arXiv subjects

Alejandro Martinez

Publications and source records attributed to Alejandro Martinez.

14 recordsLinked to original sources

arXiv2026

A Conceptual Framework for Enhancing Workforce Readiness for Smart Manufacturing in the AI Era

The convergence of artificial intelligence (AI), Industrial Internet of Things, cyber-physical systems, and advanced robotics is reshaping manufacturing faster than engineering curricula can adapt, widening the gap between the competencies required on the shop floor and those delivered by traditional engineering and technology education. This paper proposes a Workforce Readiness Level (WRL) framework, which adapts the Technology Readiness Level scale into nine progressive competency stages and a four-pillar rubric, digital and AI literacy, cyber-physical systems fluency, human-machine collaboration, and data-driven decision making, aggregated through a composite stage score and a cohort-level workforce-readiness index under a ``no-thin-pillar'' rule. The framework is instantiated at a university smart-manufacturing teaching laboratory and draws on 89 sponsored capstone projects delivered over four semesters, four of which are analyzed in depth. Four pillars jointly span the relevant ABET student outcomes. Across the highlighted cohorts the workforce-readiness index ranged from 5.2 to 6.4, and the no-thin-pillar rule was diagnostically informative in three of the four cases and the binding certification constraint in one, repeatedly surfacing cyber-physical and data-driven-decision gaps concealed behind strong analytics profiles; advancement to the highest stages was gated by industry-embedded experience rather than additional coursework. WRL offers educators, accreditation bodies, and regional workforce systems a common, evidence-based instrument for diagnosing and advancing workforce readiness; future work will calibrate pillar weights and test reliability and predictive validity.

eess.SY↗

arXiv2024

Bio-inspired site characterization -- towards soundings with lightweight equipment

Equipment used for site investigation activities like drill rigs are typically large and heavy to provide sufficient reaction mass to overcome the soil's penetration resistance. The need for large and heavy equipment creates challenges for performing site investigations at sites with limited accessibility, such as urban centres, vegetated areas, locations with height restrictions and surficial soft soils, and steep slopes. Also, mobilization of large equipment to the project site is responsible for a significant portion of the carbon footprint of site investigations. Successful development of self burrowing technology can have enormous implications for geotechnical site investigation, ranging from performance of in situ tests to installation of instrumentation without the need of heavy equipment. During the last decade there has been an acceleration of research in the field of bioinspired geotechnics, whose premise is that certain animals and plants have developed efficient strategies to interact with geomaterials in ways that are analogous to those in geotechnical engineering. This paper provides a synthesis of advances in bioinspired site investigation related to the reduction of penetration resistance by means of modifying the tip shape, expanding a shaft section near the probe tip, applying motions to the tip like rotation and oscillation, and injecting fluids and generation of reaction forces with temporary anchors that enable self burrowing. Examples of prototypes that have been tested experimentally are highlighted. However, there are important research gaps associated with testing in a broader range of conditions, interpretation of results, and development of hardware that need to be addressed to develop field ready equipment that can provide useful data for geotechnical design.

physics.geo-ph↗

arXiv2024

Gravity effects on a bio-inspired self-burrowing probe in granular soils

In recent years, self-burrowing probes have been studied since they can be suitable for soil monitoring in locations with limited access such as outer space bodies and underneath existing structures. We study the performance of a self-burrowing probe under different gravity conditions, from low gravity (i.e., 1/6g, 1/3g and 1g) to high gravity (i.e., 5g, 10g and 15g), specifically in terms of penetration distance and energy consumption. Results show that the probe reaches efficient penetration in all gravity conditions and that it achieves larger penetration distances in high gravity conditions. However, the penetration efficiency, shown as unit energy per meter, is higher in low gravity. Additionally, we prove that a simple dimensional analysis provides reasonable scaling factors for first order effects in forces, velocities and energy. The findings in this study give confidence to the potential use of self-burrowing probes in campaigns of soil testing and sensor deployment in outer space or centrifuges in which the gravity conditions can differ from Earth.

cond-mat.soft↗

arXiv2022

Experimental observation of higher-order anapoles in individual silicon disks under in-plane illumination

Anapole states - characterized by a strong suppression of far-field scattering - naturally arise in high-index nanoparticles as a result of the interference between certain multipolar moments. Recently, the first-order electric anapole, resulting from the interference between the electric and toroidal dipoles, was characterized under in-plane illumination as required in on-chip photonics. Here, we go a step further and report on the observation of higher-order (magnetic and second-order electric) anapole states in individual silicon disks under in-plane illumination. To do so, we increase the disk dimensions (radius and thickness) so that such anapoles occur at telecom wavelengths. Experiments show dips in the far-field scattering perpendicular to the disk plane at the expected wavelengths and the selected polarizations, which we interpret as a signature of high-order anapoles. Some differences between normal and in-plane excitation are discussed, in particular the non-cancellation of the sum of the Cartesian electric and toroidal moments for in-plane incidence. Our results pave the way towards the use of different anapole states in photonic integrated circuits, either on silicon or other high-index dielectric materials.

physics.optics↗

arXiv2022

Hybrid photonic-plasmonic cavity design for very large Purcell factors at telecom wavelengths

Hybrid photonic-plasmonic cavities can be tailored to display high Q-factors and extremely small mode volumes simultaneously, which results in large values of the Purcell factor, FP. Amongst the different hybrid configurations, those based on a nanoparticle-on-a-mirror (NPoM) plasmonic cavity provide one of the lowest mode volumes, though so far their operation has been constrained to wavelengths below 1 {\mu}m. Here, we propose a hybrid configuration consisting of a silicon photonic crystal cavity with a slot at its center in which a gold nanoparticle is introduced. This hybrid system operates at telecom wavelengths and provides high Q-factor values (Q ${\approx} 10^{5}$) and small normalized mode volumes (Vm ${\approx} 10^{-4}$), leading to extremely large Purcell factor values, FP ${\approx} 10^{7}$ - ${10^{8}}$. The proposed cavity could be used in different applications such as molecular optomechanics, bio- and chemo-sensing, all-optical signal processing or enhanced Raman spectroscopy in the relevant telecom wavelength regime.

physics.optics↗

arXiv2021

Thermal properties of nanocrystalline silicon nanobeams

Controlling thermal energy transfer at the nanoscale has become critically important in many applications and thermal properties since it often limits device performance. In this work, we study the effects on thermal conductivity arising from the nanoscale structure of free-standing nanocrystalline silicon films and the increasing surface-to-volume ratio when fabricated into suspended optomechanical nanobeams. We characterize thermal transport in structures with different grain sizes and elucidate the relative impact of grain size and geometrical dimensions on thermal conductivity. We use a micro-time-domain thermoreflectance method to study the impact of the grain size distribution, from 10 to 400 nm, on the thermal conductivity in free-standing nanocrystalline silicon films considering surface phonon and grain boundary scattering. We find a drastic reduction in the thermal conductivity, down to values of 10 W.m^{-1}.K^{-1} and below, which is just a fraction of the conductivity of single crystalline silicon. Decreasing the grain size further decreases the thermal conductivity. We also observe that this effect is smaller in OM nanostructures than in membranes due to the competition of surface scattering in decreasing thermal conductivity. Finally, we introduce a novel versatile contactless characterization technique that can be adapted to any structure supporting a thermally shifted optical resonance and use it to evaluate the thermal conductivity. This method can be used with optical resonances exhibiting different mode profiles and the data is shown to agrees quantitatively with the thermoreflectance measurements. This work opens the way to a more generalized thermal characterization of optomechanical cavities and to create hot-spots with engineered shapes at desired position in the structures as a means to study thermal transport in coupled photon-phonon structures.

physics.app-ph↗

arXiv2021

A Variable Vector Length SIMD Architecture for HW/SW Co-designed Processors

Hardware/Software (HW/SW) co-designed processors provide a promising solution to the power and complexity problems of the modern microprocessors by keeping their hardware simple. Moreover, they employ several runtime optimizations to improve the performance. One of the most potent optimizations, vectorization, has been utilized by modern microprocessors, to exploit the data level parallelism through SIMD accelerators. Due to their hardware simplicity, these accelerators have evolved in terms of width from 64-bit vectors in Intel MMX to 512-bit wide vector units in Intel Xeon Phi and AVX-512. Although SIMD accelerators are simple in terms of hardware design, code generation for them has always been a challenge. Moreover, increasing vector lengths with each new generation add to this complexity. This paper explores the scalability of SIMD accelerators from the code generation point of view. We discover that the SIMD accelerators remain underutilized at higher vector lengths mainly due to: a) reduced dynamic instruction stream coverage for vectorization and b) increase in permutations. Both of these factors can be attributed to the rigidness of the SIMD architecture. We propose a novel SIMD architecture that possesses the flexibility needed to support higher vector lengths. Furthermore, we propose Variable Length Vectorization and Selective Writing in a HW/SW co-designed environment to transparently target the flexibility of the proposed architecture. We evaluate our proposals using a set of SPECFP2006 and Physicsbench applications. Our experimental results show an average dynamic instruction reduction of 31% and 40% and an average speed up of 13% and 10% for SPECFP2006 and Physicsbench respectively, for 512-bit vector length, over the scalar baseline code.

cs.AR↗

arXiv2019

Microwave generation and frequency comb in a silicon optomechanical cavity with a full phononic bandgap

Cavity optomechanics has become a powerful tool to manipulate mechanical motion via optical fields. When driving an optomechanical cavity with blue-detuned laser the mechanical motion is amplified, ultimately resulting in phonon lasing. In this work, we show that a silicon optomechanical crystal cavity can be used as an optoelectronic oscillator when driven to the phonon lasing condition. To this end, we use an optomechanical cavity designed to have a breathing-like mechanical mode vibrating at $\Omega_{m}/2\pi=$3.897 GHz in a full phononic bandgap. Our measurements show that the first harmonic displays a phase noise of -100 dBc/Hz at 100 kHz, which is a considerable value for a free running oscillator. Stronger blue-detuned driving leads eventually to the formation of an optomechanical frequency comb, with lines spaced by the mechanical frequency. We also measure the phase noise for higher-order harmonics and show that, unlike in Brillouin oscillators, the noise is increased as corresponding to classical harmonic mixing. Finally, we present real-time measurements of the comb waveform and show that it can be adjusted to a theoretical model recently presented. Our results suggest that silicon optomechanical cavities could be relevant elements in microwave photonics and optical RF processing, in particular in disciplines requiring low-weight, compactness and fiber interconnection.

physics.optics↗

arXiv2019

Properties of Nanocrystalline Silicon Probed by Optomechanics

Nanocrystalline materials exhibit properties that can differ substantially from those of their single crystal counterparts. As such, they provide ways to enhance and optimise their functionality for devices and applications. Here we report on the optical, mechanical and thermal properties of nanocrystalline silicon probed by means of optomechanical nanobeams to extract information of the dynamics of optical absorption, mechanical losses, heat generation and dissipation. The optomechanical nanobeams are fabricated using nanocrystalline films prepared by annealing amorphous silicon layers at different temperatures. The resulting crystallite sizes and the stress in the films can be controlled by the annealing temperature and time and, consequently, the properties of the films can be tuned relatively freely, as demonstrated here by means of electron microscopy and Raman scattering. We show that the nanocrystallite size and the volume fraction of the grain boundaries play a key role in the dissipation rates through non-linear optical and thermal processes. Promising optical (13000) and mechanical (1700) quality factors were found in the optomechanical cavity realised in the nanocrystalline Si resulting from annealing at 950 C. The enhanced absorption and recombination rates via the intra-gap states and the reduced thermal conductivity boost the potential to exploit these non-linear effects in applications, including NEMS, phonon lasing and chaos-based devices.

physics.app-ph↗

arXiv2018

The ARM Scalable Vector Extension

This article describes the ARM Scalable Vector Extension (SVE). Several goals guided the design of the architecture. First was the need to extend the vector processing capability associated with the ARM AArch64 execution state to better address the computational requirements in domains such as high-performance computing, data analytics, computer vision, and machine learning. Second was the desire to introduce an extension that can scale across multiple implementations, both now and into the future, allowing CPU designers to choose the vector length most suitable for their power, performance, and area targets. Finally, the architecture should avoid imposing a software development cost as the vector length changes and where possible reduce it by improving the reach of compiler auto-vectorization technologies. SVE achieves these goals. It allows implementations to choose a vector register length between 128 and 2,048 bits. It supports a vector-length agnostic programming model that lets code run and scale automatically across all vector lengths without recompilation. Finally, it introduces several innovative features that begin to overcome some of the traditional barriers to autovectorization.

cs.AR↗

arXiv2015

Universal method for the synthesis of arbitrary polarization states radiated by a nanoantenna

Optical nanoantennas efficiently convert confined optical energy into free-space radiation. The polarization of the emitted radiation depends mainly on nanoantenna shape, so it becomes extremely difficult to manipulate it unless the nanostructure is physically altered. Here we demonstrate a simple way to synthetize the polarization of the radiation emitted by a single nanoantenna so that every point on the Poincaré sphere becomes attainable. The nanoantenna consists of a single scatterer created on a dielectric waveguide and fed from its both sides so that the polarization of the emitted optical radiation is controlled by the amplitude and phase of the feeding signals. Our nanoantenna is created on a silicon chip using standard top-down nanofabrication tools, but the method is universal and can be applied to other materials, wavelengths and technologies. This work will open the way towards the synthesis and control of arbitrary polarization states in nano-optics.

physics.optics↗

arXiv2015

Transverse spin and spin-orbit coupling in silicon waveguides

Evanescent and tightly confined propagating waves exhibit a remarkable transverse spin density since the longitudinal component of the electric field is not negligible. In this work, we obtain via numerical simulations the electric field components of the fundamental guided modes of two waveguides typically used in silicon photonics: the strip and the slot waveguide. We obtain the relation between transverse and longitudinal field components, the transverse spin densities and other important parameters, such as the longitudinal component of the so-called Belinfante spin momentum density. By asymmetrically placing a circularly-polarized point-like dipole source in regions showing local circular polarization, the guided mode is excited unidirectionally via spin-orbit coupling. In contrast to metal plates supporting surface plasmons, the multimode behavior of silicon waveguides results in different spin-orbit coupling properties for each guided mode. Our results may find application in silicon photonic devices, integrated quantum optics and polarization manipulation at the nanoscale.

physics.optics↗

arXiv2014

A self-stabilized coherent phonon source driven by optical forces

Optical forces can set tiny objects into states of coherent mechanical oscillation, also known as mechanical or phonon lasing. We present a novel pumping mechanism in an opto-mechanical photonic crystal that realizes mechanical lasing with relaxed requirements for the optical-mechanical modes and their inter-coupling. It derives from a spontaneously triggered thermal/free carrier self-pulsing and the anharmonic modulation of the radiation pressure force that comes as a consequence. Moreover, the feedback of the mechanics on the self-pulsing frequency-entrains both oscillators, creating a self-stabilized indecomposable system. A manifold of frequency-entrained regions with two different mechanical modes (at 54 and 122 MHz) are observed as a result of the wide tuneability of the natural frequency of the self-pulsing. The system operates at ambient conditions of pressure and temperature in a silicon compatible platform, which enables its exploitation in sensing, intra-chip metrology or time-keeping applications.

physics.optics↗

arXiv2013

Effect of loss on the dispersion relation of photonic and phononic crystals

A theoretical analysis is made of the transformation of the dispersion relation of waves in artificial crystals under the influence of loss, including the case of photonic and phononic crystals. Considering a general dispersion relation in implicit form, an analytic procedure is derived to obtain the transformed dispersion relation. It is shown that the dispersion relation is generally shifted in the complex $(k,ω)$ plane, with $k$ the wavenumber and $ω$ the angular frequency. The value of the shift is obtained explicitly as a function of the perturbation of material constants accounting for loss. The method is shown to predict correctly the transformation of the complex band structure $k(ω)$. Several models of the dispersion relation near a symmetry point of the Brillouin zone are analyzed. A lower bound for the group velocity, related to the local shape of the band around symmetry points, is derived for each case.

physics.optics↗