Circular Input Research Articles

A review of circular economy models and success factors on public-private partnership infrastructure development

PurposeThe application of circular economy (CE) has received wide coverage in the built environment, including public-private partnership (PPP) infrastructure projects, in recent times. However, current studies and practical implementation of CE are largely associated with construction demolition, waste and recycling management. Few studies exist on circular models and success factors of public infrastructures developed within the PPP contracts. Thus, the main objective of this article is to identify the models and key success factors associated with CE implementation in PPP infrastructure projects.Design/methodology/approachA systematic review of the literature was undertaken in this study using forty-two (42) peer-reviewed journal articles from Scopus, Web of Science, Google Scholar and PubMed.FindingsThe results show that environmental factors, sustainable economic growth, effective stakeholder management, sufficient funding, utilization of low-carbon materials, effective supply chain and procurement strategies facilitate the implementation of CE in PPP infrastructure projects. Key CE business models are centered around the extension of project life cycle value, circular inputs and recycling and reuse of projects.Research limitations/implicationsAlthough the study presents relevant findings and gaps for further investigations, it has a limited sample size of 42 papers, which is expected to increase as CE gain more prominence in PPP infrastructure management in future.Practical implicationsThe findings are relevant for decision-making by PPP practitioners to attain the social, economic and environmental benefits of transitioning to circular infrastructure management.Originality/valueThis study contributes to articulating the key models and measures toward sustainable CE in public infrastructure development.

Sustainable international business model innovations for a globalizing circular economy: a review and synthesis, integrative framework, and opportunities for future research

AbstractThe global imperative has increased in recent years for international firms to respond to major threats such as unintended environmental, social, and economic problems arising from ecological destruction, population growth, and economic activity. To respond to this confluence that has created an emerging existential crisis, we identify that a globalizing circular economy (CE) is required and subsequently define a new construct: sustainable international business model innovations. In doing so, we introduce circular inputs, sharing platforms, product as a service, product use extension, and resource recovery as business models that contain the potential to reply to these grand challenges. Based on CE principles, the innovations and designs introduced are contrasted with the traditional linear economic model and are presented as actionable standardization/adaptation alternatives for companies responding to differing informal and formal international institutions. Based on the theoretical underpinnings of the resource-based, dynamic capabilities, and international business model innovation perspectives, we introduce an integrative framework that is accompanied by a series of detailed research questions to provide future research opportunities for the domain. This conceptual approach holds that international resource design influences marketing capabilities adaptation which, in turn, impacts international performance and offers a foundation from which to build the literature.

Multivariable Analysis of Nonlinear Optical Loop Mirror Operating Parameters Using Jones Matrices and Three-Dimensional Renderings

Nonlinear optical loop mirrors (NOLMs) are used in modern fiber optic devices and optical communications. In this study, we present numerical analyses of the multiple variables involved in the operation of an NOLM in low- and high-power transmissions. The Jones matrix formalism was used to model linear and circular polarization inputs. We used three-dimensional (3D) plots to identify the characteristics required in the experimental operation of the NOLM. These characteristics, including the critical power, low- and high-power transmission, and dynamic range, depend on parameters such as the fiber loop length, input power, angle of retarder plate, and input polarization. A standard single-mode fiber (SMF-28) with high twist loop lengths of 100, 300, and 500 m and input powers of 0–100 W was simulated. Three-dimensional surface graphics provided a comprehensive view of the NOLM transmission and considerably enhanced the optimal transmission by manipulating adjustable device components including the power and polarization control plates. Optimal transmission facilitates its use in integrating ultrafast pulse generation, optical signal processing, optical communication systems, and photonic integrated circuit applications.

Circular Input Rate: novel indicator to assess circularity performances of materials in a sector – Application to rare earth elements in e-vehicles motors

A smarter and sustainable mobility is key for a carbon-neutral and circular Europe, although electrification will require a massive supply of critical materials. Circular strategies can support the transition by maximizing the materials’ value and through effective actions, which however require an adequate monitoring framework.To assess materials’ circularity in a given sector, the novel Circular Input Rate (CIR) indicator is proposed and applied to rare-earths in e-motors’ permanent magnets to monitor recent progresses of circular strategies and estimate their effects in future scenarios. Results prove that the CIR effectively captures the contribution of all circular strategies: in 2030, reuse and remanufacturing can keep in the loop about 90tons of Nd, to be added to 161tons of secondary Nd from functional recycling (captured by the EOL-RIR indicator).In future research, the CIR could be tested to assess materials’ circularity in other sectors, which also will allow to better understand its limitations and potentials.

Partial-update strictly linear, semi-widely linear, and widely linear geometric-algebra adaptive filters

Geometric-algebra based adaptive filters have been successfully employed in many applications such as computer vision, data fusion and linear prediction where the unknown parameters of interest are high-dimensional multivectors. However, conventional geometric-algebra adaptive filters, such as the strictly linear geometric-algebra least mean square (SL-GA-LMS) algorithm, are only applicable to circular multivector-valued inputs with rotation-invariant probability distribution functions. To remove this limitation, we propose new semi-widely linear and widely linear GA-LMS algorithms. As geometric-algebra adaptive filters can have extremely high computational complexity, partial-update variants of these algorithms with reduced complexity are also developed employing stochastic, sequential and M-max partial updating strategies. Steady-state and transient performances of the proposed partial-update algorithms are analysed. As an isomorphism to the partial-update GA-LMS algorithms, widely linear, semi-widely linear and strictly linear quaternion LMS algorithms with partial updates are proposed and analysed for noncircular quaternion inputs. Finally, numerical studies are carried out to confirm the advantages of the proposed methods and the convergence analysis results for multivector and quaternion-valued inputs.

A simple 3D printed microfluidic device for point-of-care analysis of urinary uric acid

Point-of-care testing (POCT) technology allows scientists to monitor and diagnose diseases at the patient site, much faster than classical lab-based methods. Herein, a rapid, simple, and sensitive 3D printed microfluidic device integrated with smartphone-based on-chip detection is described for POCT quantification of urinary uric acid. The device includes two circular inputs each connected to a microliter-scale chamber, separated by an integrated porous membrane, located between the sample and reagent chambers. The microfluidic device was fabricated from a transparent photopolymer using a 3D printer, in a single run. The concentration of uric acid was determined based on a chromogenic reaction in which ferrous ion, produced via the reduction of ferric ion by the analyte, complexed with 1,10-phenanthroline, and the color was recorded by a smartphone. Response surface methodology including a central composed design was utilized to evaluate the experimental parameters and subsequent introduction of a multivariate model to describe the experimental conditions. Under the optimum conditions, the calibration curve was linear over the concentration range of 30–600 mg L−1. The limit of detection was determined to be 10.5 mg L−1. The microfluidic device was successfully utilized for the recovery and quantification of uric acid in the urine, with recoveries ranging from 91.7 to 99.7%.

Formation of TiN coatings by air plasma spraying

Titanium nitride (TiN) coatings were obtained on the surface of 12Kh18N10T steel by air plasma spraying (APS) of TiN powders using an arc plasmatron made by the authors. The plasmatron has a node of circular input and gas-dynamic focusing of the powder and the output apertures of the nozzle-anode are made in the form of rectangular narrowing-expanding channels (No.34334 RK: IPC H05H 1/42). A study of operation modes of a plasmatron for spraying of powder coatings was carried out. The structural-phase state, microhardness and wear resistance of TiN coatings were systematically investigated. The optimum APS operating mode for deposition of TiN powder was determined: current 250 A, voltage 68 V, argon gas flow 34 L/min, spraying distance 150 mm. To reduce the oxidation of TiN powder in the APS process, a method of creating a nitrogen environment at the outlet of the anode nozzle, nitrogen flow rate 2.3 bar was used. The results of structural analysis showed that TiN is the main phase of the coating. The mechanism of formation of TiN structures was characterized by analyzing SEM results of TiN coating surface morphology and TiN droplets sprayed on the surface of the sample. The results showed that the TiN(1) coating has better wear resistance than the TiN(2) and TiN(3) coatings. The cross-sectional and longitudinal microhardness of the TiN coating was investigated. The highest cross-sectional hardness of TiN coating is 1250 HV0.1, which is in accordance with mode 1.

Quantitative analysis of trace N2, Ar in O2 using glow discharge optical emission spectroscopy.

A trace level of N2 and Ar gases in O2 ambience were quantitatively analyzed for the first time by glow discharge optical emission spectroscopy. Microplasma was generated in a compact gas cell by a metal (Au) electrode pair of 1mm diameter and ∼1mm separation with the driving voltage of ∼0.9kV and the current of ∼5 mA in ∼60 Torr. 358 and 813nm optical emission bands were used for N2 and Ar detection, respectively. A spectroscopy fiber bundle having a circular input cross section of ∼700 µm in diameter and an output of 100 µm in width and 3mm in height was employed to promote the signal collection efficiency while preserving high spectral resolution. As a result, the detection sensitivities <1 ppm (3 - σ) were attained for both N2 and Ar within 10s. The detection accuracy was also promoted by correcting the N2 and Ar band signal intensities using the neighboring O emission band intensities, which led to detection errors <2% (3 - σ) for both N2 and Ar.

Waveguide Linear-to-Circular Polarization Converter With Cross Polarization Below −40 dB Within 16% Band

A passive waveguide component with circular input and output ports that converts the incident TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1,1</sub> mode polarization from circular to linear and vise versa (a polarizer) is under investigation. Compared with a number of previous researches on this topic, including structures with elliptical, rectangular, truncated cross sections, and rectangular waveguides with periodically perturbed walls, the problem of realization of an ultralow cross-polarization factor (below −40 dB) within the maximum bandwidth is theoretically analyzed in detail based on dispersion evaluation. The solution in the form of a rectangular structure with a pair of corrugated walls with precise mechanical adjustment was manufactured and measured yielding the bandwidth of 16%. A polarizer with such characteristics is extremely important when served as an element of a microwave system for input–output through one window of a high-power high-gain gyrotron traveling-wave tube (gyro-TWT) with a helically corrugated waveguide.

Formation of highly concentrated heterogeneous flows during plasma deposition of powder materials

Most industrial installations for plasma spraying of powder materials are equipped by nozzles with local (radial) powder input into the thermal plasma jet generated by the plasma torch. Such a local input of the sprayed material significantly perturbs the flow of the plasma jet, and causes dispersion of temperature and velocity of the particles of the sprayed powder materials. This work presents study of high-temperature heterogeneous flows generated by the electric arc plasma torch PNK - 50 with an annular (circular) input unit of powder materials with their gas-dynamic focusing developed at ITAM SB RAS. The performed experiments proved that the annular injection of a powder material guarantees the stable formation of a highly concentrated flow of thermal plasma with particles of sprayed powder materials. The comparative analysis clearly showed the advantages of annular powder input unit with its gas-dynamic focusing. In contrast to local point injection, axisymmetric annular injection practically does not disturb the jet of thermal plasma and, thus, significantly increases the efficiency of interphase exchange.

Qualitative and Numerical Research of Body Motion in a Resisting Medium

Proposed activity presents next stage of the study of the problem of the plane-parallel motion of a rigid body interacting with a resistant medium through the frontal plane part of its external surface. Under constructing of the force acting of medium, we use the information on the properties of medium streamline fl w around in quasistationarity conditions (for instance, on the homogeneous circular cylinder input into the water). The medium motion is not studied, and we consider such problem in which the characteristic time of the body motion with respect to its center of masses is comparable with the characteristic time of motion of the center of masses itself.

Parametric spatial post-filtering utilising high-order circular harmonics with applications to underwater sound-field visualisation.

Beamforming using a circular array of hydrophones may be employed for the task of two-dimensional (2D) underwater sound-field visualisation. In this article, a parametric spatial post-filtering method is proposed, which is specifically intended for applications involving large circular arrays and aims to improve the spatial selectivity of traditional beamformers. In essence, the proposed method is a reformulation of the cross-pattern coherence (CroPaC) spatial post-filter, which involves calculating the normalised cross-spectral density between two signals originating from coincident beamformers. The resulting parameter may be used to sharpen another beamformer steered in the same look-direction, while attenuating ambient noise and interferers from other directions. However, while the original 2D version of the algorithm has been demonstrated to work well with second-order circular harmonic input, it becomes increasingly less suitable with increasing input order. Therefore, the proposed reformulation extends the applicability of CroPaC for much higher orders of circular harmonic input. The method is evaluated with simulated data of a 96-channel circular hydrophone array in three different passive sonar scenarios, where the proposed post-filter is shown to improve the spatial selectivity of both delay-and-sum and minimum-variance distortionless response beamformers.

Improved accuracy of quantitative birefringence imaging by polarization sensitive OCT with simple noise correction and its application to neuroimaging.

Polarization-sensitive optical coherence tomography (PS-OCT) enables three-dimensional imaging of biological tissues based on the inherent contrast provided by scattering and polarization properties. In fibrous tissue such as the white matter of the brain, PS-OCT allows quantitative mapping of tissue birefringence. For the popular PS-OCT layout using a single circular input state, birefringence measurements are based on a straight-forward evaluation of phase retardation data. However, the accuracy of these measurements strongly depends on the signal-to-noise ratio (SNR) and is prone to mapping artifacts when the SNR is low. Here we present a simple yet effective approach for improving the accuracy of PS-OCT phase retardation and birefringence measurements. By performing a noise bias correction of the detected OCT signal amplitudes, the impact of the noise floor on retardation measurements can be markedly reduced. We present simulation data to illustrate the influence of the noise bias correction on phase retardation measurements and support our analysis with real-world PS-OCT image data.

A high resolution multi-phase clock Time-Digital Convertor implemented on Kintex-7 FPGA

Time-digital Converter (TDC) aims to measure the arrival time of the leading edge of the pulse signal. Our recent work presented a high resolution multi-phase TDC based on the Kintex-7 Field Programmable Gate Array (FPGA) device. A simple I/O tile based circular input buffer is employed to oscillate the input signal periodically, and then a multi-phase TDC based on ISERDES core with a 625 ps bin size is used to accomplish the multiple measurements for getting higher resolution performance. In this paper, the design concept, architecture, as well as kernel implementation considerations are all discussed. To evaluate the TDC's performance, we built a verification system based on Kintex-7 FPGA. Initial test results indicate that the TDC's effective bin size is successfully reduced from 625 ps to 78.125 ps, and the measured dual-channel time resolution is better than 35 ps RMS.

Interplay between reverse logistics and circular economy: Critical success factors-based taxonomy and framework

The production and consumption practices that follow the “take-make-dispose” flow have negatively impacted the environment over time. This has propelled the society to evaluate and seek sustainable development options, where Circular Economy (CE) emerged as a relevant concept. This embraced the accountability for reverse logistics of the end-of-life products, which is seen as a costly and complex effort to be managed. This article develops a taxonomy for critical success factors (CSFs) of the reverse logistics capable of creating value for the company and its supply chain, from the perspective of the CE technical cycle, and provides a framework that represents the relationship between the CSFs and reverse logistics in the context of the circular supply chain. The methodology adopted was the tertiary literature review using content analysis with a sample of 66 reviews. The proposed taxonomy embraced five CSFs: Material Planning and Management, Life Cycle Assessment, Industrial Sustainability, Information and Communication Technology, and Promoters and Relationships. The framework illustrates how each component of the circular supply chain (i.e. Circular Inputs, Product Design, Process Design and Circular Flows) is influenced by the five CSFs of the reverse logistics obtained, highlighting the Promoters and Relationships CSF, since it influences all components of the circular supply chain and, consequently, reverse logistics.

Analysis of the Unconstrained Frequency-Domain Block LMS for Second-Order Noncircular Inputs

The unconstrained frequency-domain block least mean square (UFBLMS) algorithm is a de facto standard in frequency-domain adaptive filtering, owing to its fast convergence for correlated input signals. However, although many complex-valued signals in real-world applications are second-order noncircular (improper), for computational convenience, existing mean square analyses of UFBLMS assume second-order circular (proper) input data. This, in turn, makes conventional mean square evaluations of UFBLMS inadequate. To address this issue, we propose a novel performance evaluation framework of UFBLMS, which makes it possible to investigate how the full second-order statistics of second-order noncircular correlated input signals, i.e., both their covariance and complementary covariance, influence the output error and the weight error of UFBLMS. A unified stability bound on the step-size of UFBLMS is next provided, enabling intuitive closed-form relations, in the steady-state stage, between the terms within full second-order error statistics, namely, the mean square error (MSE) and complementary MSE, and the input noncircularity. Furthermore, this proposed full second-order statistical framework is shown to enable more physical insight into the underlying physics of the contribution of the real and imaginary channels of UFBLMS, which cannot be achieved using the standard MSE analysis due to its insufficient degrees of freedom. Simulations and real-world experiments in the system identification setting support the analysis.

Ultra-directional high-efficiency chiral silicon photonic circuits

Chiral light matter interaction enables new fundamental researches and applications of light. The interaction has traditionally faced challenges in low directionality and efficiency based on spin orbit interaction of light in microscopic waveguides. It is pivotal to exploit photonic integrated circuits to efficiently engineer photonic chiral behavior. Here, we present ultra directional high efficient chiral coupling in silicon photonic circuits based on low order to high order mode conversion and interference. We show that the directionality of chiral coupling, in principle, can approach minus/plus 1 with circular polarization inputs, benefited from the underlying mechanism of complete destructive and constructive interference. The chiral coupling efficiency can exceed 70%, with negligible scattering to nonguided modes, much higher than conventional coupling mechanisms. Moreover, the chiral silicon photonic circuits can function as a perfect 3 dB power splitter for arbitrarily linear polarization inputs, and also open up the possibility of on chip chirality determination to further flourish the development of chiral optics.

Steady-State Mean-Square Deviation Analysis of the Zero-Attracting CLMS Algorithm With Circular Gaussian Input

When the complex least mean-square (CLMS) algorithm is used to estimate a complex sparse system, its convergence rate is relatively slow. To make full use of the sparsity of the unknown system to improve convergence rate, a zero-attracting CLMS (ZA-CLMS) algorithm has recently been proposed. In order to predict the statistical behavior of the complex adaptive filter after converging, this paper analyzes the steady-state mean-square deviation (MSD) performance of ZA-CLMS with circular Gaussian input. For mathematical tractability, in the analysis, the unknown system weights are divided into two sets according to their values and some statistical assumptions are used. The simulation results are provided to show the superior performance of ZA-CLMS for complex sparse system identification and to verify the validity of the theoretical expressions for predicting the steady-state MSD performance.

Degree of optical polarization as a tool for detecting melanoma: proof of principle.

Determining the optical polarization properties of a skin lesion is a proposed method to differentiate melanoma from other skin lesions. We developed an in vivo Stokes polarimetry probe that fires a laser of known polarization at the skin and measures the Stokes parameters of the backscattered light in one shot. From these measured Stokes parameters, we can calculate the degree of polarization (DOP). Through testing on rough skin phantoms, a correlation between backscattered DOP and skin roughness was identified for both linear and circular input polarization, the latter of which was found to be more useful. In a pilot clinical trial of 69 skin lesions in vivo, it was found that the mean DOP for melanoma (linear input on melanoma: 0.46 ± 0.09) was greater than that of other lesions (linear input on all other lesions: 0.28 ± 0.01). This separation is greater for circular polarized input light, and it is likely that circular polarized light's greater sensitivity to surface roughness contributes to this result. In addition, all skin lesions demonstrated a stronger depolarizing effect on circular polarized light than linear polarized light. We have identified DOP as a potentially useful measurement to identify melanoma among other types of skin lesions.

Tighter focus for ultrashort pulse vector light beams: change of the relative contribution of different field components to the focal spot upon pulse shortening.

We investigate the focusing of Poisson-spectrum few cycle pulsed light beams for linear, circular, azimuthal, and radial input polarizations with and without a first-order vortex. It is shown that, for all the considered cases, the focal spot is tighter when compared to long pulses due to the increased blue frequency content in the ultrashort pulses spectrum. More significantly, we show, for what we believe is the first time, that upon pulse shortening different focused beam vector components associated with different Bessel functions J0 and J1 undergo a change in the relative weight of their respective contribution to the focal spot size. This effect is caused by the different spectral dependencies of J0 and J1 near the focus. This newly discovered property of broadband ultrashort pulses could be exploited in light-matter interactions advantageously.