151 resultados para NANOPARTICLE ARRAYS
Synthesis of Directional Modulation Arrays for Circular Polarization Transmission (Best Paper Award)
Resumo:
We investigate periodic optomechanical arrays as reconfigurable platforms for engineering the coupling between multiple mechanical and electromagnetic modes and for exploring many-body phonon dynamics. Exploiting structural resonances in the coupling between light fields and collective motional modes of the array, we show that tunable effective long-range interactions between mechanical modes can be achieved. This paves the way towards the implementation of controlled phononic walks and heat transfer on densely connected graphs as well as the coherent transfer of excitations between distant elements of optomechanical arrays.
Resumo:
Purpose: To investigate, for the first time, the influence of pharmacist intervention and the use of a patient information leaflet on self-application of hydrogel-forming microneedle arrays by human volunteers without the aid of an applicator device.
Methods: A patient information leaflet was drafted and pharmacist counselling strategy devised. Twenty human volunteers applied 11 × 11 arrays of 400 μm hydrogel-forming microneedle arrays to their own skin following the instructions provided. Skin barrier function disruption was assessed using transepidermal water loss measurements and optical coherence tomography and results compared to those obtained when more experienced researchers applied the microneedles to the volunteers or themselves.
Results: Volunteer self-application of the 400 μm microneedle design resulted in an approximately 30% increase in skin transepidermal water loss, which was not significantly different from that seen with self-application by the more experienced researchers or application to the volunteers. Use of optical coherence tomography showed that self-application of microneedles of the same density (400 μm, 600 μm and 900 μm) led to percentage penetration depths of approximately 75%, 70% and 60%, respectively, though the diameter of the micropores created remained quite constant at approximately 200 μm. Transepidermal water loss progressively increased with increasing height of the applied microneedles and this data, like that for penetration depth, was consistent, regardless of applicant.
Conclusion: We have shown that hydrogel-forming microneedle arrays can be successfully and reproducibly applied by human volunteers given appropriate instruction. If these outcomes were able to be extrapolated to the general patient population, then use of bespoke MN applicator devices may not be necessary, thus possibly enhancing patient compliance.
Resumo:
Engineering plasmonic nanomaterials or nanostructures towards ultrasensitive biosensing for disease markers or pathogens is of high importance. Here we demonstrate a systematic approach to tailor effective plasmonic nanorod arrays by combining both comprehensive numerical discrete dipole approximations (DDA) simulation and transmission spectroscopy experiments. The results indicate that 200×50 nm nanorod arrays with 300×500 nm period provide the highest FOM of 2.4 and a sensitivity of 310 nm/RIU. Furthermore, we demonstrate the use of nanorod arrays for the detection of single nucleotide polymorphism in codon 12 of the K-ras gene that are frequently occurring in early stages of colon cancer, with a sensitivity down to 10 nM in the presence of 100-fold higher concentration of the homozygous genotypes. Our work shows significant potential of nanorod arrays towards point-of-care applications in diagnosis and clinical studies.
Resumo:
In this work we present core–shell nanowire arrays of gold coated with a nanometric layer of cobalt. Despite the extremely small Co volume, these core–shell nanowires display large magneto-optical activity and plasmonic resonance determined by the geometry of the structure. Therefore, we are able to tune both the plasmonic and magneto-optical response in the visible range. Through optical and ellipsometric measurements in transmission, and applying a magnetic field to the sample, it is possible to modulate the value of the phase angle (Del {Δ}) between the S and P polarised components. It was found that the core–shell sample produced an order of magnitude larger variation in Del with changing magnetic field direction, compared with hollow cobalt tubes. The enhancement of magneto optical properties through the plasmonic nature of the gold core is complemented with the ability to induce magnetic influence over optical properties via an externally applied field. Moreover, we demonstrate for the first time the ability to use the remanent magnetisation of the Co, in conjunction with the optical properties defined by the Au, to observe remanent optical states in this uniquely designed structure. This new class of magnetoplasmonic metamaterial has great potential in a wide range of applications, from bio-sensing to data storage due to the tuneable nature of multiple resonance modes and dual functionality.
Resumo:
Massive multiple-input multiple-output (MIMO) systems are cellular networks where the base stations (BSs) are equipped with unconventionally many antennas, deployed on colocated or distributed arrays. Huge spatial degrees-of-freedom are achieved by coherent processing over these massive arrays, which provide strong signal gains, resilience to imperfect channel knowledge, and low interference. This comes at the price of more infrastructure; the hardware cost and circuit power consumption scale linearly/affinely with the number of BS antennas N. Hence, the key to cost-efficient deployment of large arrays is low-cost antenna branches with low circuit power, in contrast to today’s conventional expensive and power-hungry BS antenna branches. Such low-cost transceivers are prone to hardware imperfections, but it has been conjectured that the huge degrees-of-freedom would bring robustness to such imperfections. We prove this claim for a generalized uplink system with multiplicative phasedrifts, additive distortion noise, and noise amplification. Specifically, we derive closed-form expressions for the user rates and a scaling law that shows how fast the hardware imperfections can increase with N while maintaining high rates. The connection between this scaling law and the power consumption of different transceiver circuits is rigorously exemplified. This reveals that one can make the circuit power increase as p N, instead of linearly, by careful circuit-aware system design.
Resumo:
We consider a multipair decode-and-forward relay channel, where multiple sources transmit simultaneously their signals to multiple destinations with the help of a full-duplex relay station. We assume that the relay station is equipped with massive arrays, while all sources and destinations have a single antenna. The relay station uses channel estimates obtained from received pilots and zero-forcing (ZF) or maximum-ratio combining/maximum-ratio transmission (MRC/MRT) to process the signals. To reduce significantly the loop interference effect, we propose two techniques: i) using a massive receive antenna array; or ii) using a massive transmit antenna array together with very low transmit power at the relay station. We derive an exact achievable rate in closed-form for MRC/MRT processing and an analytical approximation of the achievable rate for ZF processing. This approximation is very tight, especially for large number of relay station antennas. These closed-form expressions enable us to determine the regions where the full-duplex mode outperforms the half-duplex mode, as well as, to design an optimal power allocation scheme. This optimal power allocation scheme aims to maximize the energy efficiency for a given sum spectral efficiency and under peak power constraints at the relay station and sources. Numerical results verify the effectiveness of the optimal power allocation scheme. Furthermore, we show that, by doubling the number of transmit/receive antennas at the relay station, the transmit power of each source and of the relay station can be reduced by 1.5dB if the pilot power is equal to the signal power, and by 3dB if the pilot power is kept fixed, while maintaining a given quality-of-service.
Resumo:
The properties of metasurfaces composed of doubly periodic arrays of interwoven quadrifilar spiral conductors on magnetized ferrite substrates have been investigated with the aid of the full-wave electromagnetic simulator. The effects of incident wave polarization and ferrite magnetization on the scattering characteristics have been analysed at both normal and in-plane dc magnetic bias. The features of the fundamental topological resonances in the interwoven spiral arrays on ferrite substrates are illustrated by the simulation results and the effects of ferrite gyrotropy and dispersion on the array resonance response and fractional bandwidth are discussed.
Resumo:
The absolute yield of hydroxyl radicals per unit of deposited X-ray energy is determined for the first time for irradiated aqueous solutions containing metal nanoparticles based on a “reference” protocol. Measurements are made as a function of dose rate and nanoparticle concentration. Possible mechanisms for hydroxyl radical production are considered in turn: energy deposition in the nanoparticles followed by its transport into the surrounding environment is unable to account for observed yield whereas energy deposition in the water followed by a catalytic-like reaction at the water-nanoparticle interface can account for the total yield and its dependence on dose rate and nanoparticle concentration. This finding is important because current models used to account for nanoparticle enhancement to radiobiological damage only consider the primary interaction with the nanoparticle, not with the surrounding media. Nothing about the new mechanism appears to be specific to gold, the main requirements being the formation of a structured water layer in the vicinity of the nanoparticle possibly through the interaction of its charge and the water dipoles. The massive hydroxyl radical production is relevant to a number of application fields, particularly nanomedicine since the hydroxyl radical is responsible for the majority of radiation-induced DNA damage.
Resumo:
Background and purpose: Gold nanoparticles (GNPs) are novel agents that have been shown to cause radiosensitisation in vitro and in vivo. Tumour hypoxia is associated with radiation resistance and reduced survival in cancer patients. The interaction of GNPs with cells in hypoxia is explored.
Materials and methods: GNP uptake, localization, toxicity and radiosensitisation were assessed in vitro under oxic and hypoxic conditions.
Results: GNP cellular uptake was significantly lower under hypoxic than oxic conditions. A significant reduction in cell proliferation in hypoxic MDA-MB-231 breast cancer cells exposed to GNPs was observed. In these cells significant radiosensitisation occurred in normoxia and moderate hypoxia. However, in near anoxia no significant sensitisation occurred.
Conclusions: GNP uptake occurred in hypoxic conditions, causing radiosensitisation in moderate, but not extreme hypoxia in a breast cancer cell line. These findings may be important for the development of GNPs for cancer therapy.
Resumo:
Gold nanoparticles (GNPs), have been demonstrated as effective preclinical radiosensitising agents in a range of cell models and radiation sources. These studies have also highlighted difficulty in predicted cellular radiobiological responses mediated by GNPs, based on physical assumptions alone, and therefore suggest a significant underlying biological component of response. This study aimed to determine the role of mitochondrial function in GNP radiosensitisation. Using assays of DNA damage and mitochondrial function through levels of oxidation and loss of membrane potential, we demonstrate a potential role of mitochondria as a central biological mechanism of GNP mediated radiosensitisation.
Resumo:
Interweaving planar spiral conductors in doubly periodic arrays enable substantially sub-wavelength resonant response along with broadening fractional bandwidth. A self-contained analytical model is proposed to accurately predict the characteristics of the intertwined quadrifilar spiral array near the fundamental resonance. The model, based upon a multiconductor transmission line (MTL) approach, provides physical insight into the unique properties of the distributed interactions between the interleaved counter-wound spiral arms extended beyond a single unit cell and elucidates the mechanisms underlying the array performance at normal and oblique incidence of TE and TM polarised waves. The developed MTL model is instrumental in the design of the artificial surfaces with the specified response.