Gradient metasurfaces: a review of fundamentals and applications

In the wake of intense research on metamaterials the two-dimensional analogue, known as metasurfaces, has attracted progressively increasing attention in recent years due to the ease of fabrication and smaller insertion losses, while enabling an unprecedented control over spatial distributions of transmitted and reflected optical fields. Metasurfaces represent optically thin planar arrays of resonant subwavelength elements that can be arranged in a strictly or quasi periodic fashion, or even in an aperiodic manner, depending on targeted optical wavefronts to be molded with their help. This paper reviews a broad subclass of metasurfaces, viz. gradient metasurfaces, which are devised to exhibit spatially varying optical responses resulting in spatially varying amplitudes, phases and polarizations of scattered fields. Starting with introducing the concept of gradient metasurfaces, we present classification of different metasurfaces from the viewpoint of their responses, differentiating electrical-dipole, geometric, reflective and Huygens' metasurfaces. The fundamental building blocks essential for the realization of metasurfaces are then discussed in order to elucidate the underlying physics of various physical realizations of both plasmonic and purely dielectric metasurfaces. We then overview the main applications of gradient metasurfaces, including waveplates, flat lenses, spiral phase plates, broadband absorbers, color printing, holograms, polarimeters and surface wave couplers. The review is terminated with a short section on recently developed nonlinear metasurfaces, followed by the outlook presenting our view on possible future developments and perspectives for future applications.Comment: Accepted for publication in Reports on Progress in Physic

Fundamentals of crude oil and natural gas processing

This training manual includes term project methodical guide on the course "Fundamentals of crude oil and natural gas processing" in English. The main purpose of the training manual is to provide students the theoretical and methodological assistance at performance the term project on the course "Fundamentals of crude oil and natural gas processing". The manual contains the initial data and reference material needed to perform the calculations. The manual is intended for the students of speciality 6.050304 "Oil and gas production" in English

Using problem descriptions to represent variabilities for context-aware applications

This paper investigates the potential use of problem descriptions to represent and analyse variability in context-aware software products. By context-aware, we refer to recognition of changes in properties of external domains, which are recognised as affecting the behaviour of products. There are many reasons for changes in the operating environment, from fluctuating resources upon which the product relies, to different operating locations or the presence of objects. There is an increasing expectation for software intensivedevices to be context-aware which, in turn, adds further variability to problem description and analysis. However, we argue in this paper that the capture of contextual variability on current variability representations and analyses has yet to be explored. We illustrate the representation of this type of variability in a pilot study, and conclude with lessons learnt and an agenda for further work

Optimizing Control of a Batch Reaction Process

The batch chemical reaction is chosen as the process model to be optimized and the rate constants are functions of pressure only, as the reactions are assumed to occur isothermally. The time optimal control problem considered here means to determine the minimum time path from the given initial compositions to desired final compositions by manipulating the process pressure. A gradient method or a steepest-ascent method is applied to determine the control variable program by using the high speed digital computer. Numerical solutions are presented for the following three cases: (1) no constraint on the operating pressure ...... open and matched terminal constraint. (2) constraint on the operating pressure ...... open terminal constraint. (3) constant operating pressure ...... open terminal constraint

Learning through play: an educational computer game to introduce radar fundamentals

The information exchange has evolved from traditional books to computers and Internet in a few years' time. Our current university students were born in this age: they learn and have fun with different methods as previous generations did. These digital natives enjoy computer games. Thus, designing games for learning some selected topics could be a good teaching strategy for such collective and also for undergraduate university students. This paper describes the development and test of an educational computer game revolving around radar. The objective of the game RADAR Technology is to teach students about the fundamentals of radar, while having fun during the learning experience. Based on the principle that you learn better what you practice, the authors want to induce students to discover a difficult to understand topic by proposing them a different experience, in a format better adapted to their generation skills. The computer game has been tested with actual students and the obtained results seem to be very promising

Polycyclic aromatic hydrocarbons (PAHs) in air and vegetation: case study at three selected toll stations along North South Expressway in Johor, Malaysia

Polycyclic aromatic hydrocarbons (PAHs) from vehicular emission are products of the incomplete combustion of organic fuel, and are usually attached to the particulate matter from the emission and can caused pollution and hazard to human health due to its carcinogenic, mutagenic and teratogenic characteristics. The objective of this study is i) to determine the concentration PAHs in the air of sampling area, ii) to determine the concentration PAHs in vegetation, iii) to determine the relationship of concentration of PAHs in plants and air of sampling area and iv) to study the different composition of PAHs in different species of plants to determine the potential biomonitoring agent. The study is carried out at three toll stations along PLUS’ North-South Expressway in Johor. Air sample and plant leaves sample collected were extracted with ultrasonic agitation in dichloromethane and fractionated according to polarity before submitted to gas chromatography – mass spectrometry analysis to determine the concentration of the PAHs compounds. Spearman’s rank correlation test was carried out using SPSS to determine the correlation between concentration of PAHs in air and plant leaves sample. Seven PAHs were identified and quantified in the atmospheric sample and plant leaves sample. Those PAHs were acenaphtylene (ACN), phenanthrene (PHE), fluorene (FL), pyrene (PY), chrysene (CHR), benzo[a]anthracene (BaA), and benzo[a]pyrene (BaP). Significant correlation at 0.05 level (2-tailed) was observed in samples of Ficus microcarpa, Cordyline fruticosa, Hibiscus spp., and Ixora coccinea with the value 0.622, 0.643, 0.680 and 0.608 respectively. The positive correlation shows that the plants have capabilities to absorb organic pollutants from the environment. Based from this research, the most suitable species to be introduced into the environment as a biomonitoring agent and to be further studied as a medium for low and medium level pollution bioremediation is Ficus microcarpa, Cordyline fruticosa, and Ixora coccine

Spectral selectivity in capillary dye lasers

We explore the spectral properties of a capillary dye laser in the highly multimode regime. Our experiments indicate that the spectral behavior of the laser does not conform with a simple Fabry-Perot analysis; rather, it is strongly dictated by a Vernier resonant mechanism involving multiple modes, which propagate with different group velocities. The laser operates over a very broad spectral range and the Vernier effect gives rise to a free spectral range which is orders of magnitude larger than that expected from a simple Fabry-Perot mechanism. The presented theoretical calculations confirm the experimental results. Propagating modes of the capillary fiber are calculated using the finite element method (FEM) and it is shown that the optical pathlengths resulting from simultaneous beatings of these modes are in close agreement with the optical pathlengths directly extracted from the Fourier Transform of the experimentally measured laser emission spectra

Digital Ecosystems: Ecosystem-Oriented Architectures

We view Digital Ecosystems to be the digital counterparts of biological ecosystems. Here, we are concerned with the creation of these Digital Ecosystems, exploiting the self-organising properties of biological ecosystems to evolve high-level software applications. Therefore, we created the Digital Ecosystem, a novel optimisation technique inspired by biological ecosystems, where the optimisation works at two levels: a first optimisation, migration of agents which are distributed in a decentralised peer-to-peer network, operating continuously in time; this process feeds a second optimisation based on evolutionary computing that operates locally on single peers and is aimed at finding solutions to satisfy locally relevant constraints. The Digital Ecosystem was then measured experimentally through simulations, with measures originating from theoretical ecology, evaluating its likeness to biological ecosystems. This included its responsiveness to requests for applications from the user base, as a measure of the ecological succession (ecosystem maturity). Overall, we have advanced the understanding of Digital Ecosystems, creating Ecosystem-Oriented Architectures where the word ecosystem is more than just a metaphor.Comment: 39 pages, 26 figures, journa