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At least 649 records · Page 36Linked to original sources
PubMed2002

Mapping the light field of the Waldmann PDT 1200 lamp: potential for wide-field low light irradiance aminolevulinic acid photodynamic therapy.

A quantitative assessment of the light field produced by a Waldmann PDT 1200 lamp is presented. A photodiode detector array capable of measuring a beam diameter of 30 cm was used to map the light field. The irradiance was measured as a function of voltage. For lamp-detector distances of 10 cm (central axis irradiance = 250 mW/cm2), the spatial profile of irradiance was typically Gaussian. For lamp-detector distances of 30 cm (central axis irradiance = 79 mW/cm2), the spatial profile appeared more hemispherical in shape but with some asymmetry. The relative percentage variation between the maximum and minimum irradiance with respect to the central axis irradiance was approximately 13% and 3%, respectively, for a beam width of 12 cm. Beyond a lamp-detector distance of 50 cm (central axis irradiance = 32 mW/cm2), the spatial profile of irradiance was observed to become more crater-like in structure, with a minimum on the central axis and an approximately symmetric peak at a radial distance of 9 cm from the center. The relative percentage variation of this peak irradiance with respect to the central axis irradiance was approximately 17%. At lamp-detector distances of 70 and 90 cm (central axis irradiance = 19 and 13 mW/cm2, respectively), the beam's profile was asymmetric, and the irradiance was observed to increase from the center to a radial distance of 15 cm (beam width 30 cm). For a lamp-detector distance of 70 and 90 cm, the relative percentage variation between the maximum irradiance and the central axis irradiance was approximately 25% and 35%, respectively.

Aminolevulinic Acid↗
PubMed1995

Growth and photomorphogenesis of pepper plants under red light-emitting diodes with supplemental blue or far-red lighting.

Light-emitting diodes (LEDs) are a potential irradiation source for intensive plant culture systems and photobiological research. They have small size, low mass, a long functional life, and narrow spectral output. In this study, we measured the growth and dry matter partitioning of 'Hungarian Wax' pepper (Capsicum annuum L.) plants grown under red LEDs compared with similar plants grown under red LEDs with supplemental blue or far-red radiation or under broad spectrum metal halide (MH) lamps. Additionally, we describe the thermal and spectral characteristics of these sources. The LEDs used in this study had a narrow bandwidth at half peak height (25 nm) and a focused maximum spectral output at 660 nm for the red and 735 nm for the far-red. Near infrared radiation (800 to 3000 nm) was below detection and thermal infrared radiation (3000 to 50,000 nm) was lower in the LEDs compared to the MH source. Although the red to far-red ratio varied considerably, the calculated phytochrome photostationary state (phi) was only slightly different between the radiation sources. Plant biomass was reduced when peppers were grown under red LEDs in the absence of blue wavelengths compared to plants grown under supplemental blue fluorescent lamps or MH lamps. The addition of far-red radiation resulted in taller plants with greater stem mass than red LEDs alone. There were fewer leaves under red or red plus far-red radiation than with lamps producing blue wavelengths. These results indicate that red LEDs may be suitable, in proper combination with other wavelengths of light, for the culture of plants in tightly controlled environments such as space-based plant culture systems.

Biomass↗
PubMed1998

Characterizations of high-intensity red and blue light-emitting diodes (LEDs) as a light source for plant growth.

Recently developed high-intensity red and blue light-emitting diodes (LEDs), which constitute a potentially improved light source for controlled-environment plant growth applications such as in vitro micropropagation and biologically based advanced life support (ALS) for space missions, were characterized in this study. Blue 2 LED and Red 1 LED consistently yielded the highest and lowest voltage drop readings, respectively, for all the electrical current settings tested (5-50 mA), with Blue 1 LED producing voltage drops falling nearly in the middle of the readings for the first two LEDs. At the standard current setting of 20 mA, Blue 2 LED and Blue 1 LED required 2.5 and 1.6 times more electrical power, respectively, than did Red 1 LED. At the standard current of 20 mA, the average photosynthetic photon flux (PPF) for Red 1 LED, Blue 1 LED, and Blue 2 LED were 180, 145, and 36 micromoles m-2 s-1, respectively. Red 1 LED peaked at 460 micromoles m-2 s-1 at 50 mA, Blue 1 LED at 200 micromoles m-2 s-1 at 40 mA, and Blue 2 LED at 40 micromoles m-2 s-1 at about 25 mA. For all current settings, the electrical conversion efficiency of Red 1 was approximately two times greater than that of Blue 1 LED. The electrical conversion efficiency of Blue 1 and of Red 1 LED peaked in between 10 and 20 mA, at about 13 mA for Blue 1 LED and at about 15 mA for Red 1 LED. The normalized PPF distributions for both Red 1 LED and Blue 1 LED were independent of the various magnitudes of electrical current (20, 30, 40, and 50 mA) that were applied to the LEDs.

Ecological Systems, Closed↗
PubMed2003

The characterization of Ca(2+)-calmodulin independent phosphorylation of myosin light chains by a fragment from myosin light chain kinase.

A constitutively active myosin light chain kinase (MLCK) fragment (MLCKF) was found to phosphorylate myosin light chains (MLC(20)) in a Ca(2+)-CaM independent way more effectively than the intact MLCK. The MLCKF was prepared by tryptic digestion of MLCK. Western blot was used to demonstrate the homogeneity of trypsin-digested MLCKF and intact MLCK. Phosphorylation of MLC(20) was detected by Gly-PAGE and Scoin Image Software, and Mg(2+)-ATPase activity of myosin was measured with spectrophotometry. Our results indicated that Ca(2+)-CaM independent phosphorylation of myosin (CIPM) by MLCKF was more efficient than CIPM by MLCK and less efficient than Ca(2+)-CaM dependent phosphorylation of myosin (CDPM) by MLCK in phosphorylating MLC(20) and stimulating myosin Mg(2+)-ATPase activity; both CIPM by MLCKF and CIPM by MLCK were less influenced by the rise of incubation-temperature, the prolonging of incubation-time, the increase of ionic strength of KCl and less sensitive to MLCK inhibitor ML-9 1-(5-chloronaphthalene-1-sulfonyl) -1H-hexahydro-1,4-diazepine than CDPM by MLCK. The differences were statistically significant ((P)<0.01, or (P)<0.05). The results may be valuable to further investigating the mechanisms of sustained tension characterized by less energy consumption.

Blotting, Western↗
PubMedDate not supplied

[Improvement of the parameters of luminous lighting, diagnostic and therapeutic light devices].

The paper is concerned with certain potentialities of enhancing the intensity of illumination of luminous devices fitted out with light guides used for shadowless illumination, diagnosis and thermal polymerization of filling photocompositions. Optimization of the geometry of the light concentrator is regarded as the main factor of enhancing the intensity of illuminations. Recommendations are given for the use of metallo-halogenic lamps for the same purposes.

Algorithms↗
PubMed1978

Light and lighting in the dental office.

For any task, the eye can respond effectively if there is enough light, if that light is properly distributed, if the appropriate color correction is provided, and if visual contrasts are balanced. Dental offices differ in the types of work performed, the number of people engaged in various tasks, and the types of patients treated. Each office and each room can be planned according to the guidelines herein suggested as long as a rational analysis is applied to the result desired and the tasks being accomplished. The authors suggest that all concerned with office design, the architect, the contractors, and even other illuminating engineers be asked to read this article before integrating their efforts, for the dental office presents some variations not frequently encountered by these people. The need for conservation of our energy sources mandates wise use of all our energy expenditures. There is another resource conservation need that is sometimes overlooked--the effective use of talented people such as the dentist and his staff. The employment of adequate illumination design heeds both demands while giving a rewarding pleasantness and enjoyment of the work environment.

Age Factors↗
PubMed1996

Light-sensitive response in melanophores of Xenopus laevis: II.Rho is involved in light-induced melanin aggregation.

Melanophores of the isolated tail fin of the Xenopus tadpole aggregate melanin granules in response to light. This aggregation was found to be inhibited by subcutaneous injection of exoenzyme C3 of Clostridium botulinum. A 26 kDa protein in homogenate obtained from the Xenopus tail fin was ADP-ribosylated by exoenzyme C3. This reaction was inhibited effectively by a monoclonal antibody, anti-Rho mab A5. raised against the small GTP-binding protein Rho. The extent of ADP-ribosylation depended on light and guanine nucleotide. Incubation under illumination partly reduced ADP-ribosylation and the reduction was restored by addition of guanine nucleotide during incubation. These findings suggest that Rho is involved in the photo-sensitive melanophore response as a signal transducer linking photo-stimuli to melanin granule translocation with Xenopus melanophores.

ADP Ribose Transferases↗
PubMedDate not supplied

Alcohol- and light-induced electro-oculographic responses in age-related macular degeneration & central serous chorioretinopathy. alcohol- and light-induced EOG responses in ARMD & CSC.

The non-photic electro-oculographic (EOG) response induced by alcohol has been proposed as an indicator of retinal pigment epithelial (RPE) integrity, and reported to be abnormal in age-related macular degeneration (ARMD). To evaluate this proposal, we have measured the alcohol-EOG as well as the ISCEV-standard EOG in patients with ARMD (n=11 patients, 4 eyes with drusen, 8 eyes with 'dry' and 7 eyes with 'wet' lesions) and central serous chorioretinopathy (CSC, n=11 patients, 7 eyes with active and 6 eyes with inactive lesions), compared with 29 normal controls. We recorded the alcohol-induced EOG response after a single oral administration of ethanol at 160 mg/kg, followed by an ISCEV-standard EOG. Blood alcohol levels were monitored with a breath analyzer. We found that neither the alcohol-EOG nor the light-induced EOG response showed any difference between either ARMD or CSC patients and normal controls. Nor was there difference among eyes of different ARMD or CSC subgroups. In addition, blood alcohol concentrations near the time of the alcohol-EOG peak showed no obvious relationship with peak/baseline ratios. These data suggest that neither the alcohol- nor the light-induced EOG is a sensitive indicator of these diseases.

Adult↗
PubMed1976

Light-independent stoichometry of galactosyl diglyceride and chlorophyll accretion during light-induced chloroplast membrane synthesis in Euglena.

In photobiotic Euglena gracilis, chlorophyll biosynthesis takes place at a rate which is a direct function of light intensity. There is stoichiometry between chlorophyll accumulation and that of galactosyl diglycerides. This stoichiometry remains relatively invariant, regardless of the wide changes in chlorophyll content brought about in response to controlled variation of light intensity. These findings suggest that the formation of chlorophyll-containing photoreceptor membranes may be paced and stabilized by concurrent synthesis of galactosyl diglycerides.

Animals↗
PubMed1995

Inhibition of 20-kDa myosin light chain exchange by monoclonal antibodies against 17-kDa myosin light chain.

Two anti-17,000 Da myosin light chain (LC17) monoclonal antibodies (MM2 and MM10), which increase the actin-activated Mg(2+)-ATPase activity of dephosphorylated smooth muscle myosin, inhibited the exchange of the 20,000 Da regulatory light chain of myosin (LC20). MM2, which shows higher potency of activation of ATPase activity, inhibited the exchange more extensively than MM10, suggesting that there is a correlation between the activation of ATPase activity and the inhibition of the LC20 exchange. The inhibition of the exchange was observed for intact myosin and heavy meromyosin but not subfragment 1, suggesting that the heavy chain at the head-rod junction is involved in the inhibition of LC20 exchange by anti-LC17 antibodies. Alternatively, the interaction between the two heads of the myosin molecule may influence the inhibition of LC20 exchange. These results suggest that LC20 interacts with both LC17 and the heavy chain, and the interaction between LC20 and LC17 is involved in the activation of actin-activated ATPase activity of smooth muscle myosin.

Actins↗
PubMed1993

Molecular mass determination of low-molecular-mass heparins. Application of wide collection angle measurements of light scattering using a high-performance gel permeation chromatographic system equipped with a low-angle laser light-scattering photometer.

A high-performance gel permeation chromatographic system with on-line low-angle laser light-scattering detection (HPGPC-LALLS) was used to determine molecular masses of low-molecular-mass heparins (LMMHs). Measurements at wide and narrow collection angles were compared and the application of the HPGPC-LALLS method to small molecules, with molecular masses in the range 1000-10,000, was assessed. The molecular mass averages of fractionated heparins and commercially available LMMHs were also determined by ordinary HPGPC analysis using an LMMH molecular-mass calibrant, supplied by the National Institute for Biological Standards and Control for the calibration of columns. The LALLS intensity at the routinely used narrow collection angle (theta col = 1 degree) about doubled at the wide collection angle (theta col = 2 degrees) and the signal-to-noise ratio was improved. The present study thus indicates that wide collection angle measurement of light scattering allows the application of the HPGPC-LALLS method to very small biopolymers of molecular mass < 10,000.

Chromatography, Gel↗
PubMed1991

Comparison of initial yields of DNA-to-protein crosslinks and single-strand breaks induced in cultured human cells by far- and near-ultraviolet light, blue light and X-rays.

The initial yields of DNA-to-protein crosslinks (dpc) caused by ionizing and nonionizing radiations were compared, with emphasis upon values within the biological dose ranges (D0). Induction of dpc in cold (0-0.5 degrees C) human P3 teratocarcinoma cells was measured by using alkaline elution techniques after exposure to monochromatic UVC (254 nm), UVB (313 nm), UVA (365 and 405 nm), and blue light (434 nm). UVC and UVB light induced detectable numbers (about 100 dpc per cell per D0). Monochromatic UVA radiations produced yields about 8 times higher than UVC or UVB (for 365 nm, about 1500 dpc per cell per D0) Similar results at low doses were obtained for measurements of single-strand breaks induced by the different radiations. The action spectra for dpc were closely similar. The biological significance of these relatively high numbers of DNA lesions caused by environmental nonionizing radiation that readily penetrates into human skin is not understood.

Cells, Cultured↗
PubMed1989

Optical probes of intradiskal processes in rod photoreceptors. II: Light-scattering study of ATP-dependent light reactions.

Rod outer segment (ROS) disks, either stacked or freely floating, respond to flash illumination to yield a specific, ATP-dependent, light-scattering signal AL. In broken ROS AL signals occur only when AD signals have preceded them. The degree to which the preceding AD signal has been completed determines the amplitude of the following AL signal. However, in freshly detached ROS from dark-adapted frogs Al signals with maximal size can be obtained without pre-incubation with exogenous ATP. The energized state, which is restored in broken ROS with the help of ATP, appears to prevail in the living retina and must therefore be considered to be "physiological". AL signals require structurally intact disks. Neither peripheral ROS proteins nor connecting filaments between adjacent disks are necessary. Their structural origin is the same as that of the preceding AD signal, i.e. osmotic disk swelling. AL signals consist of a single slow kinetic component (half-life 10 s at room temperature) and multiphase fast kinetic component (70 ms). The slow phase corresponds to a light-stimulated resumption of ATPase activity (this has been dealt with in a previous paper) whereas the fast component reflects an immediate response of the energized disk to the metarhodopsin I to metarhodopsin II transition. The latter effect is the subject of this paper. A variety of experiments, using different ATPase inhibitors, ionophores and membrane-permeable salts, have been carried out; they are all consistent with notion that AL originates in the disk interior and probes the existence of a proton electrochemical potential difference delta mu (H+) across the disk membrane. A model is presented which can explain all given properties of AL satisfactorily. According to this model the photolysis of rhodopsin causes a proton release in the disk lumen. This, in turn, results in osmotic swelling of the disks, provided that the internal buffer sites have been (at least partially) titrated with protons prior to the flash. Such conditions, i.e. a low internal pH, are provided by the proton transport across the disk membrane, which presumably takes place during the course of the preceding AD signal.

Adenosine Triphosphate↗
PubMed2005

Visual outcome and risk factors for light perception and no light perception vision after vitrectomy for diabetic retinopathy.

PURPOSE: To assess the visual outcome following vitrectomy for diabetic retinopathy compared with previous studies; to evaluate risk factors for light perception (LP) and no light perception (NLP) vision after diabetic vitrectomy. DESIGN: Retrospective medical record review. METHODS: The charts of 100 consecutive patients who underwent vitrectomy for proliferative diabetic retinopathy between November 1, 1997, and November 30, 1998, were reviewed. Surgical technique included standard pars plana vitrectomy with combination of delamination and segmentation of gliotic tractional membranes using bimanual techniques. All patients had post-operative follow-up of at least 12 months. Several factors were analyzed for their effect on poor visual outcome (LP and NLP) using Fisher's exact test. RESULTS: Post-vitrectomy, 73% of diabetic patients had stable or improved vision; 16% had worsened but functional vision, defined as worse but still >or= 20/400; 4% had worsened but ambulatory vision, defined as worse but still count fingers (CF) or hand motion (HM); and 7% had poor visual outcome, LP or NLP. Resultant visual acuity was >or=20/40 in 38% of patients, 20/50 to 20/100 in 34%, 20/120 to CF in 18%, HM in 3%, LP in 4%, and NLP in 3%. Risk factors for eyes with LP and NLP vision included pre-operative iris neovascularization (INV), P = .05, post-operative INV, P = .02, post-operative macular ischemia, P = .0001, and post-operative vitreous hemorrhage (VH), P = .02. CONCLUSIONS: Pre-operative and post-operative INV, post-operative macular ischemia, and post-operative VH appear to be risk factors for LP and NLP vision following diabetic vitrectomy, whereas overall improvements in surgical technique and visual outcome continue to be reported.

Adult↗
PubMed2005

Identification and quantification of (polymeric) hindered-amine light stabilizers in polymers using pyrolysis-gas chromatography-mass spectrometry and liquid chromatography-ultraviolet absorbance detection-evaporative light scattering detection.

Direct analysis of polymers containing polymeric hindered amine light stabilizers (HALS) by using pyrolysis coupled to GC-MS is applied successfully for fast and straightforward identification of these HALS additives. Each of the HALS additives shows different pyrolysis gas chromatograms containing characteristic pyrolysis products. As a result, HALS additives with very similar chemical structures, e.g. Chimassorb 944 and Chimassorb 2020, can be distinguished. A HPLC method with both ultraviolet (UV) and evaporative light scattering detection (ELSD) is developed to quantify the various HALS additives in extracts of polymers. The critical factor of the HPLC method is the use of a basic amine, like n-hexylamine, as a solvent additive to facilitate the elution of HALS additives. The various HALS additives can be distinguished according to retention time and peak shape and by using different detection methods. The suitability of the developed methods is demonstrated by the analytical performance of the HPLC method and the identification and determination of the actual content of HALS additives in polyolefines using pyrolysis GC-MS and HPLC. The HPLC method can also be used for the determination of the specific migration of HALS additives from food contact materials.

Amines↗
PubMed1966

Studies of chloroplast development in Euglena. XIV. Sequential interactions of ultraviolet light and photoreactivating light in green colony formation.

Photoreactivation (PR) of green colony-forming ability in Euglena is pH-insensitive from pH 6.0 to 8.0 and temperature-sensitive with a maximum rate at 35 degrees C. There is no PR at 0 degrees C. The rate of PR varies with the growth stage of the cells; PR of exponential phase cells is slower than that of stationary phase cells. The reciprocity rule holds for PR over a 6-fold range of intensity. The shape of PR curves is a function of the UV dose; there appears to be a progressive increase in multiplicity until a limiting multiplicity is reached as indicated by the fact that curves for high doses are superposable. Dark-grown and light-grown cells give the same PR response for comparable UV doses. UV inactivation of cells which have been treated with UV and then with PR light shows that, if the PR dose is sufficiently large, the same UV-inactivation curve is obtained as for nonpretreated control cells. Doses of PR lower than the saturating dose produce UV-inactivation curves, the ultimate slopes of which are parallel to the slope of the control curve, but which show reduced multiplicity. The multiplicity of these curves increases with increasing PR dose. The UV inactivation of green colony-forming ability in Euglena is completely photoreactivable at the doses studied, in contrast with the UV inactivation of colony-forming ability, which occurs at considerably higher UV doses and behaves like most other photoreactivable systems, showing a photoreactivable sector of 0.32.

Cell Division↗
PubMed1997

Measurement of inherent particle properties by dynamic light scattering: introducing electrorotational light scattering.

Common dynamic light scattering (DLS) methods determine the size and zeta-potential of particles by analyzing the motion resulting from thermal noise or electrophoretic force. Dielectric particle spectroscopy by common microscopic electrorotation (ER) measures the frequency dependence of field-induced rotation of single particles to analyze their inherent dielectric structure. We propose a new technique, electrorotational light scattering (ERLS). It measures ER in a particle ensemble by a homodyne DLS setup. ER-induced particle rotation is extracted from the initial decorrelation of the intensity autocorrelation function (ACF) by a simple optical particle model. Human red blood cells were used as test particles, and changes of the characteristic frequency of membrane dispersion induced by the ionophore nystatin were monitored by ERLS. For untreated control cells, a rotation frequency of 2 s-1 was induced at the membrane peak frequency of 150 kHz and a field strength of 12 kV/m. This rotation led to a decorrelation of the ACF about 10 times steeper than that of the field free control. For deduction of ERLS frequency spectra, different criteria are discussed. Particle shape and additional field-induced motions like dielectrophoresis and particle-particle attraction do not significantly influence the criteria. For nystatin-treated cells, recalculation of dielectric cell properties revealed an ionophore-induced decrease in the internal conductivity. Although the absolute rotation speed and the rotation sense are not yet directly accessible, ERLS eliminates the tedious microscopic measurements. It offers computerized, statistically significant measurements of dielectric particle properties that are especially suitable for nonbiological applications, e.g., the study of colloidal particles.

Equipment Design↗