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At least 1,171 records · Page 65Linked to original sources

PubMed2006

All-solid-state Z-scheme in CdS-Au-TiO2 three-component nanojunction system.

Natural photosynthesis, which achieves efficient solar energy conversion through the combined actions of many types of molecules ingeniously arranged in a nanospace, highlights the importance of a technique for site-selective coupling of different materials to realize artificial high-efficiency devices. In view of increasingly serious energy and environmental problems, semiconductor-based artificial photosynthetic systems consisting of isolated photochemical system 1 (PS1), PS2 and the electron-transfer system have recently been developed. However, the direct coupling of the components is crucial for retarding back reactions to increase the reaction efficiency. Here, we report a simple technique for forming an anisotropic CdS-Au-TiO2 nanojunction, in which PS1(CdS), PS2(TiO2) and the electron-transfer system (Au) are spatially fixed. This three-component system exhibits a high photocatalytic activity, far exceeding those of the single- and two-component systems, as a result of vectorial electron transfer driven by the two-step excitation of TiO2 and CdS.

Journal Article↗

PubMed2002

System times and time horizons for biospheric near-matches of primarily non-photic environmental cycles.

System time is defined as the duration (T) and sampling density (deltat) of a given study. A time horizon is obtained by combining analytical results on endpoints of time structures (chronomes), usually on control groups, from accumulating diverse studies carried out with drastically different values of T and deltat. These two design considerations depend upon and are limited by resources. The desideratum of a small At e.g., for studies of chaotic endpoints, limits T, e.g., has thus far precluded a continuous mapping of decadal cycles in endpoints such as the approximate entropy or the correlation dimension. Time horizons are being documented for an increasing number of variables that undergo cycles with infra-annual frequencies - with one cycle in about one, two and/or five decades - in the biosphere as in the environment. These infra-annuals, in and around us, modulate ultra-annuals, including circadians, as well as about 7-day (circaseptan) and about half-yearly (circasemiannual) cycles, all prominent, e.g., in geophysical and biospheric specta. Neglect of infra-annual chronomics can lead to blunders. A statistically highly significant decrease in the excretion of steroidal metabolites (or in heart rate variability) may be misinterpreted as premature aging if it lasts for several years, and may be unnecessarily acted upon, e.g., by drugs. The decrease, however, may only be transient, occurring only during a given stage of a circadecadal cycle, and it may be followed for the next several years by an also spurious "rejuvenation", possibly misinterpreted as a drug effect. When recognized as the alternating stages of decadal cycles and assessed with an affordable deltat, infra-annuals of variables involved in major problems of our day, including homicides and wars, may lead us to manipulable internal or external mechanisms, and thus, eventually, possibly to countermeasures to crime and terror as well as to the optimization of aims such as spirituality.

Circadian Rhythm↗

PubMedDate not supplied

Human roles in future space operations.

Mankind has evolved in the biosphere from essentially another animal to the level that his industries and societies are powerful components of the life-cycles of Earth. Terrestrial industrial experience can be extended to the use of matter from the Moon and other non-terrestrial sources to create permanent habitats and industry in space. Space stations in low Earth orbit and small bases on the Moon can be the foci of early space industries for learning how to grow in space with local resources. Several near term and long range research topics appropriate to permanent human occupancy of space are reviewed.

Biological Evolution↗

PubMed2003

A task scheduler framework for self-powered wireless sensors.

The cost and inconvenience of cabling is a factor limiting widespread use of intelligent sensors. Recent developments in short-range, low-power radio seem to provide an opening to this problem, making development of wireless sensors feasible. However, for these sensors the energy availability is a main concern. The common solution is either to use a battery or to harvest ambient energy. The benefit of harvested ambient energy is that the energy feeder can be considered as lasting a lifetime, thus it saves the user from concerns related to energy management. The problem is, however, the unpredictability and unsteady behavior of ambient energy sources. This becomes a main concern for sensors that run multiple tasks at different priorities. This paper proposes a new scheduler framework that enables the reliable assignment of task priorities and scheduling in sensors powered by ambient energy. The framework being based on environment parameters, virtual queues, and a state machine with transition conditions, dynamically manages task execution according to priorities. The framework is assessed in a test system powered by a solar panel. The results show the functionality of the framework and how task execution reliably is handled without violating the priority scheme that has been assigned to it.

Algorithms↗

PubMed2000

Accelerated photostability testing of precision UV(TM) contact lenses.

Precision UV(TM) contact lenses were photoaged beyond their expected lifetime in an accelerated manner with a SUNTEST(R) CPS(+) system, which is a solar spectrum equivalent. Ultraviolet spectra of lenses irradiated for 30 h in saline at 41 degrees C and 44 degrees C at the highest power setting were statistically indistinguishable from those measured prior to the exposure. In a similar experiment run at 79 degrees C, the UVB range of the spectra showed small but statistically significant differences, whereas the UVA range of the spectra were not distinguishable. Lenses photoaged at half power and twice the time at 43 degrees C gave UV spectra that could be distinguished. Refractive indices of lenses were indistinguishable before and after irradiation. Eluted materials could not be detected in the saline used to maintain lenses in any irradiation experiment. Lens parameters and water contents remained within manufacturing specifications before and after irradiation.

Journal Article↗

PubMed2006

Triphenylamine-thienylenevinylene hybrid systems with internal charge transfer as donor materials for heterojunction solar cells.

Star-shaped molecules based on a triphenylamine core derivatized with various combinations of thienylenevinylene conjugated branches and electron-withdrawing indanedione or dicyanovinyl groups have been synthesized. UV-vis absorption and fluorescence emission data show that the introduction of the electron-acceptor groups induces an intramolecular charge transfer that results in a shift of the absorption onset toward longer wavelengths and a quenching of photoluminescence. Cyclic voltammetry shows that all compounds present a reversible first oxidation process whose potential increases with the number of electron-withdrawing groups in the structure. Prototype bulk and bilayer heterojunction solar cells have been realized using fullerene C60 derivatives as acceptor material. The results obtained with both kinds of devices show that the introduction of electron-acceptor groups in the donor structure induces an extension of the photoresponse in the visible spectral region, an increase of the maximum external quantum efficiency, and an increase of the open-circuit voltage under white light illumination. These synergistic effects allow reaching power conversion efficiencies of approximately 1.20% under simulated AM 1.5 solar irradiation at 100 mW cm(-2).

Journal Article↗

PubMed2005

Chromopore-linked conducting polymers attached to semiconductor surfaces: a strategy for development of dye-sensitized solar cells.

It is suggested that attaching chromopores to a conducting polymer chain anchored to a semiconductor surface is a good strategy for development of dye-sensitized solar cells. A model system that illustrates this principle is constructed by bonding mercurochrome to poly(vinyl alcohol) films adsorbed onto nanocrystalline TiO2 films. The dye-polymer structure enables transport of electrons (released in excitation of the dye) along the polymer chain to TiO2 as states in the lowest unoccupied molecular orbital of the polymer. By attaching several chromopores to a polymer chain, panchromatic sensitization can be achieved in principle by avoiding concentration quenching and the insulation by thick dye layers.

Journal Article↗

PubMed1997

Solar inactivation of faecal bacteria in water: the critical role of oxygen.

Suspensions of the faecal indicator bacteria Escherichia coli and Enterococcus faecalis were incubated in full sunlight in plastic bottles containing either (i) air-equilibrated (oxygenated) water or (ii) anaerobic (deoxygenated) water. A rapid decrease in cfu ml-1 was observed for actively growing and stationary phase cells of both types of faecal bacteria when illuminated under aerobic conditions, with Ent. faecalis showing the greater enhancement in the rate of inactivation in air-equilibrated water. The demonstration of an oxygen requirement for the inactivation of faecal bacteria in sunlight indicates that solar-based water disinfection systems are likely to require fully aerobic conditions in order to function effectively.

Aerobiosis↗

PubMed2003

Sunscreens inadequately protect against ultraviolet-A-induced free radicals in skin: implications for skin aging and melanoma?

Sunscreens are employed to mitigate the adverse effects of sunlight on skin but are primarily designed to prevent ultraviolet-B-associated burning and damage. The increasingly recognized role of ultraviolet A in aging, and possibly melanoma, highlights the need to include ultraviolet A screens; however, validation remains difficult. We have used a novel method to establish the efficacy of sunscreens, by measuring ultraviolet-A-induced free-radical production (thought to contribute towards ultraviolet-A-related aging and malignant change). Electron spin resonance spectroscopy was used to detect free radicals directly in human Caucasian skin during irradiation with levels of ultraviolet comparable to solar intensities. Using this system the protection afforded by three high factor sunscreens (sun protection factor 20+) that claim ultraviolet A protection was examined. Each sunscreen behaved similarly: at recommended application levels (> or = 2 mg per cm2) the ultraviolet-induced free radicals were reduced by only about 55%, and by about 45% at 0.5-1.5 mg per cm (0.5 mg per cm2 reported for common usage). A "free-radical protection factor" calculated on the basis of these results was only 2 at the recommended application level, which contrasts strongly with the erythema-based sun protection factors (mainly indicative of ultraviolet B protection) quoted by the manufacturers (20+). The disparity between these protection factors suggests that prolonged sunbathing (encouraged by use of these creams) would disproportionately increase exposure to ultraviolet A and consequently the risk of ultraviolet-A-related skin damage.

Free Radicals↗

PubMed2005

Improved photobiological H2 production in engineered green algal cells.

Oxygenic photosynthetic organisms use solar energy to split water (H2O) into protons (H+), electrons (e-), and oxygen. A select group of photosynthetic microorganisms, including the green alga Chlamydomonas reinhardtii, has evolved the additional ability to redirect the derived H+ and e- to drive hydrogen (H2) production via the chloroplast hydrogenases HydA1 and A2 (H2 ase). This process occurs under anaerobic conditions and provides a biological basis for solar-driven H2 production. However, its relatively poor yield is a major limitation for the economic viability of this process. To improve H2 production in Chlamydomonas, we have developed a new approach to increase H+ and e- supply to the hydrogenases. In a first step, mutants blocked in the state 1 transition were selected. These mutants are inhibited in cyclic e- transfer around photosystem I, eliminating possible competition for e- with H2ase. Selected strains were further screened for increased H2 production rates, leading to the isolation of Stm6. This strain has a modified respiratory metabolism, providing it with two additional important properties as follows: large starch reserves (i.e. enhanced substrate availability), and a low dissolved O2 concentration (40% of the wild type (WT)), resulting in reduced inhibition of H2ase activation. The H2 production rates of Stm6 were 5-13 times that of the control WT strain over a range of conditions (light intensity, culture time, +/- uncoupler). Typically, approximately 540 ml of H2 liter(-1) culture (up to 98% pure) were produced over a 10-14-day period at a maximal rate of 4 ml h(-1) (efficiency = approximately 5 times the WT). Stm6 therefore represents an important step toward the development of future solar-powered H2 production systems.

Animals↗

PubMed2005

Pre-cometary ice composition from hot core chemistry.

Pre-cometary ice located around star-forming regions contains molecules that are pre-biotic compounds or pre-biotic precursors. Molecular line surveys of hot cores provide information on the composition of the ice since it sublimates near these sites. We have combined a hydrostatic hot core model with a complex network of chemical reactions to calculate the time-dependent abundances of molecules, ions, and radicals. The model considers the interaction between the ice and gas phase. It is applied to the Orion hot core where high-mass star formation occurs, and to the solar-mass binary protostar system IRAS 16293-2422. Our calculations show that at the end of the hot core phase both star-forming sites produce the same prebiotic CN-bearing molecules. However, in the Orion hot core these molecules are formed in larger abundances. A comparison of the calculated values with the abundances derived from the observed line data requires a chemically unprocessed molecular cloud as the initial state of hot core evolution. Thus, it appears that these objects are formed at a much younger cloud stage than previously thought. This implies that the ice phase of the young clouds does not contain CN-bearing molecules in large abundances before the hot core has been formed. The pre-biotic molecules synthesized in hot cores cause a chemical enrichment in the gas phase and in the pre-cometary ice. This enrichment is thought to be an important extraterrestrial aspect of the formation of life on Earth and elsewhere.

Acetonitriles↗

PubMed1997

Fast measurements of transmission of erythema effective irradiance through clothing fabrics.

For efficiently measuring ultraviolet transmission through clothing materials for a large number of samples, an automated measuring system with a broad-band method has been built and calibrated against a spectroradiometer based instrument. The apparatus can be used to test 60 samples in 25 min. A selection of clothing materials of known composition, weave, color and state have been tested, using the broad band method and the automated measuring system together with a solar ultraviolet simulator. Variations of about eleven times for different weave structure, about two times in the ultraviolet transmittance for different colors, and about 20 times for some stretched samples were observed. For wet conditions, an increment in ultraviolet transmittance for cotton and lycra materials and a decrement for polyester and polyester(65%)/cotton(35%) were also observed.

Clothing↗

PubMed1999

Ethanol synthesis by genetic engineering in cyanobacteria.

Cyanobacteria are autotrophic prokaryotes which carry out oxygenic photosynthesis and accumulate glycogen as the major form of stored carbon. In this research, we introduced new genes into a cyanobacterium in order to create a novel pathway for fixed carbon utilization which results in the synthesis of ethanol. The coding sequences of pyruvate decarboxylase (pdc) and alcohol dehydrogenase II (adh) from the bacterium Zymomonas mobilis were cloned into the shuttle vector pCB4 and then used to transform the cyanobacterium Synechococcus sp. strain PCC 7942. Under control of the promoter from the rbcLS operon encoding the cyanobacterial ribulose-1, 5-bisphosphate carboxylase/oxygenase, the pdc and adh genes were expressed at high levels, as demonstrated by Western blotting and enzyme activity analyses. The transformed cyanobacterium synthesized ethanol, which diffused from the cells into the culture medium. As cyanobacteria have simple growth requirements and use light, CO2, and inorganic elements efficiently, production of ethanol by cyanobacteria is a potential system for bioconversion of solar energy and CO2 into a valuable resource.

Journal Article↗

PubMed2004

The application of the biosphere reserve concept to urban areas: the case of green rooftops for habitat network in Seoul.

This article consists of two parts. The first shows how the principles of the ecosystem approach can be applied to green rooftops, and the second attempts to illustrate it through a case study. In particular, it suggests new approaches and techniques for creation of green rooftops in a perspective of urban habitat network and urban biosphere reserve. To endow urban rooftops with the roles and functions of urban habitat network and urban biosphere reserve, it is necessary to apply "an ecosystem approach to urban management." In this article, an ecosystem approach to urban management is illustrated with Seoul as an example. The Habitat Network in Seoul will be reviewed with a focus on the model suggested by MAB Urban Group. Then, the roles and functions of Myeongdong UNESCO Green Rooftop and its possible contribution to building the Seoul Urban Biosphere Network will be described. The UNESCO Green Rooftop is 628 m(2) and was created on the 12th floor rooftop of UNESCO Building in Myeongdong 2-ga, Jung-ku, Seoul. In the green rooftop, which was created with goals of securing green areas and biotopes in downtown, creating an urban econetwork, securing a base for urban ecosystem study and environment education, and disseminating an idea of coexistence between nature and humankind, wetland, meadow, scrub and woodland, wall revegetation, and a vegetable field are created. Also, rainwater recycling facilities and a solar energy water circulation system were set up. Rest facilities including observation and education facilities were built. Based on the Seoul example, as well as urban biosphere reserve models suggested by the MAB Urban Group, we suggest several principles to be applied for a green rooftops to qualify as a category of urban biosphere reserves.

Architecture↗

PubMedDate not supplied

Glacial influences on solar radiation in a subarctic sea.

Understanding macroscale processes controlling solar radiation in marine systems will be important in interpreting the potential effects of global change from increasing ultraviolet radiation (UV) and glacial retreat. This study provides the first quantitative assessment of UV in the water column of Prince William Sound, a subarctic, semienclosed sea surrounded by mountains, glaciers, rivers, bays and fjords in south central Alaska. Glacial influences on diffuse attenuation coefficients (Kd) were determined along an approximate 120 km transect running NE (61 degrees 07'43''N, 146 degrees 17'1''W) to SW (60 degrees 27'25''N, 148 degrees 05'27'' W). Glacial meltwater and flour caused a 10-fold increase in Kd for visible light, UV-A and UV-B, whereas high optical clarity was present in a diversity of areas away from glacial influences. Transition areas and locations affected by calving of a tidewater glacier had intermediate Kd values. Depths at 99% attenuation ranged from less than 0.2 m near glacial streams to greater than 5 m in bays and open ocean distant from sources of glacial sediments. These results suggest that potential global change from increasing UV and glacial retreat may have heterogeneous effects on subarctic marine systems.

Journal Article↗

PubMed2000

Oxygen concentrators for the delivery of supplemental oxygen in remote high-altitude areas.

Oxygen concentrators are a relatively new technology for the delivery of supplemental oxygen. Readily available for domicile use in modern countries, these machines have proved reliable. The application of oxygen concentrators for the supply of medical oxygen in remote high-altitude settings has important cost-saving and supply implications. In our experience at a remote hospital at 3,900 m in the Nepal Himalayas, oxygen concentrators constitute an effective and affordable means to supply medical oxygen. Using an air compressor and 2 zeolite chambers, the machine traps nitrogen from room air compressed to 4 atm, thus concentrating oxygen in the expressed gas. At delivery flow rates of 2 to 5 liters per minute, oxygen concentrations greater than 80% can be maintained. An electric power requirement of less than 400 W can be provided from a variety of sources, including a small gasoline generator, a solar or wind power system with battery store, or a domestic or commercial power source. At our facility, a cost savings of 75% for supplemental oxygen was found in favor of the oxygen concentrator over cylinders (0.17 US cents per liter vs 0.79 US cents per liter).

Altitude Sickness↗

PubMed2006

Relating daily solar ultraviolet radiation dose in salt marsh-associated estuarine systems to laboratory assessments of photoactivated polycyclic aromatic hydrocarbon toxicity.

Estuaries of the southeastern United States not only serve an important nursery function but also are common repositories of polycyclic aromatic hydrocarbons (PAHs) derived from upland activities. Thus, these habitats may be at risk for PAH phototoxicity. To better characterize this risk, a daily survey of ultraviolet-A (UV-A; 320-400 nm) irradiance was performed at Leadenwah Creek (Wadmalaw Island, SC, USA) on June 27 and August 1, 2003. In addition, laboratory assays were completed using two light exposure regimes: One that was typical of historical phototoxicity assessments (continuous light [C-UV]), and a more environmentally realistic regime (ER-UV). On both survey days, irradiance at a depth of 10 cm exhibited a pattern generally similar to that observed at the surface, whereas irradiance at the bottom of the creek was a function of both tidal height and time of day. Total UV-A dose at a 10-cm depth on June 27 and August 1, 2003 was 4.37 and 4.78 J/cm2, respectively. Attenuation coefficients on both days varied as a function of tidal height. In the laboratory, larval grass shrimp (Palaemonetes pugio) exposed to an ER-UV regime for these habitats (photoperiod, 12:12-h light:dark; total daily UV-A dose, 4.40 J/cm2) exhibited a 2.5-fold decrease in toxicity compared with those exposed to the C-UV regime (photoperiod, 24:0-h light:dark; total daily UV dose, 1.50 J/cm2), despite a threefold higher UV dose in the ER-UV regime. The lower potency under the ER-UV regime likely is attributable to the presence of a 12-h dark period allowing for recovery. The consequences of these results are discussed in the context of habitat-specific UV-A dose and its relevance to future laboratory assessments of PAH phototoxicity.

Animals↗

PubMed2001

[Influence of Adam Schall's changing calendar on Yun - qi theory in the early Qing Dynasty].

The Yun - qi theory is closely related to the calendar system. In Chinese history, the change of the calendar system by Adam Schall von Bell in early Qing Dynasty was a disputable event. Studying its effect on Yun - qi theory, we find out the issue of changing the order of Zi and Shen lunar mansions, which annoyed many Chinese astronomers and scholars, had no significant influence on Yun - qi theory. As for the new calculation system of clepsydra and solar terms, these changes increased the accuracy of the Yun - qi calendar.

Astronomy↗