Relevance of sunscreen application method, visible light and sunlight intensity to free-radical protection: A study of ex vivo human skin

With the continued rise in skin cancers worldwide there is a need for effective skin protection against sunlight damage. It was shown previously that sunscreens, which claimed UVA protection (SPF 20+), provided limited protection against UV-induced ascorbate radicals in human skin. Here the results of an electron spin resonance (ESR) investigation to irradiate ex vivo human skin with solar-simulated light are reported. The ascorbate radical signal in the majority of skin samples was directly proportional to the irradiance over relevant sunlight intensities (0.9-2.9 mW cm(-2)). Radical production (substratum-corneum) by UV (wavelengths < 400 nm) and visible components (> 400 nm) was approximately 67% and 33% respectively. Ascorbate radicals were in steady state concentration at low irradiance (approximately 1 mW cm(-2) equivalent to UK sunlight), but at higher irradiance (approximately 3 mW cm(-2)) decreased with time, suggesting ascorbate depletion. Radical protection by a four star-rated sunscreen (with UVA protection) was optimal when applied as a thin film (40-60% at 2 mg cm(-2)) but less so when rubbed into the skin (37% at 4 mg cm(-2) and no significant protection at 2 mg cm(-2)), possibly due to cream filling crevices, which reduced film thickness. This study validates ESR determinations of the ascorbate radical for quantitative protection measurements. Visible light contribution to radical production, and loss of protection when sunscreen is rubbed into skin, has implications for sunscreen design and use for the prevention of free-radical damage.     

Measurement of photoneutrons in the output of 15 MV varian clinac 2100C LINAC using bubble detectors

Photoneutron contamination in the output of Varian Clinac 2100C medical linear accelerator (LINAC) operated at 15 MV photon beam energy has been investigated using bubble detectors. Photoneutrons are produced from the photo-disintegration reaction of photons with materials of the head components with threshold energy of approximately 8 MeV. Measurements were conducted in the patient plane at 100 cm source-to-detector distance on beam axis and at stipulated distances outside the irradiated field for 5×5 cm² to 40×40 cm² field sizes for in-air and 5×5 cm² to 20×20 cm² for water phantom measurements. Neutron dose equivalent of 1.57±0.10 mSv·Gy⁻¹ was measured for 10×10 cm² field size for in-air. For in phantom, neutron dose equivalent of 1.42 mSv·Gy⁻¹ was measured for 10×10 cm² field size on the beam axis at a depth of 1 cm but independent of field size at depth >5 cm.     

Effects of physics change in Monte Carlo code on electron pencil beam dose distributions

Pencil beam algorithms used in computerized electron beam dose planning are usually described using the small angle multiple scattering theory. Alternatively, the pencil beams can be generated by Monte Carlo simulation of electron transport. In a previous work, the 4th version of the Electron Gamma Shower (EGS) Monte Carlo code was used to obtain dose distributions from monoenergetic electron pencil beam, with incident energy between 1 MeV and 50 MeV, interacting at the surface of a large cylindrical homogeneous water phantom. In 2000, a new version of this Monte Carlo code has been made available by the National Research Council of Canada (NRC), which includes various improvements in its electron-transport algorithms. In the present work, we were interested to see if the new physics in this version produces pencil beam dose distributions very different from those calculated with oldest one. The purpose of this study is to quantify as well as to understand these differences. We have compared a series of pencil beam dose distributions scored in cylindrical geometry, for electron energies between 1 MeV and 50 MeV calculated with two versions of the Electron Gamma Shower Monte Carlo Code. Data calculated and compared include isodose distributions, radial dose distributions and fractions of energy deposition. Our results for radial dose distributions show agreement within 10% between doses calculated by the two codes for voxels closer to the pencil beam central axis, while the differences are up to 30% for longer distances. For fractions of energy deposition, the results of the EGS4 are in good agreement (within 2%) with those calculated by EGSnrc at shallow depths for all energies, whereas a slightly worse agreement (15%) is observed at deeper distances. These differences may be mainly attributed to the different multiple scattering for electron transport adopted in these two codes and the inclusion of spin effect, which produces an increase of the effective range of electrons.     

In vivo optical properties of normal canine prostate at 732 nm using motexafin lutetium-mediated photodynamic therapy

The optical properties (absorption [mu(a)], transport scattering [mu('s)] and effective attenuation [mu(eff)] coefficients) of normal canine prostate were measured in vivo using interstitial isotropic detectors. Measurements were made at 732 nm before, during and after motexafin lutetium (MLu)-mediated photodynamic therapy (PDT). They were derived by applying the diffusion theory to the in vivo peak fluence rates measured at several distances (3, 6, 9, 12 and 15 mm) from the central axis of a 2.5 cm cylindrical diffusing fiber (CDF). Mu(a) and mu('s) varied between 0.03-0.58 and 1.0-20 cm(-1), respectively. Mu(a) was proportional to the concentration of MLu.Mu(eff) varied between 0.33 and 4.9 cm(-1) (mean 1.3 +/- 1.1 cm(-1)), corresponding to an optical penetration depth (8 = 1/(mu(eff)) of 0.5-3 cm (mean 1.3 +/- 0.8 cm). The mean light fluence rate at 0.5 cm from the CDF was 126 +/- 48 mW/cm2 (N = 22) when the total power from the fiber was 375 mW (150 mW/cm). This study showed significant inter- and intraprostatic differences in the optical properties, suggesting that a real-time dosimetry measurement and feedback system for monitoring light fluences during treatment should be advocated for future PDT studies. However, no significant changes were observed before, during and after PDT within a single treatment site.     

Scattering of light by disordered spherulites

The scattering of light by a two-dimensional spherulite of radius R is calculated when there is disorder of optic axis orientation with respect to the radius. Special cases are considered when (1) the disorder occurs in the radial direction only, (2) the disorder occurs in the angular direction only, (3) there is combined radial and angular disorder, and (4) the optic axis makes a constant angle with the radius but there is disorder in the twist angle about the axis. In all of these calculations, a correlation function for disorder is defined and the scattering pattern depends on the ratio of the associated correlation distance to the size of the spherulite. With decreasing correlation distance, the azimuthal dependence of the scattering becomes less and there is a change in the variation of scattered intensity with scattering angles in a manner dependent upon the type of disorder.     

Effect of Cloud Cover on UVB Exposure Under Tree Canopies: Will Climate Change Affect UVB Exposure?

The effect of cloud cover on the amount of solar UV radiation that reaches pedestrians under tree cover was evaluated with a three-dimensional canopy radiation transport model. The spatial distribution of UVB irradiance at the base of a regular array of spherical tree crowns was modeled under the full range of sky conditions. The spatial mean relative irradiance (I), and erythemal irradiance of the entire below-canopy domain and the spatial mean relative irradiance and erythemal irradiance in the shaded regions of the domain were determined for solar zenith angles from 15° to 60°. The erythemal UV irradiance under skies with 50% or less cloud cover was not remarkably different from that under clear skies. In the shade, the actual irradiance was greater under partly cloudy than under clear skies. The mean ultraviolet protection factor for tree canopies under skies with 50% or less cloud cover was nearly equivalent to that for clear sky days. Regression equations of spatially averaged I_r . as a function of cloud cover fraction, solar zenith angle and canopy cover were used to predict the variation in erythemal irradiance in different land uses across Baltimore, MD.     

Laser-Induced Breakdown Spectroscopy in open-path configuration for the analysis of distant objects

A review of recent results on stand-off Laser-Induced Breakdown Spectroscopy (LIBS) analysis and applications is presented. Stand-off LIBS was suggested for elemental analysis of materials located in environments where any physical access was not possible but optical access could be envisaged. This review only refers to the use of the open-path LIBS configuration in which the laser beam and the returning plasma light are transmitted through the atmosphere. It does not present the results obtained with a transportation of the laser pulses to the target through an optical fiber. Open-path stand-off LIBS has mainly been used with nanosecond laser pulses for solid sample analysis at distances of tens of meters. Liquid samples have also been analyzed at distances of a few meters. The distances achievable depend on many parameters including the laser characteristics (pulse energy and power, beam divergence, spatial profile) and the optical system used to focus the pulses at a distance. A large variety of laser focusing systems have been employed for stand-off analysis comprising refracting or reflecting telescope. Efficient collection of the plasma light is also needed to obtain analytically useful signals. For stand-off LIBS analysis, a lens or a mirror is required to increase the solid angle over which the plasma light can be collected. The light collection device can be either at an angle from the laser beam path or collinear with the optical axis of the system used to focus the laser pulses on the target surface. These different configurations have been used depending on the application such as rapid sorting of metal samples, identification of material in nuclear industry, process control and monitoring in metallurgical industry, applications in future planetary missions, detection of environmental contamination or cleaning of objects of cultural heritage. Recent stand-off analyses of metal samples have been reported using femtosecond laser pulses to extend LIBS capabilities to very long distances. The high-power densities achievable with these laser pulses can also induce self-guided filaments in the atmosphere which produce LIBS excitation of a sample. The first results obtained with remote filament-induced breakdown spectroscopy predict sample analysis at kilometer ranges.     

Quadrupolelike electrostatic guiding for cold polar molecules

We demonstrate electrostatic guiding of cold heavy water (D(2)O) molecules over a distance of 44.5 cm by using a quadrupolelike electrostatic field, which is generated by the combination of two parallel charged poles and two grounded metal plates. We measure the transverse spatial distribution of the guided D(2)O molecular beam and study the dependence of the relative guiding efficiency and the transverse temperature of the guided molecular beam on the guiding voltage. Our study shows that the maximum guiding efficiency of approximately 50% can be obtained, and our experimental results are in good agreement with ones of theoretical calculation and Monte Carlo simulations, and this guiding scheme has some potential applications in molecule optics, such as molecular-beam splitter, integrated molecular optics, etc.     

High intensity light emitting diode array as an alternative exposure source for the fabrication of electrophoretic microfluidic devices

A commercially available array of light emitting diodes (LEDs), namely a UV Shark series LED high flux array, was evaluated as a light source for photolithographic patterning of SU-8 photoresist for the fabrication of templates suitable to make poly(dimethylsiloxane) (PDMS) microchips for electrophoresis. At a distance of 15 cm from the substrate, a relatively even intensity of 0.76+/-0.05 mW/cm(2) was obtained over an area sufficient for patterning a 10 cm (4 in.) silicon wafer. The exposure source was evaluated using a spiral mask design covering a 10 cm wafer. PDMS replicates of this template made in a 25 microm thick layer of SU-8 3025 showed little variation in width over the surface of the substrate, with a variation of 3.2% RSD (n=36) and a maximum range in widths of 7.8% of the mean channel width. The use of the optional metal reflector available with the LED array provided partial collimation of the light allowing near vertical structures to be produced across the entire wafer, something which was not possible without the reflector. SU-8 masters prepared using the LED array were compared to masters made using an alternative cheap lithographic source, namely a gel crosslinker. The SU-8 features were much narrower with the LED array than the crosslinker due to the multiple light sources in the crosslinker. A PDMS microchip made using a SU-8 template created using the Shark UV LED array was used for the electrophoretic separation of three anionic fluorescent dyes, with efficiencies up to 32,000 plates. Given that the LED array can be purchased and assembled for less than US$ 500, the Shark UV LED array is a promising alternative to more expensive lithographic light sources and will have significant appeal to many researchers wishing to undertake research in microfluidics around the world.     

Molecular beam diagnostics with internal state selection. II. Intensity distribution of a Na/Na2 supersonic beam

The profile of an Na₂ molecular beam is measured with internal state selection via laser induced fluorescence behind narrow collimating slits (slit width 0.2 to 0.5 mm). A flexible connection between the rotatable detector and the laser as well as the photomultiplex is provided by optical fibres. It is found that for pd < 0.5 Torr cm (p is the pressure in the oven, d is the nozzle diameter) the profile is approximately of trapezoidal form independent of the internal energy of the molecules. For pd > 0.5 Torr cm excessive wings appear. The population of the wings increases with pd and with the internal energy of the molecules. It is shown that scattering processes of molecules at the centerline do not cause the wings. The appearances of the wings is correlated with the onset of dimer formation in the beam outside the nozzle. Therefore, it is assumed that a large percentage of those molecules, that are formed in the free jet in intermediate energy levels with excess kinetic energy, diffuse rapidly off the centerline. Some of them are eventually deflected towards the collimating slit. An estimate of the total number of collisions shows that the relaxation of the internal energy along an off-axis path will be less complete than along the centerline. Thus, molecules that are already present in the oven or are formed in the nozzle channel are predominantly found in the narrow central part of the beam profile. A relatively large percentage of those molecules formed in the free jet are found in the wings. The cooling of the internal degrees of freedom is less efficient for the latter.     

Unusual high exposure to ultraviolet-C radiation

UV radiation is known to cause acute and chronic eye and skin damage. The present case report describes a 90 min accidental exposure to UV-C radiation of 26 medical school students. Germicidal lamps were lit due to a malfunctioning of the timer system. Several hours after irradiation exposure, all subjects reported the onset of ocular symptoms, subsequently diagnosed as photokeratitis, and skin damage to the face, scalp and neck. While the ocular symptoms lasted 2-4 days, the sunburn-like condition produced significant erythema followed by deep skin exfoliation. The irradiation was calculated to be approximately 700 mJ cm(-2) absorbed energy, whereas the actual radiation emitted by the lamps was 0.14 mW cm(-2) (the radiometric measurements confirmed these calculi, because the effective irradiance measured from the height of the autopsy table to about 1 m under the UV-C lamp varied from 0.05 to 0.25 mW cm(-2)) but, more likely, the effective irradiance, according to skin phototype and symptoms, was between 50 and 100 mJ cm(-2). The ocular and skin effects produced by such a high irradiation (largely higher than that accepted by the American Conference of Governmental Industrial Hygienists [ACGIH] threshold limit values [TLVs]) appeared reversible in a relatively short time.     

MALDI-MS imaging of features smaller than the size of the laser beam

The feasibility of matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) imaging of features smaller than the laser beam size has been demonstrated. The method involves the complete ablation of the MALDI matrix coating the sample at each sample position and moving the sample target a distance less than the diameter of the laser beam before repeating the process. In the limit of complete sample ablation, acquiring signal from adjacent positions spaced by distances smaller than the sample probe enhances image resolution as the measured analyte signal only arises from the overlap of the laser beam size and the non-ablated sample surface. Image acquisition of features smaller than the laser beam size has been demonstrated with peptide standards deposited on electron microscopy calibration grids and with neuropeptides originating from single cells. The presented MS imaging technique enables approximately 25 microm imaging spatial resolution using commercial MALDI mass spectrometers having irregular laser beam sizes of several hundred micron diameters. With appropriate sampling, the size of the laser beam is not a strict barrier to the attainable MALDI-MS imaging resolution.     

EFFECTS OF LIGHT BEAM SIZE ON FLUENCE DISTRIBUTION AND DEPTH OF NECROSIS IN SUPERFICIALLY APPLIED PHOTODYNAMIC THERAPY OF NORMAL RAT BRAIN

The light fluence distributions of 632.8 nm light incident on the exposed surface of normal rat brain in vivo have been measured using an interstitial, stereotactically-mounted optical fiber detector with isotropic response. The dependence of the relative fluence rate on depth and the spatial distribution of fluence were compared for incident beam diameters of 3 and 5 mm. The fluence rate at depth of 1-6 mm along the optical axis within the brain tissue was approximately 70% greater for a 5 mm diameter beam than for a 3 mm beam, at the same incident fluence rate, although the plots of the relative fluence rate vs depth were parallel over the depth range 1-6 mm. The depths of necrosis resulting from photodynamic treatment of brain tissue using the photosensitizer Photofrin and irradiation by 632 nm light with 3 and 5 mm incident beams were also measured. The observed difference in necrosis depths was consistent with the measured difference in fluence. The importance of beam size in photodynamic treatment with small diameter incident light fields is discussed.     

Effects of UVB irradiance on conidia and germinants of the entomopathogenic Hyphomycete Metarhizium anisopliae: a study of reciprocity and recovery

We tested the effects of irradiances of 920 and 1200 mW m-2 (weighted irradiance) on the conidia and germinants of the entomopathogenic Hyphomycete Metarhizium anisopliae. The conidia were exposed to the two irradiances for 1, 2, 4, 6, 7 or 8 h. Increased exposure decreased relative percent culturability. The inactivation provoked by the irradiance of 1200 mW m-2 was higher than for the 920 mW m-2, with a reduction in the 50% lethal time (LT50) from 6 h 40 min to 4 h 26 min. Reciprocity was not observed when conidia in water suspension and germinants in different stages of the germinative process were exposed to a 17.3 kJ m-2 total dose at both irradiance levels. Although nonreciprocity was observed in all situations, its magnitude varied as a function of metabolic state and/or cell-cycle phase in which the conidia were at the exposure time. The least difference between the effects of the two irradiance levels was observed when nongerminating conidia in suspension were exposed, and the greatest was observed when conidia were exposed during an advanced germination phase. Doses of 6.6 and 17.3 kJ m-2 supplied through the two irradiance levels delayed the germination of the surviving conidia. At both doses, delay was greater during exposure to the higher irradiance. Nonreciprocity was higher for the 17.3 kJ m-2 dose. Nonreciprocity magnitude, in addition to depending on the conidial physiological state, also depended on dose. The results demonstrate the importance of evaluating the impact of the increase in irradiance during the different stages of the fungal life cycle, especially during the stages which are more sensitive to UV, and not simply in dormant conidia.     

Determination of the CH + O2 product channels

The multichannel CH + O2 reaction was studied at room temperature, in a low-pressure fast-flow reactor. CH radical was obtained from the reaction of CHBr3 with potassium atoms. The overall rate constant was determined from the decay of CH with distance, O2 being introduced in excess. The result, after corrections for axial and radial diffusion, is k = (3.6 +/- 0.5) x 10(-11) cm3 molecule-1 s-1. The OH(A2 sigma +) chemiluminescence was observed, confirming the existence of the OH + CO channel. The vibrational population distribution of OH(A2 sigma +) is 32% in the v' = 1 level and 68% in the v' = 0 level (+/- 5%). The relative atomic concentrations were determined by resonance fluorescence in the vacuum ultraviolet. A ratio of 1.4 +/- 0.2 was found between the H atom density (H atoms being produced from the H + CO2 channel and from the HCO dissociation) and the O atom density (O + HCO). Ab initio calculations of the transition structures have been performed, associated with statistical estimations. The estimated branching ratios are: O + HCO, 20%; O + H + CO, 30%; H + CO2, 30%; and CO + OH, 20%.     

Laser Based Optical Emission Studies of Zinc Oxide (ZnO) Plasma

We present the optical emission characteristics of the zinc oxide (ZnO) plasma produced by the first (1,064 nm) and second (532 nm) harmonics of a Q switched Nd: YAG laser. The target material was placed in front of laser beam in air (at atmospheric pressure).The experimentally observed line profiles of neutral zinc (Zn I) have been used to extract the electron temperature using the Boltzmann plot method, whereas, the electron number density has been determined from the Stark broadening. The electron temperature is calculated by varying distance from the target surface along the line of propagation of plasma plume and also by varying the laser irradiance. Beside we have studied the variation of number density as a function of laser irradiance as well as its variation with distance from the target surface. It is observed that electron temperature and electron number density increases as laser energy is increased.     

Short Range Order in Noncrystalline Iron(III) Sulfide

The short range order in noncrystalline iron (III) sulfide has been studied by a radial distribution analysis of the diffuse scattered intensity from X-ray diffraction. Supplementary information was obtained from the Mayn oscillation in the Extended X-ray Absorption Edge Fine Structure (EXAFS) of the Fe? K edge. The average iron-sulfur distance determined was d(FeS) = 2.285(30) Å. The data infer the presence of Fe? Fe interactions at distances between 2.7–2.9 Å.     

Photodynamic parameters in the chick chorioallantoic membrane (CAM) bioassay for topically applied photosensitizers

The relative efficacy of Photofrin-based photodynamic therapy (PDT) has been compared with that of the second-generation photosensitizers 5-aminolevulinic acid (ALA), sulfonated chloro-aluminum phthalocyanine (AlPcSn), benzoporphyrin derivative monoacid ring A (BPD-MA), and lutetium texaphyrin (Lutex). PDT-induced vascular damage in the chick chorioallantoic membrane (CAM) is measured following topical application of the photosensitizers. In order to make meaningful comparisons, care is taken to keep treatment variables the same. These include light dose (5 and 10 J/cm2), power density (33 and 100 mW/cm2), and drug uptake time (30 and 90 min). The drug dose ranges from 0.1 microgram/cm2 for BPD to 5000 micrograms/cm2 for ALA. Results are also analyzed statistically according to CAM vessel type (arterioles versus venules), vessel diameter, and vessel development (embryonic age). For each photosensitizer, the order of importance for the various PDT parameters is found to be unique. The differences between the sensitizers are most likely due to variation in biophysical and biochemical characteristics, biodistribution, and uptake kinetics.     

The molecular structure of perfluoro-thiirane in the presence of perfluoro-cyclobutane: a gas-phase electron diffraction study

The molecular structure of perfluoro-thiirane has been studied using gas-phase electron diffraction data collected on the Balzers KDG2 instrument at UMIST. As samples are unavoidaby contaminated with perfluoro-cyclobutane, it proved possible to obtain structural parameters for this molecule simultaneously. The three-membered sulphur ring has CS = 1.799(3), CC = 1.45(1) Å, with ∠CSC = 47.5(5), ∠SCC = 66.2(3)°, and the fluorine parameters are CF = 1.322(2) Å, ∠SCF = 121.5(6) and ∠CCF = 116.2(5)°, For perfluoro-cyclobutane, values of ∠CCC = 88.8(1) and ∠FCF = 110(1)° are obtained, the fold-angle expressing the non-planarity of the ring being 23(1)°, when refined the CC distance converged to 1.58(1) Å. These results compare favourably with those obtained previously for perfluoro-cyclobutane. The percentages of the latter present in the samples studied at the 100 and 50 cm camera distances averaged about 25%, whereas around 40% was present in experiments at the 25 cm distance, which require longer exposure times.     

Electrochemical and spectroelectrochemical properties of neptunium(VI) ions in nitric acid solution

A benchmark study was carried out to verify whether MCNP is useful in the design stage of a PGNAA facility for large samples up to 1 m length and 0.15 m diameter, using a 2.54 cm diameter thermal neutron beam. For this facility neutron self-shielding and gamma-attenuation correction methods have to be developed. The relative spatial neutron-density distributions within three samples with different macroscopic scattering and absorption cross sections were studied in a comparison between an MCNP simulation and an irradiation experiment using copper wires as neutron monitors. The neutron density in the sample was within statistical agreement between experiment and simulation. Typically the relative spatial neutron-density distributions agreed to within 1%. Therefore, MCNP can be used in design studies for the development of a large sample PGNAA facility as specified. This revised version was published online in July 2006 with corrections to the Cover Date.