Increasing Duration Of Exposure Research Articles

VOCABULARY SIZE IS ASSOCIATED WITH SECOND-LANGUAGE VOWEL PERCEPTION PERFORMANCE IN ADULT LEARNERS

Improvement in second-language (L2) perception has been posited to occur early in L2 learning when the L2 vocabulary is still small, whereas a large L2 vocabulary curtails perceptual learning (the perceptual assimilation model for SLA [PAM-L2]; Best & Tyler, 2007). This proposition is extended by suggesting that early L2 lexical development facilitates the establishment of phonological categories in a manner analogous to children’s first-language (L1) acquisition before as opposed to after the vocabulary spurt. According to this view, L2 speech should be assimilated more consistently to L1 phonological categories and cross-boundary contrasts should be discriminated more accurately by learners with larger L2 vocabularies. To test this proposition, a novel whole-system approach to evaluate perception of L2 vowels in two experiments was applied. In Experiment 1, Japanese learners of Australian English (AusE) with less than 12 weeks of L2 learning in Australia completed labeling and goodness ratings on all AusE vowels, selecting from among all monomoraic and bimoraic Japanese vowels and vowel combinations. They also discriminated four L2 vowel contrasts, representing a range of PAM-L2 contrast types, and completed a L2 vocabulary size assessment. Learners with larger vocabularies had more consistent L2-L1 vowel assimilation and more accurate cross-boundary discrimination than those with smaller vocabularies, supporting the proposition that lexical development assists L2 phonological acquisition. Experiment 2 compared the perception of AusE vowels by Japanese learners after only 4–8 weeks in Australia with their perception after 6–8 months of L2 exposure. The results also supported the predicted positive association between L2 vocabulary size and L2 vowel perception rather than a general prediction of increased exposure duration leading to improved perception.

Deep UV resonant Raman spectroscopy for photodamage characterization in cells

We employed deep UV (DUV) Raman spectroscopy for characterization of molecular photodamage in cells. 244 nm light excitation Raman spectra were measured for HeLa cells exposed to the excitation light for different durations. In the spectra obtained with the shortest exposure duration (0.25 sec at 16 µW/µm2 irradiation), characteristic resonant Raman bands of adenine and guanine at 1483 cm−1 and tryptophan and tyrosine at 1618 cm−1 were clearly visible. With increasing exposure duration (up to 12.5 sec), these biomolecular Raman bands diminished, while a photoproduct Raman band at 1611 cm−1 grew. By exponential function fitting analyses, intensities of these characteristic three bands were correlated with sample exposure duration at different intensities of excitation light. We then suggest practical excitation conditions effective for DUV Raman observation of cells without photodamage-related spectral distortion.

The effect of exposure duration on the biological activity of mobile telephony radiation

In the present experiments we studied the effects of different durations of a single (continuous), daily exposure, ranging from 1 min up to 21 min, to the two established systems of digital mobile telephony radiation that are commonly used in Europe, viz. GSM 900 MHz (Global System for Mobile telecommunications) and DCS 1800 MHz (Digital Cellular System—referred to also as GSM 1800 MHz), on a well-tested biological model, the reproductive capacity of the insect Drosophila melanogaster. The insects were exposed to each type of radiation at an intensity of about 10 μW/cm 2, corresponding to a distance of 20 or 30 cm from the antenna of a DCS 1800 or a GSM 900 mobile phone handset, respectively. At these distances the bioactivity of mobile telephony radiation was found to be at a maximum due to the existence of a “window” of increased bioactivity around this value, as we have shown recently [1–4]. The results show that the reproductive capacity decreases almost linearly with increasing exposure duration to both GSM 900 and DCS 1800 radiation, suggesting that short-term exposures to these radiations have cumulative effects on living organisms. Additionally, our results show again that GSM 900 MHz radiation is slightly more bioactive than DCS 1800 MHz radiation, at the same exposure durations and under equal radiation intensities, as shown in our previous experiments [5].

The Defense Mechanism Test–Separation Theme in Two Anxiety Disorders

Two groups of 26 age- and sex-matched outpatients, with DSM-IV diagnoses of obsessive-compulsive disorder and panic disorder with agoraphobia, were compared on the Defense Mechanism Test-Separation Theme. A stimulus portraying a mother figure who is leaving a room where a baby lies alone on the floor was presented 22 times at increasing exposure durations in a single-view tachistoscope. Participants were asked to describe what they perceived at each step, according to the method of the Defense Mechanism Test. As predicted, reports of the mother seen as an inanimate object (phobic repression) were statistically significantly associated with agoraphobia, while reports of the mother entering the room or doing something other than leaving the baby (reaction formation) and reports of the baby as an angel (intellectualization) were associated with obsessive-compulsive disorder.

Investigation of degradation mechanisms in mechanical properties of polyimide films exposed to a low earth orbit environment

The degradation of the mechanical properties of polyimide films was evaluated by means of tensile tests after exposure to a low earth orbit (LEO) environment. Polyimide films irradiated with atomic oxygen (AO), ultraviolet (UV) light, and electron beam (EB) rays using ground simulation facilities were also evaluated similarly and compared. In these experiments tensile stress (7.0 MPa or less) was applied to the samples in order to assess its effects on mechanical properties. The mechanical properties of the flight samples decreased concomitantly with increased exposure duration. The fracture surfaces exhibited characteristic radiated patterns initiating from the exposed surfaces which showed a rough texture. In the AO-irradiated samples the mechanical properties degraded and the surface texture developed as the AO fluence increased; similar fracture surfaces appeared in the flight samples. In contrast, UV and EB irradiation had little impact on mechanical properties. Based on these results, the eroded surfaces by AO irradiation served as the starting points of the rupture, resulting in degradation of mechanical properties of polyimide films exposed to a LEO environment. The tensile stress states induced no difference in evaluations.

Quantifying the effects of shear stress and shear exposure duration regulation on flow induced platelet activation and aggregation

A heightened flow shear stress magnitude or increased exposure duration at any shear stress magnitude enhances platelet activation. It has been suggested that increased circulating activated platelets are an indication of enhanced cardiovascular risk and that activated platelets can perpetuate cardiovascular diseases. However, the combined effects that shear stress and shear exposure duration have on platelet activation and aggregation are not clear. Our objective was to identify a new parameter ("shear stress-exposure time") to predict platelet functional changes better than the absolute magnitude of shear stress. Platelets were exposed to shear stress waveforms, with different combinations of shear stress magnitude and exposure duration, in a circulation flow loop. Timed samples were removed from the flow loop to quantify thrombogenicity (modified prothrombinase assay), aggregation potential (optical platelet aggregometry), and cell surface marker expression (flow cytometry). Flow induced platelet activation and aggregation was enhanced with increased shear stress-exposure time. Platelets that were exposed to waveforms with the same shear stress-exposure time had the same thrombogenicity and aggregation potential. This was true even for waveforms that exposed platelets to shear stress magnitudes varying from 4 to 40 dynes/cm(2). These results indicate that shear stress-exposure time is a good predictor of platelet activation and aggregation levels and it may be able to predict the likelihood of cardiovascular disease onset.

Acute and Subchronic Toxicity of Arsenite and Zinc to Tadpoles of Rhinella arenarum Both Alone and in Combination

The current study evaluated acute and subchronic toxicity of arsenite (As3+) and zinc (Zn2+) to stage 25 tadpoles of Rhinella arenarum in both single and joint laboratory exposures. LC50 values obtained for As3+ were elevated and remained within the range of 46 to 50 mg/L of As3+ between 4 and 17 d of exposure. Growth of tadpoles was completely inhibited with 30 mg/L of As3+, demonstrating the presence of ecologically relevant sublethal effects at concentrations lower than those resulting in lethality. With respect to Zn2+, a 96-h LC50 value of 2.49 mg/L was calculated in soft water. Contrary to results obtained for As3+, LC50 values of Zn2+ gradually decreased with increasing exposure duration, from 2.49 mg/L at 96 h to 1.30 mg/L after 21 d. In joint exposures to both metals, the type of interaction observed between As3+ and Zn2+ was concentration dependent. Lethal effects of As3+ were mitigated, unaffected, or potentiated by 0.01, 0.1, and 1–2 mg/L of Zn2+, respectively. However, although 0.01 mg/L of Zn2+ significantly reduced lethality of As3+-exposed tadpoles, the same concentration of Zn2+ did not help to reverse the stunt growth of these animals. Further studies need to examine which are the lowest concentrations As3+ required to reduce growth and whether Zn2+ serves to antagonize growth effects in this range of concentrations.

Factors Influencing Metham Efficacy on Yellow Nutsedge (Cyperus esculentus) Tubers

Yellow nutsedge infests a large number of hectares in the Treasure Valley of eastern Oregon and western Idaho. Much of its continued expansion appears to be related to onion production in the valley. Fall applications of metham often produce inconsistent results when used to control yellow nutsedge before planting an onion crop. Trials were conducted in the laboratory to determine the influence on yellow nutsedge control of metham dose, duration of exposure, temperature during exposure, and tuber conditioning by washing and chilling at 3 C. All factors influenced metham efficacy against yellow nutsedge tubers. The dose causing 50% reduction in sprouting tubers (I50) for metham ranged from 22 to 76 mg kg−1 of soil and was lower for conditioned tubers than nonconditioned tubers across all conditions, except when tubers were exposed at 25 C for 3 d. Nonconditioned tubers were unaffected by metham after 1 d exposure at 5 C. Increasing exposure temperature or increasing exposure duration decreased sprouting for nonconditioned tubers. As exposure duration and exposure temperature increased, differences among conditioned and nonconditioned tubers were less. Temperature and exposure duration affects metham efficacy against yellow nutsedge, and the condition of the tubers at the time of treatment also has a significant effect. Applications of metham at a time when yellow nutsedge tubers are not dormant may improve yellow nutsedge control.

The effect of exposure duration of self etch dentin bonding on the toxicity of human gingival fibroblast of cell culture

Self etch dentin bonding created to make light easily activate the application of composite resin on tooth surface. The monomer content has acid effect that could irritate tooth pulp. The purpose of this study was to evaluate the effect of light exposure duration of self etch dentin bonding on toxicity of human gingival fibroblast of cell culture by MTT assay. Self etch dentin bonding was used as on experimental unit and the sample was exposed by visible light curing in different duration: 10, 20, 30 seconds and immerged in artificial saliva in pH 7 for 24 hours. 100 µl artificial saliva was exposed to human gingival fibroblast of cell culture 20.000 cells/100 µl RPMI for 24 hours. Toxicity was evaluated by MTT assay, optical density was measured using 550 nm spectrophotometer. The data was analyzed using Kruskal Wallis in 5% degree of significance. The result showed that increasing exposure duration (10, 20, 30 seconds) of self etch dentin bonding will reduce the toxicity of human gingival fibroblast of cell culture. It is concluded that 30 seconds-exposure of self etch dentin bonding will reduce the toxicity of human gingival fibroblast of cell culture.

Acute and chronic effects of organophosphate pesticides (Basudin) to amphibian tadpoles ( Ptychadena bibroni )

Toxicity of basudin (an organophosphate pesticide) on the larval stages of the dominant amphibian; Ptychadena bibroni of the Niger Delta ecological zone of Nigeria was assessed using acute and chronic toxicity in the laboratory. Mortality and body glycogen levels were used as ecological endpoints. The American society of testing and material (ASTM) recommended semi-static renewal bioassay was employed and LC50 was measured at 96 h. The amphibian larval stages were exposed to basudin concentrations of 0.1, 1.0, 10.0 and 25 ug/l. Derived 96 h LC50 values decreased with increased exposure duration. Estimated 96 h LC50 was 0.860 ug/l. Substantial mortality and incidence of abnormal avoidance response occurred more at higher concentrations. Body glycogen levels in all test concentrations were significantly different between the test and the control experiments at P<0.05. The decrease in glycogen level varied negatively with mortality, exposure duration and concentrations. The amphibian assay described in this study can be used to assess the toxicity of basudin pesticides in the course of regulatory surveillance and monitoring of the waters of the Niger Delta ecological zones of Nigeria.

Acute and chronic effects of organophosphate pesticides (Basudin) to amphibian tadpoles (Ptychadena bibroni)

Toxicity of basudin (an organophosphate pesticide) on the larval stages of the dominant amphibian; Ptychadena bibroni of the Niger Delta ecological zone of Nigeria was assessed using acute and chronic toxicity in the laboratory. Mortality and body glycogen levels were used as ecological endpoints. The American society of testing and material (ASTM) recommended semi-static renewal bioassay was employed and LC50 was measured at 96 h. The amphibian larval stages were exposed to basudin concentrations of 0.1, 1.0, 10.0 and 25 ug/l. Derived 96 h LC50 values decreased with increased exposure duration. Estimated 96 h LC50 was 0.860 ug/l. Substantial mortality and incidence of abnormal avoidance response occurred more at higher concentrations. Body glycogen levels in all test concentrations were significantly different between the test and the control experiments at P<0.05. The decrease in glycogen level varied negatively with mortality, exposure duration and concentrations. The amphibian assaydescribed in this study can be used to assess the toxicity of basudin pesticides in the course of regulatory surveillance and monitoring of the waters of the Niger Delta ecological zones of Nigeria. Key words: Acute toxicity, basudin, glycogen, amphibian tadpoles.

Experimental analysis of an early life‐history stage: direct or indirect selection on body size of hatchling turtles?

Summary 1Linking phenotype, performance and fitness has proven difficult to document despite the tremendous influence of this concept on microevolutionary research. One of the major issues involves identifying the target of selection when phenotype and performance are correlated. 2In a replicated manipulative field experiment, we evaluated this model by testing the hypothesis that predation on hatchling turtles during the critical period of migration from their terrestrial nests to their future aquatic home is random with respect to phenotype after controlling for performance. We decoupled migration performance from body size by exposing hatchling red-eared slider turtles Trachemys scripta elegans of all body sizes to environmental conditions and potential predators for four different time durations. 3Body size (measured at initiation of the experiment either as carapace length or as mass) of turtles that were not recovered alive was slightly smaller than that of turtles that survived the experiment. More significantly, however, the number of turtles that survived decreased with increasing exposure duration, particularly after 60 h and was unrelated to meteorological conditions. 4Our experiment thus suggests that selective predation largely acts indirectly on body size of hatchling turtles during this important life stage, consistent with the random predation hypothesis. As enhanced migration performance minimizes exposure of larger hatchlings to predators under natural conditions upon leaving the nests, our experimental results provides strong support for the model linking phenotype, performance and fitness.

Morphology and properties of UV/ozone treated graphite nanoplatelet/epoxy nanocomposites

The nanoscopic morphologies, thermo-mechanical, mechanical and electrical properties of graphite nanoplatelet (GNP)/epoxy nanocomposites were evaluated after UV/O 3 treatment of graphite. Composites containing uniformly distributed GNP reinforcements of well controlled exfoliation were prepared through the graphite intercalation compound technique, graphite surface treatment and optimized ultrasonication process with the aid of solvent. The UV/O 3 treatment showed ameliorating effects on various properties of nanocomposites arising from the enhanced graphite-epoxy interfacial adhesion. The flexural moduli and strengths were higher after treatment for a given GNP content. The thermo-mechanical properties, such as glass transition temperature and storage modulus, increased with increasing exposure duration before saturation after about 30 min of exposure. The electrical resistivity of treated nanocomposites decreased with increasing GNP content much faster than those containing untreated GNPs. The percolation thresholds of both nanocomposites with and without UV/O 3 treatment were similarly about 1 wt%, which is much lower than the values reported in the literature. The interparticle distances were predicted for different particle aspect ratios and volume fractions, and the comparison between the prediction and the experimental aspect ratio for a given percolation threshold indicates reasonable agreement.

Crossed optical and chemical evaluations of modern glass soiling in various European urban environments

As part of the MULTI-ASSESS and VIDRIO EC projects, the soiling of modern glass is characterised in various European urban atmospheres. Our original methodology relies on crossed chemical measurements of the deposit (evaluation of the ion, elemental and organic carbon contents, and subsequent “mass closure”) and exhaustive measurements of glass optical properties (light reflectance, transmittance and absorption). Samples were exposed sheltered from rain in Athens, Krakow, London, Montelibretti (Italy), Prague and Troyes (France), during increasing exposure durations, up to more than two years. Although a slowing down of the deposition rate is observed for some species at some sites, no obvious saturation phenomenon seems to occur for the particle deposition. The chemical composition of the deposit is shown to reflect the atmospheric environment of the exposure site. Some post-deposit evolutions, such as the disappearance of ammonium and possibly of particulate organic matter, are found to occur. For thin deposits, the glass optical properties (e.g. light absorption and diffuse transmittance) are found to evolve quasi-linearly with species concentrations (EC and ions, respectively). However, for conditions creating heavier deposits such as long time exposures in rather polluted environments, a saturation phenomenon is observed. Using a simple model, light absorption, which is primarily due to EC particles, is shown to reach the saturation level ( S) for A≈16% and the concentration for which the semi-saturation level is reached (C 1/2) is found to be about 15 μgC of EC/cm 2. For diffuse transmittance, due to scattering species, these parameters are found to be about 30% and 65 μg of ions/cm 2, respectively. These values may be considered as representative of the soiling in Europe.

Effects of Whole-Body VX Vapor Exposure on Lethality in Rats

Male and female rats were whole-body exposed to VX vapor in a 1000-L single-pass exposure chamber. Estimated exposure dosages producing lethal (LCT50) effects in 50% of exposed male and female rats were established for 10, 60, and 240 min exposure durations. A potency comparison with GB and GF shows that VX becomes increasingly more potent than these G agents with increasing exposure duration. VX is approximately 4–30 times more potent than GB and 5–15 times more potent than GF. Gender differences in the estimated median dosages were not significant at the 10, 60, and 240 min exposure durations. An empirical toxic load model was developed and the toxic load exponent for lethality (n) in the equation Cn× T = k was determined to be n = 0.92. The VX–G regeneration assay was successfully used as a biomarker for the presence of VX in the blood plasma and RBC fractions of the blood 24 h postexposure.

Visual bias of unseen hand position with a mirror: spatial and temporal factors

Two experiments examined the integration of visual and proprioceptive information concerning the location of an unseen hand, using a mirror positioned along the midsagittal plane. In experiment 1, participants tapped the fingers of both hands in synchrony, while viewing the mirror-reflection of their left hand. After 6 s, participants made reaching movements to a target with their unseen right hand behind the mirror. Reaches were accurate when visually and proprioceptively specified hand positions were congruent prior to the reach, but significantly biased by vision when the visual location conflicted with the real location. This effect was independent of the target location and depended strongly upon the relative position of the mirror-reflected hand. In experiment 2, participants made reaching movements following 4, 8, or 12 s active visuomotor or passive visual exposure to the mirror, or following passive exposure without the mirror. Reaching was biased more by the visual location following active visuomotor compared to passive visual exposure, and this bias increased with the duration of visual exposure. These results suggest that the felt position of the hand depends upon an integrated, weighted sum of visual and proprioceptive information. Visual information is weighted more strongly under active visuomotor than passive visual exposure, and with increasing exposure duration to the mirror reflected hand.

Sand grain threshold, in relation to bed ‘stress history’: an experimental study

AbstractBesides particle size, density and shape, the erodibility of a sediment bed depends also upon the exposure to prethreshold velocities in the overlying flow. Such flow effectively rearranges the grains (at and below the bed surface), causing them to become more resistant to subsequent erosion. The effects of the ‘stress history’, leading up to the critical condition for sediment movement, are investigated for unidirectional flows generated in a recirculating laboratory flume. The sediment beds investigated consisted of cohesionless quartz sand grains, with mean grain diameters of 0·194 mm (fine sand), 0·387 mm (medium sand) and 0·774 mm (coarse sand), with narrow particle‐size distributions. The critical (threshold) shear velocity (target value) for the three beds was established, within 2·5 min of increasing the flow from zero velocity. The subsequent experiments were performed under prethreshold velocities at 70% (for 5, 10, 20, 40 and 80 min exposure duration), 80% (for 5, 10, 20, 40 and 80 min exposure duration), 90 and 95% (for 5, 10, 20, 40, 80 and 120 min exposure duration) of the target value. Following exposure to these different prethreshold conditions, the flow was increased then to reach actual critical conditions, within a period of 2·5 min. The critical condition for the initiation of sediment movement was established using visual observation (supplemented by video recordings), according to the Yalin criterion. The results show that if the exposure duration to prethreshold velocities remains constant, then the critical shear velocity increases with increasing prethreshold velocity. Likewise, if the prethreshold velocity remains constant, then the critical shear velocity increases with increasing exposure duration. In some circumstances, the critical shear velocity was found to increase by as much as 27%. An empirical formula is proposed to account for the exposure correction to be applied to the critical shear velocities of sand‐sized sediment beds; this is prior to their inclusion into bedload transport formulae, for an improved prediction of the magnitude and nature of transport.

Local heating of human skin by millimeter waves: Effect of blood flow

We investigated the influence of blood perfusion on local heating of the forearm and middle finger skin following 42.25 GHz exposure with an open ended waveguide (WG) and with a YAV mm wave therapeutic device. Both sources had bell-shaped distributions of the incident power density (IPD) with peak intensities of 208 and 55 mW/cm(2), respectively. Blood perfusion was changed in two ways: by blood flow occlusion and by externally applied vasodilator (nonivamide/nicoboxil) cream to the skin. For thermal modeling, we used the bioheat transfer equation (BHTE) and the hybrid bioheat equation (HBHE) which combines the BHTE and the scalar effective thermal conductivity equation (ETCE). Under normal conditions with the 208 mW/cm(2) exposure, the cutaneous temperature elevation (DeltaT) in the finger (2.5 +/- 0.3 degrees C) having higher blood flow was notably smaller than the cutaneous DeltaT in the forearm (4.7 +/- 0.4 degrees C). However, heating of the forearm and finger skin with blood flow occluded was the same, indicating that the thermal conductivity of tissue in the absence of blood flow at both locations was also the same. The BHTE accurately predicted local hyperthermia in the forearm only at low blood flow. The HBHE made accurate predictions at both low and high perfusion rates. The relationship between blood flow and the effective thermal conductivity (k(eff)) was found to be linear. The heat dissipating effect of higher perfusion was mostly due to an apparent increase in k(eff). It was shown that mm wave exposure could result in steady state heating of tissue layers located much deeper than the penetration depth (0.56 mm). The surface DeltaT and heat penetration into tissue increased with enlarging the irradiating beam area and with increasing exposure duration. Thus, mm waves at sufficient intensities could thermally affect thermo-sensitive structures located in the skin and underlying tissue.

Carcinogenicity of radon/radon decay product inhalation in rats – effect of dose, dose rate and unattached fraction

Purpose: The effects of inhalation of radon/radon decay products at different total doses, dose rates and ‘unattached’ fractions were investigated in a life span study in rats.Materials and methods: 1574 rats inhaled radon/radon decay products in a purpose-built recirculating exposure system that provided stable/reproducible exposure conditions. 501 were maintained as controls.Results: Lung tumour incidences were significantly elevated in most exposed groups. The study power was insufficient to resolve the shape of the dose and dose rate response curves, but combination of this data with that from other studies demonstrated that for high cumulative exposures, the lifetime excess absolute risk increases with increasing exposure durations and for low cumulative exposures the opposite trend occurs. Exposure did not increase leukaemia incidences. A small number of non-lung tumour types including mammary fibroadenoma showed elevated incidences in some exposed groups, however not consistently across all exposure groups and showed no dose or dose rate relationship.Conclusions: Radon/radon decay product exposure caused excess lung tumours in rats along with limited non-lung effects. The results are consistent with the findings that at low cumulative exposures decreasing exposure concentrations or protracting the time over which the dose is delivered, reduces lung tumour risk. At higher levels, decreasing exposure concentrations or protracting exposure time increases lung tumour risk.

Effect of exposure duration on lung hemorrhage from low-frequency underwater sound

Previous research from our lab has shown that low-frequency (∼100–1000 Hz) underwater sound exposure can produce lung hemorrhage in laboratory mammals. The threshold for damage is lowest for exposure at the resonance frequency of lung. In adult mice, the threshold for lung damage is ∼2 kPa using a 3-min continuous wave (cw) exposure at the resonance frequency (∼300 Hz). The objective of this study was to determine the effect of exposure duration on lung damage produced by low-frequency sound. Experiments were performed with anesthetized adult mice. The resonance frequency of each mouse lung was determined using an acoustic scattering technique. Mice were exposed cw at the resonance frequency for durations of 1, 5, 10, 30 s, 1 and 3 min. The threshold for lung hemorrhage was relatively independent of duration for exposures greater than or equal to 1 min. For short exposure durations, the threshold increased and the mean extent of lung damage decreased. In some instances, extensive damage to the lung was observed to occur even for the 5-s exposure duration. However, the likelihood of extensive lung hemorrhage increased with increasing exposure duration.