Modulation Length Research Articles

Dynamic Modeling of CO2 Absorption Process Using Hollow-Fiber Membrane Contactor in MEA Solution

In this work, a comprehensive mathematical model was developed in order to evaluate the CO2 capture process in a microporous polypropylene hollow-fiber membrane countercurrent contactor, using monoethanolamine (MEA) as the chemical solvent. In terms of CO2 chemical absorption, the developed model showed excellent agreement with the experimental data published in the literature for a wide range of operating conditions (R2 > 0.96), 1–2.7 L/min gas flow rates and 10–30 L/h liquid flow rates. Based on developed model, the effects of the gas flow rate, aqueous liquid absorbents’ flow rate and also inlet CO2 concentration on the removal efficiency of CO2 were determined. The % removal of CO2 increased while increasing the MEA solution flow rate; 81% of CO2 was removed at the high flow rate. The CO2 removal efficiency decreased while increasing the gas flow rate, and the residence time in the hollow-fiber membrane contactors increased when the gas flow rate was lower, reaching 97% at a gas flow rate of 1 L‧min−1. However, the effect was more pronounced while operating at high gas flow rates. Additionally, the influence of momentous operational parameters such as the number of fibers and module length on the CO2 separation efficiency was evaluated. On this basis, the developed model was also used to evaluate CO2 capture process in hollow-fiber membrane contactors in a flexible operation scenario (with variation in operating conditions) in order to predict the process parameters (liquid and gaseous flows, composition of the streams, mass transfer area, mass transfer coefficient, etc.).

High Sensitivity Hollow-Core Fiber Strain Sensor Based on Signal Processing Assisted Vernier Effect

A fiber strain sensor with improved sensitivity is proposed and experimentally demonstrated, based on a single Fabry–Perot interferometer (FPI) using a signal processing assisted Vernier effect. The FPI structure is simply fabricated by splicing a segment of hollow-core fiber (HCF) between two pieces of single-mode fiber (SMF) with a commercial fusion splicer. Through data processing, we do not need to precisely manufacture two interferometers with very small detuning between their optical path differences (OPDs), as in the traditional schemes based on Vernier effect, since it is difficult to control the detuning strictly. The optical spectra of the reference interferometer (RIM) are replaced by an artificial reference spectrum (ARS), which is produced by spatial frequency down-conversion of the interference spectra of the sensing interferometer (SIM) in the initial state. Then, the optical spectrum envelope of Vernier-effect can be obtained by multiplying the SIM intensity with the constructed ARS intensity. When the length of HCF is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1201\mu \text{m}$ </tex-math></inline-formula> , the sensitivity can reach 315pm/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \varepsilon $ </tex-math></inline-formula> with the modulation length of 5 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula> m. Compared with the sensitivity without signal processing, the sensitivity magnification is 188.6 times. The proposed scheme to realize sensitivity-enhancement using a single FPI based on the HCF, could simplify the sensor structure and device fabrication.

Photothermally heated and mesh-gridded solar-driven direct contact membrane distillation for high saline water desalination

Photothermally heated and mesh-gridded membrane distillation (PHMD) system is proposed for desalination of high saline aqueous solutions. A triple-layered membrane, composed of a photothermal top nanofibrous layer containing polyacrylonitrile and dispersed carbon black nanoparticles and a polyvinylidene fluoride porous membrane supported on a nonwoven polyester, was prepared. A polypropylene mesh was used to hold the membrane. A 3D numerical simulation of the PHMD system was carried out by COMSOL and the appropriate length of the membrane module was determined. The effects of various operating parameters including solar radiation intensity on the permeate flux and thermal efficiency were investigated. The increase of the feed flow rate reduced both the permeate flux and the thermal efficiency due to the reduction of the residence time of the feed solution on the photothermal membrane module. In addition, the increase of the solar radiation intensity from 500 to 1100 W/m2 and the ambient temperature from 293 to 313 K resulted in a significant enhancement of the permeate flux and thermal efficiency. In general, good agreements were found between the experimental and simulated results.

Micromagnetics of magnetic chemical modulations in soft-magnetic cylindrical nanowires

We analyze the micromagnetics of short longitudinal modulations of a high-magnetization material in cylindrical nanowires made of a soft-magnetic material of lower magnetization such as permalloy, combining magnetic microscopy, analytical modeling, and micromagnetic simulations. The mismatch of magnetization induces curling of magnetization around the axis in the modulations, in an attempt to screen the interfacial magnetic charges. The curling angle increases with modulation length, until a plateau is reached with nearly full charge screening for a specific length scale~$\Delta_\mathrm{mod}$, larger than the dipolar exchange length of any of the two materials. The curling circulation can be switched by the Oersted field arising from a charge current with typical magnitude $10^{12} A/m^{2}$ for a diameter of $\sim$100 nm, and reaching a maximum for $\Delta_\mathrm{mod}$.

Heterochronies and allometries in the evolution of the hominid cranium: a morphometric approach using classical anthropometric variables.

This article studies the evolutionary change of allometries in the relative size of the two main cranial modules (neurocranium and splanchnocranium) in the five living hominid species and a diverse sample of extinct hominins. We use six standard craniometric variables as proxies for the length, width and height of each cranial module. Factor analysis and two-block partial least squares (2B-PLS) show that the great apes and modern humans share a pervasive negative ontogenetic allometry in the neurocranium and a positive one in the splanchnocranium. This developmental constraint makes it possible to interpret the cranial heterochronies in terms of ontogenetic scaling processes (i.e., extensions or truncations of the ancestral ontogenetic trajectory) and lateral transpositions (i.e., parallel translations of the entire trajectory starting from a different shape for a given cranial size). We hypothesize that ontogenetic scaling is the main evolutionary modality in the australopithecines while in the species of Homo it is also necessary to apply transpositions. Both types of processes are coordinated in Homo, which result in an evolutionary trend toward an increase in brain size and in the degree of paedomorphosis from the earliest habilines.

Capacitively-Loaded Thin-Film Lithium Niobate Modulator With Ultra-Flat Frequency Response

Traveling-wave electro-optic (E-O) modulators based on thin-film lithium niobate (TFLN) have attracted much attention recently, as low half-wave voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{V}_{\pi }$ </tex-math></inline-formula> ) and wide modulation bandwidth can be realized with a small footprint. A flat E-O response of the modulator relies on low microwave loss, perfect velocity match and suitable terminal resistance. In this Letter, we present velocity-matched TFLN modulator based on low-loss capacitively-loaded traveling-wave electrodes (CL-TWEs) with an on-chip terminal resistor. The effect of termination resistance on the E-O frequency response is theoretically analyzed and experimentally confirmed. The TFLN modulator with 6-mm modulation length exhibit a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{V}_{\pi }$ </tex-math></inline-formula> of 2.7 V and a 6.4-dB electrical bandwidth over 160 GHz. By adopting a termination resistance slightly lower than the characteristic impedance of the CL-TWEs, an ultra-flat E-O response has been demonstrated with fluctuation less than 1-dB up to 50 GHz, consistent with the theoretical prediction.

Theoretical analysis of liquefied natural gas cold energy recovery using thermoelectric generators

This paper presents a complex thermo-electric analysis of liquefied natural gas (LNG) cold energy recovery system using thermoelectric generators (TEG). The modeling uses the concept of effective thermal conductivity. In addition, it includes not only heat transfer and electric phenomena in TEG module but also all other secondary heat transfer processes: boiling of liquefied natural gas, conduction through walls, thermal contacts at both side of TEG and convection at the water side. Analysis is firstly made for commercial TEGs which are designed for operation at different temperatures. Next part of the analysis aims to optimize the geometry of TEG to temperature specific for liquefied natural gas. It is shown that the optimization of TEGs geometry for LNG conditions can lead to 50% increase of electric power generation. Moreover, for assumed filling factor of between 0.4 to 0.6, the length of TEG module should be between 0.4 mm to 0.7 mm. The conducted analysis provides important information on the possibility of recovering the cold energy of LNG using TEG modules.

Connector configuration effect on the dynamic characteristics of multi-modular floating structure

In this study, a wave flume experiment is implemented in order to investigate the effect of connector topology on the dynamic characteristics of a modular floating structure. Three configurations of flexible connectors were designed for the experiment tests of a three-modular floating platform under various wave conditions. The results illustrate the module responses, relative displacements of connecting points between adjacent modules, and connector loads for floating structures with different types of connectors in the parameters region of non-dimensional module length. The comparison study demonstrates that the connector type III, which can provide appropriate constraint stiffness in all three degrees of freedom, generally delivers better dynamic stability to the floating platform. The longitudinal loads for the three types of connectors remain at the same level. Additionally, the mechanism of different types of connectors on the dynamic features of system is analyzed. This work can provide a few experimental guidelines for the connector design of floating structure in engineering practice.

A 𝜏-tilting approach to the first Brauer-Thrall conjecture

In this paper we study the behaviour of modules over finite dimensional algebras whose endomorphism algebra is a division ring. We show that there are finitely many such modules in the module category of an algebra if and only if the length of all such modules is bounded.

Investigation of The Effect of Design Variables on Slip Assembly: Spline Module and Slip Length

The driveshaft which transmits the power from the engine to the wheels in the motor vehicles is one of the vital elements in the driveline. Driveshafts have two basic motions depending on the road conditions, angular and axial movements. Angular movement is provided by the universal joints while the axial movement is provided by the slip assembly which involves a group of sliding components. Therefore, the slip assembly is an important part of the drive shaft. Basically, a slip assembly consists of two parts which are connected to each other by means of their spline forms. The parts can move back and forth longitudinally while they transmit the torque thanks to the connection interface of their spline forms. And so, they can slide and adjust the drive shaft lengths due to the position of the axles under road conditions.&#x0D; During the motor vehicle movement, slip assembly are subjected to torsion like the other components on the driveshaft. In this context, spline size and magnitude of the length compensation are highly important in the design process of the slip assembly. In this study, the effect of the spline size and the slip length have been investigated for the yoke shaft design, by using analytical and numerical methods in terms of shear stress. It has been observed that the analytical and the numerical methods give the similar results in shear stress on the pitch diameter of the spline. Thus, the analytical method can be preferred instead of the finite element analysis (FEA), especially considering that the FEA is a time consuming method compared to the analytical method in the design process.

Proposal of compact multimode interference optical modulator with high extinction ratio

We proposed a compact 1 × 1 multimode interference (MMI) optical modulator with a high extinction ratio. A triply coupled quantum well structure is designed for the core layer for the enhancement of the quantum-confined Stark effect, and the MMI waveguide with isolation trenches is symmetrically designed. The length of the MMI modulator is reduced by 30%, and the wavelength dependence was reduced compared with that observed in the previously reported MMI modulator. Owing to both the electroabsorption effect and the electric-field induced refractive index change in a multiple-quantum-well core layer, the extinction ratio is expected to be approximately 45 dB at an operating voltage of 3.3 V.

Spinodal Decomposition in Plastically Deformed Fe–Cr–Co Magnet Alloy

Fe–Cr–Co alloys are becoming important as half-hard magnet which can be subjected to plastic deformation process for their novel applications including non-contact electromagnetic brake because of its large hysteresis loss. Its magnetic hardness depends on the modulated structure formed by spinodal decomposition. It is important to clarify the effect of plastic deformation on the spinodal decomposition for optimizing the heat treatment after plastic deformation process. In the present study, we examined the spinodal-decomposed structures in Fe–Cr–Co sheets cold-rolled to 25% reduction and that without rolling to clarify the influences of cold rolling. Also, spinodal decomposition under the presence of dislocation structure have been simulated by phase field method for the case with the presence of dislocation cell boundary with a high in-plane solute diffusivity at various migrating speed. It has been found that the spinodal decomposition is accelerated around dislocation owing to the elastic field and higher diffusivity, which results in inhomogeneous microstructure with various wave length of modulation. The existence of dislocation enhances the initiation of phase decomposition and the growth particles. The decomposed structure greatly depends on the in-plane solute diffusivity and migrating speed of the dislocation cell boundary.

Multistage Testing in Heterogeneous Populations: Some Design and Implementation Considerations.

A central challenge in international large-scale assessments is adequately measuring dozens of highly heterogeneous populations, many of which are low performers. To that end, multistage adaptive testing offers one possibility for better assessing across the achievement continuum. This study examines the way that several multistage test design and implementation choices can impact measurement performance in this setting. To attend to gaps in the knowledge base, we extended previous research to include multiple, linked panels, more appropriate estimates of achievement, and multiple populations of varied proficiency. Including achievement distributions from varied populations and associated item parameters, we design and execute a simulation study that mimics an established international assessment. We compare several routing schemes and varied module lengths in terms of item and person parameter recovery. Our findings suggest that, particularly for low performing populations, multistage testing offers precision advantages. Further, findings indicate that equal module lengths-desirable for controlling position effects-and classical routing methods, which lower the technological burden of implementing such a design, produce good results. Finally, probabilistic misrouting offers advantages over merit routing for controlling bias in item and person parameters. Overall, multistage testing shows promise for extending the scope of international assessments. We discuss the importance of our findings for operational work in the international assessment domain.

Component assignment and layout optimization for multi-module microsatellite considering variable module size

The general satellite component layout optimization problems have always focused on satellites with fixed module size, and each component is limited to a specific module or panel. In actual engineering practice, dimensions of microsatellite are no longer constrained strictly, but adjustable within an allowed range. The assignment of the components and the dimensions of the modules should be considered as variable to get better global performance. In this paper, a TS+DE+AFT hybrid algorithm is proposed to solve this component assignment and layout optimization problem for multi-module microsatellite (CALO-MM) considering variable module size, in which tabu search (TS) is mainly used to assign components to the appropriate module, and differential evolution (DE) is used to optimize the layout of the components in each module. An adaptive fine-tuning (AFT) strategy is applied to dynamically adjust the length and height of modules within a maximum envelope size. Demonstration and engineering cases are studied to verify the effectiveness of proposed hybrid algorithm.

An insight into hybrid membrane‐based air conditioning system performance using gray relational analysis methods: Structural versus operational parameters

AbstractVarious parameters have an impact on the fresh air temperature and input power of a hybrid membrane‐based air conditioning (HMBAC) system, such as pressure ratio, membrane selectivity, membrane permeance, membrane area, air flowrate of the dehumidification unit, and module length, number of fibers, and fiber outer diameter of the humidification unit, which comprise both operational and structural parameters. Therefore, in this study, the effects of these parameters on the system performance are examined separately based on a statistical approach. The importance order of each parameter and its contribution ratio are determined by using Taguchi method and ANOVA analysis. The optimum level for each input parameter is determined using statistical analysis for the fresh air temperature and input power. Then, for the simultaneous minimization of fresh air temperature and input power Taguchi‐gray relational grade (GRG) is used. GRG revealed that membrane selectivity, pressure ratio, and membrane permeance with the contribution ratio of 37.87%, 32.51%, and 10.55%, respectively, are the most critical parameters of the multiperformance of an HMBAC system. Interestingly dehumidification from a humid airflow can be more effective when membranes with low selectivity and high permeability are used. In conclusion, the optimization outputs disclosed that both structural and operational parameters have significant effects on the performance of the HMBAC system and this optimization can be a helpful tool for designing a HMBAC systems to cover the optimal conditions to develop a sustainable membrane‐based air conditioning system.

Monolithic GaAs/Si V-groove depletion-type optical phase shifters integrated in a 300 mm Si photonics platform

We demonstrate monolithically integrated n-GaAs/p-Si depletion-type optical phase shifters fabricated on a 300 mm wafer-scale Si photonics platform. We measured the phase shifter performance using Mach–Zehnder modulators with the GaAs/Si optical phase shifters in both arms. A modulation efficiency of V π L as low as 0.3 V·cm has been achieved, which is much lower compared to a carrier-depletion type Si optical phase shifter with pn junction. While propagation loss is relatively high at ∼ 6.5 dB / mm , the modulator length can be reduced by the factor of ∼ 4.2 for the same optical modulation amplitude of a Si reference Mach–Zehnder modulator, owing to the high modulation efficiency of the shifters.

Modulation of turbulent Rayleigh-Bénard convection under spatially harmonic heating.

We numerically study turbulent Rayleigh-Bénard (RB) convection under spatial temperature modulation, where the bottom temperature varies sinusoidally around a mean value in space. Both two- and three-dimensional simulations are performed over the Rayleigh number range 10^{7}≤Ra≤10^{10} and the wave number range 1≤k≤120 at fixed Prandtl number Pr=0.7. It is demonstrated that spatial temperature modulation with small wave numbers can enhance the global heat transfer (characterized by the Nusselt number Nu) in the turbulent regime, while Nu is close to that in standard RB convection in the case of large wave numbers. Further, we propose two characteristic modulation length scales: one is the penetration depth δ_{k} above which spatial modulation is negligible, the other is the inversion depth δ_{k2} below which there exists a stable inverse temperature gradient. Based on the relative thickness of the thermal boundary layer (BL) δ_{th} compared with these two length scales, the underlying modulation mechanism is physically explained and three regimes are identified: (1) an unperturbed BL regime (δ_{k}<δ_{th}), in which the modulation effect does not penetrate through the thermal BL and Nu is nearly unchanged; (2) a partially modulated BL regime (δ_{k2}<δ_{th}<δ_{k}), in which hot spots trigger more plume emissions from the thermal BL, resulting in Nu enhancement; and (3) a fully modulated BL regime (δ_{th}<δ_{k2}), in which the stable temperature inversion over the cold phases begins to affect convective flows, which alters the trend of Nu enhancement.

Noise-like pulses from all-normal dispersion ytterbium doped all-fiber oscillator with semiconductor saturable absorber

We report generation of stable train of noise like pulses (NLPs) from all-normal dispersion ytterbium doped all-fiber unidirectional ring cavity consisting of semiconductor saturable absorber (SeSA) without any bandpass filter (BPF). NLPs are characterized by their autocorrelation traces which exhibit ∼500 fs spike riding on a broad pedestal of ∼200 ps. NLP operation is also supported by its relatively broad optical spectrum along with reasonably stable longer pulse profile on oscilloscope. Numerical simulations have also been performed in detail to study the effects of cavity parameters like the cavity length, BPF bandwidth and depth of modulation (q 0) of SeSA on the evolved pulses from the cavity. The simulation results suggest that stable single clean pulse (SSCP) is generated for a certain range of cavity parameters and in the absence of BPF no SSCP is possible from the cavity if the value of q 0 is below a certain value. Under this condition either NLP or no pulse is generated in the simulation. Numerically simulated NLP in a ring cavity matches qualitatively with the experimentally obtained results for NLP. The study carried out on NLP will enrich database of pulse dynamics in modelocked oscillators and has potential application in optical coherence tomography and supercontinuum generation.

Design of Ultracompact High‐Speed‐Integrated Lithium–Niobate Periodic Dielectric Waveguide Modulator

Modern communications and microwave photonics require compact electro‐optic modulators with ultrahigh bandwidth and low power consumption. These requirements can be satisfied by integrated lithium–niobate electro‐optic modulators with high bandwidth and low power consumption. However, most integrated lithium–niobate modulators cannot achieve a good balance between an ultracompact size and a high modulation bandwidth. These challenges are overcome by designing an integrated lithium–niobate periodic dielectric waveguide modulator, featuring a compact modulation length of 87.4 μm, a theoretical modulation bandwidth over 600 GHz, a voltage‐length product of 0.0874 V cm, and a high sideband suppression ratio up to 36.1 dB. These performances are achieved by taking advantage of a capacitor configuration consisting of a nonresonant periodic dielectric waveguides sandwiched between two indium tin oxide (ITO) electrodes. This design provides an ultrabroadband and compact solution to next‐generation communications and microwave photonics.

Broadband Meandered Thin-Film Lithium Niobate Modulator With Ultra-Low Half-Wave Voltage

Compact thin-film lithium niobate (TFLN) modulators with low half-wave voltage <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{V}_{\pi }$ </tex-math></inline-formula> are highly desirable for many applications. In particular, modulators with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{V}_{\pi }~\sim ~1$ </tex-math></inline-formula> V would allow direct driving by CMOS circuits, but they normally require a long modulation length of several centimeters. Folded TFLN modulators exhibit reduced <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{V}_{\pi }$ </tex-math></inline-formula> together with a small device footprint. However, previously reported schemes suffer from complicated device fabrication procedure to maintain the relative direction of electric field with respect to the TFLN crystal polarization after electrode folding. In this work, a meandered X-cut TFLN Mach–Zehnder (MZ) modulator with specially designed capacitively-loaded traveling-wave electrodes (CL-TWEs) is demonstrated. Interdigitated T-rails are employed to reverse the electric field in the folded region for continuous accumulation of optical phase shift. Ultra-low <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{V}_{\pi }$ </tex-math></inline-formula> of 1.08 V is achieved on an 8-mm-long modulator containing three-segments of 7-mm-long modulation sections, together with a 3-dB electro-optic bandwidth around 43 GHz. The broadband meandered modulator with ultra-low half-wave voltage as well as a compact footprint has the potential to be directly driven by CMOS electronics.