Mixed Configuration Research Articles

Periphyton enzymatic activities in the water column along internal low-phosphorus nutrient gradients in the Everglades Stormwater Treatment Areas

The Everglades Stormwater Treatment Areas (STAs), important components in the Everglades Restoration efforts, were built to remove excess phosphorus (P) from stormwater runoff before it enters the Everglades Protection Area. The STAs operate within the low phosphorus domain of constructed wetlands and are mandated to achieve ultra-low P outflow concentrations to protect the receiving water bodies. Microbial processing by periphyton enzymatic activity under these low-P conditions may be critical for achieving nutrient reduction, particularly in the lower reaches of the STA treatment cells where nutrients are primarily in the dissolved organic and particulate forms. Enzymes are produced by periphyton to liberate required nitrogen (N), carbon (C), and P from dissolved organic matter under nutrient limiting conditions. Enzyme activity had not been measured within the STA treatment cells and this study was conducted to evaluate if enzyme activity occurs along the nutrient transect from inflow to outflow in well-performing treatment cells and if this activity differs within the dominant vegetation communities (i.e., emergent or submerged aquatic vegetation, EAV and SAV, respectively). The STAs receive variable hydraulic and nutrient loadings and the potential influence of these conditions on enzyme activity was evaluated under a range of loadings. The periphyton response in three different well-performing STA treatment cells (STA-2 Cells 1 and 3 and STA-3/4 Cell 3B) was evaluated using periphyton that accrued in the water column over a 7-d period. Because nutrient cycling is interrelated, a suite of enzyme activity associated with nutrient acquisition from dissolved organic material was measured. Enzymes associate with P-acquisition (phosphatase; alkaline phosphatase and bis-phosphodiesterase), C-acquisition (β-glucosidase), and N-acquisition (leucine aminopeptidase) were measured along internal transects from inflow to outflow.We found that enzyme activity occurs in the STA treatment cells and the most reactive enzymes were the phosphatase and N-acquisition enzymes; there was little activity and variability measured in the C-acquisition enzyme. Phosphatase activity increased along the nutrient gradient and the rates became more variable at the midflow and outflow transect locations. When dissolved organic P (DOP) in the surface water was above 10 μg/L, the phosphatase rates were reduced, an expected response since enzyme production occurs only during nutrient limiting conditions. When DOP concentrations were <10 μg/L, greatly increased rates were observed but there were still also times when the rates were reduced that did not appear to be influenced by surface water organic P or N concentrations or water depths. The activity for N-acquisition enzyme was also found to be variable, but this variability was between each treatment cell rather than along the transect as observed for phosphatase activity. The proportional change of each enzyme activity to the other was used to evaluate nutrient limiting conditions in the periphyton. Along the transect, both N- and P-limiting conditions were found in the periphyton at the inflow and midflow sites and solely P-limiting conditions at the outflows in all treatment cells. This implies that the mineralization processes can be disrupted under higher nutrient conditions, impacting cycling of the organic material. There were also indications that nutrient cycling may differ between periphyton from the EAV and SAV communities under low-P conditions, suggesting there may be a complementary enzymatic response within a mixed marsh configuration that may enhance nutrient cycling.

Effect of mixed wettability surfaces on flow boiling heat transfer at subatmospheric pressures

Subatmospheric flow boiling heat transfer is a promising method for electronics cooling due to lower saturation temperatures. However, pressure is a crucial parameter that affects surface tension and vapor density. In this study, the effect of surface mixed wettability configuration on bubble dynamics and flow boiling was investigated under atmospheric and subatmospheric pressure conditions. Superhydrophilic, superhydrophobic, and mixed-wettability surfaces were prepared and tested at various heat fluxes and three system pressures of 48 kPa, 68 kPa, and 101 kPa. The channel dimensions were 50 mm × 15 mm, and the channel had a depth of 1 mm. The results showed that biphilic surfaces enhanced the performance up to 28% compared to superhydrophilic surfaces at high heat fluxes for subatmospheric boiling. Flow visualization efforts reveal that mixed-wettability surfaces improve heat transfer by extending the efficient slug regime to higher heat fluxes by preventing dried spot formation. These surfaces benefit from high density nucleation sites at low and medium heat fluxes, resulting in a noticeable performance improvement compared to the superhydrophilic surface. The obtained experimental data in this study will be helpful for the development of thermal-fluid systems operating under subatmospheric conditions.

Evaluating Power Sharing Performance of Distributed Generators in Microgrids With Hybrid Sources and Mixed Tie-Lines

Proportional output power sharing amongst distributed sources in islanded microgrids is necessary to maintain a good voltage profile, avoid tripping of sources and avoid circulating current flows. Underground (UG) cables are popular in densely populated areas and military applications. However, researchers typically consider microgrid networks with overhead lines (OHL) in their studies. This paper examines the power sharing performance among droop controlled inverters and virtual synchronous generators in a system with mixed tie-line configurations i.e., network sections with both OHL and UG cable tie-lines. Furthermore, two proposed control strategies to vary the virtual impedance linearly as a function of the DG output currents are examined for their effectiveness to improve the proportional power sharing. The studies are performed considering a system with four inverter based sources operated with the popularly used <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$L$</tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$RL$</tex-math></inline-formula> droop controllers through detailed simulations in MATLAB/Simulink. The enhancement of power sharing is verified for both uniform and non-uniform inverter controls, different R/X ratios of the OHL and UG cables, and in a meshed network configuration with different loading conditions. Controller hardware in the loop (CHIL) based experiment validation is carried out in Typhoon HIL with linear, non-linear and induction motor load, showing that proposed control strategy results in enhanced power sharing in addition to damping oscillations due to dynamic loads.

Excitonic interactions and Stark fluorescence spectra.

We develop the theory for the Stark fluorescence (SF) of molecular aggregates by taking into account the mixing of the excited states [including the states with charge-transfer (CT) characters]. We use the sum-over-state approach and modified rotating wave approximation to describe interactions of the static and optical fields with the permanent and transition dipoles of the excited states. The SF spectral profiles are calculated using the standard and modified Redfield theories for the emission lineshapes. The resulting expression allows an interpretation of the SF response based on the calculation of only one-exciton states (i.e., the calculation of two-exciton states is not needed). The shape and amplitude of the SF spectrum can exhibit dramatic changes in the presence of the CT states, especially when the CT state is mixed with the red-most emitting exciton levels. In this case, the SF responses are much more sensitive to the exciton-CT mixing as compared with the usual Stark absorption. The limitation of the proposed theory is related to the simplified nature of the Redfield picture, which neglects the dynamic localization within the mixed exciton-CT configuration.

A rule of mixtures approach for delamination damage analysis in composite materials

The present study aims at investigating the delamination behavior of laminated composites in different loading modes within a homogenization theory of mixtures. The delamination damage phenomenon is introduced at the bulk level by eliminating the explicit representation of interfaces. Potential delamination planes are identified according to the developed interfacial stresses, and damage evolution is computed for each mode independently through a stress-based formulation. An arc-length strategy is employed to solve equilibrium equations owing to the snap-back effects. Reliability of the adopted mixing theory, as a framework for integrating the delamination theory into, is assessed by comparing the results with the ones obtained from micromechanical models in a fiber metal laminate structure. Considering delamination, a good agreement is observed in mode I, mode II and mixed mode configurations by evaluating the results against available numerical and experimental data in thermoset and thermoplastic composite systems. The present method has the capability to be used in the conventional finite element codes with the number of elements kinematically needed in the thickness, regardless of the number of layers, which dramatically reduces the computational cost in modeling composites with large number of layers. The proposed approach is not intended to replace other exact methods at the coupon scale, however, its main application would be in modeling delamination on large scale systems with minimum loss of accuracy.

Optimal Components Selection for a DAB Model of CHB Converter

This paper proposes a sizing procedure for the cascaded H-bridge (CHB) converters integrating the battery energy storage system at the submodule level through a dual active bridge (DAB) converter. The suggested methodology considers different parameters, such as the adopted modulation strategies and the topology of the DAB converter employed. Three possible DAB configurations are considered: the one using only full-bridges (for both sides), the one using only half-bridges (for both sides) or a mixed configuration using half-bridge on one side and full-bridge on the other side. After determining the system parameters, the solution capable of reaching the required efficiency target at the minimum cost is obtained. The cost analysis and the efficiency evaluation are carried out considering a dataset containing almost 1000 semiconductor devices whose datasheets have been taken from the manufacturers' websites. The procedure has been developed in the framework of a collaboration with NHOA Energy and its effectiveness is demonstrated by sizing a 1 MW-CHB converter combined with energy storage systems at 11 kV.

Combined capture and reduction of CO2 to methanol using a dual-bed packed reactor

Recently, carbon capture and reduction (CCR) technology has gained interest to directly convert CO2 to value-added products without requiring purification of CO2 and its subsequent transportation. CCR to methanol in one dual function material (DFM) poses mechanistic and kinetic challenges. To counteract this, a process combining Na/Al2O3 as a capture component and Cu/ZnO/Al2O3 (CZA) as methanol synthesis catalyst was developed to allow CCR to methanol. With a 5 vol% CO2 flow for capture and subsequent H2 stream combined with a temperature swing, a methanol selectivity of 26 % was achieved at 9 bar. Further investigation found that Na/Al2O3 significantly increased methanol yield, while a stacked configuration of Na/Al2O3 followed by CZA significantly outperformed a mixed configuration of the two catalysts. With further investigation of operation at higher pressure and surface mechanism, an effective CCR to methanol process using two affordable yet readily available catalysts can be realized.

Development of a compact fast-neutron spectrometer for nuclear emergency response applications

We have developed a Compact Fast Neutron Spectrometer (CFNS) for passive assay of special nuclear material (SNM) through the observation of fast neutrons. The CFNS consists of eight organic glass scintillators (OGS) coupled to silicon photomultipliers and a waveform digitizer, which are integrated within a human-portable box. The CFNS determines the neutron energy profile by spectrum unfolding using the Maximum-Likelihood Expectation Maximization method. The detector acquisition system was optimized to have a dynamic range of up to 10 MeV neutron energy. Bulk special nuclear material (SNM) measurements from the National Criticality Experiments Research Center were analyzed for SNM validation/examination. The results show that the CFNS can be used to distinguish between fission and (α, n) neutron emitters, regardless of intervening material type (Cu and polyethylene) and thickness, by taking the ratio of neutron counts at different regions in the unfolded energy spectrum. Additionally, by fitting an exponential curve to the unfolded energy spectrum of PuO2 and Pu neutron emitters, the CFNS showed the ability of distinguishing between pure Pu oxide, pure Pu metal and mixed oxide-metal configurations.

MHD mixed convection and heatlines approach of nanofluids in rectangular wavy enclosures with multiple solid fins

Two dimensional wavy walls rectangular cavity with inclined magnetohydrodynamic has been examined in mixed convection configurations. Triple fins arranged in the upwards ladder were filled within alumina nanoliquid in the cavity. Vertical sinusoidal walls were heated, and the other side was kept cold while both horizontal walls were kept adiabatic. All walls were motionless except the top cavity that was driven to the right. The diversified range of control parameter in Richardson number, Hartmann number, number of undulations, length of the cavity has been performed in this study. The analysis was simulated using finite element method by employing the governing equation formula, and the results were delineated in the form of streamlines, isotherms, heatlines, and comparisons on several relationships between the local velocity in the y-axis line of 0.6, local and average Nusselt number along the heated surface and dimensionless average temperature. The findings revealed that high concentration nanofluids boost the rate of heat transfer without the need to apply any magnetic field. Results found that the best heat mechanisms are natural convection with significant-high Richardson number as well as constructing two waves on the vertical walls in the cavity.

Alloy Catalysts for Electrocatalytic CO2 Reduction.

CO2 conversion is an anticipated route to resolve the energy crisis and environmental pollution, in which electrocatalysis is one of the technologies closest to industrialization. Alloy catalysts are promising candidates for electrocatalysis, and the high tenability in electronic structures and surface physical and chemical properties allows alloy catalysts high catalytic activity and selectivity for electrocatalytic CO2 reduction. Herein, the recent advances in alloy catalysts for electrocatalytic CO2 reduction have been systematically summarized, with insight into the structure of the active center, catalytic performance, and mechanism, to uncover the key to their high catalytic performance. The alloy catalysts are mainly classified as binary and multi-metallic alloys (medium entropy and high entropy alloy) based on components and mixed configuration entropy, on which the relationship among the active center, catalytic performance, and mechanism has been fully discussed to inspire the rational design of alloy catalysts. Finally, the current challenges and future perspectives are presented to propose the dilemma and development direction for alloy catalysts. This review provides an overview of about the recent progress and future development of alloy catalysts to present a guideline for future research work on relevant catalysts.

Quantum capacitance of supercapacitor electrodes based on M2C MXenes with pure -O and mixed termination: A first-principles study

MXenes have drawn great attention as potential electrode material because of the high capacitive performance. However, there are little information about the quantum capacitance (Cdiff) and surface storage charge (Q) of M2C MXene with pure -O and mixed surface termination. In this paper, density functional theory (DFT) is utilized to explore the Cdiff and Q of M2CO2 monolayers with 3d, 4d and 5d transitional metals (TM) in aqueous and ionic/organic systems. The most stable configurations for the studied systems are confirmed. Sc2CO2, Zr2CO2 and Hf2CO2 monolayers are potential cathode materials. Ti2CO2 monolayer is a potential anode material. The wide voltage has little influence on the electrode type of materials. M2CO2 monolayers gradually transfer from cathode to anode material with the weakening metallicity of transitional metal atom. M2C MXenes with mixed configuration are further explored. M2CO0.42F1.19(OH)0.39 (M = Sc, Cr, Nb, Ta) are cathode materials in aqueous system, M2CO0.42F1.19(OH)0.39 (M = Ti, V, Zr, Mo, Hf, W) are suitable for anode materials.

Mixed Dimer Configuration Model in Type D Cluster Algebras

We define a combinatorial model for $F$-polynomials and $g$-vectors for type $D_n$ cluster algebras where the associated quiver is acyclic. Our model utilizes a combination of dimer configurations and double dimer configurations which we refer to as mixed dimer configurations. In particular, we give a graph theoretic recipe that describes which monomials appear in such $F$-polynomials, as well as a graph theoretic way to determine the coefficients of each of these monomials. In addition, we prove that a weighting on our mixed dimer configuration model yields the associated $g$-vector. To prove this formula, we use a combinatorial formula due to Thao Tran (arXiv:0911.4462, 2009) and provide explicit bijections between her combinatorial model and our own.

An in silico study of sustainable drug pollutants removal using carboxylic acid functionalized-MOF nanostructures (MIL-53 (Al)-(COOH)2): Towards a greener future

Emerging environmental pollutants have become a major environmental challenge due to the highly toxic effluents produced by industries. Among these emerging pollutants, pharmaceutical drugs, which are consumed and are highly soluble, lead to the severe degradation of water resources. To address this issue, adsorptive capturing methods have been considered as a potential solution due to their efficiency and environmental compatibility. This study focuses on the use of carboxylic acid functionalized MIL-53 (Al) (CA/MIL-53 (Al)) for the removal of pharmaceutical pollutants (PhPs) such as acetaminophen, ibuprofen, aspirin and methyl salicylate. The study was conducted employing quantum mechanical (QM), Monte Carlo (MC) and molecular dynamics (MD) simulations. The results of QM analysis exhibited that the functionalization of MIL-53 (Al) with carboxylic acid (CA) groups improved its adsorption affinity. Moreover, the MOF-water-Ibuprofen mixed configurations showed higher chemical reactivity and adsorption capacity. It was demonstrated that the MIL-53 (Al) adsorption characteristics were significantly improved following its functionalization with CA groups. This study highlights the potential of functionalized MOFs as a promising solution for PhPs removal from water resources. The results of this study provide valuable information for further research and the development of new adsorbents for the removal of emerging pollutants in the environment.

Collapse arrest of two-color vector optical solitons in nonlocal nonlinear media

In 2017, Sukhinin et al. investigated optical self-focusing that leads to collapse events for copropagating beams with different colors, which show that collapse events depend on the combined critical power of two beams as well as on the ratio of their individual powers [Phys. Rev. A 95, 031801 (2017)PLRAAN1050-294710.1103/PhysRevA.95.031801]. In this paper, we demonstrate that these collapse events of the two-color vector solitons can be eliminated in self-focusing media with nonlocal nonlinearity. We employ the variational approach to derive an approximate solution of the two-color vector solitons for fundamental, vortex, and mixed configurations. In the regime of strong nonlocality, we also show numerically the collapse arrest of the two-color vector solitons with the split-step Fourier transform method.

Environmental and thermoecological comparative assessment of improved humid air waste heat recovery configurations

This paper provides a comprehensive assessment of the humid air turbine-based waste heat recovery system with respect to different flow configurations in the air saturator. The novelty of this work is to provide a holistic approach to the environmental and thermoecological assessment of Maistosenko cycle-based waste heat recovery units by considering three configurations of air saturator namely, counter-flow, cross-flow, and mixed-flow configuration. In other words, the assessment is carried out to evaluate the performance improvements while comparing the environmental as well as thermoecological perspectives. This provides a broader and wholesome perspective allowing a wider application of these configurations, especially in different climatic conditions experiencing varying ambient temperatures. The ambient temperature is particularly important when air is used as working fluid and routed in three different configurations within the heat recovery unit i.e., air saturator. The addition of humidity in the air saturator tends to improve the performance of bottoming cycle depending on the air direction within the saturator which has a counter, cross and mixed flow configurations. Moreover, ambient or dead state temperature is considered one of the influencing parameters on the performance of considered heat recovery configurations. With the rising ambient temperatures up to 50 °C, owing to intensive heat waves and sustained droughts; the performance indicators of power generation units indicate as much as 25% reduction in the sustainability index along with 10% lowering of energy and exergy efficiencies. In this regard, the flow configuration and efficiency of air saturators become critically important especially as a heat recovery unit while working in intense operating conditions. The results have suggested that counter configuration can offer the highest among of net-work marking 51.9 MW whereas the cross-flow configuration can mark only 49.78 MW. Thermoecological assessment has suggested that the ambient temperature of this type of powerplant can be less than 40 °C. It is concluded that the optimal configuration is counter-flow configuration for the waste heat recovery in gas turbines based upon second law and thermoecological assessment.

Design of an ultra‐wideband picosecond pulse generator based on step recovery diodes with an improved SPICE model

SummaryThis article proposed an ultra‐wideband ultra‐short picosecond pulse generator based on step recovery diodes (SRDs). The equivalent circuit model of SRD is analyzed, and an improved nonlinear simulation program with integrated circuit emphasis (SPICE) model is presented for appropriate circuit simulation in Advanced Design System (ADS) software. An external direct current (DC) voltage source is added to bias the SRD. In this article, a conventional shunt SRD topology configuration is developed to generate the Gaussian pulse. According to the measured data, the Gaussian pulse duration for the shunt SRD pulse generator is 210 ps, with the full width at half‐maximum (FWHM) of 110 ps, and the ringing level is −7.8 dB. Moreover, to further improve the tail ringing level, an SRD's mixed topology configuration is introduced and fabricated. The experimental results indicate that the two SRD mixed pulse generator has a pulse duration of 220 ps with FWHM of 120 ps, validating the reasonability of the improved SRD nonlinear SPICE model in ADS. Additionally, there is a considerable improvement in the ringing level of −11.4 dB.

New insights on precise regulation of pollutant distribution inside a street canyon by different vegetation planting patterns.

Mixed-vegetation planting patterns are commonly seen in urban areas for specific reasons like aesthetic, cooling, and particle deposition effects of the vegetation. However, they may have a negative impact on human health by worsening the air quality inside the street canyon due to the decreased air exchange rate. From the view of precise control of pollutant concentration in the sensitive areas of people's concern in the existed street canyons, thirty-four cases with different vegetation planting patterns and pressure loss coefficients (λ) are studied numerically to investigate the effects of vegetation on airflow and pollutant dispersion inside the canyon. The cases of treeless and 2 rows of tree planting patterns in wind-tunnel measurements were selected for the model validation. The results demonstrate that compared to the treeless case, the greenbelts can greatly change the airflow features and reduce the pollutant concentration at the leeward side, while the only-tree planting patterns have little impact on the flow and deteriorate dispersion within the street canyon. Moreover, rows of greenbelts planted under the corresponding trees can reduce the average pollutant concentrations on the leeward wall and the footpath of the street canyon by up to 22.6% and 33.2%, respectively. Besides, the pattern of 1 row of trees with 1 row of greenbelts planted in the street canyon center should be suggested as the optimal mixed vegetation configuration in this study. That is because compared to the treeless case the pollutant concentration on leeward wall, windward wall, leeward footpath, and windward footpath can be reduced by 14.2%, 10.0%, 24.6%, and 37%, respectively. It is helpful to the city planners to consider whether the disadvantages of planting vegetation inside the street canyon would overwhelm the advantages.

Effects of the configuration of the delta winglet longitudinal vortex generators and channel height on flow and heat transfer in minichannels

Minichannels with the delta winglet longitudinal vortex generators (LVGs) is commonly used in the heat exchanger. However, there are few studies on the configuration of LVGs on the opposite walls and the large aspect ratio of the channel in the existing literature. In this paper, five LVGs configurations including arrangement on the opposite walls are considered, and four channel heights (1, 2, 4 and 8 mm) are considered to achieve a wide coverage of the channel aspect ratio (0.125–1). In the Reynolds number range of 3000 to 18,000, the effects of LVGs configuration and channel height on flow and heat transfer are obtained by evaluating parameters such as friction factor, Nusselt number, thermal performance factor (TPF), field synergy and frictional entropy generation rate and analyzing the vortex structure displayed by Ω method. The results show that the LVGs configuration and channel height mainly affect the main vortex behavior downstream of LVGs, but have little effect on the vortex structure near LVGs. The Mixed configuration at H = 1 mm and the CFU1 configuration at H = 2 mm have better heat transfer enhancement performance, and their Nusselt numbers are increased by 28–35% and 27–33%, respectively, compared with smooth channels. In addition, the configuration selection aiming at high overall performance under different conditions is given.

Mixed neutron-star-plus-wormhole systems: Rotating configurations

We present rapidly rotating neutron stars featuring wormholes in their centers. They arise in general relativity in the presence of a ghost scalar field. The nuclear matter is described by a polytropic equation of state, yielding realistic masses and radii for the neutron stars. The wormholes possess small circumferential radii of size up to 3 km. With increasing wormhole size, the masses and radii of the stars decrease, while the domain of existence of these rotating mixed neutron-star-plus-wormhole systems retains the characteristic properties of a rotating neutron star domain. The question of stability of the mixed configurations under consideration is briefly discussed.

Reflected entropy for communicating black holes. Part I. Karch-Randall braneworlds

We obtain the reflected entropy for bipartite mixed state configurations of two adjacent and disjoint intervals at a finite temperature in BCFT2s with two distinct boundaries through a replica technique in the large central charge limit. Subsequently these field theory results are reproduced from bulk computations involving the entanglement wedge cross section in the dual BTZ black hole geometry truncated by two Karch-Randall branes. Our result confirms the holographic duality between the reflected entropy and the bulk entanglement wedge cross section in the context of the AdS3/BCFT2 scenario. We further investigate the critical issue of the holographic Markov gap between the reflected entropy and the mutual information for these configurations from the bulk braneworld geometry and study its variation with subsystem sizes and time.