Modulation Length Research Articles

Broadband, Integrated, Micron-Scale, All-Optical Si3N4/VO2 Modulators with pJ Switching Energy

The expansion of optical network traffic demands the implementation of all-optical signal processing functions such as switching and modulation within the network nodes to scale data speeds and curb power consumption. Toward this end, we experimentally demonstrate ultracompact all-optical modulators based on vanadium dioxide that can be operated by broadband control (800–1000 nm) and signal (1500–1600 nm) wavelengths and are simultaneously switched by pulse energies as low as 6.4 pJ. The devices are integrated on-chip and enable planar propagation of both control and signal light beams. For a 4 μm length modulator, the extinction ratio is 1.68 dB/μm and the insertion loss is 0.98 dB/μm at λ = 1550 nm. To our knowledge, these characteristics together have not been demonstrated previously in a single device. Furthermore, the extinction ratio, switching energy, and switching efficiency have been observed to depend on the modulator length in subtle ways, which is due to the finite distance required for the el...

Structural and Magnetic Properties of Gd-Ni-co-doped BiFeO₃ Nanoparticles

Single-phase (GdNi)SUBx/SUB(BiFe)SUB1-x/SUB O₃ (x = 0, 0.025, and 0.05) nanoparticles of 30-40 nm particle size on average were fabricated using a sol-gel method. Transmission electron microscopy, X-ray diffraction as well as Raman spectral measurements and analyses revealed that the (GdNi)SUBx/SUB(BiFe)SUB1-x/SUBO₃ nanoparticles undergo a structural transformation from the rhombohedral R3c structure (for x = 0 and 0.025) to the triclinic P1 (for x = 0.05). X-ray photoemission spectroscopy served to confirm that co-doping of GdSUP3+/SUP and NiSUP2+/SUP ions decreases oxygen-vacancy concentration, reflecting less FeSUP2+/SUP content in the co-doped samples compared with pure BiFeO₃. Magnetization hysteresis loops showed that the magnetization value for x = 0.05 at 50 kOe increases significantly to M = 5.32 emu/g at 300 K and to 14.47 emu/g at 5 K, representing 760 and 690 % enhancements relative to those for x = 0. Fitting of the Curie-Weiss law to the observed magnetization-versus-temperature curves indicated the presence of weak ferromagnetic coupling in the samples. We also noted the exchange bias effect in the nano-size particles, possibly originating from exchange coupling between surface spins of an uncompensated ferromagnetic nature and core spins of an antiferromagnetic nature. We ascribed these significant improvements in the Gd-Ni-co-doped BiFeO₃ nanoparticles’ magnetic properties to the rhombohedral R3c to triclinic P1 structural transformation, due to the samples’ particle size being smaller than the modulation length of the canted antiferromagnetic ordering of the FeSUP3+/SUP spins. These enhanced magnetic properties, notably, might prove useful for a variety of spintronic applications.

Hybrid plasmonic graphene modulator with buried silicon waveguide

We propose a low-loss broadband modulator by combining plasmonic effect with graphene to realize highly efficient modulation on the SOI (Silicon-On-Insulator) platform. Due to a hybrid plasmonic waveguide including buried silicon waveguide and silver waveguides, the fundamental mode is mainly confined in two single-layer graphene sheets, and the electric field vector is parallel to the graphene sheets ensuring the high efficient light absorption of graphene. The specific hybrid structure makes it easy for graphene transfer. Also, non-coplanar structure of silicon waveguide and silver waveguides provides simplified fabrication process and fabrication tolerance. The simulation results demonstrated that modulation bandwidth of 346 GHz is obtained, and the 3 dB modulation length is only 9.493μm. In addition, competitively low propagation loss of 0.85 dB was realized of the hybrid modulator.

Optimization of module length and number of stages in a multistage membrane distillation configuration

ABSTRACT Multistage membrane distillation units connected in series for water desalination is considered. The influence of the number of stages and the module length per stage on the overall economics is investigated via simulations using a validated model. Depending on the degree of feed salinity, a suboptimal condition occurs at a structure size of 40 ~ 35 stages with an average module length of 15 ~ 12 m. The corresponding specific operating and fixed costs are $8 ~ 12.5/m3 and $0.97~−.8/m3, respectively. For a high salinity feed, the optimum specific operating cost increases due to reduced mass production. Membrane porosity and thickness showed a pronounced effect on cascade structure economics. The specific operating cost can be further reduced by an average of 60% using permeate heat recovery systems.

Photonics of Sub-Wavelength Nanowire Superlattices

Semiconductor nanowires (NWs) have widely been studied as an ideal platform for developing electronic, photovoltaic, photonic devices and biological probes in the nanoscale. The ability to synthesize high-quality NWs of various materials with a precise control in shape, doping and crystal structure is the key to the growth of NW-based technologies. In the past decade, there has been growing interest in controllably creating NW heterojunctions and periodically-modulated superlattices (SLs) because it is expected to bring new functionalities that are not present in uniform NWs. In particular, the interaction of NW SLs with light has been one of the central interests because the diameter and modulation length scale are on the same order as the wavelength of light in the optical regime. Also, degenerately-doped semiconductor NWs exhibit localized surface plasmon resonances (LSPRs), which comprises unexpected long-range interactions when the plasmon resonators are regularly placed in NW SLs. In this review, I will summarize the recent progress in photonics research of NW SLs. The topics discussed include preparation and types of NW SLs, light-trapping and light-emission properties, and plasmonic optical- and thermal-transport properties.

P12.07 Minimal bimodular G-quadruplex nano-construct as cryptic therapeutic DNA oligonucleotide to suppress glioblastoma cell functioning

Abstract BACKGROUND G-quadruplex folding oligodeoxyribonucleotides (G4 ODNs) are considers to be potential anticancer agents, because G4 interferes with some functions of cell, like survival, proliferation, ets, by interacting with G4 binding regulatory proteins. There are some experimental data on anti-proliferative activities of G4: for telomerase complex, aptamers for STAT3, nucleolin, TOP1, SP1, VEGF, and SHP-2, but there is no molecular mechanism yet. Because ODNs are supposed to block regulatory proteins, like cryptic aptamers do, they could be potentially therapeutics, like monoclonal antibodies. The only current approach to find proper model for G4 plus reference cell line, is to screen sets of G4 for sets of cancer cell lines. To avoid selection from large number of G4 structures, we have initiated anti-proliferative study of minimal DNA nano-construct biHD1, built from two minimal active G4 15-mer, by testing 7 human cancer cell lines, including glioblastoma (GBM): U87 and primary cultures from GBM surgery samples. MATERIAL AND METHODS ODN were from Evrogen (Russia). ODN were folded: heated to 950C, slowly cooled to 250C. biHD1, GGTTGGTGTGGTTGG TGGTTGGTGTGGTTGG, and derivatives with G4 structure variations. CD in saline phosphate, pH 7.5; CHIRASCAN (UK) and MARK-5 (France); melting curves at 294 nm. 7 human cancer cell lines: colon, HCT116; prostate, PC3; lung, RL-67; breast adenocarcinoma, MCF7; melanoma, mS; HeLa; GBM, U87 and primary cultures from surgery samples; and human embryonic fibroblast, hEF, as control. MTT for cell viability by colorimetric measurements of metabolic activity (Tecan plate reader, Switzerland). ODN: 0.10 μM, 1.0 μM, 10 μM for 3 days. RESULTS biHD1 is dose-dependent toxic for several human cancer cell lines, most active for lung cancer RL-67 and GBM U87, survival at 10 μM ODN 35% and 45%, respectively. According to data for biHD1 derivatives with deviations from G4 conformation: length of linker joining modules, light distortions of loops, strong distortions of G4, freezing of G4 conformation, it is G4 fold which is responsible for toxicity for U87 cell line. CONCLUSION Cell survival after treatment with G4 minimal bimodular DNA oligonucleotide biHD1 and its derivatives have been tested for 7 human cancer cell lines, including CNS, U87. biHD1 is toxic for cancer cells, but not for embryonic fibroblast, as control; activity depends on G4 fold. Therefore, it is possible to manipulate with minimal G4 as module, and build G4 nano-construct being toxic for cancer cells, including GBM, U87. Research is supported by RFBR grants 17-00-00157, 18-29-01047

CO2 capture in a hollow fiber membrane contactor coupled with ionic liquid: Influence of membrane wetting and process parameters

The present work demonstrates the potential of coupling ionic liquid 1-ethyl-3-methylimidazolium ethylsulfate ([emim][EtSO4]) and hollow fiber membrane contactors for post-combustion CO2 capture. CO2 absorption experiments in counter-current configuration were carried out, followed by a comprehensive two-dimensional dynamic modeling based on steady state and pseudo-steady state operating modes. The model considers the level of wetting of porous hollow fibers. An overall mass transfer coefficient of 3.99 · 10−5 m s−1 and CO2 flux 6.1 · 10−5 mol m−2 s−1 were obtained for 100 ml min−1 of gas flowing inside the fibers. The model predicted the effects of membrane wetting, porosity, tortuosity, module length, fiber inner diameter, gas and absorbent flow rates. Membrane wetting has a noteworthy effect on CO2 capture efficiency. A smaller amount of wetting can cause a huge resistance in CO2 transport through the membrane. The separation efficiency was enhanced by using membranes with high porosity and low tortuosity and decreased by enhancing the gas flow rate and absorbent flow rate reduction. CO2 capture is enhanced by increasing module length and reduction of inner diameter of fibers.

Efficiency evaluation of novel liquid potassium lysinate chemical solution for CO2 molecular removal inside the hollow fiber membrane contactor: Comprehensive modeling and CFD simulation

The efficacious removal of greenhouse gases is an indisputable necessity to mitigate their detrimental anthropogenic effects on environment. This paper aims to evaluate the performance of novel reactive potassium lysinate (PL) amino acid solution to remove the CO2 acidic contaminant from CO2/CH4 gaseous blend through the hollow fiber membrane contactor (HFMC) employing computational fluid dynamics (CFD) and finite element method (FEM). For this purpose, a 2D simulation and consequently a mathematical modeling is developed and simultaneously solved. Due to the application of a novel amino acid solution, there is no experimental data for validating the simulation results. Therefore, the validity of simulation results is confirmed by comparison of simulation/experimental results for CO2 flux using deionized water (DIW). The results imply a brilliant agreement between model results and experimental data with average relative error (ARE) of about 6%. Based on the results, PL solution is appointed as an effective absorbent due to removing about 91% of inlet CO2. Furthermore, evaluation of computational simulation outcomes illustrates the encouragement of CO2 removal percentage by increasing some design/operational parameters like the hollow fibers total number, membrane porosity and module length.

Concrete based high temperature thermal energy storage system: Experimental and numerical studies

This paper presents the concept of developing a cost-effective Concrete based Thermal Energy Storage (CTES) system by performing extensive experimental studies and numerical simulations. A stand-alone experiment facility to study the performance of high-temperature thermal energy storage system which operates up to 500 °C using air as the heat transfer fluid has been developed. The CTES module is made of shell and tube configuration, where concrete is filled in the shell side, and 22 air passages are provided on the tube side. The inlet air temperature and velocity are the decision parameters used for analyzing the thermal behaviour of the CTES module. From the spatial variations of temperature, it is observed that the heat transfer rate is uniform and faster along all radial planes, whereas, the heat transfer rate drops gradually along the length of the CTES module due to drop in Heat Transfer Fluid (HTF) temperature. The parametric investigation conducted shows that the charging and discharging times were reduced by approximately 48% and 29%, respectively, with a change in inlet temperature of 40 °C at a fixed air velocity of 2 m/s. A 3-D model for CTES module developed using the finite element method has been validated with experimental results. The temperature contours plotted from 3-D simulation describes the spatial variation of CTES temperature at different inlet air temperatures. Further, a 1-D dynamic model has been developed, which is fast and accurate with a maximum error of ±4.9 °C with reference to real-time experiments and also provides a substantial scope of integrating the CTES with industrial applications. The outcomes of the present studies conclude that the developed CTES module is highly recommended for the high-temperature applications.

Wind actions on large-aperture parabolic trough solar collectors: Wind tunnel tests and structural analysis

Green energy structures are subject of on-going optimization, which involves the shape contours and the wind sensitivity of the structure. Current developments of parabolic troughs show that the aperture width increases to save assembling and operating costs to be more competitive on market compared to conventional power plantsis increased. Alternative structural concepts based on thin-walled, high-performance concrete shells combine structural stiffness and low self-weights despite large apertures to high-potential technologies. This paper presents wind tunnel tests on 3D-printed shell-like parabolic trough collector modules with an aperture width of 10 m and a module length of 30 m. Experimental investigations are performed on solitary modules (1:75 and 1:150) and on modules arranged in arrays (1:150). Pressure, pitching moment and force coefficients are determined for various pitch angles and wind directions. The coefficients are applicable to full-scale large-aperture collector modules. Subsequent numerical analysis shows trends towards effects of e.g. scaling, shadowing in solar fields regarding maximum internal forces for operation and stow mode. Results reveal that wind directions of 0°/30°/150°/180° and pitch angles of 0°/45°/60° are most significant. By means of the numerically determined internal forces and identified shadowing effects the solar field can be categorized into four characteristic sectors in which trough modules are mainly equally stressed.

A Computational Fluid Dynamics Approach for the Modeling of Gas Separation in Membrane Modules

Natural gas demand has increased rapidly across the globe in the last decade, and it is set to play an important role in meeting future energy requirements. Natural gas is mainly produced from fossil fuel and is a side product of crude oil produced beneath the earth’s crust. Materials hazardous to the environment, like CO2, H2S, and C2H4, are present in raw natural gas. Therefore, purification of the gaseous mixture is required for use in different industrial applications. A comprehensive computational fluid dynamics (CFD) model was proposed to perform the separation of natural gas from other gases using membrane modules. The CFD technique was utilized to estimate gas flow variations in membrane modules for gas separation. CFD was applied to different membrane modules to study gas transport through the membrane and flux, and to separate the binary gas mixtures. The different parameters of membrane modules, like feed and permeate pressure, module length, and membrane thickness, have been investigated successfully. CFD allows changing the specifications of membrane modules to better configure the simulation results. It was concluded that in a membrane module with increasing feed pressure, the pressure gradient also increased, which resulted in higher flux, higher permeation, and maximum purity of the permeate. Due to the high purity of the gaseous product in the permeate, the concentration polarization effect was determined to be negligible. The results obtained from the proposed CFD approach were verified by comparing with the values available in the literature.

Computational simulation and theoretical modeling of CO2 separation using EDA, PZEA and PS absorbents inside the hollow fiber membrane contactor

This paper deals with developing a theoretical modeling and a two dimensional (2D) computational simulation to evaluate the CO2 separation percentage from CO2/CH4 gaseous mixture under non-wetting mode of operation inside the membrane pores and counter-current adjustment of liquid and gas flows. As the novelty, the effect of ethylenediamine (EDA), 2-(1-piperazinyl)-ethylamine (PZEA) and potassium sarcosinate (PS) liquid absorbents on the CO2 separation performance is studied and the most efficient absorbent is introduced. The results show that PZEA can sequester 88.75% of inlet CO2 while the separation percentage of CO2 using PS and EDA is 82.2 and 81%, respectively. In addition, the mathematical model outcomes corroborate that increase in some operational factors and hollow fiber module specifications such as liquid flow rate, fiber packing density, module length and number of fibers encourages the separation efficiency of CO2 due to enhancing the residence time, contact area and consequently mass transfer rates inside the HFMC while increment of tortuosity factor and gas flow rate negatively deteriorates the separation percentage of CO2 which is able to be justified due to enhancement of mass transfer resistance through the pores of microporous membrane.

Energy efficiency of hollow fibre membrane module in the forward osmosis seawater desalination process

This study provided new insights regarding the energy efficiency of hollow fibre forward osmosis modules for seawater desalination; and as a consequence an approach was developed to improve the process performance. Previous analysis overlooked the relationship between the energy efficiency and operating modes of the hollow fibre forward osmosis membrane when the process was scaled-up. In this study, the module length and operating parameters were incorporated in the design of an energy-efficient forward osmosis system. The minimum specific power consumption for seawater desalination was calculated at the thermodynamic limits. Two FO operating modes: (1) draw solution in the lumen and (2) feed solution in the lumen, were evaluated in terms of the desalination energy requirements at a minimum draw solution flow rate. The results revealed that the operating mode of the forward osmosis membrane was important in terms of reducing the desalination energy. In addition, the length of the forward osmosis module was also a significant factor and surprisingly increasing the length of the forward osmosis module was not always advantageous in improving the performance. The study outcomes also showed that seawater desalination by the forward osmosis process was less energy efficient at low and high osmotic draw solution concentration and performed better at 1.2–1.4 M sodium chloride draw solution concentrations. The findings of this study provided a platform to the manufacturers and operators of hollow fibre forward osmosis membrane to improve the energy efficiency of the desalination process.

Measurement and modeling of electrowetting lens oscillations using digital holographic interferometry and Bessel and Legendre polynomial functions.

The function of electrowetting liquid lenses is expanding beyond tunable focal length lensing. Recently, single and multi-mode oscillations on the meniscus profile of two non-miscible liquids have been used for optical phase modulation and fast focal length sweeping. To achieve a user-defined phase modulation, a prediction model of oscillation patterns and amplitudes is needed. We present digital holographic interferometry (DHI) measurements of oscillation patterns and amplitudes on a 5.8mm aperture lens up to 160 Hz, including frequency responses from 26-100 Hz. We discuss using Bessel function and Legendre polynomial models for oscillations on a conical frustum shaped electrowetting lens.

Membrane contactors modelled for process intensification post combustion solvent regeneration

Membrane gas-solvent contactors are potentially more efficient at undertaking solvent regeneration in carbon capture applications compared to traditional desorber columns. This potential is investigated here through modelling of two experimentally reported membrane contactors based on Teflon AF1600 and polydimethylsiloxane active layers, by a simple approximate model and a one-dimensional mass transfer model. The respective membrane contactors could be operated at temperatures below that corresponding to the vaporisation of the solvent, due to the separation of the solvent and gas phase by the membrane. This required a steam sweep operating under vacuum conditions. The calculated module length for the Teflon AF1600 membrane varied between 8.9–70.2 m with decreasing regeneration temperature. This increase in required length was due to reductions in overall mass transfer coefficient and mass transfer driving force as temperature is lowered. It was determined that at 110 °C a PDMS contactor of length 1.1 m was required to regenerate the solvent, achievable with commercial modules. A comparison of the equipment volume footprint, known as process intensification, revealed that both the Teflon AF1600 and PDMS membranes required a lower volume than a standard packed column when operating at temperatures above 90 °C. Temperatures higher than 95 °C also designated the transition above which membrane contactors have a lower energy duty than the corresponding solvent column approach. This energy duty is a trade-off between the reduction in latent heat required to produce CO2 and regenerate the solvent at lower temperatures, countered by the work duty of the vacuum pump needed to operate the steam sweep at pressures below atmospheric. The investigation demonstrated that membrane contactors are a viable alternative technology for solvent regeneration.

Performance Comparison between Polyvinylidene Fluoride and Polytetrafluoroethylene Hollow Fiber Membranes for Direct Contact Membrane Distillation.

Increasing water demand coupled with projected climate change puts the Southwestern United States at the highest risk of water sustainability by 2050. Membrane distillation offers a unique opportunity to utilize the substantial, but largely untapped geothermal brackish groundwater for desalination to lessen the stress. Two types of hydrophobic, microporous hollow fiber membranes (HFMs), including polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), were evaluated for their effectiveness in direct contact membrane distillation (DCMD). Water flux and salt rejection were measured as a function of module packing density and length in lab-scale systems. The PVDF HFMs generally exhibited higher water flux than the PTFE HFMs possibly due to thinner membrane wall and higher porosity. As the packing density or module length increased, water flux declined. The water production rate per module, however, increased due to the larger membrane surface area. A pilot-scale DCMD system was deployed to the 2nd largest geothermally-heated greenhouse in the United States for field testing over a duration of about 22 days. The results demonstrated the robustness of the DCMD system in the face of environmental fluctuation at the facility.

Silicon Photonic IQ Modulators for 400 Gb/s and Beyond

Silicon photonics has enormous potential for ultrahigh-capacity coherent optical transceivers. We demonstrate an in-phase and quadrature (IQ) modulator using silicon photonic traveling-wave modulators optimized for higher order quadrature amplitude modulation (QAM). Its optical and RF characteristics are studied thoroughly in simulation and experiment. We propose a system-orientated approach to optimization of the silicon photonic IQ modulator, which minimizes modulator-induced power penalty in a QAM transmission link. We examine the tradeoff between modulation efficiency and bandwidth for the optimal combination of modulator length and bias voltage to maximize the clear distance between adjacent constellation points. This optimum depends on baud rate and modulation format, as well as achievable driving voltage swing. Measured results confirm our prediction using the proposed methodology. Without precompensating bandwidth limitation of the modulator, net data rates up to 232 Gb/s (70 Gbaud 16-QAM) on single polarization are captured, indicating great potential for 400+ Gb/s dual-polarization transmission.

Homology, mixed multiplies and Hilbert coefficients of the fiber cone

In this paper, we compare the depth of the fiber cone and the associated graded ring. To achieve this, we construct a bi-graded complex corresponding to a bi-graded, Noetherian, Hilbert filtration. The vanishing of the homology modules of this complex helps us to compare the depth of the fiber cone of the filtration and the depth of the corresponding associated graded ring. We also give a formula for the fiber coefficients in terms of the lengths of certain homology modules. We give an upper bound for the first fiber coefficient and show that when this bound is attained, the fiber cone has good depth.

Deep Learning for Joint Adaptations of Transmission Rate and Payload Length in Vehicular Networks.

Recently, vehicular networks have emerged to facilitate intelligent transportation systems (ITS). They enable vehicles to communicate with each other in order to provide various services such as traffic safety, autonomous driving, and entertainments. The vehicle-to-vehicle (V2V) communication channel is doubly selective, where the channel changes within the transmission bandwidth and the frame duration. This necessitates robust algorithms to provide reliable V2V communications. In this paper, we propose a scheme that provides joint adaptive modulation, coding and payload length selection (AMCPLS) for V2V communications. Our AMCPLS scheme selects both the modulation and coding scheme (MCS) and the payload length of transmission frames for V2V communication links, according to the V2V channel condition. Our aim is to achieve both reliability and spectrum efficiency. Our proposed AMCPLS scheme improves the V2V effective throughput performance while satisfying a predefined frame error rate (FER). Furthermore, we present a deep learning approach that exploits deep convolutional neural networks (DCNN) for implementing the proposed AMCPLS. Simulation results reveal that the proposed DCNN-based AMCPLS approach outperforms other competing machine learning algorithms such as k-nearest neighbors (k-NN) and support vector machines (SVM) in terms of FER, effective throughput, and prediction time.

Lech's inequality, the Stückrad–Vogel conjecture, and uniform behavior of Koszul homology

Let (R,m) be a Noetherian local ring, and let M be a finitely generated R-module of dimension d. We prove that the set {l(M/IM)e(I,M)}I=m is bounded below by 1/d!e(R‾) where R‾=R/Ann(M). Moreover, when Mˆ is equidimensional, this set is bounded above by a finite constant depending only on M. The lower bound extends a classical inequality of Lech, and the upper bound answers a question of Stückrad–Vogel in the affirmative. As an application, we obtain results on uniform behavior of the lengths of Koszul homology modules.