo, Manuela; González Álvarez, Marcos Aurelio; Mukha, I.; Moro Muñoz, Antonio Matías; Lay Valera, José Antonio; Gómez Camacho, Joaquín José; Cubero, M.; Universidad de Sevilla. Departamento de Física Atómica, Molecular y Nuclear; European Union (UE)
The inclusive breakup for the 11Li+208Pb reaction at energies around the Coulomb barrier has been measured for the first time. A sizable yield of 9Li following the 11Li dissociation has been observed, even at energies well below the Coulomb barrier. Using the first-order semiclassical perturbation theory of Coulomb excitation it is shown that the breakup probability data measured at small angles can be used to extract effective breakup energy as well as the slope of B(E1) distribution close to the threshold. Four-body continuum-discretized coupled-channels calculations, including both nuclear and Coulomb couplings between the target and projectile to all orders, reproduce the measured inclusive breakup cross sections and support the presence of a dipole resonance in the 11Li continuum at low excitation energy.
11Li structural information from inclusive break-up measurements
(EDP Sciences, 2015) Fernández García, Juan Pablo; Cubero, M.; Acosta, Luis; Alcorta, Martín; González Álvarez, Marcos Aurelio; Borge, María José G.; Gómez Camacho, Joaquín José; Lay Valera, José Antonio; Martel Bravo, Ismael; Moro Muñoz, Antonio Matías; Rodríguez Gallardo, Manuela; Sánchez Benítez, A. M.; Universidad de Sevilla. Departamento de Física Atómica, Molecular y Nuclear
Structure information of 11Li halo nucleus has been obtained from the inclusive break-up measurements of the 11Li+208Pb reactions at energies around the Coulomb barrier (Elab = 24.3 and 29.8 MeV). The effective break-up energy and the slope of B(E1) distribution close to the threshold have been extracted from the experimental data
129I in sediment cores from the Celtic Sea by AMS through a microwave digestion process
(Elsevier, 2022) Lérida Toro, Victoria; Abascal Ruíz, Unai; Villa Alfageme, María; Klar, Jessica K.; Hicks, Natalie; López Gutiérrez, José María; Universidad de Sevilla. Departamento de Física Aplicada II; Universidad de Sevilla. Departamento de Física Aplicada I
Radiochemical methods before measurement are indispensable to determine Iodine-129 by Accelerator Mass Spectrometry (AMS) in environmental samples. In particular, in sediments, iodine is associated with both inorganic and organic matter, and it presents in several chemical forms. Therefore, the radiochemical procedure must be designed to extract all the different iodine species from the matrix, whilst being as robust and time effective as possible. In this work, different microwave digestion methods, together with the processing of the iodine species to be measured by AMS, were tested and their performances are presented here. Two sediment cores, one with muddy sediment (core A) and one with permeable sandy sediment (core I), collected in the Celtic Sea, were used and the results were evaluated to determine an optimized iodine extraction. The method consisted of a microwave digestion with concentrated nitric acid followed by a double liquid–liquid extraction and the final precipitation of silver iodide (AgI), required to measure iodine by AMS. Back extraction of iodine in a reducing solution during purification was carried out with hydrazine (NH2-NH2). Subsequent additional steps were added to optimize all iodine species extraction. First, hydrochloric hydroxylamine (NH2OH⋅HCl) and so dium bisulfite (Na2S2O5) were used to homogenize all iodine species before extraction through a redox process. Second, sodium hypochlorite (NaOCl) was added to remove any final organic matter after digestion. The final method incorporated sodium hydroxide (NaOH) combined with NaOCl to facilitate reduction of iodine in so lution and enhance the NaOCl effect. The different methods were validated against an internal standard and the last method was chosen, as it showed the most reproducible and accurate results. As practical application, Iodine129 concentration from both cores were compared, showing concentrations between 0.19 × 1012 at/kg and 7.16 × 1012 at/kg for core A and between 0.28 × 1012 at/kg and 2.40 × 1012 at/kg for core I. Despite the 129I diffusion detected in the deeper layers, depth profiles accurately reproduced Sellafield discharges, which is the nuclear fuel reprocessing plant closest to the cores.
129I, 236U, 239Pu and 240Pu profiles in a peatbog from the Southern Hemisphere
(2016) Chamizo, E.; López Gutiérrez, José María; Holm, Elis; García-Tenorio García-Balmaseda, Rafael; Universidad de Sevilla. Departamento de Física Aplicada II
129I, 236U, 239Pu and 240Pu isotopes have been analyzed in the different layers of a peatbog core collected in Madagascar Island (South Hemisphere) and representing at least the last 100 years of atmospheric deposition. The determination of ultra-low levels of these isotopes has been possible by applying the Accelerator Mass Spectrometric Technique (AMS) by using the 1 MV Tandetrom AMS facility located at CNA (Seville, Spain). The elements of interest were extracted and isolated previous to the measurements by applying validated radiochemical procedures. In this contribution, the behavior along the core of the different isotopes under analysis will be discussed, evaluating in particular the magnitude of their post-depositional retention/migration. In this sense, it will be highlighted the great mobility of the 129I with a near uniform profile along the core, in opposition for example with the preservation for the Pu isotopes of the fallout bomb peak. In the case of 236U, the 236U/239Pu atomic ratios determined in a total of eight layers of the core are ranging in the interval 0.02 – 0.29 with an average value of 0.15. As far as we know, these are the first 236U results seeing the light that were obtained in deposits as peatbogs collected in the southern hemisphere.
14 MeV calibration of JET neutron detectors-phase 1: calibration and characterization of the neutron source
(IOP Publishing, 2018-02) Batistoni, P.; Popovichev, S.; Cufar, A.; Ghani, Z.; Giacomelli, L.; Jet Contributors; García Muñoz, Manuel; Universidad de Sevilla. Departamento de Física Atómica, Molecular y Nuclear; Universidad de Sevilla. RNM138: Física Nuclear Aplicada
In view of the planned DT operations at JET, a calibration of the JET neutron monitors at 14 MeV neutron energy is needed using a 14 MeV neutron generator deployed inside the vacuum vessel by the JET remote handling system. The target accuracy of this calibration is ±10% as also required by ITER, where a precise neutron yield measurement is important, e.g. for tritium accountancy. To achieve this accuracy, the 14 MeV neutron generator selected as the calibration source has been fully characterised and calibrated prior to the in-vessel calibration of the JET monitors. This paper describes the measurements performed using different types of neutron detectors, spectrometers, calibrated long counters and activation foils which allowed us to obtain the neutron emission rate and the anisotropy of the neutron generator, i.e. the neutron flux and energy spectrum dependence on emission angle, and to derive the absolute emission rate in 4π sr. The use of high resolution diamond spectrometers made it possible to resolve the complex features of the neutron energy spectra resulting from the mixed D/T beam ions reacting with the D/T nuclei present in the neutron generator target. As the neutron generator is not a stable neutron source, several monitoring detectors were attached to it by means of an ad hoc mechanical structure to continuously monitor the neutron emission rate during the in-vessel calibration. These monitoring detectors, two diamond diodes and activation foils, have been calibrated in terms of neutrons/counts within ±5% total uncertainty. A neutron source routine has been developed, able to produce the neutron spectra resulting from all possible reactions occurring with the D/T ions in the beam impinging on the Ti D/T target. The neutron energy spectra calculated by combining the source routine with a MCNP model of the neutron generator have been validated by the measurements. These numerical tools will be key in analysing the results from the in-vessel calibration and to derive the response of the JET neutron detectors to DT plasma neutrons starting from the response to the generator neutrons, and taking into account all the calibration circumstances.
15O+α resonant elastic scattering to study cluster states in19Ne
(Institute of Physics Publishing, 2017) Torresi, Domenico; Wheldon, C.; Kokalova, Tz.; Bailey, S.; Boiano, Alfonso; Boiano, Ciro; Fernández García, Juan Pablo; Zadro, Mile; Universidad de Sevilla. Departamento de Física Atómica, Molecular y Nuclear; European Union (UE). H2020
Clustering phenomena are well known in nuclear physics for stable nuclei, both α-conjugate (N=Z, A=2N), like8Be,16O,20Ne, and non-α-conjugate, like6Li and7Li. In general, it is expected that light exotic nuclei may also exhibit cluster behavior. Moving out of the valley of stability configurations can be found where at least one of the clusters is unbound or weakly bound, thus not satisfying the strong internal correlation requirement of classical clusters. This is so-called exotic clustering. The study of such systems presents many difficulties, due, mainly, to the low intensities typical of radioactive ion beams. Therefore, few significant experimental studies have been performed so far. In this work we searched for α-cluster states in19Ne above its α-decay threshold measuring, for the first time, the15O(4He,4He) elastic scattering excitation function. Moreover, this study classified low-energy states in Ne in the astrophysically important region in this HCNO-break-out nucleus.
18 O -induced single-nucleon transfer reactions on 40 Ca at 15.3 A MeV within a multichannel analysis
(American Physical Society, 2021) Calabrese, S.; Cavallaro, Manuela; Carbone, D.; Cappuzzello, F.; Agodi, Clementina; Burrello, S.; Lay Valera, José Antonio; Zagatto, Vinicius A. B.; Universidad de Sevilla. Departamento de Física Atómica, Molecular y Nuclear; European Union (UE). H2020; Instituto Nacional de Ciência e Tecnologia. Brasil; Conselho Nacional de Desenvolvimento Científico e Tecnológico. Brasil; Fundação de Amparo à Pesquisa no Estado. Rio de Janeiro. Brasil; Fundação de Amparo à Pesquisa de Sao Paulo. Brasil; Ministerio de Ciencia, Innovación y Universidades (MICINN). España; European Commission (EC). Fondo Europeo de Desarrollo Regional (FEDER)
Background: Nucleon transfer reactions are selective tools for nuclear physics investigations. The theoretical and computational limits affecting in the past their data analysis could be nowadays surmounted thanks to the advent of methods with refined approximations and constraints, even when heavy-ion collisions are considered. Purpose: Modern microscopic calculations of heavy-ion-induced transfer reactions combined with precise experimental data offer the chance for accurately testing different reaction models as well as the nuclear structure description of the involved nuclear states. Method: Single proton and neutron transfer reactions were measured with the MAGNEX magnetic spectrometer for the 18 O + 40 Ca system at 15.3 A MeV. Excitation energy spectra and angular differential cross section distributions were extracted. The experimental results are compared with theoretical calculations performed in distorted wave and coupled channel Born approximation. The use of a coupled channel equivalent polarization potential to effectively describe the coupling effects affecting the initial state interaction is also considered. Spectroscopic amplitudes derived from a large-scale shell model with appropriate interactions adapted for the involved nuclei are employed. Results: Our theoretical calculations are in good agreement with experimental data, without the need for any scaling factor, validating the adopted reaction and nuclear structure parameters. Moreover, under the present experimental conditions, a weak dependence of the obtained results on the choice of the reaction models was observed. Conclusions: The good agreement between experimental and theoretical results validates the reliability of the parameter sets entering the calculations. They are extracted from or tested in complementary analyses of other reaction channels under the same experimental conditions. Such a multichannel approach represents the best option to pursue a solid, comprehensive, and model-independent description of the single-nucleon transfer reactions. The successful description of the present one-nucleon transfer data is also propaedeutic to the accurate assessment, under the same theoretical description, of higher-order transfer processes, like the sequential nucleon transfer mechanisms which are in competition with the direct charge exchange reactions.
197Au(n,γ) cross section in the resonance region
(The American Physical Society, 2010) Massimi, C.; Domingo Pardo, César; Vannini, Gianni; Audouin, Laurent; Guerrero Sánchez, Carlos; Abbondanno, U.; Wisshak, K.; Capote, Roberto; Lozano Leyva, Manuel Luis; Quesada Molina, José Manuel; Universidad de Sevilla. Departamento de Física Atómica, Molecular y Nuclear; European Commission (EC)
The (n,γ) cross section of 197Au has been measured at n-TOF in the resolved resonance region, up to 5keV, with the aim of improving the accuracy in an energy range where it is not yet considered standard. The measurements were performed with two different experimental setup and detection techniques, the total energy method based on C6D6 detectors, and the total absorption calorimetry based on a 4π BaF2 array. By comparing the data collected with the two techniques, two accurate sets of neutron-capture yields have been obtained, which could be the basis for a new evaluation leading to an extended cross-section standard. Overall good agreement is found between the n-TOF results and evaluated cross sections, with some significant exceptions for small resonances. A few resonances not included in the existing databases have also been observed.
197Au(n,γ) cross section in the unresolved resonance region
(American Physical Society, 2011) Lederer Woods, Claudia; Colonna, Nicola; Domingo Pardo, César; Gunsing, F.; Käppeler, F.; Massimi, C.; Wisshak, K.; Capote, Roberto; Praena Rodríguez, Javier; Quesada Molina, José Manuel; Guerrero Sánchez, Carlos; Lozano Leyva, Manuel Luis; Universidad de Sevilla. Departamento de Física Atómica, Molecular y Nuclear
The cross section of the reaction 197Au(n,γ) was measured with the time-of-flight technique at the n-TOF (neutron time-of-flight) facility in the unresolved resonance region between 5 and 400 keV using a pair of C 6D6 (where D denotes 2H) liquid scintillators for the detection of prompt capture γ rays. The results with a total uncertainty of 3.9%-6.7% for a resolution of 20 bins per energy decade show fair agreement with the Evaluated Nuclear Data File Version B-VII.0 (ENDF/B-VII.0), which contains the standard evaluation. The Maxwellian-averaged cross section (MACS) at 30 keV is in excellent agreement with the one according to the ENDF/B-VII.0 evaluation and 4.7% higher than the MACS measured independently by activation technique. Structures in the cross section, which had also been reported earlier, have been interpreted as being due to clusters of resonances.

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