Initial Stage Of Exposure Research Articles

Corrosion Behavior of the 2024 Aluminum Alloy in the Atmospheric Environment of the South China Sea Islands

The 2024 aluminum alloy, a structural material commonly used in aviation aircraft bodies, is susceptible to serious corrosion in marine atmospheric environments. This paper comprehensively studies the corrosion behavior of the 2024 aluminum alloy in the South China Sea atmosphere. Weighing, morphology observation, phase analysis, electrochemical testing, and other methods were used to study the corrosion law and corrosion mechanism of the 2024 aluminum alloy. The main conclusions are as follows: At the initial stage of exposure, pitting corrosion occurred on the surface of the 2024 aluminum alloy. After 3 months of exposure, the self-corrosion current density increased from 0.456 μA·cm−2 to 8.338 μA·cm−2. After 6 months of exposure, the corrosion developed into general corrosion. The main component of the corrosion product was Al2O3·3H2O. The product covered the surface to form a loose corrosion product layer, which had an inhibitory effect on corrosion. The self-corrosion current density was reduced to 2.359 μA·cm−2. After 12 months of exposure, the corrosion product layer fell off and became thinner, and the self-corrosion current density increased to 2.849 μA·cm−2. The corrosion kinetics conformed to the functional equation W = 0.00346t0.73891, indicating that the corrosion products have a certain protective effect on the matrix.

Feature distribution learning by passive exposure

Humans can rapidly estimate the statistical properties of groups of stimuli, including their average and variability. But recent studies of so-called Feature Distribution Learning (FDL) have shown that observers can quickly learn even more complex aspects of feature distributions. In FDL, observers learn the full shape of a distribution of features in a set of distractor stimuli and use this information to improve visual search: response times (RT) are slowed if the target feature lies inside the previous distractor distribution, and the RT patterns closely reflect the distribution shape. FDL requires only a few trials and is markedly sensitive to different distribution types. It is unknown, however, whether our perceptual system encodes feature distributions automatically and by passive exposure, or whether this learning requires active engagement with the stimuli. In two experiments, we sought to answer this question. During an initial exposure stage, participants passively viewed a display of 36 lines that included one orientation singleton or no singletons. In the following search display, they had to find an oddly oriented target. The orientations of the lines were determined either by a Gaussian or a uniform distribution. We found evidence for FDL only when the passive trials contained an orientation singleton. Under these conditions, RT's decreased as a function of the orientation distance between the target and the mean of the exposed distractor distribution. These results suggest that passive exposure to a distribution of visual features can affect subsequent search performance, but only if a singleton appears during exposure to the distribution.

Comparison of the performance of lipoperoxidation-antioxidant protection system in rats at different periods under immobilization stress effects.

Background: Under physiological conditions, the activity of the formation of active oxygen is low. The activity of these processes is intensified under stress-induced situations. This study aimed to investigate the role of free-radical oxidation (FRO) in adrenal tissues and immunocompetent organs and cells in mature white rats after 6 hours of immobilization stress. Methods: The studies were performed on 40 White male rats of the Wistar line with a bodyweight of 200 to 240 g. Two series of experiments were conducted: I series: determination of indices in intact rats (10 rats); II series: determination of indices after a 6-hour immobilization stress action on them. Animals of II series were divided into 3 groups of 10 rats in each: group 1: those undergoing acute immobilization stress, withdrawal from the experiment in 1 hour; group 2: those undergoing acute immobilization stress, withdrawal from the experiment in 25 hours; and group 3: those undergoing acute immobilization stress, withdrawal from the experiment in 49 hours. The obtained data were processed by statistical methods with the help of the "Biostat" and "Excel" software packages. Results: In groups 1, 2, and 3, the animals were simulated acute immobilization stress by fixing the animals for 6 hours in bright light. The results of the conducted studies indicate changes in lipid peroxidation and antioxidant system (LPO-AOS) in case of immobilization stress-excitation. In developing free-radical pathology at immobilization stress-excitation, the more expressed disturbance of LPO-AOS, and accordingly the intensity of lipoperoxidation in the structural membrane of all investigated organs was high at the initial stage of exposure. Conclusion: At 49 hours after immobilization, stress less pronounced influence on the lipoperoxidation process was noted. The increase in the intensity of excessive lipoperoxidation testifies to the inhibited manifestation of AOS in the organism.

Bond durability and degradation mechanism of GFRP bars in seawater sea-sand concrete under the coupling effect of seawater immersion and sustained load

In this paper, the bond durability of glass fiber-reinforced polymer (GFRP) bars in seawater sea-sand concrete (SWSSC) under the coupling effect of seawater immersion and sustained load was experimentally investigated. The test parameters included bar diameter (12 and 16 mm), immersion time (90, 180, and 270 days), and sustained load condition (loaded and unloaded). Test results showed that for the specimens with a small bar diameter, the bond strength had a slight growth at the initial stage of exposure mainly due to the water swelling of the bar, and then decreased due to the bond degradation. For the specimens with a large bar diameter, the bond strength increased with the increase of immersion time, which was determined by the increasing compressive strength of SWSSC. The sustained load reduced the bond strength of the specimens with a small bar diameter due to its acceleration of bond degradation, but had little effect on the bond strength of the specimens with a large bar diameter. The degradation mechanism was the rib deterioration of the bars caused by seawater immersion. Moreover, the sustained load could accelerate the degradation. The predicted bond strength retention of the specimen with a bar diameter of 12 mm under the coupling effect of the marine environment (moisture saturated and the mean annual temperature of 25–35 °C) and sustained load is 52% after 50 years of service.

Effects of NO2 gas concentration on the degradation of polyphenylene sulfide non-woven bag filter at high temperature

The influence of NO2 concentration and exposure time on the degradation of polyphenylene sulfide (PPS) fabric filter at high temperature was investigated in detail. PPS fiber damage in the filter became more severe with increasing NO2 concentration and exposure time. The elastic modulus of the PPS filter increased rapidly during the initial stage of exposure, and then increased more slowly to reach an almost constant value, nearly independent of NO2 concentration. The tensile strength also decreased significantly during the initial stage, gradually attaining a constant value with increasing exposure time. Higher NO2 concentrations resulted in rapid reducing of the tensile strength. Short exposure time to lower NO2 concentrations caused the oxidation of S atoms in PPS to SO and OSO, whereas oxidation of benzene rings in PPS were induced only with longer exposure times and higher NO2 concentrations. The model proposed in our previous paper accurately expresses the change in PPS conversion and reaction rate for every NO2 concentration. An improved model that successfully estimated the degradation of tensile strength in both the machine direction and transverse direction, regardless of NO2 concentration, was also proposed.

Retention of Pantoea agglomerans Sc1R across stadia of the southern green stink bug, Nezara viridula (L.) (Hemiptera: Pentatomidae).

Southern green stink bug [Nezara viridula (L.)] adults and other pentatomid pests can transmit pathogens (e.g., the bacterium Pantoea agglomerans) that cause disease in cotton (Gossypium hirsutum L.) and other high-value cash crops worldwide. First instars of N. viridula were recently shown to ingest P. agglomerans strain Sc1R with rifampicin-resistance, and to retain the pathogen to the 2nd instar. The objective of this study was to determine the acquisition of P. agglomerans Sc1R by early instars of N. viridula and determine persistence of P. agglomerans Sc1R across subsequent stadia. In three trials, early instars (1st and 2nd) were exposed to P. agglomerans Sc1R and subsequently maintained to adulthood; cohorts were sampled at 3rd and 5th instars, as well as adults. In every trial, P. agglomerans Sc1R was detected in all stadia, including adults, but significantly higher frequencies of infection than expected were observed at the initial stage of infection (either 1st or 2nd instar). Higher densities of P. agglomerans Sc1R were detected in 1st and 2nd instars, and lower densities were observed in subsequent stadia. Densities of innate microbiota were generally lower when the initial stage of exposure was at 1st instar than when the initial stage of exposure was at the 2nd instar. Overall, half of the adults possessed P. agglomerans Sc1R. These findings demonstrated that N. viridula nymphs can acquire P. agglomerans Sc1R and retain the pathogen to adulthood. Potential avenues of research to further elucidate the implications of nymphs harboring pathogens to adulthood are discussed.

Acute toxicity of heavy metal, nickel and chromium on fresh water edible fishes

Industrial effluent are the major sources of heavy metal pollution and it is released into fresh waterbodies. Catla catla and Clarias batrachus were exposed to Nickel and Chromium for 24, 48, 72 and 96 hrs. The median lethal concentration (LC50) of nickel to Catla catla and Clarias batrachus for 96 h of exposure were 5.77 mg/l and 7.595mg/l, respectively. The median lethal concentration (LC50) of chromium to Catla catla and Clarias batrachus for 96 h of exposure were 16.468 mg/l and 34.476 mg/l, respectively. The result also revealed that mortality rate depends upon concentrations of heavy metals and duration of exposure. The acute toxicity levels were derived from LC50 concentrations of the heavy metals. Both the heavy metals produced lethality at smaller doses. Physiological responses like rapid opercular movement and frequent gulping of air was observed during the initial stages of exposure after which it became occasional. All these observations can be considered to monitor the quality of aquatic eco system and severity of pollution.

The dynamic effects of different inorganic arsenic species in crucian carp (Carassius auratus) liver during chronic dietborne exposure: Bioaccumulation, biotransformation and oxidative stress

Inorganic arsenic (iAs) is highly toxic to aquatic species, but the chronic effect of iAs on fish following dietborne exposure is still unclear. In this study, freshwater fish crucian carp (Carassius auratus) was exposed to iAs [arsenite (AsIII) and arsenate (AsV)] for 40 days through dietary exposure. The bioaccumulation and biotransformation of arsenic in the main metabolic organ, liver, were measured. The oxidative stress responses to iAs exposure in liver were analyzed to be linked to arsenic biotransformation, especially methylation. In both AsIII and AsV groups, the total As contents gradually increased during the exposure and then fleetly decreased at the end of exposure (40 d). Arsenobetaine was found to be the predominated As species (34–66%) and the fraction remained on an increasing trend, while the inorganic As percentages decreased 84–91% during the 40-day exposure, suggesting that the capability of As biotransformation increased to acclimate iAs during chronic dietborne exposure. Both the activities of the enzymatic antioxidants (superoxide dismutase and catalase) and the level of the nonenzymatic antioxidant (glutathione) increased initially and then decreased, thus lowering the malondialdehyde levels and displaying a typical antioxidant defense mechanism. The opposite correlations were observed between arsenic secondary methylation index and the malondialdehyde level in different iAs treatment. This indicated that the As dimethylation played an significant role toward oxidative damage; the toxic action of As dimethylation was dependent upon the parent iAs species at the initial stage of exposure. Therefore, the effectiveness of the detoxification relied on both the biomethylation rate of As and the anti-oxidation ability based on nonenzymatic antioxidant and enzymatic antioxidant.

Quantification of the Atmospheric Corrosion of 304 and 2205 Stainless Steels Using Electrochemical Probes Based on Thevenin Electrochemical Equivalent Circuit Model

Stainless steel (SS) is one of the most widely used engineering materials in marine engineering. However, its corrosion in the marine atmospheric environment due to the high concentration of Cl− is a problem. The SS corrosion is a threat to the development and security of marine industry; therefore, evaluating the corrosion resistance of SSs is necessary. In this work, atmospheric corrosion detection probes based on a symmetrical electrode system were used to study the corrosion behaviors of 304 SS and 2205 duplex stainless steel (DSS) in a simulated marine atmosphere. A theoretical model for electrochemical noise (EN) data analysis based on the Thevenin electrochemical equivalent circuit (EEC) model was established. The relationship between the EN characteristic parameters and the corrosion rate was obtained. The Thevenin EEC model analysis showed that the relationship between the noise resistance (Rn), the noise impedance [Rsn(f)], and the impedance modulus (|Z(f)|) was R_{{text{n}}} approx R_{{{text{sn}}}} = {}^{sqrt 3 }left| {Z(f)} right|. Thus, Rn and Rsn can be used as indicators for quantitative corrosion evaluation. The results of EN detection for the 304 SS and 2205 DSS showed that in a simulated marine atmospheric environment, the passive films on the two SSs were relatively intact at the initial exposure stage, and their dissolution rates were slow. The corrosion resistance of the 2205 DSS was higher than that of the 304 SS. With the deposition of Cl− on the SS surface, pitting was initiated and the dissolution rate increased. The pitting initiation process on the SS surface was random, and part of the active pores could be repassivated.

Atmospheric corrosion behavior of low-alloy steels in a tropical marine environment

The corrosion behavior of carbon steels and weathering steels was investigated in a tropical marine environment. And both exhibited similar corrosion weight-loss behavior in tropical marine environments. Corrosion weight loss (W) as a function of exposure time (t) can be calculated using the power function, W = Atn. The values of the initial corrosion rate, A, and corrosion tendency, n, can be easily obtained by taking the logarithm of the power equation. However, the corrosion rust-layer structure of the two materials was quite different. The rust layer of carbon steel presents a single-layer structure. Meanwhile, the rust layer of weathering steel exhibits a single-layer structure after exposure for about 24 months and then gradually evolves into a double-layer structure. The main corrosion products of the steels are β-FeOOH, γ-FeOOH, and Fe3O4 in the initial stage of exposure. In the rust layers, α-FeOOH appeared after 12 months of exposure.

Silver nanoparticle-induced expression of proteins related to oxidative stress and neurodegeneration in an in vitro human blood-brain barrier model

Silver nanoparticles (AgNPs) have been reported to penetrate the central nervous system (CNS) and induce neurotoxicity. However, there is a paucity of understanding of the toxicity of AgNPs and their effect on the blood-brain barrier (BBB) including the underlying molecular mechanism(s) of action. Such information is important for the formulation of new strategies for delivery of biological therapeutics to central nervous system (CNS) targets. Using an in vitro BBB model and mass spectrometry-based proteomics, we investigated alterations in the proteomes of brain endothelial cells and astrocytes at different time points after AgNPs exposure (24 and 48 h). Our data showed that several proteins involved in neurodisorders and neurodegeneration were significantly upregulated in endothelial cells (e.g. 7-dehydrocholesterol reductase, zinc transporters 1 and 6), while proteins responsible for maintaining brain homeostasis were significantly downregulated (e.g anti-oxidative proteins glutathione peroxidase 1 and glutathione peroxidase 4). Many inflammatory pathways were significantly upregulated at 24 h post-AgNPs exposure (C9 pathway), while at 48 h proteins involved in BBB damage and anti-inflammatory responses were upregulated (quinoneoxidoreductase1 and glutamate cysteine ligase catalytic subunit) suggesting that by the later time point, cellular protection pathways had been activated to rescue the cells from AgNPs-induced toxicity. Our study suggests that in the initial stage of exposure, AgNPs exerted direct cellular stress on the endothelial cells by triggering a pro-inflammatory cascade. This study provides detailed insight into the toxic potency of AgNPs on in vitro BBB model and adds to the understanding of the adaptive role of BBB with regards to AgNPs-mediated toxicity.

Synergistic effects of Radiofrequency Hyperthermia temperature rate with magnetic Graphene oxide nanoparticles drug targeting on CT26 colon cancer cell line

Introduction: Graphene oxide (GO) sheets are carbon-networking nanomaterials offering excellent potential for drug delivery platforms due to hydrophobic interactions and high drug-loading efficiency. Superparamagnetic iron oxide nanoparticles can be used in certain applications such as cell labeling, drug delivery, targeting, magnetic resonance imaging and hyperthermia. Due to the larger surface to volume ratio for unmodified iron oxide nanoparticles, they usually possess high surface energy leading to particle aggregation. The magnetic nanoparticles could induce heat energy in an alternating magnetic field (AMF). The absorption of radiofrequency energy by biological tissue results in higher tissue temperatures as a function of time, which eventually causes cell death due to hyperthermia. Mensuration of the temperatures inside the tumors and in normal tissues within AMF demonstrated that this treatment could induce tumor-specific hyperthermia. Materials and Methods: CT26 colon cancer cell line was cultured in vitro as a monolayer. The monolayer culture was treated with of 5-FU, 5-FU- MGO nanoparticles, and MGO nanoparticles for 24 hours. then the flasks were located at the centre of the RF coil where the alternative magnetic field strength had reached its maximum value (40 kA/m) and was exposed to the AMF (forward power, 70 W), for 12 min (43°C) without MGO nanoparticles and 4 min (43°C) with MGO nanoparticles. During the AMF exposure, the temperature increase was monitored using a T-type thermocouple (copperconstantan, 0.1 mm diameter) linked to a digital thermometer (Lutron thermometer TM-917, Taiwan) every 1 min for 15 min with ± 0.1°C accuracy. Results: Increase in the temperature was measured. The results revealed that the temperature increase of the culture depends on the nanoparticles concentrations. The results also indicated that the temperature of cells exposed to AMF (13.56 MHz) at a forward power of 70 W reached to 43°C after 12 min, whereas the combination of accumulated 50 μg/ml 5-FU- MGO nanoparticles and RF hyperthermia was 3 min and for 25 and 5 μg/ml, it was calculated as 4 and 9 min, respectively. The significant difference was observed between the 5-FU, 5- FU- MGO nanoparticles, and MGO nanoparticles in RF hyperthermia at power of 70 W (P < 0.05). This suggests that MGO nanoparticles act as effective thermal agents in AMF hyperthermia. Conclusion: On the basis of this study is According to the temperature-time curves at different intensities, the rate of temperature rise was very sharp during the first few minutes of AMF exposure; however, it then reached a near equilibrium because cell heat transfer parameters (conduction and convection) started to perform, The radiofrequency heats cells with a steep gradient pending the initial stage of exposure.

Non-destructive evaluation of localised heat damage occurring in carbon composites using thermography and thermal diffusivity measurement

Carbon fibre reinforced polymer (CFRP) composites are now a common occurrence in the aerospace sector especially with their introduction into the aero-engine. With their ever-increasing use in harsh and extreme environments, it is important to understand their behaviour and performance when exposed to such working conditions. This paper presents a novel approach to understand the thermal degradation mechanism of CFRP composites based on the measurement of thermal diffusivity through non-destructive testing (NDT) when exposed to heat in a localised area. The study explored the suitability of pulsed thermography in detecting the physical damage caused due to localised heat exposure together with its ability to identify chemical change that occurs during the initial stages of exposure. The results showed the ability of thermography in detecting discolouration damage through the use of diffusivity measurements acquired by reconstructing the thermography dataset.

Influences of Cr and Co on the Growth of Thermally Grown Oxide in Thermal Barrier Coating during High-Temperature Exposure

Thermal barrier coating (TBC) is a critical material in the aerospace domain to increase the lifetime of gas turbine components subjected to thermal load. The properties of TBC are strongly related to the growth of thermally grown oxide (TGO) whose main constituent is Al2O3. However, the oxidation of Cr and Co can affect the growth of TGO, which is not studied sufficiently. In this paper, high-temperature exposure at 1000 °C was performed to investigate the effect of Cr and Co oxides on TGO growth. The morphology and composition analysis of the interface between the ceramic top coat and the bond coat (TC/BC) were investigated by using scanning electron microscopy (SEM) and the energy dispersion spectrum (EDS). The thermodynamics and kinetics of oxidation were analyzed. The results indicated that the oxidation kinetics basically followed the sub-parabolic law with exposure time. Additionally, the major factor affecting the formation of oxides was the diffusion rate at the initial stage of exposure, then oxides depended on thermodynamics, and the oxidation was influenced by both of them in the last stage. The major elements to be oxidized were different at different stages. Moreover, the replacement reaction of Cr2O3 and the phase conversion of Al2O3 resulted in thickness variations of the TGO and Al-depleted zone during high-temperature exposure.

Performance evaluation of Iris pseudacorus constructed wetland for advanced wastewater treatment under long-term exposure to nanosilver

The presence of nanoparticles in the wastewater treatment plants (WWTPs) effluent is a potential threat to the ecosystem due to their effective antimicrobial properties. The aim of this study was to investigate the performance of a pilot-scale vertical flow constructed wetland (VFCW) for advanced wastewater treatment under long-term exposure to silver nanoparticles (AgNPs). The migration and fate of AgNPs were also examined to explore whether the CW had a capability of nanoparticles removal. The results suggested that AgNPs (20 µg/L) showed acutely inhibitory effects on nitrogen and phosphorus removal at the initial exposure stage, followed by the persistent inhibition with time. The average removal efficiencies decreased by 16%, 11%, and 11% for NH+ 4-N, TN, and TP, respectively. For COD removal, no changes were found. The effluent of CW under AgNPs exposure could still reach the first level A of the People's Republic of China's Discharge standard of pollutants for municipal wastewater treatment plant (GB18918-2002). In addition, CW showed a satisfactory AgNPs removal efficiency of 93%. The accumulation of AgNPs in different parts from high to low was soil (88.93%), effluent (7.35%), substrate (3.40%), and plant (0.32%). AgNPs enriched by plant roots were mainly transported to above ground. It demonstrated that the presence of soil layer and wetland plant Iris pseudacorus is essential for AgNPs removal. The study may provide valuable references for evaluating the ecological effects of nanoparticles.

Can Thermally Sprayed Aluminum (TSA) Mitigate Corrosion of Carbon Steel in Carbon Capture and Storage (CCS) Environments?

Transport of CO2 for carbon capture and storage (CCS) uses low-cost carbon steel pipelines owing to their negligible corrosion rates in dry CO2. However, in the presence of liquid water, CO2 forms corrosive carbonic acid. In order to mitigate wet CO2 corrosion, use of expensive corrosion-resistant alloys is recommended; however, the increased cost makes such selection economically unfeasible; hence, new corrosion mitigation methods are sought. One such method is the use of thermally sprayed aluminum (TSA), which has been used to mitigate corrosion of carbon steel in seawater, but there are concerns regarding its suitability in CO2-containing solutions. A 30-day test was carried out during which carbon steel specimens arc-sprayed with aluminum were immersed in deionized water at ambient temperature bubbled with 0.1 MPa CO2. The acidity (pH) and potential were continuously monitored, and the amount of dissolved Al3+ ions was measured after completion of the test. Some dissolution of TSA occurred in the test solution leading to nominal loss in coating thickness. Potential measurements revealed that polarity reversal occurs during the initial stages of exposure which could lead to preferential dissolution of carbon steel in the case of coating damage. Thus, one needs to be careful while using TSA in CCS environments.

Risk assessment for changes in the metabolic profile and body weights of pre-pubertal gilts during long-term monotonic exposure to low doses of zearalenone (ZEN)

The aim of the study was to examine whether the process of exposure to low doses of ZEN generates changes in the hematological and biochemical image of blood serum. During the experiment, pre-pubertal gilts (up to 25kg) were administered per os ZEN at a dose of 40μg/kg BW (Group E, n=18) or placebo (Group C, n=21) on a daily basis for 42days. Blood samples for investigation were collected seven times at intervals of one week. In the experimental groups, slight but statistically significant changes in the values of selected biochemical blood indices such as glucose, ALT, Pin, total protein and Fe, or in hematological indices such as RBC, MCV, PLT, WBC, basophils, eosinophils and monocytes were observed. Based on statistical analysis between the groups, differences in the values of WBC, basophils, peroxidase negative cells, Hb, Ht, MCV, HDW, glucose, ALT, AP, total protein, iron or potassium were found. In Group E, decreasing trends in the values of PLT and glucose, and increasing trends in the values of total protein, Pin, Na and Cl were found. The described situations occurred during the last three weeks of exposure. Low levels of exposure to ZEN lead to completely different changes in the metabolic profile than those resulting from higher doses of the toxin. The stimulatory effect of mycotoxins, observed in initial stages of exposure, is eliminated when the compensatory response and adaptive mechanisms are triggered, and due to excessive loss of energy, which may point to more efficient feed utilization and/or detoxification processes. The values of body weight gain obtained in Group E were monotonically higher in four out of the six investigated weeks of exposure. The above changes were accompanied by a decrease in glucose concentrations and higher total protein levels (a rising tendency), which could have affected the rate of body weight gain.

Acute Mountain Sickness Symptoms Depend on Normobaric versus Hypobaric Hypoxia.

Acute mountain sickness (AMS), characterized by headache, nausea, fatigue, and dizziness when unacclimatized individuals rapidly ascend to high altitude, is exacerbated by exercise and can be disabling. Although AMS is observed in both normobaric (NH) and hypobaric hypoxia (HH), recent evidence suggests that NH and HH produce different physiological responses. We evaluated whether AMS symptoms were different in NH and HH during the initial stages of exposure and if the assessment tool mattered. Seventy-two 8 h exposures to normobaric normoxia (NN), NH, or HH were experienced by 36 subjects. The Environmental Symptoms Questionnaire (ESQ) and Lake Louise Self-report (LLS) were administered, resulting in a total of 360 assessments, with each subject answering the questionnaire 5 times during each of their 2 exposure days. Classification tree analysis indicated that symptoms contributing most to AMS were different in NH (namely, feeling sick and shortness of breath) compared to HH (characterized most by feeling faint, appetite loss, light headedness, and dim vision). However, the differences were not detected using the LLS. These results suggest that during the initial hours of exposure (1) AMS in HH may be a qualitatively different experience than in NH and (2) NH and HH may not be interchangeable environments.

Label-free Raman imaging of the macrophage response to the malaria pigment hemozoin.

Hemozoin, the 'malaria pigment', is engulfed by phagocytic cells, such as macrophages, during malaria infection. This biocrystalline substance is difficult to degrade and often accumulates in phagocytes. The macrophage response to hemozoin relates to the severity of the disease and the potential for malaria-related disease complications. In this study we have used Raman spectroscopy as a label-free method to investigate the biochemical changes occurring in macrophages during the first few hours of hemozoin uptake. We found a number of distinct spectral groups, spectrally or spatially related to the presence of the hemozoin inside the cell. Intracellular hemozoin was spectrally identical to extracellular hemozoin, regardless of the location in the cell. A small proportion of hemozoin was found to be associated with lipid-based components, consistent with the uptake of hemozoin into vesicles such as phagosomes and lysosomes. The spatial distribution of the hemozoin was observed to be inhomogeneous, and its presence largely excluded that of proteins and lipids, demonstrating that cells were not able to break down the biocrystals on the time scales studied here. These results show that Raman imaging can be used to answer some of the open questions regarding the role of hemozoin in the immune response. How different combinations of hemozoin and other molecules are treated by macrophages, whether hemozoin can be broken down by the cell, and more importantly, which co-factors or products are involved in the subsequent cell reaction are the expected issues to be elucidated by this technique.

Probing the Interplay of Ultraviolet Cross-Linking and Noncovalent Interactions in Supramolecular Elastomers

Ultraviolet (UV) irradiated supramolecular polybutadienes (PBs) containing 2-ureido-4-[1H]-pyrimidone (UPy) linkages were examined as a simple model for curable supramolecular elastomers. Via precise control of UV exposure, the cure and the degradation of the vinyl groups within the PB elastomeric core were investigated. The combination of UPy binding and covalent cross-linking by UV irradiation dramatically enhanced mechanical properties of these UPy-functionalized elastomers, yielding toughness enhancement up to ∼200× at the 5 min UV cure. UV-initiated cross-linking dominated the curing process up to ∼50 min exposure time. Beyond this cure time, dominant degradation of the vinyl linkages was observed. Control of this UV-initiated process yielded supramolecular elastomers with a covalently cross-linked phase induced by UV irradiation combined with a noncovalent UPy cross-linked phase induced by secondary hydrogen bonding interactions. Of particular note, it was determined that the presence of UPy hydrogen-bonded aggregates accelerated the UV cross-linking process during the initial stage of exposure. This observation was attributed to microphase-separated structure of UV-irradiated supramolecular elastomer, where UPy aggregation increased the probability of interaction between the pendant vinyls responsible for UV cross-linking. The systematic study of uniaxial tensile behavior of the UV-irradiated supramolecular elastomers offers new insight into the design and architecture of mechanically tunable supramolecular elastomers.