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At least 739 records · Page 41Linked to original sources
PubMed1981

Inhibition of induced ornithine decarboxylase activity in Chinese hamster cells by gamma radiation, far ultraviolet light and psoralen plus near-ultraviolet light: a comparative study.

Inhibition by radiation of the transcriptionally controlled induction of ornithine decarboxylase (ODC) was studied in plateau-phase Chinese hamster cells. The effects of gamma radiation, far ultraviolet (254nm, UV-C) light and psoralen plus near-U.V. light (360nm, PUV-A) were compared. Increasing doses of all three treatments caused an exponential decrease in the capacity for ODC induction. This was preceded by a large shoulder region in the case of PUV-A. There was no shoulder for gamma radiation and possibly none or a small one for UV-C. When compared on the basis of cell killing UV-C is 13 times more efficient in inhibiting ODC induction than PUV-A and 69 times more than gamma radiation. The doses required to produce an inactivating hit for inhibition of ODC induction (D0) are 106 krad for gamma radiation, 2400 J m-2 for PUV-A and 14 J m-2 for UV-C. These doses produce about one gamma ray lesion, one psoralen adduct and one pyrimidine dimer in the structural gene of ODC. However, the number of lesions per transcription unit may be up to 10, depending on the contribution to the effect by lesions in transcribed and non-transcribed spacers and introns. Thus, assuming that most of the inhibition is due to effects on RNA synthesis, the various DNA lesions appear to have a similar efficiency in terminating RNA transcription, in spite of their greatly different efficiency in cell killing.

Animals↗
PubMed1997

Modelling light distributions of homogeneous versus discrete absorbers in light irradiated turbid media.

Laser treatment of port wine stains has often been modelled assuming that blood is distributed homogeneously over the dermal volume, instead of enclosed within discrete vessels. The purpose of this paper is to analyse the consequences of this assumption. Due to strong light absorption by blood, fluence rate near the centre of the vessel is much lower than at the periphery. Red blood cells near the centre of the vessel therefore absorb less light than those at the periphery. Effectively, when distributed homogeneously over the dermis, fewer red blood cells would produce the same absorption as the actual number of red blood cells distributed in discrete vessels. We quantified this effect by defining a correction factor for the effective absorbing blood volume of a single vessel. For a dermis with multiple vessels, we used this factor to define an effective homogeneous blood concentration. This was used in Monte Carlo computations of the fluence rate in a homogeneous skin model, and compared with fluence rate distributions using discrete blood vessels with equal dermal blood concentration. For realistic values of skin parameters the homogeneous model with corrected blood concentration accurately represents fluence rates in the model with discrete blood vessels. In conclusion, the correction procedure simplifies the calculation of fluence rate distributions in turbid media with discrete absorbers. This will allow future Monte Carlo computations of, for example, colour perception and optimization of vascular damage by laser treatment of port wine stain models with realistic vessel anatomy.

Erythrocytes↗
PubMed2006

Determination of eye safety filter protection factors associated with retinal thermal hazard and blue light photochemical hazard for intense pulsed light sources.

An assessment is provided of protection factors afforded for retinal thermal hazard and blue light photochemical hazard for a range of filters used with intense pulsed light sources (IPLs). A characteristic IPL spectrum based on black body radiation at 5000 K with a low cut filter at 515 nm was identified as suitable for such estimations. Specific filters assessed included types with idealized transmission properties and also a range of types whose transmission characteristics were measured by means of a Bentham DMc150 spectroradiometer. Predicted behaviour based on these spectra is outlined which describes both the effectiveness of protection and the level of luminous transmittance afforded. The analysis showed it was possible to describe a figure of merit for a particular filter material relating the degree of protection provided and corresponding value of luminous transmittance. This consideration is important for providing users of IPL equipment with safety eyewear with adequate level of visual transmittance.

Computer-Aided Design↗
PubMed1983

Akazara scallop myosins hybridized with DTNB-light chains of skeletal myosin and with regulatory light chains of gizzard myosin.

Two different hybrid myosins were obtained by combining "desensitized" myosin (DM) of Akazara scallop striated adductor with rabbit skeletal DTNB-light chains (DTNB-LC) and with chicken gizzard regulatory light chains (GR-LC). Using the two hybrid myosins, the following were found: (a) DTNB-LC has an inhibitory effect on the Mg-ATPase activities of Akazara DM and acto-DM both in the absence of calcium and in its presence. (b) DTNB-LC also has an enhancing effect on the superprecipitation activity of acto-DM. (c) The Mg-ATPase activities of DM and acto-DM are made sensitive to calcium by GR-LC, regardless of whether GR-LC is phosphorylated or unphosphorylated. (d) However, the Mg-ATPase activity of acto-myosin hybridized with phosphorylated GR-LC is definitely higher than that of acto-myosin hybridized with unphosphorylated GR-LC.

Adenosine Triphosphatases↗
PubMed2002

Can the minimal supersymmetric standard model with light bottom squark and light gluino survive Z-peak constraints?

In the framework of the minimal supersymmetric model we examine the Z-peak constraints on the scenario of one light bottom squark (sbottom) ( approximately 2-5.5 GeV) and light gluino (approximately 12-16 GeV), which has been successfully used to explain the excess of bottom quark production in hadron collisions. Such a scenario is found to be severely constrained by the CERN LEP Z-peak observables, especially by R(b), due to the large effect of gluino-sbottom loops. To account for the R(b) data in this scenario, the other mass eigenstate of sbottom, i.e., the heavier one, must be lighter than 125 (195) GeV at 2sigma(3sigma) level, which, however, is disfavored by CERN LEP II experiments.

Journal Article↗
PubMed2002

Hadronic light-by-light contribution to muon g - 2 in chiral perturbation theory.

We compute the hadronic light-by-light scattering contributions to the muon anomalous magnetic moment, a(LL)(mu)(had), in chiral perturbation theory that are enhanced by large logarithms and a factor of N(C). They depend on a low-energy constant constrained by eta-->mu(+) mu(-) and pi(0)-->e(+)e(-) branching ratios. However, the dependence of a(LL)(mu)(had) on nonlogarithmically enhanced effects cannot be constrained except through the measurement of the anomalous moment itself.

Journal Article↗
PubMed2002

Light gluino, light bottom squark scenario, and LEP predictions.

The scenario of light gluinos and light sbottoms was advocated to explain the discrepancy between the measured and theoretical production of b quarks at the Tevatron. This scenario will have model-independent predictions for Z-->qqgg at the Z0 pole, and e(+)e(-)-->qqgg at LEPII. We show that the data for Z-->qqg*-->qqbb; at LEPI cannot constrain the scenario, because the ratio Gamma(Z-->qqgg)/Gamma(Z-->qqg*-->qqbb)=0.15-0.04 for m(g)=12-16 GeV is smaller than the uncertainty of the data. However, at LEPII the ratio sigma(e(+)e(-)-->qqgg)/sigma(e(+)e(-)-->qqg*-->qqbb) approximately 0.4-0.2 for m(g)=12-16 GeV, which may give an observable excess in qqbb events; especially, the 4b events.

Journal Article↗
PubMed2004

Fast light, slow light, and phase singularities: a connection to generalized weak values.

We demonstrate that Aharonov-Albert-Vaidman weak values have a direct relationship with the response function of a system, and have a much wider range of applicability in both the classical and quantum domains than previously thought. Using this idea, we have built an optical system, based on a birefringent photonic crystal, with an infinite number of weak values. In this system, the propagation speed of a polarized light pulse displays both superluminal and slow light behavior with a sharp transition between the two regimes. We show that this system's response possesses two-dimensional, vortex-antivortex phase singularities. Important consequences for optical signal processing are discussed.

Journal Article↗
PubMed2006

Upper bound on the hadronic light-by-light contribution to the muon g - 2.

There are indications that hadronic loops in some electroweak observables are almost saturated by parton level effects. Taking this as the hypothesis for this work, we propose a genuine parton level estimate of the hadronic light-by-light contribution to the anomalous magnetic moment of the muon, a(LBL)/(mu)(had). Our quark mass definitions and values are motivated in detail, and the simplicity of our approach allows for a transparent error estimate. For infinitely heavy quarks our treatment is exact, while for asymptotically small quark masses a(LBL)/(mu)(had) is overestimated. Interpolating, this suggests quoting an upper bound. We obtain a(LBL)/(mu)(had)<1.59x10;{-9} (95% C.L.).

Journal Article↗
PubMed1981

Function of Light in the Light-induced Geotropic Response in Zea Roots.

The light doses just above the threshold energy value for inducing the geotropic responsiveness in the roots of Zea mays L., cv. Golden Cross Bantam 70, caused a drastic rise in the NADPH level and a drop in the NADP level in 2-millimeter root tips. Some reducing agents lowered the threshold energy value up to about one-third of the control. From these results, we deduce that light may exert two functions in the geotropic response of Zea primary roots, one being the photochemical transformation of a photoreceptor and the other being the induction of a reduction state in the tissue.

Journal Article↗
PubMed1989

Differential exposure of aromatic amino acids in the red-light-absorbing and far-red-light-absorbing forms of 124-kDa oat phytochrome.

The surface topography of aromatic amino acid residues and/or other hydrophobic groups of phytochrome has been investigated by ultraviolet absorption spectra and ultraviolet circular dichroism using phytochrome-cyclodextrin inclusion complexation. Three different types of cyclodextrins (alpha, beta and gamma) with varying hydrophobic cavity sizes, were used. Complexation resulted in significant changes in the circular dichroic signals of both the red-light-absorbing (Pr) and far-red-light-absorbing (Pfr) forms of phytochrome in the ultraviolet region at 222 nm, mid-ultraviolet at 280 nm and 300 nm and in the near-ultraviolet and visible regions at 365 nm and 670 mm, respectively, alpha- and beta-Cyclodextrins were markedly (1.7-4.5-fold) more effective in reducing the mid-ultraviolet CD signal of Pr than that of Pfr, indicating a differential inclusion of the aromatic amino acid residues. gamma-Cyclodextrin did not exhibit any significant differentiation. Secondary structure analysis of the phytochrome-cyclodextrin complexes revealed a considerable increase in the alpha-helical contents of both Pr and Pfr forms. The increase in the Pfr form (17-25%) was about twice that in the Pr form (8-9%), indicating a differential effect of complexation on the conformation of the phytochrome protein. Although the photostationary-state equilibrium of the phytochrome was not affected by the cyclodextrin complexation, the Pr----Pfr phototransformation rate was significantly increased. However, the Pfr----Pr photoreversion was not affected significantly. The results suggest a differential complexation of cyclodextrins with the Pr and Pfr forms of phytochrome as a result of a difference in accessibility of aromatic amino acids in the two forms. A detailed analysis of absorption difference spectra and circular dichroic spectra around 280 nm also revealed evidence for a difference in the exposure of aromatic amino acids.

Amino Acids↗
PubMed2006

Split-face comparison of photodynamic therapy with 5-aminolevulinic acid and intense pulsed light versus intense pulsed light alone for photodamage.

BACKGROUND: Photodynamic therapy (PDT) with a 5-aminolevulinic acid (ALA) photosensitizing agent and a variety of lasers and light sources has been shown to enhance the treatment of photodamaged skin and its associated actinic keratoses (AKs). The efficacy of short-contact, full-face ALA by PDT in photorejuvenation has also been demonstrated. OBJECTIVE: To evaluate short-contact (30 to 60 min) ALA-PDT with intense pulsed light (IPL) activation by comparing ALA-PDT-IPL with IPL alone. METHODS Sixteen patients were enrolled in a split-face study. One side of each patient's face received ALA-PDT-IPL and the other side received IPL alone. Three treatments were given at 1-month intervals, and follow-up visits occurred at 1 and 3 months after the final treatment. RESULTS: Thirteen patients completed the trial. Three months after the final treatment, improvement was greater in the ALA-PDT-IPL side than in IPL-alone side for all facets of photodamage-crow's feet appearance (55 vs 29.5%), tactile skin roughness (55 vs 29.5%), mottled hyperpigmentation (60.3 vs 37.2%), and telangectasias (84.6 vs 53.8%). The clearance rate of AK lesions was also higher (78 vs 53.6%). CONCLUSION: Short-contact ALA-PDT-IPL brings about greater improvement in photodamaged skin and greater clearance of AK lesions than IPL alone, further confirming the usefulness of ALA-PDT in photorejuvenation.

Adult↗
PubMed1992

Ultraviolet light burn: a cutaneous complication of visible light phototherapy of neonatal jaundice.

Visible light phototherapy is an easily administered and effective treatment for neonatal indirect hyperbilirubinemia. Reported cutaneous side effects include transient rashes and the uncommon bronze baby syndrome. A more hazardous side effect is ultraviolet burn. Two premature infants developed phototherapy-induced erythema, one associated with a second-degree burn, after exposure to fluorescent daylight bulbs inadvertently used without Plexiglass shields, thus allowing prolonged ultraviolet A (UVA) exposure. Premature infants, especially during the first two weeks of life, may be significantly susceptible to UVA-induced erythema. Plexiglass shields should always be in place during visible light phototherapy, and nursery staff should be made aware of their purpose.

Burns↗
PubMed1986

Rats on 22.5-hr light:dark cycles have vaginal opening earlier than rats on 26-hr light:dark cycles.

Rats on 22.5-hr light:dark cycles had vaginal opening significantly earlier than rats on 26-hr light:dark cycles. This finding might explain the early menarche in blind girls: Their circadian rhythms, like those of rats on 22.5-hr cycles, might be more rapid than normal. Thus a set number of cycles can occur in a shorter time than usual, allowing puberty to take place early.

Activity Cycles↗
PubMed1991

In vivo activation of human immunodeficiency virus type 1 long terminal repeat by UV type A (UV-A) light plus psoralen and UV-B light in the skin of transgenic mice.

UV irradiation has been shown to activate the human immunodeficiency virus type 1 (HIV-1) long terminal repeat (LTR) in cell culture; however, only limited studies have been described in vivo. UV light has been categorized as UV-A (400 to 315 nm), -B (315 to 280 nm), or -C (less than 280 nm); the longer wavelengths are less harmful but more penetrative. Highly penetrative UV-A radiation constitutes the vast majority of UV sunlight reaching the earth's surface but is normally harmless. UV-B irradiation is more harmful but less prevalent than UV-A. In this report, the HIV-1 LTR-luciferase gene in the skin of transgenic mice was markedly activated when exposed to UV-B irradiation. The LTR in the skin of transgenic mice pretreated topically with a photosensitizing agent (psoralen) was also activated to similar levels when exposed to UV-A light. A 2-h exposure to sunlight activated the LTR in skin treated with psoralen, whereas the LTR in skin not treated with psoralen was activated after 7 h of sunlight exposure. The HIV-1 LTR-beta-galactosidase reporter gene was preferentially activated by UV-B irradiation in a small population of epidermal cells. The transgenic mouse models carrying HIV-1 LTR-luciferase and LTR-beta-galactosidase reporter genes have been used to demonstrate the in vivo UV-induced activation of the LTR and might be used to evaluate other environmental factors or pharmacologic substances that might potentially activate the HIV-1 LTR in vivo.

Animals↗
PubMed1985

Fast and slow artificial diurnal rhythms (light-darkness-light) and the rate of progression of retinal degeneration in dystrophic RCS rats. An electroretinographic study.

The RCS rat strain is characterized by a hereditary progressive degeneration of retina and pigment epithelium. The possible influence of varying artificial diurnal rhythms on the rate of progression of the degeneration was investigated with electroretinography (ERG). Light intensity of the 'day'-periods and the total light exposure were constant in two groups of RCS rats subjected to 2 h light/2 h darkness and to 24 h light/24 h darkness periods respectively. No difference in the rate of degeneration as mirrored by the ERG was seen between the two groups. The ERGs were unrecordable after 7-8 weeks, and the experiments started at birth. No changes in the ERG of controls, genetically identical with the RCS strain except for the retinal dystrophy gene, were seen when they were subjected to the two diurnal rhythms. The results lessen the probability that careful long-term patching of an eye in patients with retinitis pigmentosa or other related hereditary degenerative diseases (in order to diminish the influence of diurnal illumination changes leading to shedding of receptor outer segments) will halt or modify the progression of the disease in man.

Animals↗
PubMed1997

Experimental reproduction of polymorphous light eruption and benign summer light eruption by whole-body UVA irradiation.

The entity 'benign summer light eruption' (BSLE) has been introduced to make a clinical subdivision in the heterogeneous group of polymorphous light eruptions (PLE). Provocation tests for PLE are not always easy to perform and require expensive apparatus. Our purpose was to evaluate a provocation test that could be readily done by a dermatologist with a UVA cabin. Provocation tests are currently required in order to obtain a financial contribution from the social security services in Belgium. In addition, we were interested in determining whether the results of the provocation test would permit us to differentiate between the clinical entities of BSLE and PLE. We studied the efficacy of whole-body UVA irradiation for BSLE and PLE patients. A total of 45 patients was tested, of whom 26 were diagnosed as having BSLE and 19 PLE. In the BSLE group, 24 patients (92%) presented lesions. In the PLE group, 15 patients (79%) had a reaction, but 3 had a positive UVB test. The mean dose to induce lesions was 65.96 J/cm2 for the BSLE group and 52.86 J/cm2 for the PLE group. We conclude that the whole-body UVA test is a high-performance provocation test for both BSLE and PLE patients although it cannot differentiate the two entities from one another.

Adolescent↗