Stable Signal Research Articles

Performance of GNSS space service for geostationary autonomous operations

Abstract The geostationary orbit (GEO) belt hosts a substantial number of high-value satellites, making the study of autonomous navigation within this area significant. Features of autonomous operations such as patrolling the GEO belt and frequent manoeuvres at a certain location make real-time positioning using the Global Navigation Satellite System (GNSS) valuable. This paper studies the performance of positioning with GNSS considering main lobe and side lobe signals at different longitudes in the GEO belt. The research delves into the visibility and Position Dilution of Precision (PDOP) across the GEO belt, analysing the performance of the Global Positioning System (GPS), GLObalnaya NAvigatsionnaya Sputnikovaya Sistema (GLONASS) in Russian, BeiDou Navigation Satellite System (BDS), Galileo Navigation Satellite System (Galileo) and multi-systems. In particular, this paper investigates the impact of asymmetric constellations of mixed GEO, Inclined Geosynchronous Orbit (IGSO) and Medium Earth Orbit (MEO) satellites. The study reveals that BDS hybrid constellation provides long-term stable signal coverage over the GEO space above North America and Atlantic Ocean, where GEO signals are more sustainable while IGSO signals have wider coverage. This advantage positions BDS favourably in terms of performance in these regions.

Non-invasive scalp recording of electroencephalograms and evoked potentials in unanesthetized horses using a 12-channel active electrode array

Despite the long history of the horse-human bond, our understanding of the brain and mind of horses remains limited due to the lack of methods to investigate their brain functions. This study introduces a novel methodology for completely non-invasive, multi-channel recording of electroencephalography (EEG) and evoked potentials in awake horses to examine equine auditory cortical processing. The new approach utilizes specially designed brush-shaped active electrodes that facilitate stable signal acquisition through the hair coat by penetrating electrode pins and integrated pre-amplifiers. A 12-channel electrode array provided greater scalp coverage than prior work. As a proof of concept, clear cortical auditory evoked potentials (CAEPs) were recorded in response to sound onsets and offsets. The equine CAEP waveform morphology resembled the human P1-N1-P2-N2 complex, although the latencies were shorter than typical human values. The CAEP amplitudes were maximal at centroparietal electrodes, contrasting with the frontocentral distribution seen in humans, potentially explained by differences in auditory cortex orientation between species. This non-invasive multi-electrode method enables the evaluation of cognitive abilities, normal and abnormal brain functions, and advances scientific understanding of the equine mind. It offers potential widespread applications for recording EEGs and evoked potentials in awake horses and other medium-to-large mammalian species.

Designing a Secretory form of RTX-A as an Anticancer Toxin: An In Silico Approach.

Cancer is a leading cause of death and a significant public health issue worldwide. Standard treatment methods such as chemotherapy, radiotherapy, and surgery are only sometimes effective. Therefore, new therapeutic approaches are needed for cancer treatment. Sea anemone actinoporins are pore-forming toxins (PFTs) with membranolytic activities. RTX-A is a type of PFT that interacts with membrane phospholipids, resulting in pore formation. The synthesis of recombinant proteins in a secretory form has several advantages, including protein solubility and easy purification. In this study, we aimed to discover suitable signal peptides for producing RTX-A in Bacillus subtilis in a secretory form. Signal peptides were selected from the Signal Peptide Web Server. The probability and secretion pathways of the selected signal peptides were evaluated using the SignalP server. ProtParam and Protein-sol were used to predict the physico-chemical properties and solubility. AlgPred was used to predict the allergenicity of RTX-A linked to suitable signal peptides. Non-allergenic, stable, and soluble signal peptides fused to proteins were chosen, and their secondary and tertiary structures were predicted using GOR IV and I-TASSER, respectively. The PROCHECK server performed the validation of 3D structures. According to bioinformatics analysis, the fusion forms of OSMY_ECOLI and MALE_ECOLI linked to RTX-A were identified as suitable signal peptides. The final proteins with signal peptides were stable, soluble, and non-allergenic for the human body. Moreover, they had appropriate secondary and tertiary structures. The signal above peptides appears ideal for rationalizing secretory and soluble RTX-A. Therefore, the signal peptides found in this study should be further investigated through experimental researches and patents.

Fishing net-inspired PVA-chitosan-CNT hydrogels with high stretchability, sensitivity, and environmentally stability for textile strain sensors

Soft electronic products are being extensively investigated in diverse applications including sensors and devices, due to their superior softness, responsiveness, and biocompatibility. One-dimensional (1-D) fiber electronic devices are recognized for their lightweight, wearable, and stretchable qualities, thus emerging as critical constituents for seamless integration with the human body and attire, exhibiting great potential in wearable applications. However, wearable conductive hydrogel fibers usually face challenges in combining stretchability and excellent stability, notably in high-temperature environment. Herein, a novel stretchable conductive hydrogel fiber, namely PVA-CS-CNT (Polyvinyl Alcohol-Chitosan-Carbon Nanotube) hydrogel fiber, was successfully prepared through a straightforward low-temperature process. This hydrogel fiber not only maintains stable signal transmission at high temperatures but also exhibits significant mechanical and sensing capabilities, ensuring signal stability during repetitive cyclic stretching. Inspired by fishing net, textile sensors were fabricated by weaving PVA-CS-CNT hydrogel fibers, which offered breathability, high stability (withstanding over 500 stretch cycles), high sensitivity (detecting strains as low as 1 %), and exceptional mechanical strength (exceeding 17 MPa). The wearable sensor could not only accurately monitor human movements like stretching and bending, but also adeptly captured delicate signals such as pulses and sounds. These characteristics demonstrated the potential applications of the hydrogel fibers encompassing human motion tracking, intelligent textiles, and soft robotics.

Signal amplification strategy electrochemiluminescence based on porous graphite-phase carbon nitride: A novel ECL sensor for ultrasensitive detection of tigecycline

Tigecycline (TGC) is a third-generation tetracycline antibiotic known for its broad-spectrum antibacterial properties. However, the misuse of tigecycline can lead to significant issues, including environmental concerns and the escalation of drug resistance. Consequently, it is essential to develop an efficient and sensitive detection method for tigecycline. In this study, a novel solid-state electrochemical luminescence sensor was firstly developed for highly sensitive detection of TGC. The sensor incorporated porous graphite-phase carbon nitride (PCN) as a luminescent reagent, triethanolamine (TEA) as a co-reagent, Fe3O4 and ZIF-8@Ag NPs as luminescence accelerators, resulting in a robust and stable luminescence signal. Detailed characterization of PCN, comparison of ECL efficiency between PCN and g-C3N4, and optimization of experimental conditions were conducted to showcase the superior ECL performance of PCN. The sensor exhibited a linear relationship between the change of ECL signal and the logarithm of tigecycline concentration in the range of 1.0 × 10−14 to 1.0 × 10−7 mol/L, with a low detection limit of 3.33 × 10−15 mol/L (S/N = 3). Furthermore, the sensor demonstrated excellent stability, selectivity, and reproducibility, making it suitable for detecting TGC in milk samples.

Scalable Melt Polymerization Synthesis of Covalent Organic Framework Films for Room Temperature Low-Concentration SO2 Detection.

The development of highly efficient sensors for low-concentration SO2 at room temperature is important for human health and fine chemistry, but it still faces critical challenges. Herein, a scalable olefin-linked covalent organic framework (COF) with an ultramicroporous structure and abundant binding sites is first developed as the SO2 sensing material. The COF can adsorb SO2 of 220 cm3/g at 1 bar and 40 cm3/g at 0.01 bar and 298 K, surpassing all reported COFs. The computational and kinetic adsorption studies deeply unveil the selective adsorption mechanism for low-concentration SO2. Furthermore, the multicomponent gas mixture breakthrough experiments confirm that the COF can specifically capture low-concentration (2000 ppm) SO2. We innovated a melt polymerization technology to fabricate COF films with adjustable substrates and film thicknesses. COF films are directly grown on the interdigital electrodes to prepare the SO2 sensor device, which possesses a low detection limit (86 ppb) and excellent selectivity for SO2 in the presence of 10 other potentially interfering gases. Compared to other reported SO2 sensors, its overall performance is among the top. Prominently, the sensor maintains a stable output signal for more than two months, and recovery can be easily achieved by simply purifying nitrogen at room temperature without heating. This study marks the first use of COFs for SO2 sensing, opening new possibilities for COFs in the detection of low-concentration toxic gases and manufacturing gas sensor devices.

Suppression of Cadra cautella (Lepidoptera: Pyralidae) development by phytosanitary irradiation doses and their impacts on physiochemical and microbiological quality of dates.

Cadra cautella is a serious insect pest of stored figs and dates. The irradiation sensitivity of different development stages of C. cautella and large-scale testing of the proposed irradiation quarantine doses (50-500 Gy), were investigated. The impact of a PI dose of 400 Gy on the physiochemical and microbiological quality of dry dates (Bartamoda cv.) stored at room temperature was also investigated. An irradiation dose of 100 Gy prevented egg hatching in the F1 generation when 1-3 days old eggs were irradiated. Irradiation doses of 200 and 300 Gy prevented adult emergence when 2nd and 4th instar larvae were irradiated. When the pupae stage was irradiated, an irradiation dose of 400 Gy prevented the hatchability of F1 generation, indicating that this stage was the most radio-tolerant. The results of large-scale testing of the proposed phytosanitary irradiation dose (400 Gy) applied to 18, 0000 pupae resulted in no reproduction (zero hatching of F1 generation). There were no significant differences in the physiochemical properties of stored dates during the storage period at room temperature. Stable ESR signal intensity was recorded for 6 months in all parts of the irradiated fruits, and the intensity was highest in the kernel. The PI dose of 400 Gy also slightly reduced all microorganisms' counts. In conclusion, the dose level of 400 Gy stopped the reproduction potential of C. cautella. and they maintained the quality characteristics of dry date Bartamoda fruits during storage at room temperature for 6 months in tightly closed packages.

A Self-Reporting Nanosensor for Detecting Bacterial Exploitation in Plants through Extracellular DNA.

Detection of extracellular DNA (exDNA) released by invasive pathogens is crucial for understanding biotic stress in plants but remains challenging due to the lack of practical sensing tools. This study introduces a fluorescent nanosensor for remote, noninvasive detection of exDNA in plant tissues. Comprising GelGreen and polyethylenimine-modified silica nanoparticles, the nanosensor forms a self-reporting nanoplatform that simultaneously captures exDNA and generates signals. DNA-induced cross-linking causes nanosensor aggregation, producing detectable fluorescence measurable by confocal microscopy and flow cytometry with sensitivity at ng mL-1 levels. After injection, the nanosensors reside in the apoplastic space, capturing exDNA over extended periods and providing stable fluorescence signals. The study also demonstrates that invasive bacteria trigger nanosensor aggregation in plant leaves via bacterial surface DNA, rapidly activating the nanosensors. This underscores the role of exDNA in pathogen infections and highlights the potential of this nanosensor for advancing plant nanotechnology and pathophysiological research.

AI-Aided Gait Analysis with a Wearable Device Featuring a Hydrogel Sensor.

Wearable devices have revolutionized real-time health monitoring, yet challenges persist in enhancing their flexibility, weight, and accuracy. This paper presents the development of a wearable device employing a conductive polyacrylamide-lithium chloride-MXene (PLM) hydrogel sensor, an electronic circuit, and artificial intelligence (AI) for gait monitoring. The PLM sensor includes tribo-negative polydimethylsiloxane (PDMS) and tribo-positive polyurethane (PU) layers, exhibiting extraordinary stretchability (317% strain) and durability (1000 cycles) while consistently delivering stable electrical signals. The wearable device weighs just 23 g and is strategically affixed to a knee brace, harnessing mechanical energy generated during knee motion which is converted into electrical signals. These signals are digitized and then analyzed using a one-dimensional (1D) convolutional neural network (CNN), achieving an impressive accuracy of 100% for the classification of four distinct gait patterns: standing, walking, jogging, and running. The wearable device demonstrates the potential for lightweight and energy-efficient sensing combined with AI analysis for advanced biomechanical monitoring in sports and healthcare applications.

A nerve-adhesive stretchable electrode for stable neural signal recording and stimulation

A nerve-adhesive stretchable electrode for stable neural signal recording and stimulation

PVA/chitosan-based multifunctional hydrogels constructed through multi-bonding synergies and their application in flexible sensors

Hydrogels have garnered significant interest as promising materials for flexible wearable devices. However, it remains a major challenge to develop multifunctional hydrogels. In this study, we prepared a multifunctional hydrogel based on the polyvinyl alcohol (PVA) and chitosan (CS), which is characterized by high strength, good electrical conductivity, and resistance to freezing and water retention. The hydrogel formulation utilizes p-carboxyphenylboronic acid (PBA) and MXene in combination with freeze-thaw cycling and glycerin (GL) immersion technology. Additionally, we explored the applications of this hydrogel in motion detection and sensing. Research results indicate that the hydrogel has excellent mechanical properties, achieving a strength of up to 3.42 MPa, with modulus and toughness improved by 7 times and 5 times, respectively, compared to pure PVA hydrogels. Moreover, when the MXene dispersion is at 8 vol%, the conductivity is 163.15 mS/m, and we explore their applications in strain sensing (GF = 7.03) and motion detection. The hydrogels exhibit a good strain range (600 %) and a fast response time (42 ms), as well as regular and stable electrical signals demonstrated at joints and breathing, providing strategic support for the application of this hydrogel in the field of smart wearable flexibility.

Silk Nanofibers/Carbon Nanotube Conductive Aerogel.

Natural silk nanofibers (SNF) are attractive conductive substrates due to their high aspect ratio, outstanding mechanical strength, excellent biocompatibility, and controllable degradability. However, the inherently non-conductivity severely restricts the potential sensor application of SNF-based aerogels. In this work, the conductive nanofibrous aerogels with low-density achieved through freeze-drying by dispersing carbon nanotubes (CNT) into SNF suspension. The addition of CNT significantly increases the conductivity with improved mechanical properties of composite aerogels. SEM results reveal that the distinct hierarchical structure comprising micropores and nanofibrous networks within the pores is formed when CNT content reached 30%. Furthermore, increased cell viability suggested the excellent biocompatibility of SNF-CNT-based conductive aerogel for tissue-engineering applications. Subsequently, the elastic water-borne polyurethane (WPU) is incorporated to SNF-CNT system to construct aerogel with good sensing properties. The introduction of WPU demonstrates enhanced compressive performances and an exceptionally high elastic recovery ratio of 99.8%, thereby exhibiting a stable and lossless strain-sensing signal output at 5% strain. This study provides a feasible choice and strategy for exploring the potential application of SNF in functional aerogels.

A soft electronic skin simulating the multi-scale human touch for the detection of fruit freshness

Realizing biomimicry for human tactile perception is a meaningful challenge. In this work, a soft matter system with multi-scale energy dissipation structure is designed to realize flexible sensing and detection by biomimetic human touch. At the molecular scale, the supramolecular interactions are introduced into the hydrogel system, including the hydrophobic interaction and the ion attraction between macromolecular segments. At the micron scale, a system of “button” permeable macromolecules is constructed to absorb external forces and store energy through the sliding of macromolecules inside the “button”. By adjusting the molecular scale and micron scale structure, the obtained hydrogels demonstrate excellent mechanical properties, electrical conductivity and response sensitivity. This novel hydrogel withstands 200 compression cycles without creep deformation and outputs a stable response signal in terms of compression cycles with the signal volatility of around 1 %. Based on its good durability, this hydrogel, which simulates human multi-scale tactility, has outstanding application potential in detecting fruit damage that is difficult to observe. Notably, the construction of this multi-scale energy dissipation structure is universal for increasing the mechanical property of ACG hydrogels. The high-strength hydrogels adjusted by this strategy is significantly toughened, and the mechanical properties increased by 38 %. This work is of guiding significance for the preparation of high-performance hydrogels.

Rapid Dynamic Surface-Enhanced Raman Spectroscopy Detection of Amoxicillin-Mediated Morphological Changes in a Pathogen for Diagnosis of Clinical Urine Samples.

The swift and stable detection of pathogens in urine samples holds significant implications for the immediate clinical diagnosis and treatment of urinary tract infections (UTIs). In this study, we propose a detection strategy utilizing a hybrid substrate composed of graphene oxide (GO) and silver nanoparticles (Ag NPs) for the detection of pathogens subjected to amoxicillin-mediated (amo-mediated) treatment. This strategy employs dynamic surface-enhanced Raman spectroscopy (D-SERS) for stable and rapid detection, capturing signal variations induced by amo-mediated changes in pathogen morphology. During the 5 min D-SERS detection time window, stable SERS signals were detected for three types of pathogens and four types of pathogens were successfully distinguished using principal component analysis (PCA). In comparison to conventional nanosubstrates, the GO/Ag NP hybrid substrate exhibits outstanding stability and enhancement effects. This approach enables the dual detection of the pathogen cell structure and metabolites, facilitating specific identification of pathogens in the urinary tract, with a detection limit for Escherichia coli reaching 1 × 104 colony-forming units (CFU)/mL, meeting the clinical microbiology laboratory diagnostic standards for UTIs (105 CFU/mL). Testing of 188 clinically collected urine samples using this strategy yielded a sensitivity (SENS) of 86.4% and a specificity (SPC) of 89.7%. This introduces a novel method for diagnosing UTIs, offering broad applications in the field of clinical pathogen detection.

A Strong and Tough Ion‐gel Enabled by Hierarchical Meshing and Ion Hybridizations Collaboration

AbstractIon‐gels, with inherent flexibility, tunable conductivity, and multi‐stimulus response, have attracted significant attention in flexible/wearable electronics. However, the design of ion‐gels that exhibit both strength and toughness is challenging. In this study, a novel ion‐gel design is proposed that mimics the hierarchical meshing structure of leaves in combination with ion hybridization. Polyacrylamide (PAM) is incorporated in TEMPO oxidized cellulose nanofibers (TOCNFs) clusters by in situ polymerization, generating a hydrogel with micro/nanoscale entangled networks. Replacement of water by a metal halide ionic liquid ([BMIm]ZnxCly) in the hydrogel resulted in the formation of an ion hybrid network with supramolecular interactions. The integration of the PAM/TOCNF polymer network with [BMIm]ZnxCly resulted in ion‐gels with high strength (5.9 MPa), toughness (22 MJ m−3), and enhanced elastic modulus (30 MPa) combined with non‐flammability, heat and cold resistance. While having fast responsiveness (36 ms) of sensing signal and stability of power supply even at 4000 cycle collisions. Stable signal output even at high (200 °C) /sub‐zero temperatures. The proposed strategy offers a new approach to the material design of flexible/wearable electronics.

Two-Dimensional Differential Positioning with Global Navigation Satellite System Signal Frequency Division Relay Forwarding to Parallel Leaky Coaxial Cables in Tunnel

To address the issue of GNSS receivers being unable to function properly in tunnels due to the loss of Global Navigation Satellite System (GNSS) signals, this paper proposes a two-dimensional differential positioning system for tunnel environments based on dual leaky coaxial (LCX) cables with GNSS signal frequency relay forwarding. The system receives mixed GNSS signals from open environments and utilizes the frequency selection capabilities of the MAX2769E chip to separate and generate radio frequency signals at different frequencies corresponding to GPS, BDS, and GLONASS. These signals are then used to drive three ports of the LCX cables, which are laid in parallel within the tunnel. By leveraging the uniform radiation characteristics of the LCX cables, stable GNSS signal coverage is achieved throughout the tunnel. On the receiving end, the GNSS receiver achieves two-dimensional positioning by utilizing inter-satellite pseudorange differences and reference point error correction. The simulation results indicate that the dual T-shaped radiating LCX cables configuration offers excellent positioning accuracy and noise resistance, achieving meter-level positioning accuracy in tunnel environments.

A Stretchable Conductive Material with High Fatigue Resistance for Strain Sensors.

Intrinsically stretchable conductive materials based on elastic substrates and conductive components play important roles in biomedical applications, such as exercise rehabilitation monitoring and disease prediction. A persistent challenge is to combine high fatigue resistance with excellent mechanical properties in stretchable conductive materials. Herein, we present a stretchable conductive material with both good fatigue resistance and high tensile properties (∼3170%) based on poly(acrylic acid)-phytic acid-trehalose-polypyrrole (denoted as PPTP). The as-prepared PPTP hydrogel electrode showed no obvious cracking or delamination after 400 loading and unloading cycles and maintained good electrical signal transmission function after 1000 cycles. We further collected stable signals for human motion and handwriting using the stretchable hydrogel electrode as a strain sensor, demonstrating the potential application of the PPTP stretchable hydrogel electrode in biomedicine.

Electrostatic Self‐Assembly of Ag‐NPs Mediated by Eu3+ Complexes for Physically Unclonable Function Labels

ABSTRACTPhysically unclonable functions (PUFs) are essential for anticounterfeiting. Creating high‐stability, multimode, and secure labels remains challenging. Herein, we present a novel self‐assembly method for modulating the optical signals of rare‐earth (RE) complexes via interactions with Ag nanoparticles (Ag‐NPs). Initially, we engineered a positively charged Eu3+ complex ([EuL3]3+), which promotes the self‐assembly of negatively charged Ag‐NPs to form Eu/Ag‐NPs composites. The assembly of Ag‐NPs induces a surface plasmon effect that boosts the luminescent quantum yield and Raman signal intensities, and modifies the luminescence lifetime of the [EuL3]3+. Crucially, these micron‐scale Eu/Ag‐NPs can be applied to substrates, facilitating high‐resolution signal acquisition and diverse information encoding within limited space. Validation experiments reveal that PUF labels crafted using Eu/Ag‐NPs exhibit inherent randomness and uniqueness, along with stable and repeatable signal output. The strategic self‐assembly of Ag‐NPs, mediated by [EuL3]3+, along with the effective modulation of material properties, paves the way for advancing high‐resolution, high‐information‐density solutions in anticounterfeiting technologies.

Photoinduced Electrochemiluminescence Immunoassays.

Optimization of electrochemiluminescence (ECL) immunoassays is highly beneficial for enhancing clinical diagnostics. A major challenge is the improvement of the operation conditions required for the bead-based immunoassays using the typical [Ru(bpy)3]2+/tri-n-propylamine (TPrA) system. In this study, we report a heterogeneous immunoassay based on near-infrared photoinduced ECL, which facilitates the imaging and quantitative analysis of [Ru(bpy)3]2+-modified immunobeads at low anodic potential. The photovoltage generated by the photoanode under near-infrared light promotes oxidation processes at the electrode/electrolyte interface, thus considerably lowering the onset potential for both TPrA oxidation and ECL emission. The anti-Stokes shift between the excitation light (invisible to the human eyes) and the visible emitted light results in a clear and stable signal from the immunobeads. In addition, it offers the possibility of site-selective photoexcitation of the ECL process. This approach not only meets the performance of traditional ECL immunoassays in accuracy but also offers the additional benefits of lower potential requirements and enhanced stability, providing a new perspective for the optimization of commercial immunoassays.

Direct synthesis of composite conductive carbon nanofiber aerogels with continuous internal networks for collaborative physiological signal monitoring under complex environments

The emergence of multifunctional wearable flexible sensors has propelled advancements in healthcare and outdoor sports. However, conventional aerogels used for multifunctional sensing often involve complex fabrication processes, lack durability, and struggle to achieve collaborative sensing in complex scenarios, sometimes even lacking conductivity. This paper presents a novel strategy for synthesizing aerogels with interconnected internal networks directly through electrospinning technology, forming a three-dimensional fluffy structure with interlinked nanofibers. Subsequently, ultra-lightweight, highly elastic, and conductive composite carbon nanofiber aerogels (CCNA) were synthesized through high-temperature calcination and in-situ polymerization, suitable for collaborative physiological signal monitoring in complex situations. By controlling the density and phase separation of the charge jet, the three-dimensional fluffy structure of CCNA can be directly formed without strict reliance on external environmental conditions. The combination of CCNA's three-dimensional fluffiness and hydrophobic-hydrophilic properties enables it to operate within an extremely wide range of relative humidity (10% RH - 95% RH), while its internally continuous fiber network structure ensures stable and reliable electrical signal response even after 5000 compression cycles, with a compression response time of only 55ms. The developed flexible wearable electronic device holds promising prospects in healthcare and intelligent sensing applications.