Nonlinear interactions between high-Q optical and acoustic modes in dielectric particles

The interaction between acoustic breathing modes and optical Mie resonances in a spherical particle made of a chalcogenide glass material is investigated by means of rigorous calculations, correct to any order in the acousto-optic coupling parameter. Our results reveal the occurrence of strong effects beyond the linear-response approximation, which lead to enhanced modulation of light by acoustic waves through multiphonon exchange mechanisms when both photons and phonons have a very long lifetime inside the particle

Multi-scale Modelling of Natural Composites Using Thermodynamics-Based Artificial Neural Networks and Dimensionality Reduction Techniques

Modelling natural composites, as the majority of real geomaterials, requires facing their intrinsic multiscale nature. This allows to consider multiphysics coupling occurring at the microscale, then reflected onto the macroscopic behavior. Geotechnics is constantly requiring reliable constitutive models of natural compolve large-scale engineering problems accurately and efficiently. This need motivates the contribution. To capture in detail the macroscopic effects of microssites to socopic processes, many authors have developed multi-scale numerical schemes. A common drawback of such methods is the prohibitive computational cost. Recently,Machine Learning based approaches have raised as promising alternatives to traditional methods. Artificial Neural Networks – ANNs – have been used to predict the constitutive behaviour of complex, heterogeneous materials, with reduced calculation costs. However, a major weakness of ANN is the lack of a rigorous framework based on principles of physics. This often implies a limited capability to extrapolate values ranging outside the training set and the need of large, high-quality datasets, on which performing the training. This work focuses on the use of Thermodynamics-based Artificial Neural Networks – TANN – to predict the constitutive behaviour of natural composites. Dimensionality reduction techniques – DRTs – are used to embed information of microscopic processes into a lower dimensional manifold. The obtained set of variables is used to characterize the state of the material at the macroscopic scale. Entanglement of DRTs with TANN allows to reproduce the complex nonlinear material response with reduced computational costs and guarantying thermodynamic admissibility. To demonstrate the method capabilities an application to a heterogeneous material model is presented

Acousto-optic interaction enhancement in dual photonic-phononic cavities

Light control through elastic waves is a well established and mature technology. The underlying mechanism is the scattering of light due to the dynamic modulation of the refractive index and the material interfaces caused by an elastic wave, the so-called acousto-optic interaction. This interaction can be enhanced in appropriately designed structures that simultaneously localize light and elastic waves in the same region of space and operate as dual optical-elastic cavities, often called phoxonic or optomechanical cavities. Typical examples of phoxonic cavities are multilayer films with a dielectric sandwiched between two Bragg mirrors or, in general, defects in macroscopically periodic structures that exhibit dual band gaps for light and elastic waves. In the present work we consider dielectric particles as phoxonic cavities and study the influence of elastic eigenmode vibrations on the optical Mie resonances. An important issue is the excitation of elastic waves in such submicron particles and, in this respect, we analyze the excitation of high-frequency vibrations following thermal expansion induced by the absorption of a femtosecond laser pulse. For spherical particles, homogeneous thermalization leads to excitation of the particle breathing modes. We report a thorough study of the acousto-optic interaction, correct to all orders in the acousto-optic coupling parameter, by means of rigorous full electrodynamic and elastodynamic calculations, in both time and frequency domains. Our results show that, under double elastic-optical resonance conditions, strong acousto-optic interaction takes place and results in large dynamical shifts of the high-Q optical Mie resonances, manifested through multiphonon exchange mechanisms

Tactile signatures and hand motion intent recognition for wearable assistive devices

Within the field of robotics and autonomous systems where there is a human in the loop, intent recognition plays an important role. This is especially true for wearable assistive devices used for rehabilitation, particularly post-stroke recovery. This paper reports results on the use of tactile patterns to detect weak muscle contractions in the forearm while at the same time associating these patterns with the muscle synergies during different grips. To investigate this concept, a series of experiments with healthy participants were carried out using a tactile arm brace (TAB) on the forearm while performing four different types of grip. The expected force patterns were established by analysing the muscle synergies of the four grip types and the forearm physiology. The results showed that the tactile signatures of the forearm recorded on the TAB align with the anticipated force patterns. Furthermore, a linear separability of the data across all four grip types was identified. Using the TAB data, machine learning algorithms achieved a 99% classification accuracy. The TAB results were highly comparable to a similar commercial intent recognition system based on a surface electromyography (sEMG) sensing

Chromosome Painting Using Microdissection Techniques

Chromosome microdissection is a technique that was first described in 1981 by Scalenge et al. Since then, several modifications have been made and it was recently applied to dissect abnormal parts of aberrant chromosomes, the origin of which was unknown, with the ultimate aim of identifying the origin of the dissected chromosomal material (Meltzer et al. 1992). The aim of this project was to develop the technique, so that it could be further used as a molecular cytogenetic tool in the delineation of chromosome aberrations encountered in the diagnostic workload of this department which remain unidentifiable by using standard cytogenetic techniques. The steps associated with the technique involved the microdissection of several copies of a specific chromosomal region, PCR amplification using a degenerate oligonucleotide primer (DOP primer with six 'N' degenerate bases), labelling of the amplified product with biotin-11-dUTP and finally, reverse chromosome painting by hybridising the labelled product on normal metaphase cells. The location of the hybridisation signal would then reveal the chromosomal origin of the microdissected DNA of interest. All parameters that could affect the efficiency of the DOP-PCR amplification, such as the primer concentration and annealing temperatures were evaluated by using low concentrations of at first, human genomic DNA and finally FACS isolated copies of chromosome 4 as a positive control. Satisfactory results meant that the values of the parameters tested were kept constant for all further attempts. Contamination was the main drawback in interpreting the PCR results. The nature of the DOP primer that could amplify literally any type of DNA template, in conjunction with the fact that the starting microdissected material did not exceed in total a few hundred femptograms (fg) (an average size band equals to 15-50fg, 1fg=10-9 mug) made the amplification extremely sensitive to extraneous contaminations. It was therefore necessary to sequentially introduce multiple specific precautions (i.e. barrier-pipette tips, autoclaving all solutions, preparing small aliquots of each of the PCR reagents to allow only a single use per experiment and performing all steps involved with the PCR inside a sterile safety cabinet) in order to prevent contamination. Several approaches to chromosome microdissection were investigated. Successfiil results were obtained by dissecting the fragment of interest and transferring it into a collection tube by gently touching the tip of the needle inside the collection drop, so as to release the DNA fragment without having to break the tip of the needle inside the tube. For this, it was very important to obtain the correct size of needles. Successfiil micro-FISH probes were produced by less than ten fragments, proving the efficiency of the technique. Successful results were obtained from microdissections of the chromosome regions 7p21-31, 21q21-22, 16cen, 16cen→q22 as well as double minutes present in an abnormal Acute Myeloid Leukaemia case (AML). Signals produced by FISH were very bright, covering fully the corresponding region. Using competitor DNA totally eliminated cross-reactivity with the other chromosomes of the cells. The successful micro-FISH results indicated that the conditions of all steps involved were appropriate for further generation of micro-FISH probes, providing that contamination was either absent or present at very low levels at the first critical round of amplification. These results suggest that chromosome microdissection should have the potential for introduction into routine clinical practice. The next stage is to use the optimised approach described here in an unselected series of cytogenetic cases to see if its potential as a diagnostic tool can be realised

A proposal for the implementation of quantum gates with photonic-crystal coupled cavity waveguides

Quantum computers require technologies that offer both sufficient control over coherent quantum phenomena and minimal spurious interactions with the environment. We show, that photons confined to photonic crystals, and in particular to highly efficient waveguides formed from linear chains of defects doped with atoms can generate strong non-linear interactions which allow to implement both single and two qubit quantum gates. The simplicity of the gate switching mechanism, the experimental feasibility of fabricating two dimensional photonic crystal structures and integrability of this device with optoelectronics offers new interesting possibilities for optical quantum information processing networks.Comment: 4 pages, 3 figure

Acousto-optic interaction enhancement in dual photonic-phononic cavities

Light control through elastic waves is a well established and mature technology. The underlying mechanism is the scattering of light due to the dynamic modulation of the refractive index and the material interfaces caused by an elastic wave, the so-called acousto-optic interaction. This interaction can be enhanced in appropriately designed structures that simultaneously localize light and elastic waves in the same region of space and operate as dual optical-elastic cavities, often called phoxonic or optomechanical cavities. Typical examples of phoxonic cavities are multilayer films with a dielectric sandwiched between two Bragg mirrors or, in general, defects in macroscopically periodic structures that exhibit dual band gaps for light and elastic waves. In the present work we consider dielectric particles as phoxonic cavities and study the influence of elastic eigenmode vibrations on the optical Mie resonances. An important issue is the excitation of elastic waves in such submicron particles and, in this respect, we analyze the excitation of high-frequency vibrations following thermal expansion induced by the absorption of a femtosecond laser pulse. For spherical particles, homogeneous thermalization leads to excitation of the particle breathing modes. We report a thorough study of the acousto-optic interaction, correct to all orders in the acousto-optic coupling parameter, by means of rigorous full electrodynamic and elastodynamic calculations, in both time and frequency domains. Our results show that, under double elastic-optical resonance conditions, strong acousto-optic interaction takes place and results in large dynamical shifts of the high-Q optical Mie resonances, manifested through multiphonon exchange mechanisms

Towards New Half-Metallic Systems: Zinc-Blende Compounds of Transition Elements with N, P, As, Sb, S, Se, and Te

We report systematic first-principles calculations for ordered zinc-blende compounds of the transition metal elements V, Cr, Mn with the sp elements N, P, As, Sb, S, Se, Te, motivated by recent fabrication of zinc-blende CrAs, CrSb, and MnAs. They show ferromagnetic half-metallic behavior for a wide range of lattice constants. We discuss the origin and trends of half-metallicity, present the calculated equilibrium lattice constants, and examine the half-metallic behavior of their transition element terminated (001) surfaces.Comment: 2nd Version: lattice constants calculations added, text revise