Showing papers in "Journal of Physics D in 2019"

The 2019 surface acoustic waves roadmap

Abstract: Today, Surface Acoustic Waves (SAWs) and Bulk Acoustic Waves (BAW) are already two of the very few phononic technologies of industrial relevance and can been found in a myriad of devices employing these nanoscale earthquakes on a chip. Acoustic radio frequency filters, for instance, are integral parts of wireless devices. SAWs in particular find applications in life sciences and microfluidics for sensing and mixing of tiny amounts of liquids. In addition to these continuously growing number of applications, SAWs are ideally suited to probe and control elementary excitations in condensed matter at the limit of single quantum excitations. Even collective excitations, classical or quantum, or integrated optomechanical are nowadays coherently interfaced by SAWs. This wide, highly diverse, interdisciplinary and continuously expanding spectrum literally unites advanced sensing and manipulation applications. Remarkably, SAW technology is inherently multiscale and span from single atomic or nanoscopic units up even to the millimeter scale. The aim of this roadmap article is to present a snapshot of the present state of Surface Acoustic Wave science and technology in 2019 and provide an opinion on the challenges and opportunities that the future holds from a group of renown experts covering the interdisciplinary key areas, ranging from fundamental quantum effects to practical applications of acoustic devices in life science.

The 2019 materials by design roadmap

Abstract: Advances in renewable and sustainable energy technologies critically depend on our ability to design and realize materials with optimal properties. Materials discovery and design efforts ideally involve close coupling between materials prediction, synthesis and characterization. The increased use of computational tools, the generation of materials databases, and advances in experimental methods have substantially accelerated these activities. It is therefore an opportune time to consider future prospects for materials by design approaches. The purpose of this Roadmap is to present an overview of the current state of computational materials prediction, synthesis and characterization approaches, materials design needs for various technologies, and future challenges and opportunities that must be addressed. The various perspectives cover topics on computational techniques, validation, materials databases, materials informatics, high-throughput combinatorial methods, advanced characterization approaches, and materials design issues in thermoelectrics, photovoltaics, solid state lighting, catalysts, batteries, metal alloys, complex oxides and transparent conducting materials. It is our hope that this Roadmap will guide researchers and funding agencies in identifying new prospects for materials design.

Chemical and antibacterial effects of plasma activated water: correlation with gaseous and aqueous reactive oxygen and nitrogen species, plasma sources and air flow conditions

Abstract: When cold atmospheric plasma comes into contact with water and biological media, antimicrobial or antitumor effects are induced, representing great potential for applications in biomedicine and agriculture. The need to control and tune the chemical composition and biomedical effects of plasma activated water/media (PAW/PAM) is emerging. By comparing two nonthermal air plasma sources, streamer corona and transient spark, interacting with water in open and closed reactors, and by enhancing the plasma–liquid interaction by water electrospray through these discharges, we demonstrate that the plasma gaseous products strongly depend on the discharge regime, its deposited power and gas flow conditions. The streamer corona strongly leads to the formation of ozone and hydrogen peroxide, while the more energetic transient spark leads to nitrogen oxides and hydrogen peroxide. The gaseous products then determine the chemical properties of the PAW and the dominant aqueous reactive oxygen and nitrogen species (RONS). The production of hydrogen peroxide depends on water evaporation and hydroxyl radical formation, which is determined by the discharge power. A transient spark produces higher concentrations of gaseous and aqueous RONS and induces stronger antibacterial effects than a streamer corona; however, the RONS production rates per joule of deposited energy are comparable for both studied discharge regimes. The net production rate per joule of gaseous nitrogen oxides strongly correlates with that of aqueous nitrites and nitrates. The antibacterial effects of the PAW tested on Escherichia coli bacteria are determined by the aqueous RONS: in the lower power streamer corona, this is ascertained mainly by the dissolved ozone and hydrogen peroxide, and in the higher power transient spark, by the combination of hydrogen peroxide, nitrite and acidic pH, while in the transient spark in the closed reactor it is determined by the acidified nitrites present.

NanoJ: a high-performance open-source super-resolution microscopy toolbox

Abstract: Super-resolution microscopy (SRM) has become essential for the study of nanoscale biological processes. This type of imaging often requires the use of specialised image analysis tools to process a large volume of recorded data and extract quantitative information. In recent years, our team has built an open-source image analysis framework for SRM designed to combine high performance and ease of use. We named it NanoJ-a reference to the popular ImageJ software it was developed for. In this paper, we highlight the current capabilities of NanoJ for several essential processing steps: spatio-temporal alignment of raw data (NanoJ-Core), super-resolution image reconstruction (NanoJ-SRRF), image quality assessment (NanoJ-SQUIRREL), structural modelling (NanoJ-VirusMapper) and control of the sample environment (NanoJ-Fluidics). We expect to expand NanoJ in the future through the development of new tools designed to improve quantitative data analysis and measure the reliability of fluorescent microscopy studies.

Device and materials requirements for neuromorphic computing

Abstract: Energy efficient hardware implementation of artificial neural network is challenging due the "memory-wall" bottleneck. Neuromorphic computing promises to address this challenge by eliminating data movement to and from off-chip memory devices. Emerging non-volatile memory devices that exhibit gradual changes in resistivity are a key enabler of in-memory computing - a type of neuromorphic computing. In this paper, we present a review of some of the non-volatile memory devices (RRAM, CBRAM, PCM) commonly used in neuromorphic application. The review focuses on the trade-off between device parameters such as retention, endurance, device-to-device variation, speed and resistance levels, and the interplay with target applications. This work aims at providing guidance for finding the optimized resistive memory devices material stack suitable for neuromorphic application.

Fundamentals and applications of zwitterionic antifouling polymers

Abstract: Zwitterionic materials as a new class of emerging materials have recently been developed and applied to a broad range of biomedical and engineering applications. Zwitterionic materials possess a unique molecular structure combining both cationic and anionic groups with overall charge neutrality and high hydrophilicity. In this review, we first provide the structure-property relationship of the zwitterionic materials at molecular level, from a molecular simulation viewpoint. Then, we discuss the recent experimental developments in the preparation, properties, and applications of zwitterionic materials, with a particular focus on their antifouling properties on coating surfaces and with additional functionality and applications. Finally, we offer our personal viewpoint of current challenges and future directions in this emerging area. Our goal is to introduce the current status of this type of new zwitterionic materials to researchers from different areas and motivate them to explore all the potentials.

Computational phase-change memory: beyond von Neumann computing

Abstract: The explosive growth in data-centric artificial intelligence related applications necessitates a radical departure from traditional von Neumann computing systems, which involve separate processing and memory units. Computational memory is one such approach where certain tasks are performed in place in the memory itself. This is enabled by the physical attributes and state dynamics of the memory devices. Naturally, memory plays a central role in this computing paradigm for which emerging post-CMOS, non-volatile memory devices based on resistance-based information storage are particularly well suited. Phase-change memory is arguably the most advanced resistive memory technology and in this article we present a comprehensive review of in-memory computing using phase-change memory (PCM) devices.

Inactivation of airborne viruses using a packed bed non-thermal plasma reactor

Abstract: Outbreaks of airborne infectious diseases such as measles or severe acute respiratory syndrome can cause significant public alarm. Where ventilation systems facilitate disease transmission to humans or animals, there exists a need for control measures that provide effective protection while imposing minimal pressure differential. In the present study, viral aerosols in an airstream were subjected to non-thermal plasma (NTP) exposure within a packed-bed dielectric barrier discharge reactor. Comparisons of plaque assays before and after NTP treatment found exponentially increasing inactivation of aerosolized MS2 phage with increasing applied voltage. At 30 kV and an air flow rate of 170 standard liters per minute, a greater than 2.3 log reduction of infective virus was achieved across the reactor. This reduction represented ~2 log of the MS2 inactivated and ~0.35 log physically removed in the packed bed. Increasing the air flow rate from 170 to 330 liters per minute did not significantly impact virus inactivation effectiveness. Activated carbon-based ozone filters greatly reduced residual ozone, in some cases down to background levels, while adding less than 20 Pa pressure differential to the 45 Pa differential pressure across the packed bed at the flow rate of 170 standard liters per minute.

Four resonators based high sensitive terahertz metamaterial biosensor used for measuring concentration of protein

Abstract: A terahertz (THz) metamaterial biosensor based on four identical resonators is experimentally demonstrated, and high sensitivity is achieved by exciting four synchronous inductor-capacitor oscillations in a unit cell. The effect of geometries on the resonance frequency of the sensor is investigated using the finite integration time domain method, and the simulated sensitivity is 85 GHz per refractive index unit. The biosensor sample is fabricated using a surface micromachining process and characterized by a THz time domain spectroscopy system combined with bovine serum albumin (BSA) solution as an analyte. The experimental results indicate that the resonance frequency shows distinct redshift when the concentration of BSA solution increases. When the concentration is high, up to 765 µmol l−1, the frequency shift reaches 50 GHz, and the measurable minimum concentration is low, down to 1.5 µmol l−1. The biosensor is small in shape, wide in measurable range, convenient in operation, and rapid in detection, which is of great significance for rapid concentration measurement, biomolecules detection, and disease diagnosis.

Machine learning for modeling, diagnostics, and control of non-equilibrium plasmas

Abstract: Author(s): Mesbah, A; Graves, DB | Abstract: Machine learning (ML) is a set of computational tools that can analyze and utilize large amounts of data for many different purposes. Recent breakthroughs in ML and artificial intelligence largely enabled by advances in computing power and parallel computing present cross-disciplinary research opportunities to exploit some of these techniques in the field of non-equilibrium plasma (NEP) studies. This paper presents our perspectives on how ML can potentially transform modeling and simulation, real-time monitoring, and control of NEP.

A thin low-frequency broadband metasurface with multi-order sound absorption

Abstract: We present a theoretical and experimental realization of a thin multi-unit metasurface with multi-order sound absorption that exhibits a continuous near-perfect absorption spectrum in the broadband range of 450 Hz–1360 Hz. The metasurface unit is a perforated composite Helmholtz-resonator (PCHR) that is constructed by inserting one or more separating plates with a small hole into the interior of a Helmholtz resonator (HR). The multi-order sound absorption mechanism can be achieved so that with the original absorption peak and the structural size unchanged, multiple near-perfect peaks are obtained in higher frequencies by a PCHR unit. This extraordinary multi-peak performance is the result of the upgraded multi-degree-of-freedom system with the separating plates, which is explained well by the equivalent acoustic circuit. The specific absorption properties of the PCHR unit are investigated thoroughly with a theoretical approach similar to the plane wave expansion method, and verified via the finite element simulations. On this basis, by precisely balancing the parameters of each unit, the absorption bandwidth of the subwavelength 8-unit metasurface is dramatically broadened about 65% by the proposed mechanism. This work would offer a new guidance for the achievement of the wider absorption band and has great potential in engineering applications.

Evolution of molten pool during selective laser melting of Ti–6Al–4V

Abstract: The characteristics of molten pools provide valuable insight into the complexity of the metal additive manufacturing process, which has a significant influence on the quality of the parts built using this process. In our work, we develop a three-dimensional multiphysics finite element model of a selective laser melting (SLM) process on a Ti–6Al–4V alloy. The dynamic characteristics of the molten pool are studied by multiphysics simulation with consideration of phase transitions, recoil pressure, surface tension, and Marangoni effect. The results show the time-evolution of temperature distribution, flow field, and surface morphology of a single track during the SLM process. The recoil pressure caused by evaporation plays a significant role in molten pool dynamics and induces a depression at the head of the molten pool. As a result of the backward Marangoni flow, the material is shifted to the tail region and a vortex is generated. In addition, a protrusion is presented at the middle and start points of the scanned track, while a depression is formed at both sides and at the terminal point. The simulation and the experimental results on the surface morphology of the molten track during the SLM process are in good agreement. Furthermore, it is found that metal evaporation may take place not only on the surface of the molten pool but also inside it, due to the drop in pressure. This is a significant contributor to the formation of porosity in SLM parts.

Quench behavior of high-temperature superconductor (RE)Ba2Cu3Ox CORC cable

Abstract: The high-temperature superconductor (HTS) (RE)Ba 2Cu 3O x (REBCO) conductor on round core (CORC) cable has great advantages with its high current capacity and power density. In REBCO CORC cables, current is redistributed among tapes through terminal contact resistance (TCR) when a local quench occurs. Therefore, its quench behavior is different from the single tape situation. To better understand the underlying physical process of local quenches in CORC cables, a new 3D multi-physics modeling tool for CORC cables is developed and presented in this paper. In this model, the REBCO tape is treated as a thin shell without thickness, and four models are coupled: a T-formulation model, an A-formulation model, a heat transfer model, and an equivalent circuit model. The T-formulation model is applied to the conductor shell only to calculate current distribution, which will be input into the A-formulation model; the A-formulation model is applied to the whole 3D domain to calculate the magnetic field, which is then fed back to the T-formulation model. The hot spot-induced quenches of CORC cables are analyzed. The results show that the thermal stability of the CORC cable can be considerably improved by reducing the TCR. The minimum quench energy (MQE) increases rapidly with the reduction of TCR when the resistance is in a middle range, which is about in this study. When the TCR is too low () or too high (), the MQE shows no obvious variation with TCR. With a low TCR, a hot spot in one tape may induce an overcurrent quench on other tapes. This will not happen in a cable with high TCR. In this case, the tape with a hot spot will quench and burn out before inducing a quench on other tapes. The developed modeling tool can be used to design CORC cables with improved thermal stability.

Dual plasmon-induced transparency and slow light effect in monolayer graphene structure with rectangular defects

Abstract: A novel monolayer graphene structure whose unit cell possesses two rectangular defects is proposed. A very obvious dual plasmon-induced transparency (PIT) effect can be successfully achieved by the destructive interference in the terahertz region. The dual PIT effect can be easily tuned by changing the Fermi energy of the monolayer graphene. Since the graphene of our structure exists in a continuous form, we can simply apply a bias voltage to achieve the tuning performance compared to those structures with discontinuous graphene patterns. We have deduced the expression of the theoretical transmittance and the numerical simulation results are very consistent with the theoretical data. Moreover, we find that this structure has a good slow light property and its group refractive index is as high as 545. Thus, the proposed structure and findings may provide a good guidance for the highly tunable optoelectronic devices and excellent slow light device.

Atmospheric pressure plasma activation of water droplets

Abstract: Low temperature plasma treatment of water is being investigated due to its use in pollution abatement, wound treatment and agriculture. Plasma produced reactive oxygen and nitrogen species (RONS) are formed in the gas phase and solvate into the liquid. Activation of the liquid is often limited by transport of these RONS species to the liquid surface. Micrometer scale droplets immersed in the plasma have a large surface to volume ratio (SVR), which increases the interaction area for a given volume of water, and can increase the rates of transport from the gas to liquid. In this paper, results from 0- and 2-dimensional modeling of air-plasma activation of water micro-droplets are discussed. The solvation dynamics are sensitive to the Henry's law constant (h) of each species, which describes its hydrophobicity (low h) or hydrophilicity (high h). The liquid densities of stable species with high h values (e.g. H2O2, HNOx) are sensitive to droplet diameter. For large droplets, hydrophilic species may deplete the gas-phase inventory of RONS before liquid-phase saturation is reached, limiting the total in liquid density for species with high h. For smaller droplets, higher average in-droplet densities of these species can be produced. Liquid concentrations of stable species with low h (e.g. O3, N2O, H2) had a weak dependence on droplet size as droplets are quickly saturated and solvation does not deplete the gas phase. An analysis of this behavior is discussed which represents the well-stirred reactor (0-dimensional) approximation. Spatial non-uniformity of the plasma also has an impact on the solvation rates and kinetics. Gas phase depletion of high-h species leads to a decrease in solvation rates. Low-h species that saturate the surface of the droplets during plasma-on periods can quickly de-solvate in the afterglow.

Two-dimensional transition metal dichalcogenides mediated long range surface plasmon resonance biosensors

Abstract: Two­dimensional transition metal dichalcogenides (TMDCs), as promising alternative plasmon supporting materials to graphene, exhibit potential applications in sensing. Here, we propose a TMDCs­mediated long range surface plasmon resonance (LRSPR) imaging biosensor, which shows tremendous improvements in both imaging sensitivity (>×2) and detection accuracy (>×10) as compared to conventional surface plasmon resonance (cSPR) biosensors. It is found that the imaging sensitivity of the LRSPR biosensor can be enhanced by the integration of TMDC layers, which is different from the previously reported graphene­ mediated cSPR imaging sensor, whose imaging sensitivity decreases with the number of graphene layers. This imaging sensitivity enhancement effect for the TMDCs­mediated LRSPR sensor originates from the propagating nature of the LRSPR at both interfaces of sensing medium/gold and gold/cytop layer (with a matching refractive index as sensing medium). By tuning the thickness of gold film and cytop layer, it is possible to achieve optimized imaging sensitivity for LRSPR sensors with any known integrated number of TMDC layers and an analyte refractive index. The proposed TMDCs­mediated LRSPR imaging sensor could provide potential applications in chemical sensing and biosensing.

Non-Thermal Plasma-Induced Immunogenic Cell Death in Cancer: A Topical Review.

Abstract: Recent advances in biomedical research in cancer immunotherapy have identified the use of an oxidative stress-based approach to treat cancers, which works by inducing immunogenic cell death (ICD) in cancer cells. Since the anti-cancer effects of non-thermal plasma (NTP) are largely attributed to the reactive oxygen and nitrogen species that are delivered to and generated inside the target cancer cells, it is reasonable to postulate that NTP would be an effective modality for ICD induction. NTP treatment of tumors has been shown to destroy cancer cells rapidly and, under specific treatment regimens, this leads to systemic tumor-specific immunity. The translational benefit of NTP for treatment of cancer relies on its ability to enhance the interactions between NTP-exposed tumor cells and local immune cells which initiates subsequent protective immune responses. This review discusses results from recent investigations of NTP application to induce immunogenic cell death in cancer cells. With further optimization of clinical devices and treatment protocols, NTP can become an essential part of the therapeutic armament against cancer.