Flexible Modulation Research Articles

Up to 64 QAM/32 Gbaud flexible dual polarization transmitter for future elastic optical networks

Next generation elastic optical networks will very likely require dual polarization (DP) optical transmitter with inherent flexibility to dynamically change its baud rate and/or modulation format. We develop a prototype of compact flexible DP M-ary quadrature amplitude modulation (MQAM) optical transmitter and demonstrate its reconfigurability to accommodate baud rates ranging from 8 to 32 Gbaud/s using the same hardware. The prototype has another advantage in that the modulation format can also be dynamically changed from binary phase shift keying up to 64 quadrature amplitude modulation (QAM) for single and DPs, all over a single optical carrier. This allows the generation of variable data rate up to 384-Gb/s over a single wavelength. Experimental results show that for the most challenging setting of DP-64 QAM/32 Gbaud, the worst case values of error vector magnitude and bit error rate are 6.7 and 3×10 −2 , respectively. For less stringent settings, i.e., lower baud rate and/or lower modulation format, forward error correction limit error free transmission is easily obtained. Further results are also reported to demonstrate transmitter flexibility and software definability, by measuring symbol streams showing instantaneous swapping between modulation schemes with a swapping time less than 10 symbols duration, i.e., 0.3 ns.

고속 철도 환경을 위한 IEEE 802.15.4/ZigBee 기반 개선된 센서 통신 알고리즘

본 논문에서는 어떠한 이진 입력 이산 퀀텀채널(quantum channel)이 주어지더라도 대칭 용량을 달성할 수 있는 qubit(quantum bit)를 생성하기 위해, 극(polar) 퀌텀 채널 코딩이라 부르는 퀀텀 채널의 결합과 분리 형태를 제시한다. 현재의 용량은 동등 확률을 갖는 임의의 qubit 입력에 따라서 결정된다. 퀀텀채널의 분극은 대칭채널이 1 에 근접하면 rate 1 로 아니면 rate 0 으로 전송하는 채널을 통해 퀀텀 데이터를 부분적으로 전송하는 퀀텀 오류정정 부호화에 아주 적합하다.

Network-based approaches for anticancer therapy

Cancer is a complex disease resulting from alterations of multiple signaling networks. Cancer networks have been identified as scale-free networks and may contain a functionally important key player called a hub that is linked to a large number of interactors. Since a hub can serve as a biological marker in a given network, targeting the hub could be an effective strategy for enhancing the efficacy of cancer treatment. Chemotherapies and radiotherapies are generally used to treat tumors not amenable to resection, and target single or multiple molecules associated with hubs. However, these therapies may unexpectedly induce the resistance of cancer cells to drugs and radiation. Cancer cells can overcome therapy-induced damage via the activation of back-up signaling pathways and flexible modulation of affected networks. These activities are considered to be the main reasons for chemoresistance and radioresistance, and subsequent failure of cancer therapies. Much effort is required to identify the key molecules that control the modulation of signaling networks in response to drugs and radiation. Network-based therapy that affects network flexibility, including rewired network structures and hub molecules in these networks, could minimize the occurrence of side-effects and be a promising strategy for enhancing the therapeutic efficacy of cancer treatments. This review is intended to offer an overview of current research efforts including ones focused on cancer-associated complex networks, their modulation in response to cancer therapy, and further strategies targeting networks that may improve cancer treatment efficacy.

An 8‐month randomized controlled exercise trial alters brain activation during cognitive tasks in overweight children

Children who are less fit reportedly have lower performance on tests of cognitive control and differences in brain function. This study examined the effect of an exercise intervention on brain function during two cognitive control tasks in overweight children. Participants included 43 unfit, overweight (BMI ≥ 85th percentile) children 8- to 11-years old (91% Black), who were randomly divided into either an aerobic exercise (n = 24) or attention control group (n = 19). Each group was offered a separate instructor-led after-school program every school day for 8 months. Before and after the program, all children performed two cognitive control tasks during functional magnetic resonance imaging (fMRI): antisaccade and flanker. Compared to the control group, the exercise group decreased activation in several regions supporting antisaccade performance, including precentral gyrus and posterior parietal cortex, and increased activation in several regions supporting flanker performance, including anterior cingulate and superior frontal gyrus. Exercise may differentially impact these two task conditions, or the paradigms in which cognitive control tasks were presented may be sensitive to distinct types of brain activation that show different effects of exercise. In sum, exercise appears to alter efficiency or flexible modulation of neural circuitry supporting cognitive control in overweight children.

Visible spatial frequency domain imaging with a digital light microprojector

There is a need for cost effective, quantitative tissue spectroscopy and imaging systems in clinical diagnostics and pre-clinical biomedical research. A platform that utilizes a commercially available light-emitting diode (LED) based projector, cameras, and scaled Monte Carlo model for calculating tissue optical properties is presented. These components are put together to perform spatial frequency domain imaging (SFDI), a model-based reflectance technique that measures and maps absorption coefficients (μa) and reduced scattering coefficients (μs') in thick tissue such as skin or brain. We validate the performance of the flexible LED and modulation element (FLaME) system at 460, 530, and 632 nm across a range of physiologically relevant μa values (0.07 to 1.5 mm-1) in tissue-simulating intralipid phantoms, showing an overall accuracy within 11% of spectrophotometer values for μa and 3% for μs'. Comparison of oxy- and total hemoglobin fits between the FLaME system and a spectrophotometer (450 to 1000 nm) is differed by 3%. Finally, we acquire optical property maps of a mouse brain in vivo with and without an overlying saline well. These results demonstrate the potential of FLaME to perform tissue optical property mapping in visible spectral regions and highlight how the optical clearing effect of saline is correlated to a decrease in μs' of the skull.

A Highly Efficient Superresolving Phase Filter for a Radially Polarized Beam

We simulate the focal intensity distribution of a radially polarized beam, in view of the vector diffraction theory. We summarize two important rules: (i) the marginal ray of the aperture determines the focal size on the focal plane; (ii) the ratio of the longitudinal component to the transversal component affects the shape of the focus. We design a continuous phase filter using these rules for a confocal system. We chose the tangent of the semi-aperture angle to build up the phase function, because it is sensitive to the marginal rays, which have large aperture angles. To achieve a flexible modulation, we use a quadratic function for unwrapping the phase. We optimize the parameters of the quadratic function and achieve a transverse superresolving focus. Aiming at different Strehl ratios, we obtain a series of superresolution phase filters. Compared with others, the filter proposed has the advantages of superior superresolution effect and higher energy utilization ratios. The phase-filter design is universal and proved to be valid. It can be employed in either high or low NA systems, superresolving or donut focus applications.

A Study of FSS in Terahertz Range for Polarization Modulation Purpose

A polarization sensitive frequency selective surface (FSS) composed of connected electric LC resonators is proposed as the terahertz wave filter. The experimental results match the simulation results well and show that the FSS has good capability of polarization control and wavelength selection. The tunability of FSS is also studied by investigating the relation between the conductivity of the joint area of bent-lines and the resonant peak position/strength. Such a device can be applied as a flexible polarization modulator.

Highly efficient beam steering with a transparent metasurface

We propose an ultra-thin planar metasurface with phase discontinuities for highly efficient beam steering. The effect benefits from the broadband transparency and flexible phase modulation of stacked metal/dielectric multi-layers that is perforated with coaxial annular apertures. Proof-of-principle experiments verify that an efficiency of 65% and a deflection angle of 18° at 10 GHz are achieved for the transmitted beam, which are also in good agreement with the finite-difference-method-in-time-domain (FDTD) simulations. The scheme shall be general for the design of beam-steering transmitters in all frequencies.

A flexible multi-16QAM transmitter based on cascaded dual-parallel Mach-Zehnder modulator and phase modulator

In this paper, we propose a novel and flexible 16-quadrature amplitude modulation (16QAM) transmitter based on cascaded dual-parallel Mach-Zehnder modulator (DPMZM) and phase modulator (PM). The proposed transmitter is able to generate three types of 16QAM signals: square 16QAM, star 16QAM and four-amplitude-four-phase-16-QAM (FAFP-16QAM). The feasibility of the transmitter is verified through experiment, 20-Gb/s eye diagrams of the 16QAM signals are obtained. In order to evaluate the performances of the 16QAM signals, simulations are also conducted using VPI Transmission Maker, clear constellations of 40-Gb/s 16QAM signals are achieved by coherent detection.

Control-oriented premixed charge compression ignition combustion timing model for a diesel engine utilizing flexible intake valve modulation

This paper describes a simple, analytical, control-oriented model for prediction of combustion timing during premixed charge compression ignition combustion with early fuel injection. The model includes direct dependence on in-cylinder temperature, in-cylinder pressure, and the total in-cylinder O2 mass fraction, including the contribution of recirculated exhaust gas, residual burned gas, and backflow during the valve overlap period. The model is extensively validated against experimental premixed charge compression ignition data from a multi-cylinder diesel engine utilizing high-pressure recirculated exhaust gas, variable geometry turbocharging, and flexible intake valve actuation, which allows control over the engine’s effective compression ratio. The results show that across a wide range of input conditions, the model predicts the start of combustion within ±2° crank angle of the experimental values for all but three of the 180 data points (98%+ accuracy), with a root mean square error of 0.86° crank angle. The experimental start of combustion ranges from as early as −19.3° crank angle to as late as +0.6° crank angle by heavily exercising the control actuators, specifically the commanded start of injection timing SOIecm, the intake valve closure timing, and the engine’s air-handling system (recirculated exhaust gas valve position and variable geometry turbocharger position). Analysis is performed to isolate the effects and control authority of each actuator on the ignition delay and start of combustion timing. During these actuator sweeps, the model captures complex relationships and predicts the start of combustion within ±2° crank angle of the experimental values. This premixed charge compression ignition combustion timing model can be coupled with a gas exchange model for control algorithm design and analysis.

Acting Alters Visual Processing: Flexible Recruitment of Visual Areas by One's Own Actions

Using functional magnetic resonance imaging, we investigated the effect of motor preparation/execution on the activation of visual cortical areas by action observation. We presented videos of human actors performing several fine manipulative actions (e.g., grasping) with the hand or foot, together with appropriate control stimuli. Subjects either responded in a central fixation task with the hand (A) or foot (B) or viewed the stimuli passively (C). Experimental conditions were arranged according to a 2 × 2 × 3 factorial design with action, effector, and response as factors. Bilateral posterior parietal cortex was more strongly activated for action videos compared with controls during active runs (A or B) contrasted with passive runs (C). Two neighboring regions in the right fusiform gyrus (FG) were activated when the effector employed to respond in the task matched that displayed in the videos (A or B), independently of whether the stimulus was an action or a control. Neighboring regions in the right posterior middle temporal gyrus (MTG) were also activated when the effector observed and that used to respond matched (A or B), but only for action videos, not controls. Our results indicate flexible modulation of visual areas during concurrent action observation and action execution/preparation, which was effector specific in the FG and MTG.

Flexible and transparent all-graphene circuits for quaternary digital modulations

In modern communication systems, modulation is a key function that embeds the baseband signal (information) into a carrier wave so that it can be successfully broadcasted through a medium such as air or cables. Here we report a flexible all-graphene modulator circuit with the capability of encoding a carrier signal with quaternary digital information. By exploiting the ambipolarity and the nonlinearity in a graphene transistor, we demonstrate two types of quaternary modulation schemes: quaternary amplitude-shift keying and quadrature phase-shift keying. Remarkably, both modulation schemes can be realized with just 1 and 2 all-graphene transistors, respectively, representing a drastic reduction in circuit complexity when compared with conventional modulators. In addition, the circuit is not only flexible but also highly transparent (~95% transmittance) owing to its all-graphene design with every component (channel, interconnects, load resistor and source/drain/gate electrodes) fabricated from graphene films.

Guaranteed Convergence of a High-Gain Input Observer Robust to Measurement Uncertainty: Application to ECR Estimation

The work presented here first briefly outlines a previously-developed high-gain input observer, which uses an auxiliary variable for estimating an un-steady input. The primary focus of this paper is on new results, namely on analysis of the aforementioned high-gain observer, including guarantees for: (1) robustness to measurement uncertainty, and (2) an upper bound on the convergence rate of the estimation error. In addition, this effort outlines a method for selecting the observer gain based on measurement uncertainty, acceptable steady-state errors, and desired estimation error convergence rates. Finally, this strategy is demonstrated in practice for estimation of the effective compression ratio (ECR) for IC engines incorporating flexible intake valve closure modulation. Convergence tests were performed at five operating conditions and the estimator is shown to converge well within the guaranteed rate of four engine cycles in the presence of up to 10% measurement uncertainty, with an average steady-state error less than roughly one half of a compression ratio.

Controllable synthesis of microporous, nanotubular and mesocage-like metal–organic frameworks by adjusting the reactant ratio and modulated luminescence properties of Alq3@MOF composites

Three metal–organic frameworks (MOFs) comprising micropore, mesocage and nanotube structures have been prepared based on the same ligands and binuclear zinc secondary building units. We have successfully achieved flexible modulation of pore size from micropore to mesopore in a binary system by adjusting the reactant ratio. With the merit of a nanoscale channel, IFMC-8 can be applied as the host material for encapsulating Alq3 chromophores to exhibit tunable luminescence. The fluorescence emission of composite material Alq3@IFMC-8 has changed from green to blue. More importantly, the inclusion of IFMC-8 effectively prolonged the excited-state lifetime of Alq3 in ethanol. To the best of our knowledge, it is the first time that a MOF was studied as the host material for modulating the fluorescence properties of Alq3 chromophores.

Behavioral outcomes of late‐onset or early‐onset orbital frontal cortex (areas 11/13) lesions in rhesus monkeys

The orbital frontal cortex (OFC) has been implicated in a number of psychiatric disorders, including depression, anxiety, phobia, and obsessive-compulsive disorder. Thus, a better understanding of its functions will likely provide critical information to understand the specific behavioral and cognitive processes affected in these human disorders. In recent years, a growing number of studies have provided evidence for anatomical and functional differentiation within the OFC. Here we discuss the effects of selective OFC (areas 11/13) lesions on social behavior, emotional regulation, and behavioral adaptation. Damage to these specific OFC subfields in adult monkeys resulted in profound changes in the flexible modulation of responses guided by reward value that could explain the poor fear regulation and disturbed social interactions observed in the same animals. A similar pattern of results was found when the OFC lesions were done in infancy. Thus, in monkeys, self-regulation abilities mediated by OFC areas 11/13 emerge from midinfancy through adolescence.

Cross-layer design for radio resource allocation based on priority scheduling in OFDMA wireless access network

The orthogonal frequency-division multiple access (OFDMA) system has the advantages of flexible subcarrier allocation and adaptive modulation with respect to channel conditions. However, transmission overhead is required in each frame to broadcast the arrangement of radio resources to all mobile stations within the coverage of the same base station. This overhead greatly affects the utilization of valuable radio resources. In this paper, a cross layer scheme is proposed to reduce the number of traffic bursts at the downlink of an OFDMA wireless access network so that the overhead of the media access protocol (MAP) field can be minimized. The proposed scheme considers the priorities and the channel conditions of quality of service (QoS) traffic streams to arrange for them to be sent with minimum bursts in a heuristic manner. In addition, the trade-off between the degradation of the modulation level and the reduction of traffic bursts is investigated. Simulation results show that the proposed scheme can effectively reduce the traffic bursts and, therefore, increase resource utilization.

Cardiorespiratory Fitness and the Flexible Modulation of Cognitive Control in Preadolescent Children

The influence of cardiorespiratory fitness on the modulation of cognitive control was assessed in preadolescent children separated into higher- and lower-fit groups. Participants completed compatible and incompatible stimulus-response conditions of a modified flanker task, consisting of congruent and incongruent arrays, while ERPs and task performance were concurrently measured. Findings revealed decreased response accuracy for lower- relative to higher-fit participants with a selectively larger deficit in response to the incompatible stimulus-response condition, requiring the greatest amount of cognitive control. In contrast, higher-fit participants maintained response accuracy across stimulus-response compatibility conditions. Neuroelectric measures indicated that higher-fit, relative to lower-fit, participants exhibited global increases in P3 amplitude and shorter P3 latency, as well as greater modulation of P3 amplitude between the compatible and incompatible stimulus-response conditions. Similarly, higher-fit participants exhibited smaller error-related negativity (ERN) amplitudes in the compatible condition, and greater modulation of the ERN between the compatible and incompatible conditions, relative to lower-fit participants who exhibited large ERN amplitudes across both conditions. These findings suggest that lower-fit children may have more difficulty than higher-fit children in the flexible modulation of cognitive control processes to meet task demands.

Phosphopeptides Designed for 5-Methylcytosine Recognition

An artificial phosphopeptide has been developed through rational design of the interaction with 5-methylcytosine in duplex DNA. The peptide consists of two tandem zinc finger motifs, in one of which the glutamate was replaced with a phosphotyrosine, the phosphotyrosine in the peptide being effective for methylcytosine selectivity of DNA binding. The flexible modulation of the target methylated sequence by rearrangement of zinc finger peptides is possible, and the phosphopeptide provided us an important hint for expansion of the codes for the interactions of zinc fingers with DNA to methylated DNA sequences. The fluorescence-labeled phosphopeptide provided information on the methylation status of genomic DNA through fluorescence anisotropy after a 10 min incubation.

MEMS-based flexible reflective analog modulators (FRAM) for projection displays: a technology review and scale-down study

A MEMS based technology for projection display is reviewed. This technology relies on mechanically flexible and reflective microbridges made of aluminum alloy. A linear array of such micromirrors is combined with illumination and Schlieren optics to produce a pixels line. Each microbridge in the array is individually controlled using electrostatic actuation to adjust the pixels intensities. Results of the simulation, fabrication and characterization of these microdevices are presented. Activation voltages below 250 V with response times below 10 μs were obtained for 25 μm × 25 μm micromirrors. With appropriate actuation voltage waveforms, response times of 5 μs and less are achievable. A damage threshold of the mirrors above 8 kW/cm2 has been evaluated. Development of the technology has produced projector engines demonstrating this light modulation principle. The most recent of these engines is DVI compatible and displays VGA video streams at 60 Hz. Recently applications have emerged that impose more stringent requirements on the dimensions of the MEMS array and associated optical system. This triggered a scale down study to evaluate the minimum micromirror size achievable, the impact of this reduced size on the damage threshold and the achievable minimum size of the associated optical system. Preliminary results of this scale down study are reported. FRAM with active surface as small as 5 μm × 5 μm have been investigated. Simulations have shown that such micromirrors could be activated with 107 V to achieve f-number of 1.25. The damage threshold has been estimated for various FRAM sizes. Finally, design of a conceptual miniaturized projector based on 1000×1 array of 5 μm × 5 μm micromirrors is presented. The volume of this projector concept is about 12 cm3.

A flexible loop-type flow modulator for comprehensive two-dimensional gas chromatography

The present investigation is focused on a simple flow modulator (FM), for comprehensive two-dimensional gas chromatography (GC × GC). The interface is stable at high temperatures, and consists of a metallic disc (located inside the GC oven) with seven ports, which are connected to an auxiliary pressure source via two branches, to the first and second dimension, to a waste branch (linked to a needle valve) and to an exchangeable modulation loop (2 ports). The ports are connected via micro-channels, etched on one of the inner surfaces of the disc. Modulation is achieved using a two-way electrovalve, connected on one side to the additional pressure source, and to the two metal branches, on the other. An FM enantio-GC × polar-GC method (using a flame ionization detector) was optimized (a 40-μL loop was employed), for the analysis of essential oils. As an example, an application on spearmint oil is shown; the method herein proposed was subjected to validation. Finally, an FM GC × GC diesel experiment was carried out, using an apolar–polar column combination, to demonstrate the effectiveness of the modulator in the analysis of a totally different sample-type.