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At least 1,261 records · Page 70Linked to original sources
PubMed1989

DNA strand breakage in normal and solar ultraviolet-sensitive ICR 2A frog cell lines exposed to solar ultraviolet wavelengths.

ICR 2A frog cells and two solar ultraviolet (UV)-sensitive cell lines, DRP 36 and DRP 153, were irradiated with 150 kJ/m2 of the UV radiation produced by a fluorescent sun lamp, the radiation from which was passed through a sheet of 48A Mylar (DuPont, Wilmington, DE) to eliminate wavelengths shorter than approximately 315 nm. The irradiated cultures were also exposed to photoreactivating light (PRL), resulting in the removal of most of the pyrimidine dimers induced by the sun lamp UV irradiation, and then incubated 0-4 hr. At the end of the incubations, the cells were subjected to the alkaline elution assay. In these elutions, the cell lysates were either treated with proteinase K (proK) to eliminate any DNA-protein crosslinks (DPC) that may be present in the cells, or left untreated with proK. For the ICR 2A cells, the level of apparent DNA single-strand breaks (ssb) detected in elutions using proK increased with the incubation time after irradiation and remained high. However, when the DNA was eluted without proK pretreatment, the number of ssb fell rapidly. In contrast, the levels of ssb decreased in the DRP 36 and DRP 153 cells regardless of the use of proK in the elutions. Hence, this differential response in ssb induction may be indicative of a system involved with recovery following irradiation with solar UV wavelengths.

Animals↗
PubMed1975

Photosensitivity: results of investigation in 250 patients.

Between January 1972 and December 1974, 250 patients were referred for investigation of possible photosensitivity to a university-associated clinical research unit for photobiology. In addition to an appropriate history and clinical examination, phototesting was carried out with a solar simulator, monochromatic light and fluorescent light directed to patch-tested areas of skin. Photosensitivity was not demonstrated in 110 patients (44%). Among the laboratory-confirmed photosensitivities, diagnoses included polymorphous light eruption (4.4%), erythropoietic protoporphyria (3.6%), porphyria cutanea tarda (2%), photoallergic contact dermatitis (5.6%), persistent light reaction (4%), systemic drug phototoxicity (1.2%), phototoxic contact dermatitis (2%), solar urticaria (0.8%) and photoaggravated dermatoses (7.6%). It is important to establish a precise etiologic diagnosis in patients with photosensitivity in order to treat the disorder specifically or effectively or both.

Adolescent↗
PubMed2005

Self-organizing learning array.

A new machine learning concept--self-organizing learning array (SOLAR)--is presented. It is a sparsely connected, information theory-based learning machine, with a multilayer structure. It has reconfigurable processing units (neurons) and an evolvable system structure, which makes it an adaptive classification system for a variety of machine learning problems. Its multilayer structure can handle complex problems. Based on the entropy estimation, information theory-based learning is performed locally at each neuron. Neural parameters and connections that correspond to minimum entropy are adaptively set for each neuron. By choosing connections for each neuron, the system sets up its wiring and completes its self-organization. SOLAR classifies input data based on the weighted statistical information from all the neurons. The system classification ability has been simulated and experiments were conducted using test-bench data. Results show a very good performance compared to other classification methods. An important advantage of this structure is its scalability to a large system and ease of hardware implementation on regular arrays of cells.

Learning↗
PubMed2002

Detection of a novel pigment network feature in reticulated black solar lentigo by high-resolution epiluminescence microscopy.

Epiluminescence light microscopy (ELM) of pigmented skin lesions has led to a catalog of pigment network (PN) features. The objective of this study was to determine whether high-resolution ELM detects additional pigment structures not seen with conventional ELM. Epiluminescence light microscopy was performed by placing the lens of a standard light microscope directly on the skin surface, with resulting enhanced optical resolution compared with ELM systems currently in general use. Eight reticulated black solar lentigines were studied. All lesions were viewed and analyzed using dermatoscopic criteria for the PN. In addition, they were all photographed, excised, and examined histologically. Two subtypes of black solar lentigines could be distinguished using generally accepted dermatoscopic criteria for the PN. Furthermore, a new pigment structure was detected, namely, pigment spots of equal color, shape, and size, which were regularly superimposed on and juxtaposed to the PN. Clinicopathologic correlation showed these spots to represent individual hyperpigmented corneocytes. Because such cells result from physiologic excessive pigment translocation via the epidermal melanocytic unit, we called them pigmented corneocytes. Pigmented corneocytes were seen in seven of eight black solar lentigines. The ELM technique presented here allows for more detailed analysis and classification of the PN components. Pigmented corneocytes are proposed as an additional dermatoscopic criterion.

Adult↗
PubMed2000

Humic Materials Offer Photoprotective Effect to Escherichia coli Exposed to Damaging Luminous Radiation.

The behavior of Escherichia coli immersed in aqueous systems amended with humic acids, under PAR, UV-A, UV-B, and simulated solar radiation was examined. Culturability, ability to elongate, functioning of the electron transport systems, and glucose uptake were assessed. Humic substances in the range from 1 to 50 mg L-1 protected cells from photoinactivation. Decrease in culturability and cellular activities was significantly (p <0.05) less in the presence of humic material. However, humic acids were not used as nutrients. Neither irradiated nor nonirradiated humic solutions (50 mg L-1) supported the growth of 105 cells ml-1. However, humic acids dissolved in 0.9% NaC1 efficiently absorbed light over wavelengths from 270 to 500 nm. Also, a photoprotective effect against simulated sunlight was observed when humic acids were not in contact with but rather enveloped the cellular suspensions in double-wall microcosms. The protection afforded by humic acids against luminous radiation likely derives from their ability to absorb these radiations and hence reduces the amount of energy reaching the cells.

Journal Article↗
PubMed2000

Solar blind photocell--a simple element specific detector in Hg, As and Se speciation.

An element-specific detection method, based on atomic absorption spectrometry (AAS) using solar blind photocells instead of a dispersion system, is described for the determination of Hg-, As-, and Se-species. Spectrometric investigations of AAS background lamps for As and Se measured with a CsI-cathode photocell shows its quality as narrow band detector. Species determination can be carried out subsequently to prior separation by HPLC or GC. The LODs for alkylated Hg species were below 1 ng/L, and for methylated As species below 1 microg/L. The relative standard deviation was < 10%. With the components described the production of cheap and automated dedicated speciation spectrometers is possible.

Journal Article↗
PubMed1995

Results of evaluation of 203 patients for photosensitivity in a 7.3-year period.

BACKGROUND: Although photosensitivity disorders have been well described, their incidence in a referral institution had not been studied. OBJECTIVE: The purpose of this study was to evaluate the incidence of photosensitivity disorders, including photocontact dermatitis, in an academic medical center. METHODS: The results of the assessment of 203 consecutive patients, all of whom had phototests, referred for the evaluation of photosensitivity disorders during a 7.3-year period were reviewed. RESULTS: The mean age was 50 years, and 63% of the patients were women. The most frequent diagnoses were polymorphous light eruption (26% of the total patient population), chronic actinic dermatitis (17%), photoallergic contact dermatitis (8%), systemic phototoxicity to therapeutic agents (7%), and solar urticaria (4%). Positive photopatch reactions, patch test reactions, or both were observed in 40 (29%) of the 138 tested patients. The frequencies of the positive photopatch test reactions were sunscreens (57%), fragrances (18%), and antimicrobial agents (13%). Of the positive patch test responses, fragrances elicited 47% of the total positive reactions, followed by sunscreens (39%) and antimicrobial agents (7%). CONCLUSION: Polymorphous light eruption, chronic actinic dermatitis, and photoallergic contact dermatitis were the most frequently made diagnoses. Sunscreens, fragrances, and antimicrobial agents were the most common clinically relevant photoallergens and allergens.

Academic Medical Centers↗
PubMed1985

Transplantation of human malignant and premalignant skin lesions of epidermis to nude mice.

Lesions of solar keratoses and squamous cell carcinoma maintained their histological appearance and an increased tritiated thymidine autoradiographic labelling index after being grafted on to nude mice. However, the values for their mean epidermal thickness and individual cell size appeared to decrease slightly during the 24-week period of study. As judged by the immunolocalization of involucrin antibodies, the grafts maintained a human epidermal antigenic profile. However, immunolocalization studies with HLA antibodies showed only a patchy positivity in the original premalignant lesions and were negative after grafting. These results indicate the potential value of the nude mouse as a model for studying the progress of premalignant and malignant skin lesions in an immunologically privileged non-human site and further indicate that solar keratoses can be maintained independently of systemic donor influences.

Animals↗
PubMed2006

Photophysical processes involved within the bichromophoric system 9-benzotriazole-1-ylmethyl-9H-carbazole and its role as an artificial photosynthetic device.

From both steady state and fluorescence lifetime measurements it reveals that due to photoexcitation of benzotriazole (BZ) part of the bichromophore, 9(1-H-benzotriazole-lylmethyl)-9H-carbazole (BHC), singlet-singlet energy transfer takes place to populate the lowest excited singlet of carbazole (CZ). CZ, thus being excited indirectly via energy transfer process, undergoes strong charge transfer (CT) reaction with the surrounding polar medium acetonitrile (ACN). On the other hand, very weak CT band was apparent when CZ part, within BHC, was directly excited. In less polar tetrahydrofuran (THF) and polar benzonitrile (BN) environment, lack of formation of CT band strongly suggests in favor of the electron-accepting behavior of ACN. Moreover, by measuring the emission spectra of BHC in microcrystals and of 30 bilayers mixed LB film at high mole fraction of BHC molecules, the possibility of excimer formation or aggregation has been ruled out. Thus, BHC, when dissolved in ACN, acts as a triad system of BZ-CZ-ACN where BZ acts as an antenna molecule and CZ as a reaction center. The possible role of the bichromophoric system BHC as an artificial photosynthetic or solar energy conversion device has been hinted.

Acetonitriles↗
PubMed2006

Preliminary investigation of proton and helium ion radiation effects on fluorescent dyes for use in astrobiology applications.

The Specific Molecular Identification of Life Experiment (SMILE) instrument (Sims et al. Planet. Space Science 2005, 53, 781-791) proposes to use specific molecular receptors for the detection of organic biomarkers on future astrobiology missions (e.g., to Mars). Such receptors will be used in assays with fluorescently labeled assay reagents. A key uncertainty of this approach is whether the fluorescent labels used in the system will survive exposure to levels of solar and galactic particle radiation encountered during a flight to Mars. Therefore, two fluorescent dyes (fluorescein and Alexa Fluor 633) have been exposed to low-energy proton and alpha radiation with total fluences comparable or exceeding that expected during an unshielded cruise to Mars. The results of these initial experiments are presented, which show that both dyes retain their fluorescent properties after irradiation. No significant alteration in the absorption and emission wavelengths or the quantum yields of the dyes with either radiation exposure was found. These results suggest other structurally similar fluorophores will likely retain their fluorescent properties after exposure to similar levels of proton and alpha radiation. However, more extensive radiation fluorophore testing is needed before their suitability for astrobiology missions to Mars can be fully confirmed.

Absorption↗
PubMed2006

Effect of iodine addition on solid-state electrolyte LiI/3-hydroxypropionitrile (1:4) for dye-sensitized solar cells.

It was observed that the ionic conductivity of the solid-state electrolyte LiI/3-hydroxypropionitrile (HPN) = 1:4 (molar ratio) decreased dramatically with increasing iodine (I(2)) concentration, which differs from the conduction behavior of the Grotthuss transport mechanism observed in liquid or gel electrolytes. The short-circuit photocurrent density (J(sc)) of the dye-sensitized solar cell (DSSC) based on this electrolyte system increases with increasing I(2) concentration until LiI/I(2) is 1:0.05 (molar ratio). Beyond this limitation, the J(sc) decreases. At low I(2) concentrations (I(2)/LiI < or = 0.05), the J(sc) is mainly affected by the diffusion of I(3)(-). An increase of the I(2) concentration leads to the enhancement of the diffusion of I(3)(-) and an increase of the J(sc). At high I(2) concentrations (I(2)/LiI > 0.05), the factors, including the increased light absorption by the I(3)(-), the increased recombination of electrons at the photoanode with I(3)(-), and the reduced ionic conductivity of the electrolyte, lead to a decrease of J(sc). At the same time, the open-circuit voltage (V(oc)) of the DSSC decreases monotonically with the ratio of I(2)/LiI due to increased dark current in the DSSC. The increased absorption of visible light by the electrolyte, the enhanced dark current, and the reduced ionic conductivity of the electrolyte contribute to the performance variation of the corresponding solid-state DSSC with increasing I(2) concentration.

Journal Article↗
PubMed2002

A topographically forced asymmetry in the martian circulation and climate.

Large seasonal and hemispheric asymmetries in the martian climate system are generally ascribed to variations in solar heating associated with orbital eccentricity. As the orbital elements slowly change (over a period of >104 years), characteristics of the climate such as dustiness and the vigour of atmospheric circulation are thought to vary, as should asymmetries in the climate (for example, the deposition of water ice at the northern versus the southern pole). Such orbitally driven climate change might be responsible for the observed layering in Mars' polar deposits by modulating deposition of dust and water ice. Most current theories assume that climate asymmetries completely reverse as the angular distance between equinox and perihelion changes by 180 degrees. Here we describe a major climate mechanism that will not precess in this way. We show that Mars' global north-south elevation difference forces a dominant southern summer Hadley circulation that is independent of perihelion timing. The Hadley circulation, a tropical overturning cell responsible for trade winds, largely controls interhemispheric transport of water and the bulk dustiness of the atmosphere. The topography therefore imprints a strong handedness on climate, with water ice and the active formation of polar layered deposits more likely in the north.

Atmosphere↗
PubMed2006

Photoprotection in an ecological context: the remarkable complexity of thermal energy dissipation.

This review places photoprotection into the context of ecology and species diversity. The focus is on photoprotection via the safe removal - as thermal energy - of excess solar energy absorbed by the light collecting system, which counteracts the formation of reactive oxygen species. An update on the surprisingly complex, multiple variations of thermal energy dissipation is presented, placing these different forms into ecological and genetic contexts. Zeaxanthin-facilitated, flexible thermal dissipation associated with the PsbS protein and controlled by the trans-thylakoid pH gradient apparently occurs ubiquitously in plants, and can become sustained (and thus less flexible) at low temperatures. Long-lived, slow-growing plants with low intrinsic capacities for photosynthesis have greater capacities for this flexible dissipation than short-lived, fast-growing species. Furthermore, potent, but inflexible (zeaxanthin-facilitated) thermal dissipation, prominent in evergreen species under prolonged environmental stress, is characterized with respect to the involvement of photosystem II core rearrangement and/or degradation as well as the absence of control by trans-thylakoid pH and, possibly, PsbS. A role of PsbS-related proteins in photoprotection is discussed.

Carbon↗
PubMed1988

Photo-induced events in the human melanocytic system: photoaggression and photoprotection.

The human skin is submitted to solar, essentially ultraviolet radiation (UVR), aggressions, and develops, for sufficient doses, erythema and pigmentation. The individual sun-sensitivity depends on the nature and the quantity of melanins present in the epidermis. These parameters are inherited as genetic traits which account for the large variations of the constitutive and adaptive pigmentation encountered in the caucasian populations. From red-haired skin-sensitive individuals, to dark-haired sun-resistant individuals, phaeomelanins (red) and eumelanins (black) are mixed in variable proportions. Pure melanins extracted from red hairs and black hairs behave differently when submitted to ultraviolet radiations: phaeomelanins develop aggressive species of molecules responsible for DNA damages, mutations, and cell death. On the contrary, eumelanins are less toxic for the major cellular metabolisms. The sun-sensitive populations suffer from more skin cancer of all types than the dark ones. In particular, they are exposed significantly to higher risk of melanoma and to the risk of bearing more nevi following large solar exposures early in the life.

Humans↗
PubMed2005

Simultaneous inhibition and redistribution of spontaneous light emission in photonic crystals.

Inhibiting spontaneous light emission and redistributing the energy into useful forms are desirable objectives for advances in various fields, including photonics, illuminations, displays, solar cells, and even quantum-information systems. We demonstrate both the "inhibition" and "redistribution" of spontaneous light emission by using two-dimensional (2D) photonic crystals, in which the refractive index is changed two-dimensionally. The overall spontaneous emission rate is found to be reduced by a factor of 5 as a result of the 2D photonic bandgap effect. Simultaneously, the light energy is redistributed from the 2D plane to the direction normal to the photonic crystal.

Journal Article↗
PubMed2003

[Medical and biological studies of Ukrainian scientists in Antarctic region].

People adaptation problem in Antarctic conditions, prophylactics of the desinchronostic disturbances, destability of psycho-emotion state, pathological manifestation of the heart-vessel system, tasks of regional waste influences on the people organism are not insolvable up to now and is the base of medical-biological researches. In accordance with the peculiarities of the geographical positions of Academician Vernadsky station and long period of staying in extremely conditions of Antarctic the medical-physiological researches will executed on the each stage. During the selection of candidates for the work at Ukrainian Antarctic station we studied new medico-biological criteria including genetic markers with aim to forecast antagonism functional state during wintering. At the period of staying in Antarctic in the conditions of season inversions and hour belts removals it will executed the researches of biorhythmological peculiarities of the psychophysiological function and heart-vessel system states, outer system of breathing and biochemistry indexes of people fluids. It was shown that the biggest part of disturbances in organisms functional system at the period of Antarctic winter has an ability to restoration after returning to homeland. However, disturbances in immunology system state are prolonged, harmful influence of solar radiation are revealed on the people sight, especially, when one use the not recommended lighting filters. With the purpose of prophylactic of desynchronic disturbances, which was find after wintering at the more then 90% expedition personnel, it was worked out an non invasion methods of correction by using the individual polychromatic influence on organism. It is studied the teleconnection results of long period staying of expedition staff in Antarctic. It was established, that Ukrainian members of expedition have the fixed number of radionuclids of Cesium in organism. After staying in Antarctic radionuclids of Cesium in organism do not reveal.

Adaptation, Physiological↗