295 research outputs found

    A Noise-Shifting Differential Colpitts VCO

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    A novel noise-shifting differential Colpitts VCO is presented. It uses current switching to lower phase noise by cyclostationary noise alignment and improve the start-up condition. A design strategy is also devised to enhance the phase noise performance of quadrature coupled oscillators. Two integrated VCOs are presented as design examples

    Moduli Stabilisation with Nilpotent Goldstino: Vacuum Structure and SUSY Breaking

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    We study the effective field theory of KKLT and LVS moduli stabilisation scenarios coupled to an anti-D3-brane at the tip of a warped throat. We describe the presence of the anti-brane in terms of a nilpotent goldstino superfield in a supersymmetric effective field theory. The introduction of this superfield produces a term that can lead to a de Sitter minimum. We fix the Kaehler moduli dependence of the nilpotent field couplings by matching this term with the anti-D3-brane uplifting contribution. The main result of this paper is the computation, within this EFT, of the soft supersymmetry breaking terms in both KKLT and LVS for matter living on D3-brane (leaving the D7-brane analysis to an appendix). A handful of distinct phenomenological scenarios emerge that could have low energy implications, most of them having a split spectrum of soft masses. Some cosmological and phenomenological properties of these models are discussed. We also check that the attraction between the D3-brane and the anti-D3-brane does not affect the leading contribution to the soft masses and does not destabilise the system.Comment: 26+14 pages, 1 figure; references and clarifications added, typos fixe

    Quantum prices

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    Many retailers practice an extreme form of discrete pricing defined as quantum prices: differentiated products are priced using few and sparse price buckets. To show this, online data was collected for 350,000 products from over 65 fashion retailers in the U.S. and the U.K. This pricing strategy is observed within categories and across categories (i.e., similar or even disparately distinct products like jeans and bags have an identical price), as well as in product introductions, where new products come in at previous price buckets. Normalized indices indicate substantial price clustering after controlling for popular prices, convenient prices, assortment size, or digit endings. Quantum prices have implications for price adjustments through product shares, markdown prices, and for the law-of-one-price. A behavioral model of price salience and recall is discussed

    Spatial dependence of the Star Formation History in the Central Regions of the Fornax Dwarf Spheroidal Galaxy

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    We present the Star Formation History (SFH) and the age-metallicity relation (AMR) in three fields of the Fornax dwarf spheroidal galaxy. They sample a region spanning from the centre of the galaxy to beyond one core radius, which allows studying galactocentric gradients. In all the cases, we found stars as old as 12 Gyr, together with intermediate-age and young stellar populations. The last star formation events, as young as 1 Gyr old, are mainly located in the central region, which may indicate that the gas reservoir in the outer parts of the galaxy would have been exhausted earlier than in the centre or removed by tidal interactions. The AMR is smoothly increasing in the three analyzed regions and similar to each other, indicating that no significant metallicity gradient is apparent within and around the core radius of Fornax. No significant traces of global UV-reionization or local SNe feedback are appreciated in the early SFH of Fornax. Our study is based on FORS1@VLT photometry as deep as I~24.5 and the IAC-star/IAC-pop/MinnIAC suite of codes for the determination of the SFH in resolved stellar populations.Comment: 13 pages, 8 figures, 4 table

    Elasto-thermoelectric beam formulation for modeling thermoelectric devices

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    [EN] The present paper provides a dynamic, non-linear and fully coupled Finite Element (FE) formulation based on the Timoshenko beam theory to study elasto-thermoelectric responses in thermoelectric devices. The two main motivations of this work are: i) to study mechanical responses in thermoelectric devices, which must be taken into account in the design of Peltier cells due to the fragility and relative low strength of the semiconductors, and ii) to provide a numerical tool that decreases the CPU time to allow the introduction of designs based on optimization processes and on sensitivity analyses that could require many evaluations. In order to undertake the objectives of this work, the general three-dimensional governing equations are reduced to one-dimensional ones by means of several assumptions. Then, a set of five multi-coupled partial differential equations is obtained. The resultant expressions are thermodynamically consistent and form a multi-coupled monolithic FE formulation, differently to stagger formulations that require two separated steps to reach the final result. Numerically, this set of multi-coupled equations is discretized using the FE method and implemented into FEAP Taylor, 2010 [1]. For a proper validation of the code, four benchmarks are performed using one- dimensional dynamic analytical solutions developed by the authors. Finally, this formulation is compared with a three-dimensional FE formulation also developed by the authors in Pe ́rez-Aparicio et al., 2015 [2] to model a commercial Peltier cell. This comparison reveals that: i) relative errors are lower than 13% and ii) CPU times decrease significantly, more than one order of magnitude. In conclusion, the beam thermoelectric formulation is an accurate model that reduces CPU time and could be used in future design of thermoelectric devices.Palma, R.; Moliner, E.; Pérez-Aparicio, JL. (2017). Elasto-thermoelectric beam formulation for modeling thermoelectric devices. Finite Elements in Analysis and Design. 129:32-41. doi:10.1016/j.finel.2017.02.001S324112

    Non-linear finite element formulation applied to thermoelectric materials under hyperbolic heat conduction model

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    In the present work, a three-dimensional, dynamic and non-linear finite element to simulate thermoelectric behavior under a hyperbolic heat conduction model is presented. The transport equations, which couple electric and thermal energies by the Seebeck, Peltier and Thomson effects, are analytically obtained through extended non-equilibrium thermodynamics, since the local equilibrium hypothesis is not valid under the hyperbolic model. In addition, unidimensional analytical solutions are obtained to validate the finite element formulation. Numerically, isoparametric eight-node elements with two degrees of freedom (voltage and temperature) per node are used. Non-linearities due to the temperature-dependence on the transport properties and the Joule effects are addressed with the Newton-Raphson algorithm. For the dynamic problem, HHT and Newmark-ß algorithms are compared to obtain accurate results, since numerical oscillations (Gibbs phenomena) are present when the initial boundary conditions are discontinuous. The last algorithm, which is regularized by relating time steps and element sizes, provides the best results. Finally, the finite element implementation is validated, comparing the analytical and the numerical solutions, and a three-dimensional example is presented.This research was partially supported by the Spanish Ministry of Education through Grant No. FPU AP-2006-02372 and also from Grants MICINN BIA-2008-00522, CSD2008-00037 Canfranc Under-ground Physics, Excelencia Junta Andalucia P08-TEP-03641 and "Ayudas Investigacion" from UPV. The authors would also like to thank Prof. Guillermo Rus for his valuable contributions.Palma, R.; Pérez-Aparicio, JL.; Taylor, R. (2012). Non-linear finite element formulation applied to thermoelectric materials under hyperbolic heat conduction model. Computer Methods in Applied Mechanics and Engineering. 213-216:93-103. https://doi.org/10.1016/j.cma.2011.11.011S93103213-21

    A Fully-Integrated Quad-Band GSM/GPRS CMOS Power Amplifier

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    Concentric distributed active transformers (DAT) are used to implement a fully-integrated quad-band power amplifier (PA) in a standard 130 nm CMOS process. The DAT enables the power amplifier to integrate the input and output matching networks on the same silicon die. The PA integrates on-chip closed-loop power control and operates under supply voltages from 2.9 V to 5.5 V in a standard micro-lead-frame package. It shows no oscillations, degradation, or failures for over 2000 hours of operation with a supply of 6 V at 135° under a VSWR of 15:1 at all phase angles and has also been tested for more than 2 million device-hours (with ongoing reliability monitoring) without a single failure under nominal operation conditions. It produces up to +35 dBm of RF power with power-added efficiency of 51%

    Inspección visual automática de superficies continuas, caracterizando anomalías locales en el dominio Espacio-Frecuencial

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    Esta tesis propone una metodología para la inspección visual automática de superficies continuas que abarca las etapas de adquisición de imágenes, su procesamiento y la utilización de los resultados obtenidos. Su objetivo es determinar qué zonas de la superficie son defectuosas por alejarse de la homogeneidad esperada y cuál es el tipo de defecto presente. Para ello, se caracterizan anomalías en el dominio espacio-frecuencial, explotando las posibilidades que ofrece el filtro de Gabor. Se ha definido una metodología para el diseño de bancos de filtros de Gabor que analiza una zona del espacio de frecuencias y orientaciones. La información extraída por estos filtros son las características evaluadas en la detección y clasificación de defectos. Este enfoque general ha sido particularizado a la resolución de tres problemas reales de reconocida trascendencia: la inspección de bobinas de chapa de acero laminado, del pavimento de carreteras y del revestimiento de túneles de hormigón.Departamento de Ingeniería de Sistemas y Automátic

    Dissipative Finite-Element Formulation Applied to Piezoelectric Materials With the Debye Memory

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    © 2018 IEEE. Personal use of this material is permitted. Permissíon from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertisíng or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.[EN] This work presents a finite-element study of the Debye memory in piezoelectric devices. The memory dependence is due to the spontaneous polarization of the electric dipoles, and it can be understood as a transient viscosity-like effect. The formulation assumes a small strain and rotation hypothesis, and the main contribution is the inclusion of the time-dependent constitutive behavior. For this purpose, a unique numerical formulation that uses convolution integrals is developed to solve the time-dependent electric constitutive equation. A consistent and monolithic finite-element formulation is then obtained and implemented. Finally, a commercial piezoelectric device is simulated for two operational modes, an actuator and a sensor. Several important conclusions on the coupled mechanical and electric fields are reported, and the stability of the time integration scheme is tested by representing the time evolution of the electromechanic energy.Palma, R.; Pérez-Aparicio, JL.; Taylor, RL. (2018). Dissipative Finite-Element Formulation Applied to Piezoelectric Materials With the Debye Memory. IEEE/ASME Transactions on Mechatronics. 23(2):856-863. https://doi.org/10.1109/TMECH.2018.2792308S85686323
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