Tunable Configuration Research Articles

A Heptacene Analogue Entailing a Quinoidal Benzodi[7]annulene (7/6/7 Ring) Core with a Tunable Configuration and Multiple Redox Properties.

Non-benzenoid acenes containing heptagons have received increasing attention. We herein report a heptacene analogue containing a quinoidal benzodi[7]annulene core. Derivatives of this new non-benzenoid acene were obtained through an efficient synthetic strategy involving an Aldol condensation and a Diels-Alder reaction as key steps. The configuration of this heptacene analogue can be modulated from a wavy to a curved one by just varying the substituents from a (triisopropylsilyl)ethynyl group to a 2,4,6-triisopropylphenyl (Trip) group. When mesityl (Mes) groups are linked to the heptagons, the resulting non-benzenoid acene displays polymorphism with a tunable configuration from a curved to a wavy one upon varying the crystallization conditions. In addition, this new non-benzenoid acene can be oxidized or reduced by NOSbF6 or KC8 to the respective radical cation or radical anion. Compared with the neutral acene, the radical anion shows a wavy configuration and the central hexagon becomes aromatic.

A Heptacene Analogue Entailing a Quinoidal Benzodi[7]annulene (7/6/7 Ring) Core with a Tunable Configuration and Multiple Redox Properties

AbstractNon‐benzenoid acenes containing heptagons have received increasing attention. We herein report a heptacene analogue containing a quinoidal benzodi[7]annulene core. Derivatives of this new non‐benzenoid acene were obtained through an efficient synthetic strategy involving an Aldol condensation and a Diels–Alder reaction as key steps. The configuration of this heptacene analogue can be modulated from a wavy to a curved one by just varying the substituents from a (triisopropylsilyl)ethynyl group to a 2,4,6‐triisopropylphenyl (Trip) group. When mesityl (Mes) groups are linked to the heptagons, the resulting non‐benzenoid acene displays polymorphism with a tunable configuration from a curved to a wavy one upon varying the crystallization conditions. In addition, this new non‐benzenoid acene can be oxidized or reduced by NOSbF6 or KC8 to the respective radical cation or radical anion. Compared with the neutral acene, the radical anion shows a wavy configuration and the central hexagon becomes aromatic.

High-Flexibility Control of Structured Light with Combined Adaptive Optical Systems

Combining the specific advantages of high-resolution liquid-crystal-on-silicon spatial light modulators (LCoS-SLMs) and reflective or refractive micro-electro-mechanical systems (MEMS) presents new prospects for the generation of structured light fields. In particular, adaptive self-apodization schemes can significantly reduce diffraction by low-loss spatial filtering. The concept enables one to realize low-dispersion shaping of nondiffracting femtosecond wavepackets and to temporally switch, modulate or deflect spatially structured beams. Adaptive diffraction management by structured illumination is demonstrated for piezo-based and thermally actuated axicons, spiral phase plates (SPPs) and Fresnel bi-mirrors. Improved non-collinear autocorrelation with angular-tunable Fresnel-bi-mirrors via self-apodized illumination and phase contrast of an SLM is proposed. An extension of the recently introduced nondiffractive Talbot effect to a tunable configuration by combining an SLM and a fluid lens is reported. Experimental results for hexagonal as well as orthogonal array beams are presented.

Nanoantioxidants: Pioneer Types, Advantages, Limitations, and Future Insights.

Free radicals are generated as byproducts of normal metabolic processes as well as due to exposure to several environmental pollutants. They are highly reactive species, causing cellular damage and are associated with a plethora of oxidative stress-related diseases and disorders. Antioxidants can control autoxidation by interfering with free radical propagation or inhibiting free radical formation, reducing oxidative stress, improving immune function, and increasing health longevity. Antioxidant functionalized metal nanoparticles, transition metal oxides, and nanocomposites have been identified as potent nanoantioxidants. They can be formulated in monometallic, bimetallic, and multi-metallic combinations via chemical and green synthesis techniques. The intrinsic antioxidant properties of nanomaterials are dependent on their tunable configuration, physico-chemical properties, crystallinity, surface charge, particle size, surface-to-volume ratio, and surface coating. Nanoantioxidants have several advantages over conventional antioxidants, involving increased bioavailability, controlled release, and targeted delivery to the site of action. This review emphasizes the most pioneering types of nanoantioxidants such as nanoceria, silica nanoparticles, polydopamine nanoparticles, and nanocomposite-, polysaccharide-, and protein-based nanoantioxidants. This review overviews the antioxidant potential of biologically synthesized nanomaterials, which have emerged as significant alternatives due to their biocompatibility and high stability. The promising nanoencapsulation nanosystems such as solid lipid nanoparticles, nanostructured lipid carriers, and liposome nanoparticles are highlighted. The advantages, limitations, and future insights of nanoantioxidant applications are discussed.

Tunable seesaw-like 3D capacitive sensor for force and acceleration sensing

To address the resource-competing issue between high sensitivity and wide working range for a stand-alone sensor, development of capacitive sensors with an adjustable gap between two electrodes has been of growing interest. While several approaches have been developed to fabricate tunable capacitive sensors, it remains challenging to achieve, simultaneously, a broad range of tunable sensitivity and working range in a single device. In this work, a 3D capacitive sensor with a seesaw-like shape is designed and fabricated by the controlled compressive buckling assembly, which leverages the mechanically tunable configuration to achieve high-precision force sensing (resolution ~5.22 nN) and unprecedented adjustment range (by ~33 times) of sensitivity. The mechanical tests under different loading conditions demonstrate the stability and reliability of capacitive sensors. Incorporation of an asymmetric seesaw-like structure design in the capacitive sensor allows the acceleration measurement with a tunable sensitivity. These results suggest simple and low-cost routes to high-performance, tunable 3D capacitive sensors, with diverse potential applications in wearable electronics and biomedical devices.

Design and Experiment of Electronically Tunable Voltage-Mode Biquad and Output Current Amplitude Oscillator

This study presents an electronically tunable configuration for the design of a voltage-mode (VM) biquad with four input terminals and three output terminals. The proposed circuit employs four operational transconductance amplifiers (OTAs) and two grounded capacitors. Depending on the selections of the four input voltage signals, all the standard filtering functions can be realized. The proposed configuration simultaneously provides VM inverting band-pass, non-inverting low-pass, and non-inverting band-reject filtering functions without any component-matching choices. It offers the features of a resistorless structure, high-input impedance, electronic control of the pole frequency and quality factor, and low active and passive sensitivities. The measured power dissipation of the biquad is 0.96 W under 32 mA constant output current. The measured 1 dB power gain compression point of the output inverting band-pass filter is −7 dBm. The measured value of the third-order intercept point is 5.136 dBm, and the measured value of the third-order intermodulation distortion is −50.83 dBc. Moreover, the measured value of the spurious-free dynamic range is 53.49 dB, and the figure-of-merit of the biquad is 268.75 × 103. In addition, an electronically controllable quadrature oscillator (QO) with amplitude of output current can be realized using the proposed biquad. The proposed electronically controllable QO can provide an amplitude modulation signal or an amplitude shift keying signal, and is widely applied in signal processing systems and electronic communication systems. PSpice simulations and experimental results are accomplished.

CGPTuner

Properly selecting the configuration of a database management system (DBMS) is essential to increase performance and reduce costs. However, the task is astonishingly tricky due to a large number of tunable configuration parameters and their inter-dependencies. Also, the optimal configuration depends upon the workload to which the DBMS is exposed. To extract the full potential of a DBMS, we must also consider the entire IT stack on which the DBMS is running, comprising layers like the Java virtual machine, the operating system and the physical machine. Each layer offers a multitude of parameters that we should take into account. The available parameters vary as new software versions are released, making it impractical to rely on historical knowledge bases. We present a novel tuning approach for the DBMS configuration auto-tuning that quickly finds a well-performing configuration of an IT stack and adapts it to workload variations, without having to rely on a knowledge base. We evaluate the proposed approach using the Cassandra and MongoDB DBMSs, showing that it adjusts the suggested configuration to the observed workload and is portable across different IT applications. We try to minimise the memory consumption without increasing the response time, showing that the proposed approach reduces the response time and increases the memory requirements only under heavy-load conditions, reducing it again when the load decreases.

Thermally activated resonant grating using a vanadium dioxide waveguide

In this work, we report on the design of a one-dimensional subwavelength resonant grating comprised of a fused silica substrate and a bi-layer waveguide, consisting of a solgel synthetized anatase TiO2 layer followed by a thin VO2 layer that is applied using pulsed laser deposition and rapid thermal annealing. A TE waveguide mode is excited under normal incidence in the VO2/TiO2 bi-layer via a positive photoresist based grating printed on top, leading to high resonant reflection at room temperature. Increasing the temperature to about 68°C causes the VO2 to undergo a dielectric to metallic transition accompanied by optical modifications in the IR region, canceling the resonance effect. This thermally triggered absorber/emitter tunable configuration enabling the on and off switching of optical resonant excitation in a reversible manner is proposed for passive Q-switching self-protecting devices for high power lasers in the IR wavelength range. Modeling of the optimized temperature dependent resonant waveguide and preliminary experimental results are presented.

Highly active and controllable MOF-derived carbon nanosheets supported iron catalysts for Fischer-Tropsch synthesis

N-doped carbon materials as catalyst supports have shown great superiority because of rich porosity, tunable metal-support interaction and electronic promotion effect. Controllable fabrication of carbon materials with specific morphology and different configurations provides wider possibilities for applications in catalysis. Herein, N-doped carbon nanosheets (CNS) were successfully synthesized by using monoclinic ZIF-8 nanosheets as templates. Compared with commercial active carbon and cubic ZIF-8 particles-derived carbon particles, the derived CNS exhibit superior graphitization degree and electronic effect. Consequently, the promoted Fe carburization improved the intrinsic activity for Fe/CNS catalysts in FTS. Further investigation on pyrolysis temperature achieved tunable configuration and content of N dopant. XPS, Raman, Mössbauer spectroscopy, TEM, H2-TPR etc. were combined to elucidate the promotion effect of CNS on dispersion, electronic properties and formation of Fe carbides. By correlating the composition and structure to catalytic performance in FTS, we illustrated the significance of carbon materials in Fe supported catalysts.

Metal-clad-suspended self-biasing graphene modulator with tunable figure of merit

In this letter, a research on the metal-clad-suspended self-biasing graphene modulator is conducted theoretically. The results reveal a higher light–graphene interaction for the more compact modulator. In addition, when the light–graphene interaction is enhanced, the light–metal interaction is also higher, which causes larger insertion loss and makes the figure of merit (FOM) lower. The length of π-phase shift is reduced to 6.35 µm for the Mach–Zehnder modulator, which is the smallest size achieved up to date. The modulator’s FOM can be tuned by changing the air gap (d) between the moveable metal plates and the suspended structure. In the case when this air gap increases, the configuration represents closer fundamental limits design. Moreover, the cut-off mode is discussed, and it has potential to be used in the tunable filter application. This tunable configuration of modulator is believed to have potential that can pave the way to design tunable light–matter interaction device and has evaluated for the near fundamental limits design.

Ultrahigh Responsivity UV Photodetector Based on Cu Nanostructure/ZnO QD Hybrid Architectures.

Strong near-surface electromagnetic field formed by collective oscillation of electrons on Cu nanostructure a shows a strong dependence on geometry, offering a promising approach to boost the light absorption of ZnO photoactive layers with enhanced plasmon scattering. Here, a facile way to fabricate UV photodetectors with tunable configuration of the self-assembled Cu nanostructures on ZnO thin films is reported. The incident lights are effectively confined in ZnO photoactive layers with the existence of the uplayer Cu nanostructures, and the interdiffusion of Cu atoms during fabrication of the Cu nanostructures can improve the carrier transfer in ZnO thin films. The optical properties of the hybrid architectures are successfully tailored over a control of the geometric evolution of the Cu nanostructures, resulting in significantly enhanced photocurrent and responsivity of 2.26 mA and 234 A W-1 under a UV light illumination of 0.62 mW cm-2 at 10 V, respectively. The photodetectors also exhibit excellent reproducibility, stability, and UV-visible rejection ratio (R370 nm /R500 nm ) of ≈370, offering an approach of high-performance UV photodetectors for practical applications.

Enhanced lithium storage performance of graphene nanoribbons doped with high content of nitrogen atoms

Nitrogen doping can provide a large number of active sites for lithium-ion storage, thus can yield a higher capacity for lithium-ion batteries. However, most of the reported N-doped graphene-based materials have low nitrogen content (<10 wt%) as the introduction of nitrogen atoms prefer to be produced at edges and defects in the graphene lattices. Owing to the formation of edges and defects, the doped states or active sites can easily be located and nitrogen contents can be determined precisely. Here we present the preparation of N-doped graphene nanoribbons with high nitrogen contents (11.8 wt%) and a facile tunable configuration of doped states. The material can be used as an anode for lithium-ion batteries and shows a higher capacity (the electrode has a reversible capacity of 1100.34 mA h g−1 at a charge/discharge rate of 100 mA g−1, corresponds to a discharge time of about 9 h), better rate performance (the electrode has a reversible capacity of 471 mA h g−1 at the current density of 2 A g−1, corresponds to a discharge time of about 11.6 min) and improved cycling stability (87.37% of the initial capacity after 200 cycles). The experimental results and first-principle calculations suggest that the residual oxygen-containing functional groups of N-doped graphene nanoribbons promote the formation of pyrrolic nitrogen at edges and substantially increase the room for nitrogen doping. This work opens new strategies for designing and developing N-doped graphene anodes for high performance lithium-ion batteries.

Improving Data-Analytics Performance Via Autonomic Control of Concurrency and Resource Units

Many big-data processing jobs use data-analytics frameworks such as Apache Hadoop (currently also known as YARN). Such frameworks have tunable configuration parameters set by experienced system administrators and/or job developers. However, tuning parameters manually can be hard and time-consuming because it requires domain-specific knowledge and understanding of complex inter-dependencies among parameters. Most of the frameworks seek efficient resource management by assigning resource units to jobs, the maximum number of units allowed in a system being part of the static configuration of the system. This static resource management has limited effectiveness in coping with job diversity and workload dynamics, even in the case of a single job. The work reported in this article seeks to improve performance (e.g., multiple-jobs makespan and job completion time) without modification of either the framework or the applications and avoiding problems of previous self-tuning approaches based on performance models or resource usage. These problems include (1) the need for time-consuming training, typically offline and (2) unsuitability for multi-jobs/tenant environments. This article proposes a hierarchical self-tuning approach using (1) a fuzzy-logic controller to dynamically adjust the maximum number of concurrent jobs and (2) additional controllers (one for each cluster node) to adjust the maximum number of resource units assigned to jobs on each node. The fuzzy-logic controller uses fuzzy rules based on a concave-downward relationship between aggregate CPU usage and the number of concurrent jobs. The other controllers use a heuristic algorithm to adjust the number of resource units on the basis of both CPU and disk IO usage by jobs. To manage the maximum number of available resource units in each node, the controllers also take resource usage by other processes (e.g., system processes) into account. A prototype of our approach was implemented for Apache Hadoop on a cluster running at CloudLab. The proposed approach was demonstrated and evaluated with workloads composed of jobs with similar resource usage patterns as well as other realistic mixed-pattern workloads synthesized by SWIM, a statistical workload injector for MapReduce. The evaluation shows that the proposed approach yields up to a 48% reduction of the jobs makespan that results from using Hadoop-default settings.

Four varieties of carbonyl sandwich

Organic Chemistry Compounds with adjacent carbons sandwiched between two carbonyl (C=O) centers turn up frequently in organic chemistry. When these central carbons each have a substituent, there are four possible mutual geometries, all with potentially distinct biochemical properties. Kaldre et al. present a single method to access each stereoisomer individually. The outcome depends on the straightforwardly tunable configuration of a sulfoxide group in a precursor, which guides a rearrangement. The versatility of the method should facilitate selective access to 1,4-dicarbonyl motifs in pharmaceutical research. Science , this issue p. [664][1] [1]: /lookup/doi/10.1126/science.aat5883

Design and modeling of a tunable spatial heterodyne spectrometer for emission line studies

Spatial heterodyne spectroscopy (SHS) is an interferometric technique similar to the Fourier transform spectroscopy with heritage from the Michelson interferometer. An imaging detector is used at the output of an SHS to record the spatially heterodyned interference pattern. The spectrum of the source is obtained by Fourier transforming the recorded interferogram. The merits of the SHS—its design, including the absence of moving parts, compactness, high throughput, high SNR, and instantaneous spectral measurements—make it suitable for space as well as for ground observatories. The small bandwidth limitation of the SHS can be overcome by building it in tunable configuration [tunable spatial heterodyne spectrometer (TSHS)]. We describe the design, development, and simulation of a TSHS in refractive configuration suitable for optical wavelength regime. Here we use a beam splitter to split the incoming light compared with all-reflective SHS where a reflective grating does the beam splitting. Hence, the alignment of this instrument is simple compared with all-reflective SHS where a fold mirror and a roof mirror are used to combine the beam. This instrument is intended to study faint diffuse extended celestial objects with a resolving power above 20,000 and can cover a wavelength range from 350 to 700 nm by tuning. It is compact and rugged compared with other instruments having similar configurations.

Taking on an organic glow

Phosphorescent materials, which continue to glow even after the light that put them into an excited state has been removed, have applications in electronics, optics, and biology. But achieving phosphorescence at room temperature and in the presence of oxygen can be tough because the excited state of such molecules is sensitive to these conditions. To date, most compounds that exhibit room-temperature phosphorescence contain metals, making them more costly and potentially toxic. Chemists in China now report a series of five organic molecules that efficiently and persistently phosphoresce in a range of colors in air and at room temperature (Chem 2016, DOI: 10.1016/j.chempr.2016.08.010). The team, led by Ben Zhong Tang of Hong Kong University of Science & Technology and Qian Peng of the Institute of Chemistry, Chinese Academy of Sciences, designed the aromatic carbonyl compounds so that their excited states have a tunable configuration that promotes phosphorescence. The most promising compound,

Taking the Human Out of the Loop: A Review of Bayesian Optimization

Big Data applications are typically associated with systems involving large numbers of users, massive complex software systems, and large-scale heterogeneous computing and storage architectures. The construction of such systems involves many distributed design choices. The end products (e.g., recommendation systems, medical analysis tools, real-time game engines, speech recognizers) thus involve many tunable configuration parameters. These parameters are often specified and hard-coded into the software by various developers or teams. If optimized jointly, these parameters can result in significant improvements. Bayesian optimization is a powerful tool for the joint optimization of design choices that is gaining great popularity in recent years. It promises greater automation so as to increase both product quality and human productivity. This review paper introduces Bayesian optimization, highlights some of its methodological aspects, and showcases a wide range of applications.

Analysis of Weakly Nonlinear Effect for Varactor-Tuned Bandpass Filter

This paper presents a general analytical approach to accurately predict the nonlinear distortion of varactor-tuned bandpass filters (BPFs) with arbitrary topology. The linearized circuit and its admittance matrix are derived to study the nonlinear behavior by means of the Volterra-series representation. The effects on third-order intermodulation distortion are characterized for the principal filter parameters such as tunable resonator configuration, susceptance slope, fractional bandwidth, unloaded quality factor, and filter topology. The theoretical analysis indicates that $\lambda/2$ -type varactor-tuned BPFs possess a better linearity property due to its large susceptance slope and the fractional bandwidth also plays a dominant role in the generation of nonlinearities. This analysis also reveals that the nonlinear distortion can be further reduced by source–load coupling for the first time. The analytical results are fully coincident with the harmonic-balance simulations using computer-aided design varactor model. A two-pole 1.0–1.3-GHz tunable BPF with a constant bandwidth of 105 MHz is fabricated and measured to validate the theory.

A Wide Tuning-Range CMOS VCO with a Tunable Active Inductor

This study describes a wide tuning-range VCO using tunable active inductor (TAI) topology and cross-coupled pair configuration for radio frequency operation. The TAI used two feedback loops to form a cascode circuit to obtain more degrees of freedom for inductance value. The TAI-VCO was fabricated using a 0.18 μm CMOS technology. The coarse frequency tuning is achieved by TAIs while the fine tuning is controlled by varactors. The fabricated circuit provides an output frequency range from 0.6 to 7.2 GHz (169%). The measured phase noise is from −110.38 to −86.01 dBc/Hz at a 1 MHz offset and output power is from −11.11 to −3.89 dBm within the entire frequency range under a 1.8 V power supply.

Tunable molecular configuration for significant enhancement of two-photon absorption based on novel octupolar benzoimidazole derivatives

Abstract Two novel octupolar molecules including benzoimidazole electron-accepting (A) branches and a triphenylamine electron-donating (D) center have been synthesized and characterized (p-ETBN and m-ETBN). Their photophysical and photochemical properties were investigated systematically including single-photon absorption, two-photon absorption (2PA) and charge transfer performance. Their 2PA properties have been investigated by the open aperture Z-scan technique, and the values of the 2PA cross section at 800 nm for p-ETBN and m-ETBN are ∼300 GM and ∼100 GM, respectively. Interestingly, both of them have the same D, A and π-conjugating units with only the different molecular configuration, the 2PA response of them differs by almost three times, which are found to be the different excited-state dipole moments and intramolecular charge-transfer. Our results reveal a new rule of molecular design for obtaining some excellent 2PA materials for their potential biophotonic and optoelectronic applications.