The vegetative arctic freshwater green alga Zygnema is insensitive to experimental UV exposure

The physiological performance and ultrastructural integrity of the vegetative freshwater green alga Zygnema sp., growing under ambient polar day solar radiation and after exposure to experimentally low radiation, but with high UVR:PAR ratio were investigated. In the laboratory, algae were exposed to low photosynthetic active radiation (PAR = P, 400–700 nm, 20 μmol m⁻² s⁻¹), PAR + UV-A = PA (320–400 nm, 4.00 W m⁻² = UV-A) and PAR + UV-A + UV-B = PAB (280–320 nm, 0.42 W m⁻² = UV-B) for 24 h at 7 °C. Photosynthetic performance and ultrastructure of ambient solar radiation-exposed (field control) and experimentally treated Zygnema samples were assessed using chlorophyll fluorescence, and transmission electron microscopy (TEM). No significant treatment effect was observed in the photosynthesis–irradiance curve parameters. Exclusion of the UV-B spectrum in the laboratory treatment caused significantly lower effective photosynthetic quantum yield compared to samples exposed to the whole radiation spectrum. TEM revealed no obvious differences in the ultrastructure of field control and laboratory P-, PA- and PAB-exposed samples. Substantial amounts of lipid bodies, visualized by Sudan IV staining, were observed in all samples. Chloroplasts contained numerous plastoglobules. Organelles like mitochondria, Golgi bodies and the nucleus remained unaffected by the radiation exposures. Zygnema is well adapted to ambient solar radiation, enabling the alga to cope with experimental UV exposure and it is expected to persist in a scenario with enhanced UV radiation caused by stratospheric ozone depletion.     

The effect of loading on disturbance sounds of the Atlantic croaker Micropogonius undulatus: air versus water

Physiological work on fish sound production may require exposure of the swimbladder to air, which will change its loading (radiation mass and resistance) and could affect parameters of emitted sounds. This issue was examined in Atlantic croaker Micropogonius chromis by recording sounds from the same individuals in air and water. Although sonograms appear relatively similar in both cases, pulse duration is longer because of decreased damping, and sharpness of tuning (Q factor) is higher in water. However, pulse repetition rate and dominant frequency are unaffected. With appropriate caution it is suggested that sounds recorded in air can provide a useful tool in understanding the function of various swimbladder adaptations and provide reasonable approximation of natural sounds. Further, they provide an avenue for experimentally manipulating the sonic system, which can reveal details of its function not available from intact fish underwater.     

Effects of exposure to seismic airgun use on hearing of three fish species

Seismic airguns produce considerable amounts of acoustic energy that have the potential to affect marine life. This study investigates the effects of exposure to a 730 in.3 airgun array on hearing of three fish species in the Mackenzie River Delta, the northern pike (Esox lucius), broad whitefish (Coregonus nasus), and lake chub (Couesius plumbeus). Fish were placed in cages in the 1.9 m of water and exposed to five or 20 airgun shots, while controls were placed in the same cage but without airgun exposure. Hearing in both exposed and control fish were then tested using the auditory brainstem response (ABR). Threshold shifts were found for exposed fish as compared to controls in the northern pike and lake chub, with recovery within 24 hours of exposure, while there was no threshold shift in the broad whitefish. It is concluded that these three species are not likely to be substantially impacted by exposure to an airgun array used in a river seismic survey. Care must be taken, however, in extrapolation to other species and to fishes exposed to airguns in deeper water or where the animals are exposed to a larger number of airgun shots over a longer period of time.     

空气流场中气泡示踪粒子的跟随性研究

在流场速度场测量中 ,示踪粒子是显示流场运动的媒介和工具 ,示综粒子对流场的跟随性直接影响着流场速度场测量的精度。本文从 Bassat- Boussinesq- Oseen( BBO) [1 ]方程出发给出了粒子跟随性函数和粒子在匀角速旋转流体中的运动公式 ,讨论了影响示踪粒子跟随性的参数     

From workplace air measurement results toward estimates of exposure? Development of a strategy to assess exposure to manufactured nano-objects

In the past few years, an increasing number of studies on workplace air measurements on manufactured nano-materials and -objects have been published. Most of the studies had a more explorative character, so a direct interpretation to workers” exposure for a given exposure situation, activity, or process is not a straight-forward process. In general, the studies use a quite similar package of devices for near real-time monitoring of particle number- and mass concentration in size ranges <100 nm up to 10 μm, and the collection of samples for off-line characterization of air samples. Various approaches for addressing background concentrations and its use to indicate the potential for exposure to nano-objects could be observed. Within the EU-sponsored NANOSH project, a harmonized approach for measurement strategy, data analysis and reporting was developed. In addition to time/activity–concentration profiles as reported by most studies, this approach enables a first step to estimate the potential for exposure to manufactured nano-objects, more quantitatively. The NANOSH data will be collated into a base, which may form the starting point for a harmonized database facilitating overall analysis in near future, to derive estimates for exposure for several exposure situations.     

Reactions of bowhead whales, Balaena mysticetus, to seismic exploration in the Canadian Beaufort Sea

The behavioral reactions of bowhead whales to distant seismic vessels not under our control, a controlled approach by a seismic vessel, and controlled tests with a single airgun were observed. On 21 occasions in the summers of 1980-84, general activities of bowheads exposed to pulses of underwater noise (107-158 dB re: 1 mu Pa) from seismic vessels 6-99 km away were observed. Activities were indistinguishable from those without seismic noise; there was no detectable avoidance. Hints of subtle changes in surfacing, respiration, and diving behavior were unconfirmed, but were consistent with reactions to stronger noise pulses from closer seismic boats. In a test with a full-scale seismic boat (30 airguns totaling 471, source level 248 dB re: 1 mu Pa, closest point of approach = 1 1/2 km), bowheads began to orient away when the airgun array began to fire 7 1/2 km away. However, some whales continued apparent near-bottom feeding until the vessel was 3 km away. Whales were displaced by about 2 km. Reactions were not much stronger than those to any conventional vessel. Tests with one 0.66-1 airgun showed that some bowheads move away from sources of strong seismic impulses even in the absence of boat noise, and that bowheads can detect the direction from which seismic impulses arrive. In general, bowheads exhibit avoidance reactions when they receive seismic pulses stronger than about 160 dB re: 1 mu Pa. Evidence of reactions to lower received levels remains inconclusive.     

The effect of air exposure on palladium–copper composite membranes

It was found that when electrolessly deposited thin Pd and Pd–Cu membranes were exposed to air at temperatures above 350 °C, their H₂ flux increased substantially immediately after the air exposure, then decreased to a new steady-state value. While this was a quasi-reversible change for the H₂ flux, the flux of insoluble species, such as N₂, irreversibly increased with every air exposure but by a much smaller extent. The extent of these changes was found to be dependent on the exposure time and the temperature of the tests. Thus, we decided to investigate the effect of gas exposures on the properties of these materials.

Palladium and palladium–copper films, prepared by electroless deposition on ceramic supports, and commercial foils were exposed to air, hydrogen and helium at 500 and 900 °C for times varying from 1 h to 1 week with the objective of determining the effect of the different exposure conditions on the surface morphology, the flux of different penetrants and the crystalline structure of the materials. Atomic force microscopy (AFM) and X-ray diffraction (XRD) were used to study the changes occurring in the films under those conditions.

It was observed that the exposure of both the electroless films and the foils to hydrogen and air markedly modified their surface morphology. The hydrogen exposure tended to smooth the surface features whereas the oxygen exposure created new surface features such holes and large peaks. Additionally it was found that the air exposure produced some oxidation of the film to create PdO.

These results suggested that a common hypothesis stating that air oxidation just cleans the surface of the membrane might not be sufficient to explain all of those changes. A contributing effect of air exposure may be the increase in surface area due to the formation of palladium oxide. However, the extent of the surface area increase was insufficient to explain the increase in steady-state H₂ flux.     

Recovery of embryos of Zizania palustris following exposure to liquid nitrogen

Factors affecting survival of embryos of Zizania palustris after exposure to liquid nitrogen were investigated. Moisture content was the most critical factor. Embryos desiccated to a moisture content between 0.36 and 0.56 g water per g dry weight had highest survival after liquid nitrogen exposure (56 +/- 4% and 52 +/- 9% respectively). The recovery of embryos in the light following liquid nitrogen exposure also influenced survival. Survival increased from 35 +/- 4% to 56 +/- 4% when embryos containing 0.36 g water per g dry weight were recovered in the dark compared to light. Embryos exposed to desiccation and freezing stresses were subject to increased levels of lipid peroxidation. Light exacerbated lipid peroxidation in recovering embryos. Furthermore, catalase and peroxidase, enzymes involved in reducing reactive oxygen species, increased in activity in response to stress, and were further up-regulated in tissues recovered in the light. This study suggests that there are a number of factors influencing the survival of tissues exposed to liquid nitrogen and recovery procedures that reduce oxidative stress should be employed.     

Systematic distortions of auditory space perception following prolonged exposure to broadband noise

Perceptual distortions referred to as aftereffects may arise following exposure to an adapting sensory stimulus. The study of aftereffects has a long and distinguished history [Kohler and Wallach, Proc. Am. Philos. Soc. 88, 269-359 (1944)] and a range of aftereffects have been well described in sensory modalities such as the visual system [Barlow, in Vision: Coding and Efficiency (Cambridge University Press, Cambridge, 1990)]. In the visual system these effects have been interpreted as evidence for a population of cells or channels specific for certain features of a stimulus. However there has been relatively little work examining auditory aftereffects, particularly in respect of spatial location. In this study we have examined the effects of a stationary adapting noise stimulus on the subsequent auditory localization in the vicinity of the adapting stimulus. All human subjects in this study were trained to localize short bursts of noise in a darkened anechoic environment. Adaptation was achieved by presenting 4 min of continuous noise at the start of each block of trials and was maintained by a further 15-s noise burst between each trial. The adapting stimulus was located either directly in front of the subject or 30 degrees to the right of the midline. Subjects were required to determine the location of noise burst stimuli (150 ms) in the proximity of the adapting stimulus following each interstimulus period of adaptation. Results demonstrated that following adaptation there was a general radial displacement of perceived sound sources away from the location of the adapting stimulus. These data are more consistent with a channel-based or place-based process of sound localization rather than a simple level-based adaptation model. A simple "distribution shift" model that assumes an array of overlapping spatial channels is advanced to explain the psychophysical data.     

The contribution of two ears to the perception of vertical angle in sagittal planes

Because the input signals to the left and right ears are not identical, it is important to clarify the role of these signals in the perception of the vertical angle of a sound source at any position in the upper hemisphere. To obtain basic findings on upper hemisphere localization, this paper investigates the contribution of each pinna to the perception of vertical angle. Tests measured localization of the vertical angle in five planes parallel to the median plane. In the localization tests, the pinna cavities of one or both ears were occluded. Results showed that pinna cavities of both the near and far ears play a role in determining the perceived vertical angle of a sound source in any plane, including the median plane. As a sound source shifts laterally away from the median plane, the contribution of the near ear increases and, conversely, that of the far ear decreases. For saggital planes at azimuths greater than 60 degrees from midline, the far ear no longer contributes measurably to the determination of vertical angle.     

Detection of protective oxide layers on Cr formed by exposure to air by STEM-ELS method

Relatively thick (1000 Å) and very thin (30 Å) Cr specimens have been observed with scanning transmission electron microscopy (STEM) and energy-loss spectroscopy (ELS). They show marked differences in both diffraction (selected area electron diffraction and microdiffraction) and composition (ELS) data. The extra 2.5 Å ring in SAED and oxygen K edge loss peak in ELS are attributed to the protective oxide layer formed at the surface of Cr by exposure to air at 25°C. The average thickness of the layer is estimated to be about 10 Å.     

Workplace air measurements and likelihood of exposure to manufactured nano-objects,agglomerates, and aggregates

Workplace exposure to nanoparticles from gas metal arc welding (GMAW) process in an automobile manufacturing factory was investigated using a combination of multiple metrics and a comparison with background particles. The number concentration (NC), lung-deposited surface area concentration (SAC), estimated SAC and mass concentration (MC) of nanoparticles produced from the GMAW process were significantly higher than those of background particles before welding (P < 0.01). A bimodal size distribution by mass for welding particles with two peak values (i.e., 10,000–18,000 and 560–320 nm) and a unimodal size distribution by number with 190.7-nm mode size or 154.9-nm geometric size were observed. Nanoparticles by number comprised 60.7 % of particles, whereas nanoparticles by mass only accounted for 18.2 % of the total particles. The morphology of welding particles was dominated by the formation of chain-like agglomerates of primary particles. The metal composition of these welding particles consisted primarily of Fe, Mn, and Zn. The size distribution, morphology, and elemental compositions of welding particles were significantly different from background particles. Working activities, sampling distances from the source, air velocity, engineering control measures, and background particles in working places had significant influences on concentrations of airborne nanoparticle. In addition, SAC showed a high correlation with NC and a relatively low correlation with MC. These findings indicate that the GMAW process is able to generate significant levels of nanoparticles. It is recommended that a combination of multiple metrics is measured as part of a well-designed sampling strategy for airborne nanoparticles. Key exposure factors, such as particle agglomeration/aggregation, background particles, working activities, temporal and spatial distributions of the particles, air velocity, engineering control measures, should be investigated when measuring workplace exposure to nanoparticles.     

Effects of periodic rest on physiological measures of auditory sensitivity following exposure to noise

Whole nerve action potential (AP) and single auditory-nerve fiber thresholds were measured in chinchillas exposed to noise. The exposure stimulus was a 500-Hz octave band of noise presented at 95 dB SPL for 15 min/h, for 4 or 40 days. The AP thresholds were elevated by about 40 dB on day 4, between 0.5 kHz and approximately 8 kHz. On day 40, AP thresholds at the same frequencies were lower by 10-25 dB, even though the noise exposure had continued. Single fiber threshold tuning curves exhibited pathologies similar to those previously observed following noise exposure. Tuning curves measured on day 40 were more normal in appearance. These results confirm that similar recovery of threshold observed in psychophysical experiments [Clark et al., J. Acoust. Soc. Am. 82, 1253-1264 (1987)] can be understood in terms of the sensitivity of the peripheral auditory system.     

Effect of periodic rest on hearing loss and cochlear damage following exposure to noise

Changes in hearing sensitivity and cochlear damage were determined in two groups of chinchillas exposed to an octave band of noise (OBN) centered at 0.5 kHz, 95 dB SPL on two different schedules: 6 h per day for 36 days, or 15 min/h for 144 days. Hearing sensitivity was measured behaviorally at 1/4-oct frequency intervals from 0.125 to 16.0 kHz before, during, and for a period of 1 to 2 months after the exposure, at which time the animals' cochleas were fixed and prepared for microscopic examination. Cochlear damage was determined by counts of missing sensory cells. Both exposures produced an initial shift of thresholds of 35-45 dB; however, after a few days of exposure, thresholds began to decline and eventually recovered to within 10-15 dB of original baseline values even though the exposure continued. Measures of recovery made after completion of the exposures indicated minimal permanent threshold shifts in all animals. The behavioral and anatomical data indicated that these intermittent exposures produced less temporary and permanent hearing loss and less cochlear damage than continuous exposures of equal energy.     

The ability of the parasitoid fly Ormia ochracea to distinguish sounds in the vertical plane

The parasitic fly Ormia ochracea localizes its host, field crickets, by homing in on their calling song. Previous phonotactic studies indicate that their sound localization ability in azimuth is extraordinarily acute, but the fly's ability to localize the elevation of sound sources has not been tested to date. Here we show that in a freely-walking closed-loop Y-maze task elevational performance is well above chance, but slightly below the fly's performance in azimuth. Immobilizing the head or the halteres (sensory organs of balance) slightly lowered elevational discrimination, but performance was still well above chance. Because ormiine ears are thought to be symmetric and the pure-tone models of a cricket's call used in these experiments contained little to no spectral bandwidth, additional studies will be needed to elucidate the underlying cues. Nonetheless, it is clear that while walking, Ormia flies are capable of distinguishing sound sources that differ only in elevation.     

Enzymatic studies in foetal brain and liver of mouse following in utero exposure to ultrasound

Lactate, malate and succinate dehydrogenases (LDH, MDH and SDH) were estimated in the foetal brain and liver following in utero exposure of mice to a continuous wave of unfocussed ultrasound. Enzymes in both tissues showed a significant increase (P greater than 0.001), indicating high energy demand due to depletion of oxygen. The increase was recorded even on the twentieth day of pregnancy.     

The contribution of high frequencies to human brain activity underlying horizontal localization of natural spatial sounds

Background  

In the field of auditory neuroscience, much research has focused on the neural processes underlying human sound localization. A recent magnetoencephalography (MEG) study investigated localization-related brain activity by measuring the N1m event-related response originating in the auditory cortex. It was found that the dynamic range of the right-hemispheric N1m response, defined as the mean difference in response magnitude between contralateral and ipsilateral stimulation, reflects cortical activity related to the discrimination of horizontal sound direction. Interestingly, the results also suggested that the presence of realistic spectral information within horizontally located spatial sounds resulted in a larger right-hemispheric N1m dynamic range. Spectral cues being predominant at high frequencies, the present study further investigated the issue by removing frequencies from the spatial stimuli with low-pass filtering. This resulted in a stepwise elimination of direction-specific spectral information. Interaural time and level differences were kept constant. The original, unfiltered stimuli were broadband noise signals presented from five frontal horizontal directions and binaurally recorded for eight human subjects with miniature microphones placed in each subject's ear canals. Stimuli were presented to the subjects during MEG registration and in a behavioral listening experiment.     

Survival of four accessions of Anigozanthos manglesii (haemodoraceae) seeds following exposure to liquid nitrogen

This study investigated the survival of seeds from the prominent endemic Western Australian species Anigozanthos manglesii following exposure to liquid nitrogen (cryostorage). Seeds from four different accessions (collected in 1987, 1990, 1993 and 1998) adjusted to different water contents were tested for survival following cryostorage. Water content was a significant determining factor with survival of cryostored seeds declining rapidly at water contents above c. 18%. These water contents were deemed as critical water contents and were supported by DSC scans showing high endothermic peaks indicating ice crystallisation. In some instances, survival of cryostored seeds also declined at low water contents. Seeds from 1990 had a lower than expected survival compared to the other accessions. This may have resulted from the higher lipid content of seeds from this accession, or the reduced germination and vigour of these seeds prior to cryostorage.     

Fetal development of mice following intrauterine exposure to a static magnetic field of 6.3 T.

The study was undertaken to investigate possible teratogenic effects of a high magnetic field on fetal development in mice. Eighty-four pregnant CD-1 mice (ICR) were exposed to a static magnetic field of 6.3 T for 1 hr a day from day 7 through day 14 of gestation, a period corresponding to major organogenesis. Fifty mice served as controls. Dams were sacrificed on day 18 of gestation. Fetuses were examined for both external and skeletal abnormalities. No significant differences between exposed and control groups were observed regarding litter size, fetal weight, intrauterine mortality rate, or external and skeletal anomalies. The effects of static magnetic field of 6.3 T on the parameters studied appear negligible.