Theoretical Sensitivity Research Articles

Financial medicine as a source of moral distress: An unrecognised pathway to moral injury in the South African EMS systems

IntroductionThe phenomenon of Financial Medicine is a wide spread practice within the South African prehospital domain, which remains poorly researched. Similarly the impact of this phenomenon is not well understood, with many healthcare providers grappling with the moral dilemmas introduced into the work systems through the effects of the practice of Financial Medicine. Persisting, repetitive moral dilemmas can lead to instances of Moral Distress and Moral Injury. The practice of Financial Medicine in the South African prehospital domain proves to introduce many moral dilemmas and subsequently can serve as a source of Moral Distress and Moral Injury. MethodsThis study used a qualitative research methodology in the form of a constructivist grounded theory design. Participants voluntarily consented to be enrolled into one-on-one in-depth interviews, and were selected using purposive and theoretical sampling techniques. Data was subjected to validated coding procedures and analysed using the constant comparative analysis approach, analytical diagramming, and supported by researcher theoretical sensitivity. ResultsThe sub-category presented in this study stems from the development of 6 final analytical labels that were abstracted in the process of a theory construction, not presented in this article. This sub-category is nested under 1 of the final analytical labels, and comprised of 3 preliminary analytical labels and an associated code and proposition list. ConclusionUnderstanding the sources of Moral Distress and Moral Injury within the South African prehospital domain are key steps in promoting and supporting the adoption and sustainability of ethical practices. This article presents a key finding that demonstrates a link between the experience of the phenomenon of Financial Medicine and the suffering of a Moral Injury by South African prehospital personnel.

Super-sensitivity full-field measurement of structural vibration with an adaptive incoherent optical method

Full-field measurements of structural vibrations have been achieved by incoherent optical methods with video cameras such as digital image correlation and optical flow. In contrast to coherent optical methods such as scanning laser vibrometers, incoherent optical methods are low-cost and easy to set up. However, the sensitivity (minimum measurable displacement) of incoherent optical methods is generally lower than that of coherent optical methods. Typically, the sensitivity of incoherent optical methods is essentially limited by the finite bit depth of the digital camera due to the quantization with round-off errors. Quantitatively, this theoretical sensitivity limit is determined by the bit depth B as δp=1/(2B−1) [pixel] which corresponds to a displacement causing an intensity change of one gray level. Fortunately, natural dithering may be leveraged to overcome the quantization and exceed the sensitivity limit, achieving super-sensitivity.In this work, we first study the mechanism of the sensitivity limit induced by the quantization and the critical limitation of existing super-sensitivity methods in the full-field measurement of structural vibration. Addressing such a limitation, we present a general adaptive weighted averaging method with dithering, achieving super-sensitivity incoherent optical measurement of full-field deformational vibration of flexible structures. Specifically, both spatial and temporal samplings of the pixels are leveraged simultaneously to adaptively identify the motion (deformation) shape of the structure by principal component analysis (PCA) of spatiotemporal pixel intensities. Then, the identified deformation shape is used to perform a deformation-shape-weighted averaging over spatial pixels with dithering, revealing the sub-sensitivity displacement while retaining spatial resolution at full field. Numerical simulations and laboratory experiments are performed for principle explanation and method validation. Particularly, we derive a mathematical model of the minimum measurable vibration amplitude A∗ for the developed super-sensitivity method, which is found to be determined by the number of spatial pixels for averaging Ns and the noise level σn in the imaging system. Thus, this work provides, for the first time, a rigorous quantification of the sensitivity of incoherent optical measurement for structural vibration, and a new quantitative method to achieve super-sensitivity full-field measurement of structural vibration.

Experimental investigation on reactivation characteristics of liquid–metal heat pipes after hydrogen inactivation

The use of a hydrogen window provides an effective way for liquid–metal heat pipes (LMHPs) to prevent hydrogen inactivation when operated in a hydrogen-containing atmosphere. This work experimentally investigates the effects of various operational conditions on the reactivation characteristics of LMHPs after hydrogen inactivation. Theoretical analysis and sensitivity analysis are conducted to enhance our understanding and optimize reactivation operations. The results indicate that a slope-shaped distribution of hydrogen buffer enable faster reactivation compared to a near-column shape. A sweep-gas flow rate in 200 mL/min is preferred under test conditions, when both the reactivation time and the pure N2 consumption rate are considered. The working temperature significantly affects the reactivation time, as higher temperatures accelerate the NaH decomposition and increase the hydrogen permeability of hydrogen window. The varying of pressure and preheating temperature of sweep gas under test conditions just have little influence on the reactivation time. In practical conditions, vacuum operations are not recommended due to its extremely low hydrogen-removal rate.

Sensitivity Evaluation of Time Series InSAR Monitoring Results for Landslide Detection

Spaceborne interferometric synthetic aperture radar (InSAR) techniques are important for landslide detection and monitoring; however, several limitations and uncertainties, such as the unique north–south flying direction and side-look radar observing geometry, currently limit the ability of InSAR to credibly detect landslides, especially those related to high and steep slopes. Here, we conducted experimental and statistical analysis on the feasibility of time-series InSAR monitoring for steep slopes using ascending and descending SAR images. First, the theoretical (TGNSS), practical (PGNSS), and terrain (Hterrain) (T-P-H) indices for sensitivity evaluations of the slope displacement monitoring results from time-series InSAR were proposed for slope monitoring. Subsequently, two experimental and statistical studies were conducted for the cases with and without Global Navigation Satellite System (GNSS) monitoring data. Our experimental results of two high and steep open-pit mines showed that the defined theoretical and practical sensitivity indices can quantitatively evaluate the feasibility of ascending and descending InSAR observations in steep-slope deformation monitoring with GNSS data, and the terrain sensitivity index can qualitatively evaluate the feasibility of landslide monitoring results from ascending and descending Sentinel-1 satellite data without GNSS data. We further demonstrate the generalizability of these proposed indices using four landslide cases with both public GNSS and InSAR monitoring data and 119 landslide cases with only InSAR monitoring data. The statistical results indicated that greater indices correlated with higher reliability of the monitoring results, suggesting that these novel indices have wide suitability and applicability. This study can help to improve the practice of slope deformation monitoring using spaceborne InSAR, especially for high and steep slopes.

Sub‐Grid Representation of Vegetation Cover in Land Surface Schemes Improves the Modeling of How Climate Responds to Deforestation

AbstractUnderstanding the regional climate response to land cover change requires a realistic sub‐grid representation of vegetation cover in the land surface scheme (LSS) of climate models. The Community Land Model (CLM) is considered one of the most advanced LSSs; however, when coupled with the Weather Research and Forecasting (WRF) model, the tiling vegetation cover approach was deactivated. Here, we reactivated the theoretical sub‐grid vegetation cover representation in WRF‐CLM and applied it to assess the impacts of deforestation on regional climate in the Southeast Asian Massif region. We found that CLM‐tiling performs more accurate simulations of surface air temperature and precipitation compared to other LSSs using the in situ observations. Importantly, CLM‐tiling successfully captures the theoretical sensitivity of evapotranspiration (ET) and temperature to sub‐grid deforestation, aligning with Noah‐mosaic, and it substantially improves the spatial pattern responses of simulated ET and temperature to regional deforestation.

Dose blockchain-based agri-food supply chain guarantee the initial information authenticity? An evolutionary game perspective.

Guarantee the initial information of the agri-food supply chain (AFSC) authenticity based on the blockchain is a complex problem. This paper develops an evolutionary game model of AFSC participants based on the blockchain and discusses the impacts of the key parameters on the dynamic evolution process of participants. To verify the theoretical results, simulation experiments and sensitivity analysis were conducted through Matlab 2022b. The study results show that: (1) Guaranteeing the initial information authenticity could become the common belief of all AFSC participants, with the scientific design of parameters; (2) Higher reward and synergistic effect, lower information cost and risk contribute to improving the probability of initial true information sharing. (3) when the default penalty is too severe, the enterprise will evolve into not sharing the initial true information. Finally, this study could provide some suggestions and countermeasures for the leading enterprise in the agricultural supply chain and local governments to guarantee initial information authenticity in China. That is the way to realize the sustainability of AFSC in the long run.

Comprehensive analysis on the magnetic field error of a K–Rb–21Ne comagnetometer with low-frequency bias magnetic field sensitivity

The spin-exchange relaxation-free comagnetometer (SERFC) is of important research value compared to existing high-precision gyroscopes because of its extremely high theoretical limit sensitivity and long-term stability, in which one significant limiting factor is the magnetic field error. First, the relationship between the magnetic field gradient and the nuclear spin relaxation mechanism is introduced into the frequency response and steady-state response models of SERFC. Then, a novel method for suppression of the low-frequency magnetic field error based on the modified bias magnetic field sensitivity model is proposed. Finally, the effectiveness of the proposed suppression methods is demonstrated by optimizing the cell temperature, pump light power, and compensation magnetic field gradient to increase the suppression factor by 72.19%, 20.24%, and 69.86%, and the corresponding bias instability increased by 55.41%, 20.84%, and 27.63%, respectively. This study contributes to improving the long-term zero bias stability of the SERFC.

Noise analysis of the atomic superheterodyne receiver based on flat-top laser beams.

Since its theoretical sensitivity is limited by quantum noise, radio wave sensing based on Rydberg atoms has the potential to replace its traditional counterparts with higher sensitivity and has developed rapidly in recent years. However, as the most sensitive atomic radio wave sensor, the atomic superheterodyne receiver lacks a detailed noise analysis to pave its way to achieve theoretical sensitivity. In this work, we quantitatively study the noise power spectrum of the atomic receiver versus the number of atoms, where the number of atoms is precisely controlled by changing the diameters of flat-top excitation laser beams. The results show that under the experimental conditions that the diameters of excitation beams are less than or equal to 2 mm and the read-out frequency is larger than 70 kHz, the sensitivity of the atomic receiver is limited only by the quantum noise and, in the other conditions, limited by classical noise. However, the experimental quantum-projection-noise-limited sensitivity this atomic receiver reaches is far from the theoretical sensitivity. This is because all atoms involved in light-atom interaction will contribute to noise, but only a fraction of them participating in the radio wave transition can provide valuable signals. At the same time, the calculation of the theoretical sensitivity considers both the noise and signal are contributed by the same amount of atoms. This work is essential in making the sensitivity of the atomic receiver reach its ultimate limit and is significant in quantum precision measurement.

Comparing Performance of Spectral Image Analysis Approaches for Detection of Cellular Signals in Time-Lapse Hyperspectral Imaging Fluorescence Excitation-Scanning Microscopy.

Hyperspectral imaging (HSI) technology has been applied in a range of fields for target detection and mixture analysis. While HSI was originally developed for remote sensing applications, modern uses include agriculture, historical document authentication, and medicine. HSI has also shown great utility in fluorescence microscopy. However, traditional fluorescence microscopy HSI systems have suffered from limited signal strength due to the need to filter or disperse the emitted light across many spectral bands. We have previously demonstrated that sampling the fluorescence excitation spectrum may provide an alternative approach with improved signal strength. Here, we report on the use of excitation-scanning HSI for dynamic cell signaling studies-in this case, the study of the second messenger Ca2+. Time-lapse excitation-scanning HSI data of Ca2+ signals in human airway smooth muscle cells (HASMCs) were acquired and analyzed using four spectral analysis algorithms: linear unmixing (LU), spectral angle mapper (SAM), constrained energy minimization (CEM), and matched filter (MF), and the performances were compared. Results indicate that LU and MF provided similar linear responses to increasing Ca2+ and could both be effectively used for excitation-scanning HSI. A theoretical sensitivity framework was used to enable the filtering of analyzed images to reject pixels with signals below a minimum detectable limit. The results indicated that subtle kinetic features might be revealed through pixel filtering. Overall, the results suggest that excitation-scanning HSI can be employed for kinetic measurements of cell signals or other dynamic cellular events and that the selection of an appropriate analysis algorithm and pixel filtering may aid in the extraction of quantitative signal traces. These approaches may be especially helpful for cases where the signal of interest is masked by strong cellular autofluorescence or other competing signals.

A new neutron-gamma porosity measurement method for pulsed neutron logging tools

As an alternative method for the compensated neutron porosity measurement method, the neutron-gamma porosity measurement method is widely used in cased holes. However, the neutron-gamma porosity measurement method has some problems, such as the lack of detailed theoretical analysis and low sensitivity in high-porosity formations. The purpose of this paper is to clarify the theory of neutron-gamma porosity measurement, improve the measurement sensitivity, and eliminate the effects of environmental factors. Based on the neutron diffusion theory and the gamma transport theory, the distribution of capture gamma rays is described. A new neutron-gamma porosity measurement method is developed based on inelastic and capture gamma-ray distribution. The applicability of the new method in different environments is analyzed using the Monte Carlo method, and the effectiveness of this method is verified using the synthetic model. The results indicate that the capture gamma-ray ratio is only related to the source-detector distance, gamma-ray attenuation length, and neutron migration length. By combining density, different neutron cross sections, inelastic gamma-ray count ratio, and capture gamma-ray count ratio, the parameter secondary gamma-ray hydrogen index (SGH) related to hydrogen index can be extracted. The dynamic range of SGH is much higher than thermal neutron count ratio and the capture gamma-ray count ratio. The errors in porosity calculation by this method under different borehole and lithologic conditions are generally less than 2 pu. The calculation error of this method is close to that of the compensated neutron porosity measurement method. In addition, the applicability of the new method is analyzed without density data, and the results indicate that the calculation results are basically consistent with the results of calculation with density data. The new method has great potential for extensive applications in cased holes or open holes as an alternative for the compensated neutron porosity logging measurement method.

A theoretical and experimental investigation on a volume coil with slotted end-rings for rat MRI at 7 T

ObjectiveA volume coil with squared slots-end ring was developed to attain improved sensitivity for imaging of rat’s brain at 7 T.Material and MethodsThe principles of the high cavity resonator for the low-pass case and the law of Biot-Savart were used to derive a theoretical expression of B_1/i. The slotted-end ring resonator showed a theoretical 2.22-fold sensitivity improvement over the standard birdcage coil with similar dimensions. Numerical studies were carried out for the electromagnetic fields and specific absorption rates for our coil and a birdcage coil loaded with a saline-filled spherical phantom and a digital brain of a rat.ResultsAn improvement of the signal-to-noise ratio (SNR) can be observed for the slotted volume coil over the birdcage regardless of the load used in the electromagnetic simulations. The specific absorption rate simulations show a decrement for the digital brain and quite similar values with the saline solution phantom. Phantom and rat’s brain images were acquired at 7 T to prove the viability of the coil design. The experimental noise figure of our coil design was four times less than the standard birdcage with similar dimensions, which showed a 44.5% increase in experimental SNR.DiscussionThere is remarkable agreement among the theoretical, numerical and experimental sensitivity values, which all demonstrate that the coil performance for MR imaging of small rodents can be improved using slotted end-rings.

Interpretation of Fracture Initiation Points by In-Well Low-Frequency Distributed Acoustic Sensing in Horizontal Wells

Summary Low-frequency distributed acoustic sensing (LF-DAS) exploits the optical phase shift of Rayleigh backscatter in fiber-optic cables to obtain distributed measurements of changes in strain and temperature. Fiber-optic cables are often installed for multistage hydraulic fracture diagnostics in horizontal wells. LF-DAS in an untreated well provides far-field strain measurements, while offset wells are hydraulically fractured. Such a configuration is called crosswell LF-DAS sensing. Crosswell LF-DAS measurements have proved useful in diagnosing fracture hits, fracture azimuth, planarity, cluster efficiency, fracture propagation rates, and the dynamic distance to the fracture front. In contrast, in-well LF-DAS is conducted on the actively fractured well. Due to cool fracture fluid being injected at high injection rates, the strain component of the LF-DAS response is largely obscured by temperature changes. In permanent fiber-optic cable installations, distributed temperature sensing (DTS) is often conducted simultaneously with LF-DAS. An opportunity exists to decouple the temperature and strain components of LF-DAS sensors to observe strain changes on in-well LF-DAS. The LF-DAS response is modeled as linearly dependent on strain and temperature changes. Theoretical LF-DAS temperature and strain sensitivity coefficients are derived based on the changes to the index of refraction and length of the fiber. Using the DTS measurements, temperature changes are computed, smoothed, filtered, and compared to the LF-DAS response. Crossplots of the in-well LF-DAS measurements and temperature changes from DTS measurements far from the actively fractured region are used to validate the theoretical sensitivity coefficients. Uncertainty in the temperature component of the LF-DAS response is quantified. The difficulty in corresponding the different spatial and temporal resolutions of the DTS and LF-DAS measurements is overcome by comparing the responses over a moving temporal and spatial window. If the LF-DAS response at the center of the window agrees with the DTS response within uncertainty, the measurement is filtered out. After filtering, the remaining nonzero in-well LF-DAS measurements are due to changes in strain. The data are then visualized in waterfall plots. The results indicate that the theoretical and observed strain and temperature coefficients agree within 10%. After the temperature component of the in-well LF-DAS response is extracted, the remaining nonzero measurements are located primarily within the actively treated region. Locations with peaks in the strain response are interpreted to indicate fracture initiation points. These fracture initiation points are compared with in-well DTS and high-frequency DAS noise measurements across multiple stages to better understand fracture initiation along the horizontal well.

Sensitive Evanescence-Field Waveguide Interferometer for Aqueous Nitro-Explosive Sensing

The development of novel chemical nitro-explosive sensors with high sensitivity, low cost and a compact size is essential for homeland security, environmental protection and addressing military challenges. Polymeric optical waveguides based on refractive index sensing are widely used in biochemical detection due to their advantages of large-scale integration, low cost, high sensitivity and anti-electromagnetic interference. In this study, we designed and fabricated a polymer waveguide Mach–Zehnder interferometer (MZI) sensor to detect 2,4-dinitrotoluene (DNT) in water. One phase shifter of the MZI waveguide was functionalized by coating a thin cladding layer of polycarbonate with dipolar chromophores and used as the sensing arm; the other arm was coated with passive epoxy resin cladding and used as the reference arm. The phase difference between the two arms of the MZI was modulated using the refractive index (RI) change in the polycarbonate cladding when dipolar chromophores interacted with electro-deficient DNT. The theoretical sensitivity of the designed MZI can reach up to 24,696 nm/RIU. When used for explosive detection, our fabricated sensor had a maximum wavelength shift of 4.465 nm and good linear relation, with an R2 of 0.96 between the wavelength shift and a concentration ranging from 3.5 × 10−5 to 6.3 × 10−4 mol/L. The sensitivity of our device was 6821.6 nm/(mol/L). The design of an unbalanced MZI sensor, together with the sensing material, provides a new approach to using low-cost, compact and highly sensitive devices for in-field explosive detection.

Neutron interferometry using a single modulated phase grating.

Neutron grating interferometry provides information on phase and small-angle scatter in addition to attenuation. Previously, phase grating moiré interferometers (PGMI) with two or three phase gratings have been developed. These phase-grating systems use the moiré far-field technique to avoid the need for high-aspect absorption gratings used in Talbot-Lau interferometers (TLI) that reduce the neutron flux reaching the detector. We first demonstrate, through theory and simulations, a novel phase grating interferometer system for cold neutrons that requires a single modulated phase grating (MPG) for phase-contrast imaging, as opposed to the two or three phase gratings in previously employed PGMI systems. The theory shows the dual modulation of MPG with a large period and a smaller carrier pitch P, resulting in large fringes at the detector. The theory was compared to the full Sommerfeld-Rayleigh diffraction integral simulator. Then, we proceeded to compare the MPG system to experiments in the literature that use a two-phase-grating-based PGMI with best-case visibility of around 39%. The simulations of the MPG system show improved visibility in comparison to that of the two-phase-grating-based PGMI. An MPG with a modulation period of 300 µm, the pitch of 2 µm, and grating heights with a phase modulation of (π,0, illuminated by a monochromatic beam produces visibility of 94.2% with a comparable source-to-detector distance (SDD) as the two-phase-grating-based PGMI. Phase sensitivity, another important performance metric of the grating interferometer, was compared to values available in the literature, viz. the conventional TLI with the phase sensitivity of 4.5 × 103 for an SDD of 3.5m and a beam wavelength of 0.44nm. For a range of modulation periods, the MPG system provides comparable or greater theoretical maximum phase sensitivity of 4.1 × 103 to 10.0 × 103 for SDDs of up to 3.5m. This proposed MPG system appears capable of providing high-performance PGMI that obviates the need for the alignment of two phase gratings.

Биосенсор на основе терагерц-графеновой метаповерхности с двухрезонансным откликом как инструмент для выявления рака с использованием специфической для клеток частоты

Early detection is the most important strategy for controlling and management of cancer, which can significantly increase the survival rate by detecting disease in the early stages and rapid treating and preventing the progression of the disease. Based on existence of specific cell frequencies in the form of the response of each cell to its own specific frequency and the difference between normal and tumor cell frequency levels as a hallmark for cancer detection, we suggest using Graphene-based metasurfaces. Owing to the outstanding physical properties of graphene, its biosensing applications implemented by the terahertz metasurface are widely concerned and studied.a novel design of the graphene metasurface, proposed by ( Tan et al., 12) consists of an individual graphene ring and an Hshaped graphene structure. The graphene metasurface exhibits a dual-resonance response, whose resonance frequency strongly varies with its geometrical parameters. The simulated results clearly show that the theoretical sensitivity, figure of merit, and quantity of the proposed graphene metasurface for breast cells reach 1.21 THz/RIU, 2.75 RIU-1, and 2.43, respectively. These findings may open up new avenues for promising applications in the diagnosis of cancers.

Theoretical Saturation in Grounded Theory Studies: An Evaluative Tool

The three Grounded Theory (GT hereafter) schools, Classic, Straussian, and Constructivist GT, differ from each other based on their paradigmatic perspectives. The major difference is in terms of the data analysis procedure. Common features exist among the three GT traditions such as constant comparison method, simultaneous data collection and analysis, memos, theoretical sensitivity, theoretical sampling, and theoretical saturation. Among these features, theoretical saturation acts as a key factor that initiates each coding stage of GT while ending the preceding one. This paper focuses on Theoretical Saturation in GT and evaluates how different GT paradigms approach the concept of Theoretical Saturation. Additionally, facilitating novice GT researchers, the paper suggests the Q-Ü Theoretical Saturation instrument to offer possible solutions to overcome the paradigm-related and practical challenges.

Simulations for Planning Next-generation Exoplanet Radial Velocity Surveys

Future direct imaging missions similar to the HabEx and LUVOIR mission concepts aim to catalog and characterize Earth-mass analogs around nearby stars. The exoplanet yield of these missions will be dependent on the frequency of Earth-like planets, and potentially the a priori knowledge of which stars specifically host suitable planetary systems. Ground- or space-based radial velocity surveys can potentially perform the pre-selection of targets and assist in the optimization of observation times, as opposed to an uninformed direct imaging survey. In this paper, we present our framework for simulating future radial velocity surveys of nearby stars in support of direct imaging missions. We generate lists of exposure times, observation time-series, and radial velocity time-series given a direct imaging target list. We generate simulated surveys for a proposed set of telescopes and precise radial velocity spectrographs spanning a set of plausible global-network architectures that may be considered for next-generation extremely precise radial velocity surveys. We also develop figures of merit for observation frequency and planet detection sensitivity, and compare these across architectures. From these, we draw conclusions, given our stated assumptions and caveats, to optimize the yield of future radial velocity surveys supporting direct imaging missions. We find that all of our considered surveys obtain sufficient numbers of precise observations to meet the minimum theoretical white noise detection sensitivity for Earth-mass habitable-zone planets. While our detection rates and mass-sensitivity are optimistic, we have margin to explore systematic effects due to stellar activity and correlated noise in future work.

Broadband source-driven resonant micro-optic gyroscope based on a multi-turn waveguide-type ring resonator.

The resonant micro-optic gyroscope (RMOG) is one of the most promising candidates for chip-scale optoelectronic gyroscopes. A broadband source-driven RMOG based on a multi-turn waveguide-type ring resonator (WRR) has been proposed and demonstrated. The theoretical sensitivity is enhanced with the multi-turn structure, while the parasitic backscattering can be resolved by the use of the broadband source, thus greatly improving the long-term bias stability of the RMOG. We also reduce the relative intensity noise (RIN)-induced error of the broadband source at the gyro output by optimizing the number of loop turns of the WRR, and improve the angle random walk (ARW) by 4.8 dB compared with the case of a single-turn WRR. Finally, a bias stability of 1°/h is obtained with a 5-turn WRR of 4.05 cm diameter, achieving the tactical-grade resolution. To the best of our knowledge this is the best result reported to date for an RMOG of similar size.

Sensitive Detection of Doped Polymer Thin Films Using Terahertz Metamaterial Based on Analog of Electromagnetically Induced Transparency

We propose a novel terahertz (THz) metamaterial (MM)-based sensor for the sensitive detection of doped polymer thin films. The MM constructed by periodic quasi-ring resonators can generate the analog of electromagnetically induced transparency (EIT) at the THz region and work in a wide range of incident angles. The simulated results show that the frequency and magnitude of the EIT-like resonance can be, respectively, affected by the refractive index and dielectric loss of the analyte, which is further explained by a coupled harmonic oscillator model. The theoretical sensitivity of the proposed sensor is calculated as 185 GHz/RIU [refractive index unit (RIU)], showing a good sensing capability. In experiments, the dispersed red 1 (DR1)-doped polymethylmethacrylate (PMMA) thin films with a subwavelength thickness of 600 nm were covered on the MM surface. The measured results show that the EIT-like resonance experiences frequency redshift and magnitude attenuation as the doping concentration increases, indicating the addition of DR1 can lead to the increase in both refractive index and dielectric loss of the PMMA thin film. The proposed MM-based sensor can successfully identify the dielectric change of extremely thin polymer films caused by doping, offering a novel way to achieve high-sensitivity thin-film sensing.

Sensitivity Deterioration of Free-Space Optical Coherent/Non-Coherent OOK Modulation Receiver by Ambient Light Noise.

In free-space optical (FSO) communication systems, on-off keying (OOK) is a widely used modulation format. Coherent and non-coherent OOK receivers with sensitivities of -54.60 dBm and -51.25 dBm, respectively, were built with a communication rate of 1 Gbit/s and a bit error rate of 10-3. In an FSO communication system, the parameters must be designed to ensure a sufficient link margin. In contrast to optical fiber systems, FSO systems have ambient light (AL) noise such as sunlight. The efficiency of sunlight coupling in the single-mode fiber (SMF) of the receivers was calculated in this study. For a signal light with AL, the change in the main components of noise and the sensitivity deterioration were theoretically analyzed and experimentally verified in conditions of coherent reception and non-coherent reception with a preamplifier. For coherent reception, the theoretical sensitivity deterioration results are consistent with the experimental results which indicate that coherent reception exhibits better anti-AL noise performance than non-coherent reception when the power spectral density of the AL is the same. Coherent and non-coherent receivers coupled with SMF can work in direct sunlight. When the receiver lens diameter is greater than 4.88 × 10-4 m, the anti-AL noise performance of the receiver can be improved by increasing the receiver lens diameter.