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At least 1,207 records · Page 67Linked to original sources
PubMed2005

Ultraviolet Rayleigh-Mie lidar for daytime-temperature profiling of the troposphere.

A UV Rayleigh-Mie scattering lidar has been developed for daytime measurement of temperature and aerosol optical properties in the troposphere. The transmitter is a narrowband, injection-seeded, pulsed, third-harmonic Nd:YAG laser at an eye-safe wavelength of 355 nm. Two Fabry-Perot etalons (FPEs) with a dual-pass optical layout filter the molecular Rayleigh scattering components spectrally for retrieval of the temperature and provide a high rejection rate for aerosol Mie scattering in excess of 43 dB. The Mie signal is filtered with a third FPE filter for direct profiling of aerosol optical properties. The Mie scattering component in the Rayleigh signals, which will have influence on temperature measurements, is corrected by using a measure of aerosol scattering because of the relative insufficiency of Mie rejection of Rayleigh filters in the presence of dense aerosols or clouds, and the Mie rejection capability of system is thus improved. A narrowband interference filter is incorporated with the FPEs to block solar radiation. Also, the small field of view (0.1 mrad) of the receiver and the UV wavelength used enhance the ability of the lidar to suppress the solar background signal in daytime measurement. The system is relatively compact, with a power-aperture product of 0.18 W m(-2), and has a high sensitivity to temperature change (0.62%/K). Lidar measurements taken under different weather conditions (winter and summer) are demonstrated. Good agreement between the lidar and the radiosonde measurements was obtained in terms of lapse rates and inversions. Statistical temperature errors of less than 1 K up to a height of 2 km are obtainable, with an averaging time of approximately 12 min for daytime measurements.

Journal Article↗
PubMed1995

Sunscreen protection of contact hypersensitivity responses from chronic solar-simulated ultraviolet irradiation correlates with the absorption spectrum of the sunscreen.

This study compares the ability of two ultraviolet (UV) B-absorbing sunscreens, 2-ethylhexyl p-methoxycinnamate (2-EHMC) and 2-ethylhexyl p-aminobenzoate (Padimate O), and two physical sunscreens, microfine titanium dioxide (MTD) and zinc oxide, to protect the skin immune system from chronic (4 weeks) solar-simulated UV irradiation. Mice were exposed to suberythemal doses of UV before assessing local and systemic immunosuppression and tolerance to a contact sensitizer. Using a UV protocol that induced local but not systemic immunosuppression or tolerance in BALB/c mice, it was shown that Padimate O made the immunosuppression worse, whereas 2-EHMC and MTD protected the immune system. When the cumulative dose was increased by 12.7%, causing systemic immunosuppression and tolerance, none of the sunscreens protected from immunosuppression, but 2-EHMC provided partial, and MTD gave complete protection from tolerance. To examine this apparent lack of protection from systemic immunosuppression, C3H/HeJ mice were used. These mice had a minimal erythema dose similar to that of the BALB/c mice but were systemically immunosuppressed, with only 44% of the UV dose required to immunosuppress BALB/c mice. 2-EHMC provided some protection, whereas MTD provided complete protection from systemic immunosuppression in C3H/HeJ mice. Hence, sunscreens can protect from local and systemic immunosuppression, although this protection is limited and is not related to the sun protection factor of the sunscreens or the minimal erythema dose of the mouse strain. Instead, protection seems to be related to the sunscreens' having a broad absorption spectrum.

4-Aminobenzoic Acid↗
PubMedDate not supplied

[Possibility of using higher plants in a life-support system on the moon].

The paper discusses the possibility of repeated termination of plant vegetation by prolonged darkness approximating the lunar night. This may be helpful for the incorporation of higher plants into the life support system of lunar bases, the solar light being used for illumination. In this connection vegetables (beet Bordeaux, turnip Petrovskaya, carrot Chantanet, dill, radish Virovsky white) and wheat (variety Sonora) were cultivated during the lunar light-dark cycle (i. e. 15 day light: 15 day dark). The experiments demonstrated that traditional plant products can be obtained under the conditions of lunar photoperiod. Grain of wheat grown during the lunar photoperiod were tested as seed material for further cultivation under similar conditions.

Ecological Systems, Closed↗
PubMed2004

Carotenoid and pheophytin on semiconductor surface: self-assembly and photoinduced electron transfer.

Self-assembling of a carotenoid and pheophytin a into a supramolecular system was observed on the surface of nanocrystalline TiO2, and the photoinduced electron-transfer reactions within the system were studied by means of femtosecond transient absorption and laser flash photolysis techniques. Excitation of the pheophytin moiety results in ultrafast electron transfer from carotenoid to the excited pheophytin, creating a long-lived charge-separated state. Two decay pathways of the formed pheophytin a anion radical are proposed. The first is a direct back electron recombination forming a carotenoid triplet state on the nanosecond time scale, while the other is suggested to occur via electron injection to the TiO2 nanoparticle. These results demonstrate that a self-assembled carotenoid-pheophytin system leads to an efficient reductive quenching of the pheophytin moiety, suggesting that a similar mechanism can operate also in natural photosynthetic systems. Moreover, the formation of a long-lived charge-separated state indicates that such self-assembling strategy may be also considered for novel dye-sensitized solar cell constructions and other artificial systems aiming to mimic the electron-transfer chain in natural photosynthesis.

Carotenoids↗
PubMed2002

Treatment system for solid matrix contaminated with fluoranthene. I--Modified extraction technique.

A laboratory-scale ultrasonication technique was developed for fluoranthene extraction from soils and sediments where the utilized organic solvent would be recovered after the extraction process. Therefore, the remedied soils and sediments would be free from toxicant and trace of added chemicals. The developed ultrasonication technique outlined here is an integrated part of a complete remediation system consisting of extraction and solar detoxification reactors. This paper investigates extraction efficiencies under different conditions, outlines solvent recovery technique and compares extraction efficiency of the developed ultrasonication technique with a commercially available laboratory-scale sonication bath. The spiked soil sample with fluoranthene (19.4 microg g(-1)) and organic solvent was ultrasonicated at 40 degrees C for 20 min. The sonicated mixture was allowed to settle for 10 min before the extract gravitated into the modified solar reactor for fluoranthene detoxification. The added solvents were removed from the remedied soil before it was released to site. The mixture of cyclohexane and ethanol (CH:ETOH) (3:1) was the favorable solvent from among 10 organic solvents because of its high extraction efficiency, safety and low cost. Preliminary results indicated that the developed extraction technique recovered more than 93% of fluoranthene from soil samples.

Bioreactors↗
PubMed2002

Exchange of organic solvents between the atmosphere and grass--the use of open top chambers.

Volatile organic compounds (VOC) are of increasing environmental significance as a result of continually increasing volumes of traffic on European roads. An open-top chamber fumigation system has been devised to investigate how these contaminants transfer between the atmosphere and the ground, and how they partition between and within air-plant-soil systems. Variation in chamber temperature, solar radiation in the chamber and chamber flow rate were identified as factors that affected final air concentrations. These were assessed and quantified for all individual chambers used--effectively characterising each chamber. The real-life VOC concentrations generated were stable and readily reproducible. Grass exposed to benzene, toluene, 1,1,1-trichloroethane and tetrachloroethene, respectively, equilibrated in response to a change in air concentration within hours. The rate of equilibration in exposed grass in all cases was independent of air temperature. 1,1,1-Trichloroethane and tetrachloroethene appear to be biologically inert demonstrating a simple physico-chemical approach to equilibrium, however, benzene and toluene do not appear independent of plant metabolic activity. Aqueous solubility can account for all of the toluene and benzene in the fumigated plant material.

Air Pollutants↗
PubMed2000

222Rn emanation measurements at extremely low activities

For the solar neutrino experiment Borexino, a system has been set up to measure emanation of 222Rn in samples of up to 80 litres volume. The apparatus has been constructed to high vacuum standard and consists mainly of parts made from electropolished stainless steel. The low blank activity of the system together with a highly sensitive detection method for the extracted Rn leads to a sensitivity level in the range 70-100 microBq 222Rn. Due to the large sample capacity of the emanation chambers, it is possible to measure specific emanation rates as low as several microBq/m2. Some measurements characterizing the performance of the apparatus are discussed.

Journal Article↗
PubMed2002

The impact of handpump corrosion on water quality in rural areas of West African sub-region.

Water, even in its natural environment, contains some level of impurities. Water is nearly a universal solvent. It contains dissolved solids and gases, and hosts a number of micro-organisms. The exploitation of groundwater by means of boreholes for supplying small user groups and rural communities with water has been widely applied in certain parts of the world for several decades. In recent years this practice has spread all over the globe, and hundred of thousands of boreholes have been drilled to tap low-yield aquifers. It is evident that such boreholes require pumps for lifting the water. In developing countries these are usually handpumps, but solar as well as other systems with submersible pumps are also used, depending upon the energy sources available and the financial means of the beneficiaries. This article gives a general overview of groundwater quality with regard to its physico-chemical composition. The results presented originate from the experience gained from handpump equipped boreholes within the UNICEF through German Centre for Technical Education Transfer executed inter-regional UNDP-Handpumps Project in West African Regions. Particular attention is paid to presenting corrosion on the water quality of wells in terms of iron concentration and other parameters. Furthermore, the corrosion attack on galvanised iron, the effect of biofilms on the corrosion rate, and the difference between internal and external corrosion of rising mains are shown.

Africa, Western↗
PubMed2004

Use of time-resolved fluorescence analysis to assess molecular mobility and ionic conductivity in nanocomposite organic-inorganic gels.

This work is a short review of studies on nanocomposite organic-inorganic gels by stretched-exponential analysis of fluorescence decay profiles. Emphasis is given to the conditions which allow maximum probe mobility and minimum confinement conditions with the aim to assess ionic conductivity in these materials and with the purpose to employ them with dye-sensitized photoelectrochemical solar cells and other analogous systems.

Journal Article↗
PubMed2002

Fullerene-porphyrin architectures; photosynthetic antenna and reaction center models.

Fullerenes and porphyrins are molecular architectures ideally suited for devising integrated, multicomponent model systems to transmit and process solar energy. Implementation of C60 as a 3-dimensional electron acceptor holds great expectations on account of their small reorganization energy in electron transfer reactions and has exerted a noteworthy impact on the improvement of light-induced charge-separation. This article describes how the specific compositions of porphyrin chromophores linked to C60--yielding artificial light harvesting antenna and reaction center mimics--have been elegantly utilized to tune the electronic couplings between donor and acceptor sites and the total reorganization energy. Specifically, the effects that these parameters have on the rate, yield and lifetime of the energetic charge-separated states are considered.

Carbon↗
PubMed2000

Statistical Properties of SGR 1806-20 Bursts.

We present statistics of SGR 1806-20 bursts, combining 290 events detected with the Rossi X-Ray Timing Explorer/Proportional Counter Array, 111 events detected with the Burst and Transient Source Experiment, and 134 events detected with the International Cometary Explorer. We find that the fluence distribution of bursts observed with each instrument are well described by power laws with indices 1.43, 1.76, and 1.67, respectively. The distribution of time intervals between successive bursts from SGR 1806-20 is described by a lognormal function with a peak at 103 s. There is no correlation between the burst intensity and either the waiting times until the next burst or the time elapsed since the previous burst. In all these statistical properties, SGR 1806-20 bursts resemble a self-organized critical system, similar to earthquakes and solar flares. Our results thus support the hypothesis that the energy source for soft gamma repeater bursts is crustquakes due to the evolving, strong magnetic field of the neutron star, rather than any accretion or nuclear power.

Journal Article↗
PubMed2005

A novel sensor array for field based ocular ultraviolet radiation measurements.

The intensification of terrestrial solar ultraviolet radiation (UVR) due to the diminution of the ozone layer has promoted a variety of research into establishing the impact of this elevated potential dose of UVR on biological tissues. Certain anterior ocular tissues have been found to be susceptible to damage by incident UVR and potentially blinding diseases such as pterygium are thought to be a direct result of absorbed UVR at the nasal limbus. There is a need for more accurate quantification and localisation of incident UVR at the anterior ocular surface. A novel solar blind photodiode sensor array system has been designed, constructed and tested for this purpose. Initial measurements to quantify the irradiance across the anterior ocular surface within the latitudes known as the 'pterygium belt' provide us with a set of core data for different head orientations and tilt angles and indicate the accuracy and stability of the system.

Equipment Design↗
PubMed2001

Construction and analysis of photolyase mutants of Pseudomonas aeruginosa and Pseudomonas syringae: contribution of photoreactivation, nucleotide excision repair, and mutagenic DNA repair to cell survival and mutability following exposure to UV-B radiation.

Based on nucleotide sequence homology with the Escherichia coli photolyase gene (phr), the phr sequence of Pseudomonas aeruginosa PAO1 was identified from the genome sequence, amplified by PCR, cloned, and shown to complement a known phr mutation following expression in Escherichia coli SY2. Stable, insertional phr mutants containing a tetracycline resistance gene cassette were constructed in P. aeruginosa PAO1 and P. syringae pv. syringae FF5 by homologous recombination and sucrose-mediated counterselection. These mutants showed a decrease in survival compared to the wild type of as much as 19-fold after irradiation at UV-B doses of 1,000 to 1,550 J m(-2) followed by a recovery period under photoreactivating conditions. A phr uvrA mutant of P. aeruginosa PAO1 was markedly sensitive to UV-B irradiation exhibiting a decrease in survival of 6 orders of magnitude following a UV-B dose of 250 J m(-2). Complementation of the phr mutations in P. aeruginosa PAO1 and P. syringae pv. syringae FF5 using the cloned phr gene from strain PAO1 resulted in a restoration of survival following UV-B irradiation and recovery under photoreactivating conditions. The UV-B survival of the phr mutants could also be complemented by the P. syringae mutagenic DNA repair determinant rulAB. Assays for increases in the frequency of spontaneous rifampin-resistant mutants in UV-B-irradiated strains containing rulAB indicated that significant UV-B mutability (up to a 51-fold increase compared to a nonirradiated control strain) occurred even in the wild-type PAO1 background in which rulAB only enhanced the UV-B survival by 2-fold under photoreactivating conditions. The frequency of occurrence of spontaneous nalidixic acid-resistant mutants in the PAO1 uvrA and uvrA phr backgrounds complemented with rulAB were 3.8 x 10(-5) and 2.1 x 10(-3), respectively, following a UV-B dose of 1,550 J m(-2). The construction and characterization of phr mutants in the present study will facilitate the determination of the roles of light and dark repair systems in organisms exposed to solar radiation in their natural habitats.

Cloning, Molecular↗
PubMed2005

Preliminary evidence for a change in spectral sensitivity of the circadian system at night.

BACKGROUND: It is well established that the absolute sensitivity of the suprachiasmatic nucleus to photic stimulation received through the retino-hypothalamic tract changes throughout the 24-hour day. It is also believed that a combination of classical photoreceptors (rods and cones) and melanopsin-containing retinal ganglion cells participate in circadian phototransduction, with a spectral sensitivity peaking between 440 and 500 nm. It is still unknown, however, whether the spectral sensitivity of the circadian system also changes throughout the solar day. Reported here is a new study that was designed to determine whether the spectral sensitivity of the circadian retinal phototransduction mechanism, measured through melatonin suppression and iris constriction, varies at night. METHODS: Human adult males were exposed to a high-pressure mercury lamp [450 lux (170 microW/cm2) at the cornea] and an array of blue light emitting diodes [18 lux (29 microW/cm2) at the cornea] during two nighttime experimental sessions. Both melatonin suppression and iris constriction were measured during and after a one-hour light exposure just after midnight and just before dawn. RESULTS: An increase in the percentage of melatonin suppression and an increase in pupil constriction for the mercury source relative to the blue light source at night were found, suggesting a temporal change in the contribution of photoreceptor mechanisms leading to melatonin suppression and, possibly, iris constriction by light in humans. CONCLUSION: The preliminary data presented here suggest a change in the spectral sensitivity of circadian phototransduction mechanisms at two different times of the night. These findings are hypothesized to be the result of a change in the sensitivity of the melanopsin-expressing retinal ganglion cells to light during the night.

Journal Article↗
PubMed2002

Toxicity assays: a way for evaluating AOPs efficiency.

The technical feasibility and performance of photocatalytic degradation of aqueous methomyl (50 mg/L) have been studied at pilot scale in two well-defined systems of special interest because natural-solar UV light can be used: heterogeneous photocatalysis with titanium dioxide and homogeneous photocatalysis by photo-Fenton. The pilot plant is made up of compound parabolic collectors specially designed for solar photocatalytic applications. Experimental conditions allowed pesticide disappearance, degree of mineralisation and toxicity achieved in the two photocatalytic systems to be compared. Total disappearance of methomyl is attained by photo-Fenton in 60 min and by TiO2 in 100 min. Hundred percent of nitrogen and sulphur are recovered as ammonium and sulphate. By contrast, complete mineralisation of total organic carbon (TOC) is not achieved even after quite a long time (more than 300 min). Three different bioassays (Vibrio fischeri, Daphnia magna and a Microalga) have been used for testing the progress of toxicity during treatment. All remained toxic down to very low-pesticide concentrations and in some bioassays were still toxic after total disappearance of the pesticide. Only if treatment is maintained throughout enough mineralisation (i.e. TOC disappearance), the toxicity is reduced to below the threshold (EC50%).

Animals↗