Continuous Regime Research Articles

Optical nonlinear effects of nickel and cobalt substituents in 1D/2D manganese tungstate/rGO nanocomposite for smart filtering optical radiation

The smart filtering effects of Manganese tungstate/reduced Graphene Oxide (MnWO4/rGO,) and Nickel and cobalt doped Manganese tungstate/reduced Graphene Oxide (Mn(1-x+y)NixCoyWO4/rGO) self-assembled urchin like microspheres are explored. Their relevant optical nonlinearities are related with that of pristine MnWO4 nanorods. The third order optical nonlinearities are characterized by a Z-scan analysis with continuous wave regime of 633 nm (He:Ne laser). The highest nonlinear attenuation is attributed to Mn(1-x+y)NixCoyWO4/rGO (5 wt%) microstructures. The intensity dependent absorption β(m/W) and nonlinear index of refraction n2(cm2/W) is determined to be 4.8×10−4 and 8.8×10−7. The maximum attainable optical susceptibility χTOT3 is 16.8×10−8 esu. The morphology of pristine MnWO4 nanorods and urchin like microstructures is evidenced using HRSEM images. The defect D and optical phonon G bands from the Raman signal besides the Agυ1 modes confirms the materialization as nanocomposite.

Tracking the origin of black holes with the stochastic gravitational wave background popcorn signal

ABSTRACT Unresolved sources of gravitational waves (GWs) produced by the merger of a binary of black holes at cosmological distances combine into a stochastic background. Such a background is in the continuous or popcorn regime, depending on whether the GW rate is high enough so that two or more events overlap in the same frequency band. These two regimes respectively correspond to large and small values of the so-called duty cycle. We study the detection regime of the background in models of primordial black holes (PBHs) and compare it to the one produced by black holes of stellar origin. Focusing on ground-based detectors, we show that the duty cycle of the PBH-origin background is larger than that of astrophysical black holes because of differences in their mass function and the merger rate. Our study opens up the possibility to learn about the primordial or astrophysical nature of black hole populations by examining the statistical properties of the stochastic background.

Effects of continuous cropping Jiashi muskmelon on rhizosphere microbial community.

The continuous cropping of crops can result in the deterioration of the soil environment and cause a decline in plant health and yield, which complicates agricultural production. However, the effects of continuous melon cropping on rhizospheric microbial communities remain poorly understood. In this study, high-throughput absolute quantification 16S rRNA gene amplicon sequencing was employed to analyze the bacterial community structure of greenhouse rhizosphere soil from Jiashi muskmelon replanted for 0, 1, 2, and 3 years (CK, 1a, 2a, and 3a, respectively). The results showed that long- term continuous cropping caused significant changes in soil physicochemical properties. The bacterial absolute abundances increased, but the bacterial community richness and diversity were significantly lost (p < 0.05). The composition of bacterial community was more similar after 2 and 3 years of continuous cropping. The longer the continuous cropping years were, the greater the shift in the bacterial diversity and abundance. Analysis of potential functional components revealed that different bacterial groups were enriched in different continuous cropping years. The significant reduction of the taxa associated with nitrate reduction may be responsible for the loss of soil nitrogen in continuous cropping soil. In summary, continuous cropping had a significant impact on the bacterial community structure of Jiashi muskmelon rhizospheric soil, and these results will provide a reference for soil management and scientific fertilization of melon and other crops under a continuous cropping regime.

Increase by Substitution of Galvanized Steel for Aluminum Mirrors in the UV Solar Radiation in Canal with Fins and Side Panels That Disinfect Wastewater

The need arises to seek new depuration technological responses aimed at the reuse of wastewater, which requires the development and promotion of economically and environmentally sustainable technologies. In this paper, it studies an improvement to a disinfection system sustainable, low-cost, patented in 2019, and based on solar energy. The water passes through a canal of reflective material in the continuous regime, and in the batch regime, the water remains in the canal. The panels are located parallel to the lateral faces of the canal. The fraction of the radiation reflected outside the canal reaches the reflective side panels that return the radiation to the canal. These panels concentrate the radiation in the canal through reflection. The disinfectant canal with fins and side panels uses ultraviolet radiation to eliminate the bacterial load carried by treated wastewater. For this reason, the present work analyzes the incidence in the area of influence of the disinfectant canal. When reflective aluminum mirrors were installed on the sloping walls of the canal, global radiation increased by 4%, when they were used on the side panels, it increased 3%, and when the aluminum mirrors were used on the canal walls and side panels, it increased 8%. The important thing about this work is that it opens windows for improving the system through materiality so the new challenge is the search for the optimal material considering the impact on global radiation and consequently on the bacteriological elimination.

Visible-Light Mediated Carbamoylation of Nitrones under a Continuous Flow Regime.

Herein, we report a rapid and scalable continuous-flow photocatalytic approach for the carbamoylation of nitrones. This protocol makes use of readily available 4-amido-1,4 dihydropyridines as carbamoyl radical precursors. The scope of this transformation exhibits high compatibility with complex structures containing amino acids, peptides, and glycosides. Importantly, the developed method allows a photocatalytic synthetic strategy in combination with flow conditions, maximizing the potential and efficiency for the synthesis of valuable α-(N-hydroxy)amino amides.

Local dimensionality and inverse persistence analysis of atmospheric turbulence in the stable boundary layer.

The dynamics across different scales in the stable atmospheric boundary layer has been investigated by means of two metrics, based on instantaneous fractal dimensions and grounded in dynamical systems theory. The wind velocity fluctuations obtained from data collected during the Cooperative Atmosphere-Surface Exchange Study-1999 experiment were analyzed to provide a local (in terms of scales) and an instantaneous (in terms of time) description of the fractal properties and predictability of the system. By analyzing the phase-space projections of the continuous turbulent, intermittent, and radiative regimes, a progressive transformation, characterized by the emergence of multiple low-dimensional clusters embedded in a high-dimensional shell and a two-lobe mirror symmetrical structure of the inverse persistence, have been found. The phase space becomes increasingly complex and anisotropic as the turbulent fluctuations become uncorrelated. The phase space is characterized by a three-dimensional structure for the continuous turbulent samples in a range of scales compatible with the inertial subrange, where the phase-space-filling turbulent fluctuations dominate the dynamics, and is low dimensional in the other regimes. Moreover, lower-dimensional structures present a stronger persistence than the higher-dimensional structures. Eventually, all samples recover a three-dimensional structure and higher persistence level at large scales, far from the inertial subrange. The two metrics obtained in the analysis can be considered as proxies for the decorrelation time and the local anisotropy in the turbulent flow.

Continuous flow synthesis and separation of mandelic acid enantiomers in a modular microfluidic system

Mandelic acid enantiomers are key precursors in the synthesis of valuable chiral products. However, separating enantiomers in reasonable amounts is a challenging task despite advances in chiral chromatography and other discontinuous and expensive techniques. To tackle these problems, we designed and tested a modular microfluidic system working in a fully continuous flow regime. The system consists of two modules, namely (i) a packed-bed microreactor (PBR) with immobilized enzyme lipase and (ii) a membrane microseparator driven by an imposed electric field. The immobilized catalyst converts a racemic substrate, methyl mandelate, into mandelic acid enantiomers. The enzyme preferentially synthesizes (R)-(−)-mandelic acid within minutes. The product stream from PBR is fed into a membrane microseparator operated in a counter-current regime. An inserted dialysis membrane and an orthogonally applied electric field completely separate the electrically charged enantiomers from their mixture with unreacted and uncharged methyl mandelate within 1.5 min. Under improved reaction and separation conditions, approximately 1 g of (R)-(−)-mandelic acid are produced per day with almost 60 % enantiomeric excess. Moreover, the productivity of this system is easily scalable without compromising its excellent reaction-transport characteristics.

Reverse saturation absorption of CaWO4 and Ce3+ substituted CaWO4 growth on rGO sheets an 2D/3D nanocomposite for smart filtering optical radiation

The CaWO4, CaWO4/rGO and Ce3+:CaWO4/rGO nanocomposites are synthesized and subjected to hydrothermal treatment. The optical filtering behavior of materials was explored using reliable Z-scan analysis. It utilizes the focused Gaussian beam of He:Ne laser (632.8 nm) in a continuous wave regime. Closed aperture Z-scan analysis of the synthesized samples exhibits negative refraction evident from the pre-focal peak to post-focal valley. The explicit third order nonlinear parameters such as kerr nonlinearityΔn = 5.6 x10-7 (W/cm2), two photon absorption β = 2.3 x10-4 (W/cm) and optical susceptibility χ3 = 10.5 x10-8 esu were obtained for the Ce3+:CaWO4/rGO (5 wt%) nanocomposites. Ce3+:CaWO4 micro dumbbells grown on the sheets of rGO is observed using HRSEM and HRTEM images. The C 1 s spectra recorded from XPS displays the area of sp2 hybridized (CC) graphitic like structure increases which enhances the optical nonlinearities. Id/Ig ratio increases by increasing the addition of rGO signifies the reduction of oxygenated functional groups in the nanocomposite evidenced by Raman spectra analysis. The bandgap calculated from the Tauc-plot relation is found to be around 3.0 eV and it decreases to 2.9 eV when the wt.% of rGO is increased.

Modeling Approach to Capture the Effect of High Frequency Flashing Light in Steady-State Microalgae Cultures

With the advent of efficient artificial light systems, the possibility of exploiting pulsed light (PL) in microalgal cultivation is gaining renewed attention. In this work, a model was developed to describeArthrospira maxima production in continuous cultivation systems, under both continuous and high-frequency pulsed light regimes. The model is based on the one originally developed by Camacho-Rubio, modified to link photosynthetic units activation to biomass growth, accounting also for maintenance. The modified model, calibrated in continuous light regime, was found to properly predict steady-state microalgal growth at different light intensities and residence times. The model was then validated on experimental data carried out under extreme PL conditions (high frequencies up to 3700 Hz and duty cycles as low as 0.01). Remarkably, it was able to account for the flashing light effect (FLE, i.e., increased biomass production with respect to continuous light supply) measured under such conditions and can therefore be a valuable tool to optimize the energetic efficiency of algal cultivation.

Photo-induced temperature in optical interference coatings.

The photo-induced temperature in multilayer systems is calculated using an original analytical model based on optical/thermal analogies. Various illumination regimes are considered, ranging from ps pulses to a continuous regime, while taking into account a variable repetition rate. The temporal and spatial (3D) resolutions are quantified, and the distributions of temperature and stationary optical field are compared. The temperature spectra are given as a function of the illumination wavelength. Thermal and electromagnetic damage thresholds are compared. Lastly, the thermal fringes resulting from structured optical illumination are studied.

Modelling of flame spread over biomass fuel arrays with various inclined angles and spacings

Flame spread of combustible materials with discontinuous distribution is a typical heat and mass transfer process that contributes a lot to the thermal disaster of building fires and wildland fires. However, application models of flame spread over discrete fuels have not been well addressed. In this study, 54 groups of line arrays of birch rods, 5 mm in diameter and 55 mm long, were designed by varying nine spacings (S, 1–9 mm) and six slopes (θ, 15°−90°). Under the combined effect of fuel spacing and slope, flame spread behaviors are categorized into continuous flame spread regime (regime I) and discrete flame spread regime (regime II). Under the two regimes, calculation models of incident heat flux are respectively determined, which can predict flame spread rate well. Moreover, flame spread rate and mass loss rate per unit area present a growing tendency with increasing spacing in regime I, but have a limited dependency in regime II. The prediction models of mass loss rate and flame spread rate are developed, which match the experimental results well. Furthermore, a correlation between dimensionless flame length and modified dimensionless heat release rate is proposed in the inclined configuration. In the vertical configuration, flame length presents a power-law dependency on the heat release rate per unit width with the exponent range of 1.202–1.838.

Plug-and-play generation of non-Gaussian states of light at a telecom wavelength.

In the context of emerging quantum technologies, this work marks an important progress towards practical quantum optical systems in the continuous variable regime. It shows the feasibility of experiments where non-Gaussian state generation entirely relies on plug-and-play components from guided-wave optics technologies. This strategy is successfully demonstrated with the heralded preparation of low amplitude Schrödinger cat states via single-photon subtraction from a squeezed vacuum. All stages of the experiment are based on off-the-shelf fiber components. This leads to a stable, compact, and easily re-configurable realization, fully compatible with existing fiber networks and, more in general, with future out-of-the-laboratory applications.

A new UV-grafted photocatalytic membrane for advanced treatment of biologically treated baker’s yeast (BTY) effluent: Fabrication, characterization and performance evaluation

In this study, a superior hydrophilic polyethersulfone (PES) membrane modified with L-Lysine (C, N codoped)-TiO2/WO3 (LTW) photocatalyst is presented to endow self-antifouling properties and amelioration of the membrane performance in versatile wastewater treatment. ATR-FTIR spectra, FESEM, 3D AFM images, and water contact angle (WCA) measurement indicated that successful connection of LTW photocatalyst on PES membrane surface led to improved membrane properties like hydrophilicity and surface roughness. The PES/LTW membranes demonstrated significant enhancement in water permeability (49.79 L/m2.h) and antifouling feature (flux recovery rate (FRR) of 96.96 %). The optimal membrane (M-2, 0.03 wt%) with the highest hydrophilicity, pure water flux (PWF), and fouling resistance, was used to evaluate the filtration performance in a cross-flow setup. Response surface methodology (RSM) was utilized to model and optimize the filtration process. The effects of three influential variables, including operating pressure (P, 3–5 bar), feed COD concentration (C, 500–1500 mg/l), and effect of irradiation on four responses, i.e., flux (L/m2.h), FRR (%), dye removal efficiency (%), and COD removal efficiency (%) were assessed in a continuous regime using nanofiltration of biologically treated baker's yeast (BTY) effluent. The optimum conditions were found to be 693 mg/l of feed COD concentration and 4.44 bar of operating pressure under visible light irradiation. The experimental data compared to the predicted ones indicated a good agreement that confirms the validity of the models describing the performance of the photocatalytic membrane.

Photonic Crystal Surface Emitting Diode Lasers with λ near 2 µm

Epitaxially regrown electrically pumped photonic crystal surface emitting lasers (PCSELs) operating near 2 µm were designed and fabricated within a III-V-Sb material system. A high-index-contrast photonic crystal layer was incorporated into the laser heterostructures by air-pocket-retaining epitaxial regrowth. Transmission electron microscopy studies confirmed uniform and continuous AlGaAsSb initial growth over the nano-patterned GaSb surface, followed by the development of the air-pockets. The PCSEL threshold current density had a minimal value of ~170 A/cm2 in the 160–180 K temperature range when the QW gain spectrum aligned with the Γ2 band edge of the photonic crystal. The devices operated in a continuous wave regime at 160 K. The divergence and polarization of the multimode laser beam emitted from the 200 µm × 200 µm PCSEL aperture were controlled by filamentation.

Oxidative Fast Pyrolysis of High-Density Polyethylene on a Spent Fluid Catalytic Cracking Catalyst in a Fountain Confined Conical Spouted Bed Reactor.

The oxidative fast pyrolysis of plastics was studied in a conical spouted bed reactor with a fountain confiner and draft tube. An inexpensive fluid catalytic cracking (FCC) spent catalyst was proposed for in situ catalytic cracking in order to narrow the product distribution obtained in thermal pyrolysis. Suitable equivalence ratio (ER) values required to attain autothermal operation were assessed in this study, i.e., 0.0, 0.1, and 0.2. The experiments were carried out in continuous regime at 550 °C and using a space-time of 15 gcatalyst min gHDPE -1. The influence of an oxygen presence in the pyrolysis reactor was analyzed in detail, with special focus on product yields and their compositions. Operation under oxidative pyrolysis conditions remarkably improved the FCC catalyst performance, as it enhanced the production of gaseous products, especially light olefins, whose yields increased from 18% under conventional pyrolysis (ER = 0) to 30% under oxidative conditions (ER = 0.1 and 0.2). Thus, conventional catalytic pyrolysis led mainly to the gasoline fraction, whereas light olefins were the prevailing products in oxidative pyrolysis. Moreover, the oxygen presence in the pyrolysis reactor contributed to reducing the heavy oil fraction yield by 46%. The proposed strategy is of great relevance for the development of this process, given that, on one hand, oxygen cofeeding allows solving the heat supply to the reactor, and on the other hand, product distribution and reactor throughput are improved.

Mass burning rate and merging behaviour of double liquid pool fires under cross winds

This paper experimentally investigates the effects of cross wind on flame interaction and burning characteristics of double liquid pool fires. Two burners were used including a square burner and a line burner. The separation distance between the double fires and the speed of cross wind were varied, providing a total of 66 test conditions. The experimental results showed that the mass burning rate increases initially with increasing separation distance until a critical value, after which the mass burning rate decreases with a further increase of the separation distance. This non-monotonic behaviour was attributed to the competition between an increase of air entrainment and a decrease of the flame heat feedback from the adjacent fire, as the separation distance increases. A correlation was developed for the mass burning rate based on the stagnant layer solution of liquid fuel evaporation and combustion, incorporating the separation distance between two fires and cross wind, and is found to predict well the experimental data for all experiments. Image analysis indicated that, with increasing separation distance, the flame merging of double pool fires can be divided into three regimes: the continuous merging regime, the intermittent merging regime, and the non-merging regime. A physical model was proposed for the flame interaction and merging behaviour of the double pool fires, based on which a piecewise function is developed for predicting the flame merging probability and the criteria for the merging/non-merging flames are also determined. The proposed formulations were found to correlate well with the current measurements of liquid pool fires and published literature data of single pool fires.

Influence of Physical Fitness, Anthropometric Profile, and Biological Maturation on Technical Performance and Enjoyment of Untrained Children Who Participate in Continuous and Fractional Small-Sided Games.

A crossover-design study in which 12 children participated in two regimens of SSG (continuous and fractional). At the beginning of the study, all children were evaluated using physical fitness tests (horizontal jump test, vertical jump, cardiorespiratory fitness, and agility), anthropometric profile (weight, height, Body Mass Index (BMI), and waist circumference (WC)), and biological maturation (peak years of growth velocity). All sessions were recorded and analyzed with the Performance Assessment in Team Sports instrument, and at the end of each game each child was asked to answer a scale of enjoyment for physical activity. The results of the paired samples t-test showed no significant differences in the measures of technical performance and perceived enjoyment for the continuous and fractional regimens of SSGs (p &gt; 0.05). The correlation results showed that technical performance in the continuous and fractional regimes was related to agility, horizontal jump, and height, while biological maturation was only related to technical performance in the fractional regimen of SSGs. Perceived enjoyment showed a negative relationship with weight, height, BMI, and WC. The fractional and continuous regimens of SSGs implemented in this study induced similar technical demands and enjoyment. Furthermore, the results suggest that physical fitness, anthropometric profile, and biological maturation may influence the technical performance and enjoyment of SSGs.

Development of photon counting technique to operate from discrete photons to continuous regime using DAQ card in LabVIEW platform

A sensor like a photomultiplier tube (PMT) has shown many applications, particularly in the photon counting regime, where it generates discrete electrical pulses in response to the input photons. Commercially available photon counters used to count these pulses assuming the incident photons in the discrete form. In general, whenever two or more photons arrive concurrently, the photon counter record it as a single pulse and count it as single count. On the contrary, when continuous photons arrive, the discrete photon counting approach ceases to function, and a continuous capture technique is used to estimate the photons intensity. In this article, a photon-counting method based on a data acquisition card (DAQ Model: Agilent U1071A), which works in the discrete to continuous photon regime where the commercial photon counters stop counting is described. To facilitate the precise counting of the discrete and merged pulses, a program has been developed in LabVIEW incorporating the logic of pulse width and amplitude. The developed technique is tested for its functionality and compared with the commercially available photon counter SR400. The outcomes of the study indicate that the developed system is capable of operating from discrete photons to a continuous regime and has a better dynamic range than the SR400 gated photon counter.

Nonlinear Absorption in Plasmonic Titanium Nitride Nanocrystals

AbstractTitanium nitride nanoparticles have become a research interest due to their distinguished optical and photothermal properties. Furthermore, the search for nanoparticle solutions with tunable nonlinear optical properties for laser‐based applications is critical. More specifically, third order optical nonlinearities such as reverse saturable absorption, optical liming, and self‐focusing are important in the biomedical and electronics fields. The optical nonlinearities of titanium nitride plasmonic nanoparticles are investigated as a function of material concentration in water solutions. Furthermore, the effect of nanoparticle clustering on optical nonlinearities is investigated by fabricating micrometer‐sized clusters of ≈50 nm titanium nitride particles. These studies demonstrate that the nonlinear absorption coefficient increases linearly with concentration. However, clusters require higher concentrations compared to the freestanding nanoparticles to exhibit similar nonlinear absorption coefficient and optical density. Similarly, the optical limiting threshold for titanium nitride nanoparticles appears to be lower compared to the cluster solutions, which is impacted by the collective scattering of nanoparticles and high reverse saturable absorption. In addition, self‐focusing is observed in the continuous resonant regime. This study provides an in‐depth analysis of the nonlinear optical properties of titanium nitride, with relevant consequences for applications such as sensor protection and photothermal therapy.

Soil microbial community assembly and stability are associated with potato (Solanum tuberosum L.) fitness under continuous cropping regime.

Continuous cropping obstacles caused by the over-cultivation of a single crop trigger soil degradation, yield reduction and the occurrence of plant disease. However, the relationships among stability, complexity and the assembly process of soil microbial community with continuous cropping obstacles remains unclear. In this study, molecular ecological networks analysis (MENs) and inter-domain ecological networks analysis (IDENs), and a new index named cohesion tools were used to calculate the stability and complexity of soil microbial communities from eight potato cultivars grown under a continuous cropping regime by using the high-throughput sequencing data. The results showed that the stability (i.e., robustness index) of the bacterial and fungal communities for cultivar ZS5 was significantly higher, and that the complexity (i.e., cohesion values) was also significantly higher in the bacterial, fungal and inter-domain communities (i.e., bacterial-fungal community) of cultivar ZS5 than other cultivars. Network analysis also revealed that Actinobacteria and Ascomycota were the dominant phyla within intra-domain networks of continuous cropping potato soil communities, while the phyla Proteobacteria and Ascomycota dominated the correlation of the bacterial-fungal network. Infer community assembly mechanism by phylogenetic-bin-based null model analysis (iCAMP) tools were used to calculate the soil bacterial and fungal communities’ assembly processes of the eight potato cultivars under continuous cropping regime, and the results showed that the bacterial community was mainly dominated by deterministic processes (64.19% - 81.31%) while the fungal community was mainly dominated by stochastic processes (78.28% - 98.99%), indicating that the continuous-cropping regime mainly influenced the potato soil bacterial community assembly process. Moreover, cultivar ZS5 possessed a relatively lower homogeneous selection, and a higher TP, TN, AP and yield than other cultivars. Our results indicated that the soil microbial network stability and complexity, and community assemble might be associated with yield and soil properties, which would be helpful in the study for resistance to potato continuous cropping obstacles.