Terahertz spectral properties of melamine and its deuterated isotope,melamine-d_6

The far-infrared optical properties of melamine and its deuterated isotope,melamine-d_6 were experimentally and theoretically investigated in the frequency range from 0.2 to 3.0 THz.Under the room temperature and dry air nitrogen conditions,three absorption bands were observed at 2.0,2.3 and 2.6 THz in the melamine sample by use of terahertz time-domain spectroscopy.Whereas,in the melamine-d_6 sample,the observed absorption bands shift towards lower frequencies and the relative intensity of the absorption bands reduces.Numerical simulation results based on the Parameterized Model number 3(PM3) were compared with the experimental data and the observed vibration spectra were assigned according to the PM3 calculations.The absorption bands of the measured melamine samples at terahertz frequencies are highly correlated with the intermolecular hydrogen bond stretching and π-π stacking vibration.Also,the red shift of the absorption bands is due to hydrogen/deuterium substitution.

IN VIVO TRANS-RECTAL ULTRASOUND-COUPLED NEAR-INFRARED OPTICAL TOMOGRAPHY OF INTACT NORMAL CANINE PROSTATE

This is the first tomography-presentation of the optical properties of a normal canine prostate,in vivo,in its native intact environment in the pelvic canal.The imaging was performed by trans-rectal near-infrared(NIR)optical tomography in steady-state measurement at 840 nm on three sagittal planes across the right lobe,middle-line,and left lobe,respectively,of the prostate gland.The NIR imaging planes were position-correlated with concurrently applied trans-rectal ultrasound,albeit there was no spatial prior employed in the NIR tomography reconstruction.The reconstructed peak absorption coefficients of the prostate on the three planes were 0.014,0.012,and 0.014mm^(−1).The peak reduced scattering coefficients were 5.28,5.56,and 6.53 mm^(−1).The peak effective attenuation coefficients were 0.45,0.43,and 0.50 mm^(−1).The absorption and effective attenuation coefficients were within the ranges predictable at 840 nm by literature values which clustered sparsely from 355 nm to 1064 nm,none of which were performed on a canine prostate with similar conditions.The effective attenuation coefficients of the gland were shown to be generally higher in the internal aspects than in the peripheral aspects,which is consistent with the previous findings that the urethral regions were statistically more attenuating than the capsular regions.

Intelligent Control of SIRES Using Neural Networks and Fuzzy Logic

Development of energy-resources-poor remote rural areas of the world has been discussed by many in the past. Harnessing locally available renewable energy resources as an environmentally friendly option is gaining momentum. Smart Integrated Renewable Energy Systems (SIRES) offer a resilient and economic path to “energize” the area and reach this goal. This paper discusses its intelligent control using neural networks and fuzzy logic.

Resonance properties of THz plasmonic dipole-bowtie antenna array: The critical role of the substrate

Subwavelength arrays of dipole-bowtie antennas are designed and characterized using terahertz time-domain spectroscopy（THz-TDS） and finite element method（FEM） simulations. Two different substrates, silicon and mylar with an order of magnitude difference between their thickness values are used to study the resonance properties of the antennas.The 640-μm thick silicon substrate supports a sharper fundamental mode resonance. We discover that higher-order Fabry–Perot resonances can be excited only in 24-μm thin mylar substrates and show much higher sensitivity to dielectric changes in the environment and the geometrical parameters of the antennas than the fundamental dipole resonance.

In vivo percutaneous reflectance spectroscopy of fatty liver development in rats suggests that the elevation of the scattering power is an early indicator of hepatic steatosis

This study assessed whether there was a scat tering spectral mar ker quantifiable by reflectance measurements that could indicate early development of hepatic steatosis in rats for potential applications to pre procurement organ evaluation.Sixteen rats were fed a methionine choline-deficient(MCD)diet and eight rats were fed a normal diet.Direct assessment of the liver parenchyma of rats in vivo was performed by percut aneous reflect ance spectroscopy using a single fiber probe at the beginning of diet-intake and arbitrary post-diet-intake times up to 11 weeks to render longitudinal comparison.Histological sampling of the liver over the duration of diet adm inistration was performed on two MCD diet treated rats and one control rat eutha-nized after reflectance spectroscopy measurement.The images of hematoxylin/eosin-stained liver specimens were analyzed morphometrically to evahuate the lipid size changes associated with the level of steatosis.The MCD-diet-treated group(n=16)had mild steatosis in seven rats,moderate in three rats,severe in six rats,and no other significant pathology.No control rats(n=8)developed hepatic steatosis.Among the parameters retrieved from per-SfS,only the scat tering power(can be either positive or negative)appeared to be statist ically diferent between MCD-treated and control livers.The scattering power for the 16 MCD-diet-treated livers at the time of euthanasia and presenting various levels of steatosis was 033±0.21,in comparison to 0.036±0.25 of the eight control livers(p=0.0189).When evaluated at days 12 and 13 combined,the scattering power of the 16 MCD-diet-treated livers was 032±0.17,in comparison to 0.10±0.11 of the eight control livers(p=0.0017).All of four MCD-treated livers harvested at days 12 and 13 presented mild steatosis with sub-micron size lipid droplets,even though none of the MCD-treated livers were sonogr aphically remarkable for fatty changes.The elevation of the scattering power may be a valuable marker indicating early hepatic steatosis before the steatosis is sonographically detectable.

An Approach to Assess the Resiliency of Electric Power Grids

Modern electric power grids face a variety of new challenges and there is an urgent need to improve grid resilience more than ever before. The best approach would be to focus primarily on the grid intelligence rather than implementing redundant preventive measures. This paper presents the foundation for an intelligent operational strategy so as to enable the grid to assess its current dynamic state instantaneously. Traditional forms of real-time power system security assessment consist mainly of methods based on power flow analyses and hence, are static in nature. For dynamic security assessment, it is necessary to carry out time-domain simulations (TDS) that are computationally too involved to be performed in real-time. The paper employs machine learning (ML) techniques for real-time assessment of grid resiliency. ML techniques have the capability to organize large amounts of data gathered from such time-domain simulations and thereby extract useful information in order to better assess the system security instantaneously. Further, this paper develops an approach to show that a few operating points of the system called as landmark points contain enough information to capture the nonlinear dynamics present in the system. The proposed approach shows improvement in comparison to the case without landmark points.

Impact of Wind Energy System Integration on the Al-Zawiya Refinery Electric Grid in Libya

Libya is an oil exporting country located in the middle of the North Africa. Exporting oil is the major income resource for the economics of the country. Al-Zawea refinery is one of the oil refineries in Libya. It is the largest refinery in the region. The refinery located in the Mediterranean coast. Electricity is the main sector in the refinery to produce and export oil. This paper discusses the possibility of the penetration of the renewable energy (wind) generated electricity into the refinery power system. Although, renewable energy application in Libya was started in the middle of the seventies, it has still not found its way into industry sector. This study proposes the possible impacts of renewable (wind) energy system integration on the Al-Zawea refinery electric grid to satisfy the refinery load demand.

Terahertz spectroscopy of water in nonionic reverse micelles

The dynamics of water within a nanopool of a reverse micelle is heavily affected by the amphiphilic interface.In this work,the terahertz(THz)spectra of cyclohexane/Igepal/water nonionic reverse micelle mixture are measured by THz timedomain spectroscopy and analyzed with two Debye models and complex permittivity of background with volume ratios.Based on the fitted parameters of bulk and fast water,the molar concentration of all kinds of water molecules and hydration water molecule number per Igepal molecule are calculated.We find that slow hydration water has the highest proportion in water when the radius parameterω_(0)<10,while bulk water becomes the main component whenω_(0)≥10.The feature radius ratio of nonhydrated and hydrated water to total water nanopool is roughly obtained from 0.39 to 0.85 with increasingω_(0).

基于Pareto熵的多目标粒子群优化算法

粒子群优化算法因形式简洁、收敛快速和参数调节机制灵活等优点,同时一次运行可得到多个解,且能逼近非凸或不连续的Pareto最优前端,因而被认为是求解多目标优化问题最具潜力的方法之一.但当粒子群优化算法从单目标问题扩展到多目标问题时,Pareto最优解集的存储与维护、全局和个体最优解的选择以及开发与开采的平衡等问题亦随之出现.通过目标空间变换方法,采用Pareto前端在被称为平行格坐标系统的新目标空间中的分布熵及差熵评估种群的多样性及进化状态,并以此为反馈信息来设计进化策略,使得算法能够兼顾近似Pareto前端的收敛性和多样性.同时,引入格占优和格距离密度的概念来评估Pareto最优解的个体环境适应度,以此建立外部档案更新方法和全局最优解选择机制,最终形成了基于Pareto熵的多目标粒子群优化算法.实验结果表明:在IGD性能指标上,与另外8种对等算法相比,该算法在由ZDT和DTLZ系列组成的12个多目标测试问题集中表现出了显著的性能优势.

Study of optical and dielectric properties of annealed ZnO nanoparticles in the terahertz regime

The frequency-dependent optical and dielectric properties of annealed ZnO nanoparticles in the range of 0.1 to 0.9 THz are studied by using terahertz time-domain spectroscopy(THz-TDS).The refractive index,power absorption and complex dielectric constants are obtained and the experimental results are well fit with a simple effective medium theory in conjunction with a pseudo-harmonic model.This study reveals that annealed ZnO nanoparticles exhibit the similar phonon response characteristics to the single ZnO crystal and other ZnO nanostructures,such as tetrapods and nanowires.

An Optimal Hybrid Learning Approach for Attack Detection in Linear Networked Control Systems

A novel learning-based attack detection and estimation scheme is proposed for linear networked control systems(NCS),wherein the attacks on the communication network in the feedback loop are expected to increase network induced delays and packet losses,thus changing the physical system dynamics.First,the network traffic flow is modeled as a linear system with uncertain state matrix and an optimal Q-learning based control scheme over finite-horizon is utilized to stabilize the flow.Next,an adaptive observer is proposed to generate the detection residual,which is subsequently used to determine the onset of an attack when it exceeds a predefined threshold,followed by an estimation scheme for the signal injected by the attacker.A stochastic linear system after incorporating network-induced random delays and packet losses is considered as the uncertain physical system dynamics.The attack detection scheme at the physical system uses the magnitude of the state vector to detect attacks both on the sensor and the actuator.The maximum tolerable delay that the physical system can tolerate due to networked induced delays and packet losses is also derived.Simulations have been performed to demonstrate the effectiveness of the proposed schemes.

Active-Thermal-Tunable Terahertz Absorber with Temperature-Sensitive Material Thin Film

It is shown that active-tunable terahertz absorbers can be realized in a sandwich-structured system comprising an ultrathin dielectric film(polyimide) on a temperature-sensitive substrate(InSb) with a metal film on the back by utilizing the intrinsic carrier density(N) variation in InSb. When increasing the temperature from 250 to 320 K, N in InSb varied from ～5.50×1015 to ～2.98×1016 cm–3. Fixing the thickness of dielectric film with the value of 1.37 μm, the absorption peak shifted from 1.41 to 3.29 THz while keeping absorption higher than 99%. This active tunability can respond to even a slight temperature perturbation, and shows polarization insensitivity as well as high tolerance of incidence-angle(absorption peak can still exceed 90% even the incidence angle reaches 60°). Besides, the refractive index of polyimide(PI) has thermal stability at the terahertz range and the merit of good workability. These characteristics guarantee the stability of activetunable performance. The peculiarities and innovations of this proposal promise a wide range of high efficiency terahertz devices, such as thermal sensors, spatial light modulators(SLMs) and so on.

Active terahertz beam steering based on mechanical deformation of liquid crystal elastomer metasurface

Active metasurfaces are emerging as the core of next-generation optical devices with their tunable optical responses and flat-compact topography.Especially for the terahertz band,active metasurfaces have been developed as fascinating devices for optical chopping and compressive sensing imaging.However,performance regulation by changing the dielectric parameters of the integrated functional materials exhibits severe limitations and parasitic losses.Here,we introduce a C-shape-split-ring-based phase discontinuity metasurface with liquid crystal elastomer as the substrate for infrared modulation of terahertz wavefront.Line-focused infrared light is applied to manipulate the deflection of the liquid crystal elastomer substrate,enabling controllable and broadband wavefront steering with a maximum output angle change of 22°at 0.68THz.Heating as another control method is also investigated and compared with infrared control.We further demonstrate the performance of liquid crystal elastomer metasurface as a beam steerer,frequency modulator,and tunable beam splitter,which are highly desired in terahertz wireless communication and imaging systems.The proposed scheme demonstrates the promising prospects of mechanically deformable metasurfaces,thereby paving the path for the development of reconfigurable metasurfaces.

Recent progress in graphene terahertz modulators

Graphene has been recognized as a promising candidate in developing tunable terahertz(THz)functional devices due to its excellent optical and electronic properties,such as high carrier mobility and tunable conductivity.Here,we review graphene-based THz modulators we have recently developed.First,the optical properties of graphene are discussed.Then,graphene THz modulators realized by different methods,such as gate voltage,optical pump,and nonlinear response of graphene are presented.Finally,challenges and prospective of graphene THz modulators are also discussed.

Terahertz spoof surface-plasmon-polariton subwavelength waveguide

Surface plasmon polaritons(SPPs) with the features of subwavelength confinement and strong enhancements have sparked enormous interest. However, in the terahertz regime, due to the perfect conductivities of most metals, it is hard to realize the strong confinement of SPPs, even though the propagation loss could be sufficiently low. One main approach to circumvent this problem is to exploit spoof SPPs, which are expected to exhibit useful subwavelength confinement and relative low propagation loss at terahertz frequencies. Here we report the design,fabrication, and characterization of terahertz spoof SPP waveguides based on corrugated metal surfaces. The various waveguide components, including a straight waveguide, an S-bend waveguide, a Y-splitter, and a directional coupler, were experimentally demonstrated using scanning near-field terahertz microscopy. The proposed waveguide indeed enables propagation, bending, splitting, and coupling of terahertz SPPs and thus paves a new way for the development of flexible and compact plasmonic circuits operating at terahertz frequencies.

Equivalent circuit analysis of terahertz metamaterial filters

An equivalent circuit model for the analysis and design of terahertz （THz） metamaterial filters is presented.The proposed model,derived based on LMC equivalent circuits,takes into account the detailed geometrical parameters and the presence of a dielectric substrate with the existing analytic expressions for self-inductance,mutual inductance,and capacitance.The model is in good agreement with the experimental measurements and full-wave simulations.Exploiting the circuit model has made it possible to predict accurately the resonance frequency of the proposed structures and thus,quick and accurate process of designing THz device from artificial metamaterials is offered.

Broadband terahertz rotator with an all-dielectric metasurface

Polarization manipulation is essential in developing cutting-edge photonic devices ranging from optical communication displays to solar energy harvesting. Most previous works for efficient polarization control cannot avoid utilizing metallic components that inevitably suffer from large ohmic loss and thus low operational efficiency.Replacing metallic components with Mie resonance-based dielectric resonators will largely suppress the ohmic loss toward high-efficiency metamaterial devices. Here, we propose an efficient approach for broadband, highquality polarization rotation operating in transmission mode with all-dielectric metamaterials in the terahertz regime. By separating the orthogonal polarization components in space, we obtain rotated output waves with a conversion efficiency of 67.5%. The proposed polarization manipulation strategy shows impressive robustness and flexibility in designing metadevices of both linear-and circular-polarization incidences.

Terahertz bound states in the continuum with incident angle robustness induced by a dual period metagrating

Metasurface-empowered bound state in the continuum(BIC)provides a unique route for fascinating functional devices with infinitely high quality factors.This method is particularly attractive to the terahertz community because it may essentially solve the deficiencies in terahertz filters,sensors,lasers,and nonlinear sources.However,most BIC metasurfaces are limited to specified incident angles that seriously dim their application prospects.Here,we propose that a dual-period dielectric metagrating can support multiple families of BICs that originate from guided mode resonances in the dielectric grating and exhibit infinite quality factors at arbitrarily tilted incidence.This robustness was analyzed based on the Bloch theory and verified at tilted incident angles.We also demonstrate that inducing geometric asymmetry is an efficient way to manipulate the leakage and coupling of these BICs,which can mimic the electromagnetically induced transparency(EIT)effect in our dual-period metagrating.In this demonstration,a slow-light effect with a measured group delay of 117 ps was achieved.The incidence-insensitive BICs proposed here may greatly extend the application scenarios of the BIC effect.The high Q factor and outstanding slow-light effect in the metagrating show exciting prospects in realizing high-performance filters,sensors,and modulators for prompting terahertz applications.

Compact and high-power broadband terahertz source based on femtosecond photonic crystal fiber amplifier

We present a review of the development of a compact and high-power broadband terahertz （THz） source optically excited by a femtosecond photonic crystal fiber （PCF） amplifier.The large mode area of the PCF and the stretcher-free configuration make the pump source compact and very efficient.Broadband THz pulses of 150 μW extending from 0.1 to 3.5 THz are generated from a 3-mm-thick GaP crystal through optical rectification of 12-W pump pulses with duration of 66 fs and a repetition rate of 52 MHz.A strong saturation effect is observed,which is attributed to pump pulse absorption;a Z-scan measurement shows that three-photon absorption dominates the nonlinear absorption when the crystal is pumped by femtosecond pulses at 1 040 nm.A further scale-up of the THz source power is expected to find important applications in THz nonlinear optics and nonlinear THz spectroscopy.

Moiré-driven electromagnetic responses and magic angles in a sandwiched hyperbolic metasurface

Recent moiréconfigurations provide a new platform for tunable and sensitive photonic responses,as their enhanced light–matter interactions originate from the relative displacement or rotation angle in a stacking bilayer or multilayer periodic array.However,previous findings are mostly focused on atomically thin condensed matter,with limitations on the fabrication of multilayer structures and the control of rotation angles.Structured microwave moiréconfigurations are still difficult to realize.Here,we design a novel moiréstructure,which presents unprecedented capability in the manipulation of light–matter interactions.Based on the effective medium theory and S-parameter retrieval process,the rotation matrix is introduced into the dispersion relation to analyze the underlying physical mechanism,where the permittivity tensor transforms from a diagonal matrix to a fully populated one,whereas the permeability tensor evolves from a unit matrix to a diagonal one and finally becomes fully filled,so that the electromagnetic responses change drastically as a result of stacking and rotation.Besides,the experiment and simulation results reveal hybridization of eigenmodes,drastic manipulation of surface states,and magic angle properties by controlling the mutual rotation angles between two isolated layers.Here,not only a more precisely controllable bilayer hyperbolic metasurface is introduced to moiréphysics,the findings also open up a new avenue to realize flat bands at arbitrary frequencies,which shows great potential in active engineering of surface waves and designing multifunctional plasmonic devices.