Low Humidity Environment Research Articles

A novel air-conditioning system with cascading desiccant wheel and liquid desiccant dehumidifier for low-humidity industrial environments

Numerous industrial workshops require low-humidity environments, including lithium battery production, chip fabrication, some pharmaceutical manufacturing, etc. The desiccant wheel system is the conventional air-conditioning system for maintaining the low-humidity environments. However, only high-humidity outdoor air can be used for desiccant regeneration in some mechanical workshops requiring no mechanical ventilation, which leads to a high regeneration temperature and a poor system energy performance. To enhance the performance, a novel air-conditioning system with cascading desiccant wheel and liquid desiccant dehumidifier for low-humidity industrial workshops is proposed in this study. Solid desiccant and liquid desiccant are innovatively integrated in the proposed system for achieving a supply air dew point temperature below −10 °C. When dehumidifying process air from 5 to 1 g/kg in the basic case, the proposed system shows a competitive COP of 1.6. Under weather conditions in Guangzhou, subtropical China, the proposed system consumes 19.6 % and 58.0 % lower electricity during the summer, compared to the integrated system using outdoor air for regeneration and the desiccant wheel based system, respectively. The proposed system particularly applies to low-humidity industrial workshops in tropical and subtropical regions in summer, where there is a huge air humidity difference between indoors and outdoors. It is anticipated that this study could provide reference for energy saving and carbon emission reduction in low-humidity industrial production process.

Towards Ge-based electronic devices: Increased longevity of alkanethiol-passivated Ge(100) in low humidity environments

Germanium is a critically important material for future complementary metal-oxide-semiconductor devices, however, to maximise its potential it is necessary to develop a robust passivation process that prevents Ge re-oxidation for a queue time of 24 h. Self-assembled monolayers (SAMs) of alkanethiols on Ge have previously been shown to inhibit oxidation; however, re-oxidation eventually occurs when exposed to ambient conditions. Herein, it is shown that humidity plays a key role in the degradation of the SAM, ultimately resulting in re-oxidation. To demonstrate this, thiol-passivated Ge(100) surfaces are exposed to controlled humidity environments with different levels of relative humidity (RH). The rate of re-oxidation of the Ge surfaces are tracked using X-ray photoelectron spectroscopy and water contact angle analysis to discern what role RH plays in the re-oxidation of the Ge and the degradation of the SAM passivation. Atomic force microscopy data is presented to show that humidity-mediated re-oxidation of the Ge has little or no impact on the route mean square roughness of those surfaces. Finally, atomistic modelling of thiol-SAM passivated Ge in the presence of water molecules has been studied using first principles density functional theory in order to simulate experimental conditions and to understand the atomic level processes that determine stability in hydrophilic and hydrophobic configurations.

Two-linker MOFs-based glass fiber paper monolithic adsorbent for atmospheric water harvesting in arid climates

With the increasing demand for freshwater resources, the sustainable and effective utilization of atmospheric water has become a critical issue. Herein, an efficient and stable monolithic water-adsorbent is designed via functionalizing glass fiber paper loaded with two-linker metal-organic frameworks (CGF-mixed-MOFs(Al)). Firstly, a chitosan (CTS) polyelectrolyte layer is constructed on glass fiber paper to improve the MOFs loading capacity (306.71%) through electrostatic interaction and hydrophilic interaction. Subsequently, a series of two-linker metal-organic frameworks (mixed-MOFs(Al)) composed of MIL-160(Al) and Al-fumarate are tailor-made on CGF surface through a situ synthesis self-assembly technology. The resultant mixed-MOFs(Al) monolith exhibits better water harvesting ability and faster adsorption kinetics at low humidity owing to possessing more active adsorption sites. Different from CGF-MIL-160(Al) and CGF-Al-fumarate, the water sorption of CGF-mixed-MOFs(Al)5 at 30% RH, 25% RH and 20% RH reaches 0.37 g/g, 0.31 g/g and 0.25 g/g, respectively. The lab-scale atmospheric water harvesting device based on CGF-mixed-MOFs(Al)5 confirms the feasibility of this work-tailored product as a potential water sorbent in low-humidity environments. The cyclability results (50 times) indicate that CGF-mixed-MOFs(Al)5 maintains good water capture performance, integrity (no MOFs leakage) and crystallinity, which guarantees its working reliability and sustainable benefits. Therefore, our customized water adsorption system provides a simple, long-effective, economical and advanced strategy to capture more fresh water from atmosphere in arid climates.

Resistive Switching of Self‐Assembled Silver Nanowire Networks Governed by Environmental Conditions

AbstractPercolating networks formed by coated metallic nanowires have recently shown to exhibit memristive properties, opening a path for the development of neuromorphic systems. In this work, the resistive switching phenomena occurring in percolative networks of silver nanowires (AgNWs) coated with a thin layer of polyvinylpyrrolidone is studied. By performing voltage‐driven excursions, the highly‐conductive pristine state irreversibly changes to a higher resistance state. Such an electroforming procedure enables the switching among multiple resistance states. The stability and controllability of the resistance levels are found to be highly dependent on the initial state and the environmental conditions. In low relative humidity environments, the system displays the most controlled switching operation, while in high humidity environments the system shows a high conductance level. Samples with hysteretic response display sharp and spontaneous transitions to different resistance states, exhibiting multilevel memory device features. Both behaviors can be associated with regions of high local concentration of AgNWs that can couple or decouple from the conduction paths according to external stimuli. Conductivity is determined at a fundamental level by electrochemical processes at critical junctions in which water molecules play a key role. These results are relevant for the development of AgNWs‐based electronics and in‐hardware neuromorphic computing.

High Sensitivity SERS Substrate of a Few Nanometers Single-Layer Silver Thickness Fabricated by DC Magnetron Sputtering Technology.

Surface-enhanced Raman spectroscopy (SERS) is commonly used for super-selective analysis through nanostructured silver layers in the environment, food quality, biomedicine, and materials science. To fabricate a high-sensitivity but a more accessible device of SERS, DC magnetron sputtering technology was used to realize high sensitivity, low cost, a stable deposition rate, and rapid mass production. This study investigated various thicknesses of a silver film ranging from 3.0 to 12.1 nm by field emission scanning electron microscope, X-ray diffraction, and X-ray photoelectron spectroscopy. In the rhodamine 6G (R6G) testing irradiated by a He-Ne laser beam, the analytical enhancement factor (AEF) of 9.35 × 108, the limit of detection (LOD) of 10−8 M, and the relative standard deviation (RSD) of 1.61% were better than the other SERS substrates fabricated by the same DC sputtering process because the results showed that the 6 nm thickness silver layer had the highest sensitivity, stability, and lifetime. The paraquat and acetylcholine analytes were further investigated and high sensitivity was also achievable. The proposed SERS samples were evaluated and stored in a low humidity environment for up to forty weeks, and no spectrum attenuation could be detected. Soon, the proposed technology to fabricate high sensitivity, repeatability, and robust SERS substrate will be an optimized process technology in multiple applications.

Evaluation of gaseous and solid waste in fermentation bedding system and its impact on animal performance: A study of breeder ducks in winter.

In order to further optimize the application of fermentation bedding system and evaluate its improvements on low temperature, low humidity and other adverse environments of animal breeding in winter, we tested the waste discharge and performance of 12,921 breeder ducks from November to January. The fresh bedding materials and fermentation microbes showed significant advantages. They increased the temperature and temperature humidity index (THI) by more than 3.48 °C and 5.54, reduced the emissions of H2S, NH3, CO2, fine particulate matter (PM2.5), coarse particulate matter (PM10) and total suspended particulate (TSP) by more than 29.92%, 47.21%, 13.69%, 25.90%, 23.43% and 25.94% respectively, compared to control. The stale bedding materials increased the mortality rate and breeding egg loss rate of breeder ducks by 0.17% and 4.22% significantly, reduced the healthy duckling rate and total effective hatching rate by 2.41% and 4.22%, compared to control, had limited effects on the improvement of house environments. PM2.5, TSP, CO2, H2S and NH3 were important environmental parameters affecting the productive and reproductive performance of ducks. These data can provide an insight that the fermentation bed system could reduce the waste emission of breeder ducks, improve their production and increase the health rate of their offspring. Its application in livestock farming would create a better breeding environment and economic benefits. In addition, the stale bedding materials were not recommended to recycle in fermentation bed system for cleaner production and sustainable development.

Superhydrophobic and photothermal deicing composite coating with self-healing and anti-corrosion for anti-icing applications

The phenomenon of surface ice accumulation in low temperature and high humidity environments brings significant challenges to economy, energy, and security. Superhydrophobic surfaces with micro-nano structures are considered as effective anti-icing surfaces. However, deicing can damage the micro-nano structures and increase the ice adhesion strength. Herein, a low-adhesion, superhydrophobic photothermal response coating was introduced by combining micro-nano surface and lubricated surface, which exhibits low adhesion self-healing photothermal de-icing performance. The surface temperature rises rapidly to 85 °C under 1 solar irradiation and the frozen droplet can melt within 150 s. The prepared coating has a contact angle of up to 162° and a rolling angle as low as 4.8°. The superhydrophobicity enabled the coating to have excellent anti-icing property with icing delay times up to 596 s. Ice and frost layers on the coating surface can melt and fall off illuminating with light. In addition, beeswax as phase change materials contributes to the coating's efficient self-healing properties. The coating can restore its excellent superhydrophobicity and surface morphology quickly via a simple heat treatment after suffering chemical and mechanical damage. The coating design strategy will provide inspiration for natural solar photothermal anti-icing surfaces and engineering applications.

Environment-friendly surface acoustic wave humidity sensor with sodium alginate sensing layer

A low-cost and environment-friendly surface acoustic wave (SAW) humidity sensor was fabricated on a quartz substrate using sol-gel/spin-coated sodium alginate (SA) sensing layer. The sensing mechanism is based on the frequency shift of the SAW sensor caused by both mass loading and electrical loading, with the former being the dominant factor. The SA film prepared in this study is an environment-friendly material with a large number of hydroxyl and carboxylate groups, which easily adsorb and react with H2O molecules to form hydrogen bonds. These adsorbed H2O molecules lead to significantly enhanced mass loading and signal responses of the SAW sensor. Electrical loading effect is also generated due to the transfer of hydrogen ions in the H2O molecules, which alters the electrical resistance and results in changes of resonant frequencies of the SAW device. When the relative humidity (RH) is increased from 35% to 85%, the responses of the SAW sensor with 1 wt% SA are significantly decreased. Whereas in a low humidity environment (e.g., RH <35%), the responses of the sensor show a linear relationship with the change of humidity. The developed humidity sensor shows good short-term/long-term stabilities and a low temperature coefficient of frequency.

A comprehensive degradation assessment of silicon photovoltaic modules installed on a concrete base under hot and low-humidity environments: Building applications

Some geographical locations have low humidity, thus the impact of damp-heat (DH) stress under low humidity is crucial. Therefore, the alterations in the performance parameters (PMs) are investigated under a low RH (40%) to evaluate photovoltaic (PV) degradation in low humidity regions for 3200 h. These PMs are administrated by five PV cell parameters, and thus, the PV cell parameters are also altered over time. Consequently, determining the change in PV cell parameters over time can help to predict the performance losses occurring in the PV devices. A nearly 1.9% loss in efficiency was recorded for the PV module installed on a concrete base (CON PVM), which is 5.6% lower than the degradation in the reference PV (WO PVM) module. The Isc values of the WO and CON PVMs were found to be 105.3% and 99.8% of their corresponding initial values, respectively. Nevertheless, the series resistance of the WO and CON modules increased by ~60% and ~43%, respectively. The results demonstrate that PV modules can perform better after installation on concrete in low humidity regions. This strategy can be very efficient to increase the lifetime of the PV modules in a low humid environment.

Bacterial spot caused by Xanthomonas vesicatoria devastated tomato production of Khyber Pakhtunkhwa-Pakistan

In Khyber Pakhtunkhwa (KP) province-Pakistan, bacterial spot caused by Xanthomonas campestris pv. vesicatoria (Xcv) has decimated commercial tomato production. Field surveys were conducted in 2017 and 2018 to analyse the effects of the bacterial spot in tomato producing areas of KP, including Swat, Lower Dir, and Mansehra. During the growing seasons, diseased samples were collected from tomato fields, and disease incidence and severity were documented. The pathogen was isolated, purified, and morphologically and biochemically characterised. Most of the morphological and biochemical characteristics such as yellow colonies, were like those of Xanthomonas spp. Further, the pathogen was confirmed using XV1F/XV1R pair of species-specific primers, which amplify the atpD gene sequence solely in Xanthomonas vesicatoria. Out of 30 isolates, 16 isolates were confirmed to be Xcv. In these agro-ecological zones, this was the first report on the presence of Xcv. Furthermore, humidity and temperature were found to impact the incidence and severity of bacterial spot substantially. Most isolates grew at high temperatures and low humidity; however, some prefered high-temperature and low-humidity environments. In conclusion, bacterial spot disease caused by Xcv has now spread throughout all tomato-producing areas of KP province. To avert future plant epidemics, ongoing climate and pest monitoring is required to build an effective disease warning system for producers and other agriculture-related agencies.

Persistence of avian influenza virus (H9N2) on plastic surface

Plastics have been found to be colonized with pathogens and may become vectors for transmission of diseases. In this study, we evaluated the persistence of H9N2 avian influenza virus (AIV) on the surfaces of various plastics (PP, PE, PS, PET, PVC, PMMA) under different environmental conditions using glass and stainless steel for comparison. Our results showed that the RNA abundance of AIV on plastics was decreased over time but still detectable 14 days after AIV had been dropped on plastic surfaces. Low temperature (4 °C) was more favorable for AIV RNA preservation and infectivity maintenance. The abundance of AIV RNA was significantly greater on polyethylene terephthalate (PET) than that on glass and stainless steel at higher temperature (i.e., 25 °C and 37 °C) and lower humidity (<20% and 40–60%) (p < 0.05). Infectivity assay showed that AIV infectivity was only maintained at 4 °C after 24 h of incubation. Taken together, the persistence of AIV was more affected by environmental factors than material types. Plastics were able to preserve viral RNA more effectively in relatively high-temperature or low-humidity environments. Our study indicates that environmental factors should be taken into consideration when we evaluate the capacity of plastics to spread viruses.

The p-Anisaldehyde/β-cyclodextrin inclusion complexes as a sustained release agent: Characterization, storage stability, antibacterial and antioxidant activity

In order to develop a biodegradable agent for food preservation, β-cyclodextrin (β-CD) inclusion complexes containing p-Anisaldehyde (PAA) were prepared using co-precipitation method. Physical properties including moisture content, bulk density, hygroscopicity, entrapment efficiency and loading capacity of the inclusion complexes showed considerable results for food applications. SEM and particle size test showed notably difference between the prepared inclusion complexes and the other formulations including the raw β-CD, physical mixture, and the recrystallized β-CD in both shape and size distribution. FTIR, XRD, TGA and DTA were also carried out and confirmed the formation of inclusion complexes and inhibition of the volatility of encapsulated PAA. As a potential preservation agent, inclusion complexes demonstrated a sustained released behavior in phosphate buffer saline (PBS). Comparing with pure PAA, the inclusion complexes presented a better storage stability in low humidity environment, a higher antioxidant activity, and equal MICs against Escherichia coli and Staphylococcus aureus.

An experimental investigation on the frosting and defrosting process of an outdoor heat exchanger in an air conditioning heat pump system for electric vehicles

The heat pump air conditioning system is a promising solution for energy conservation and ensuring a good driving range can be maintained. Micro-channel heat exchangers are used as outdoor heat exchangers to improve the heat transfer efficiency. A heat pump system introduces frosting problems to the outdoor heat exchanger, especially in a low temperature and high humidity environment. This study conducted an experiment on the frosting and defrosting process of the outdoor heat exchanger of a heat pump air conditioning system for electric vehicles. The surface of the outside heat exchanger had an uneven distribution of the frost layer owing to the variation in the liquid-phase refrigeration occupation. Thermal parameters of the system were obtained. The suction pressure was sensitive to the frosting process, decreasing from (0.15–0.25) to (0.02–0.1) MPa, and it can be used as a frosting monitoring parameter. The frosting and defrosting behavior was also studied at a micrometer scale on the surface of the heat exchanger. The ice bridge phenomenon was observed in the frosting process. Hydrophilic and hydrophobic treatments of the heat exchanger surface were conducted for compassion and it was found that the hydrophilic treatment of the surface of the outdoor heat exchanger of the vehicle heat pump effectively slows frosting. Future experimental research should investigate the effects of superhydrophobic and superhydrophilic surface treatments, in addition to hydrophilic and hydrophobic surface treatments on the performance of the heat exchanger, to improve the performance of the overall heat pump system.

Effect of Nano Silica on Strength and Water Absorption of Cement Mortar Exposed Low Pressure Environment

Background: Buildings in high altitude region often face low pressure and low humidity service environment, which has a great impact on the mechanical properties and durability of cement-based materials. Objective: In this paper, the effects of nano-silica (NS) on the strength and water absorption of cement mortar exposed to the low pressure and low humidity environment were studied. Methods: Mechanical properties (compressive strength and flexural strength) and durability (water absorption) were measured. And the hydration degree of cement was tested to assist analysis. Results: The flexural strength of mortar decreased and the compressive strength increased slowly after 28 days of exposure under low pressure and low humidity environment. Especially, the introduction of 1% NS could reduce the compressive strength loss and flexural strength loss of mortar under low pressure and low humidity environment. It was also found that the water absorption of the mortar in low pressure and low humidity environment was related to the tortuous degree of the pores inside the specimen. Conclusion: The introduction of 1% NS contributed the most to the mechanical properties (compressive strength and flexural strength) and durability (water absorption) of cement mortar.

Influence of molar ratio of MAI and PbI2 on synthesis of perovskite film

This study explores the influence of molar ratio of the synthetic solution of methylammonium iodide (MAI) and PbI2 on perovskite solar cells. The complete perovskite crystals must be produced in a low-humidity environment. The substrate is spin-coated in the adjusted MAPbI3 synthesis solution and annealed by using a nitrogen furnace tube to form perovskite crystals. During the crystallization of MAPbI3, some of the PbI2 remains, which improves the efficiency of the perovskite solar cell. Therefore, we adjust the molar concentration of MAI to find the appropriate amount of the PbI2 residual. We fix the MAI molar concentration at 1 M and adjust the PbI2 molar concentration from 0.8 M to 1.4 M. The molar ratios of MAI and PbI2 are, then, 1:0.8, 1:1, 1:1.2, and 1:1.4, respectively. Then, we use UV–vis, FE-SEM, and photoelectric conversion efficiency (PCE) measurements for comparing the growth of perovskite crystals and their photoelectric characteristics. The results show that 1.2 M of PbI2 is the most appropriate concentration for perovskite solar cells among the adjusted concentrations.

Recurring exposure to low humidity induces transcriptional and protein level changes in the vocal folds of rabbits

Voice disorders are an important human health condition. Hydration is a commonly recommended preventive measure for voice disorders though it is unclear how vocal fold dehydration is harmful at the cellular level. Airway surface dehydration can result from exposure to low humidity air. Here we have induced airway surface dehydration in New Zealand White rabbits exposed to a recurring 8-h low humidity environment over 15 days. This model mimics an occupational exposure to a low humidity environment. Exposure to moderate humidity was the control condition. Full thickness soft-tissue samples, including the vocal folds and surrounding laryngeal tissue, were collected for molecular analysis. RT-qPCR demonstrated a significant upregulation of MUC4 (mucin 4) and SCL26A9 (chloride channel) and a large fold-change though statistically non-significant upregulation of SCNNA1 (epithelial sodium channel). Proteomic analysis demonstrated differential regulation of proteins clustering into prospective functional groups of muscle structure and function, oxidative stress response, and protein chaperonin stress response. Together, the data demonstrate that recurring exposure to low humidity is sufficient to induce both transcriptional and translational level changes in laryngeal tissue and suggest that low humidity exposure induces cellular stress at the level of the vocal folds.

Mechanistic understanding of the sensing process by analyzing response curves of TiO2 based humidity sensors

Sensors function by interacting with an appropriate stimulus, undergo a change in property, which is then diagnosed by making some measurements. For any sensor, the type of interaction between analyte and sensor surface determines its overall performance. This article explores the philosophy in which primary measurements like response curves can hold information on the “type” of interaction occurring between analyte and sensing material. As case study, titanium oxide (TiO2) pellet sensors fabricated by sol-gel growth of TiO2 nanoparticles (as-grown and annealed) are investigated for humidity sensing at room temperature. The sensors display a very fast response in the 0%–30% relative humidity (%RH) range and return to their initial state without applying any external heat treatment. The response curves are analysed in view of adsorption processes guided by Langmuir isotherms. Correlation between sensor microstructure, adsorption processes and response curve is used to build the mechanistic understanding of the sensing process. The results bring out a unique correlation between sensor microstructure, interaction of analyte with sensing material and profile of response curves. Further, the synthesised sensors exhibit a linear response in the 0%–30% RH range making them suitable for low humidity environments like food packaging industry.

Experimental study on a wet precooling system for fruit and vegetables with ice slurry

Aiming at the application of fruit and vegetables precooling, an innovative wet precooling system with ice slurry as a cooling medium was proposed. A small wet precooling room performance test platform was built. With apples as the precooling subject, the temperature and relative humidity in precooling room, the cooling rate and weight loss of apples as indexes, by changing the weight concentration of ice slurry additives (0%-8%), the ice fraction (0%-10%) and the ice slurry flow rate (50-150 L h−1), the precooling experiments were carried out. The results showed that increasing the concentration of ice slurry additives (NaCl) could effectively reduce the equilibrium temperature in precooling room. For the ice slurry solution with the additive concentrations of 0%, 2%, 4%, 6% and 8%, the equilibrium temperature in precooling room were 4.3°C, 1.7°C, 0.4°C, 0.0°C and -0.7°C, respectively. When the ice fractions increased from 0% to 10%, the precooling time decreased from 165 min to 96 min, and the weight loss decreased from 2.11% to 0.42%. When the ice slurry flow rate increased, the relative humidity in precooling room increased, and the cooling rate of apples firstly increased rapidly and then leveled off. When the flow rate reached 100 L h−1, the relative humidity remained above 90%. The precooling system has a strong applicability, easy to realize the stable environment of low temperature and high relative humidity (0°C, >90%), so it has a large application space in the precooling and fresh-keeping of fruit and vegetables.

Weathering on volcanic edifices under semiarid climates: insights from a regional assessment of the composition of Fogo Island regoliths (Cape Verde)

Abstract In this study, the geochemistry and mineralogy of regoliths formed on Fogo Island (Cape Verde), a polygenic strato-volcano built during the Quaternary, are used to assess the geomorphological factors that control the early stages of basalt weathering. Fogo Island soils are mainly derived from relatively homogenous silica-undersaturated basaltic rocks. However, a discernible exotic component is recognized in areas most exposed to prevailing winds via ratios of non-mobile elements that are hosted in different amounts by basaltic rocks (e.g. Th, Sc and Ti). The weathering extent is evidenced by a relative depletion in mobile elements (e.g. Na, Ca, Mg) and an enrichment in non-mobile elements (e.g. Ti, Fe, Sc, Al), the decomposition of the most labile minerals (olivines) and the formation of secondary components (phyllosilicates and some Fe-oxides, such as hematite-goethite), along with the enrichment in quartz supplied from non-volcanic areas. Weathering depends on bedrock age and type (pyroclastic deposits v. lava-flows). In particular, soils covering older volcanic units tend to be more affected by chemical alteration than those overlying younger units. In addition, more intense weathering is observed in locations characterized by a combination of moderate elevation, slopes with low gradient and relatively high rainfall. The present investigation shows that even in low humidity environments recently formed basalts are affected by weathering, with the extent of chemical decomposition being mainly determined by the age of surface exposure and local orographic/climatic features.

Influence of indoor air temperature and relative humidity on learning performance of undergraduates

The indoor thermal environment plays an important role in learning performance, but many relevant studies have focused primarily on subjective evaluation and achievement evaluation of participants and paid relatively little attention to the physiological state. To study the effects of air temperature and relative humidity on the learning performance of undergraduates, experiments coupled with a questionnaire inquiry were conducted on undergraduate students subjected to eight different indoor air temperatures and relative humidity levels. The degree of discomfort, fatigue, distraction, and learning efficiency were measured and analyzed from psychological and physiological perspectives. These results showed that undergraduates performed better at 40% relative humidity and 24 °C. Learning performance variations were consistent with environmental comfort, but relative humidity impacted learning performances more than indoor air temperature. Low humidity environments decreased the overall learning performance; rooms maintained at 40% relative humidity lowered the degree of fatigue, reading speed, and the degree of distraction by 23.3%, 12.2%, and 61.1%, respectively, as compared to a room at 20% relative humidity. Therefore, relative humidity should be emphasized when designing learning spaces. This study also confirmed that pupil diameter could be used as a physiological index to evaluate fatigue and distraction.