Showing papers on "Ultraviolet light published in 1999"
TL;DR: It is proposed that p66shc is part of a signal transduction pathway that regulates stress apoptotic responses and life span in mammals.
Abstract: Gene mutations in invertebrates have been identified that extend life span and enhance resistance to environmental stresses such as ultraviolet light or reactive oxygen species. In mammals, the mechanisms that regulate stress response are poorly understood and no genes are known to increase individual life span. Here we report that targeted mutation of the mouse p66shc gene induces stress resistance and prolongs life span. p66shc is a splice variant of p52shc/p46shc (ref. 2), a cytoplasmic signal transducer involved in the transmission of mitogenic signals from activated receptors to Ras. We show that: (1) p66shc is serine phosphorylated upon treatment with hydrogen peroxide (H2O2) or irradiation with ultraviolet light; (2) ablation of p66shc enhances cellular resistance to apoptosis induced by H2O2 or ultraviolet light; (3) a serine-phosphorylation defective mutant of p66shc cannot restore the normal stress response in p66shc-/- cells; (4) the p53 and p21 stress response is impaired in p66shc-/- cells; (5) p66shc-/- mice have increased resistance to paraquat and a 30% increase in life span. We propose that p66shc is part of a signal transduction pathway that regulates stress apoptotic responses and life span in mammals.
1,666 citations
TL;DR: In this article, the authors report repetitive, monodirectional rotation around a central carbon-carbon double bond in a chiral, helical alkene, with each 360° rotation involving four discrete isomerization steps activated by ultraviolet light or a change in the temperature of the system.
Abstract: Attempts to fabricate mechanical devices on the molecular level1,2 have yielded analogues of rotors3, gears4, switches5, shuttles6,7, turnstiles8 and ratchets9. Molecular motors, however, have not yet been made, even though they are common in biological systems10. Rotary motion as such has been induced in interlocked systems11,12,13 and directly visualized for single molecules14, but the controlled conversion of energy into unidirectional rotary motion has remained difficult to achieve. Here we report repetitive, monodirectional rotation around a central carbon–carbon double bond in a chiral, helical alkene, with each 360° rotation involving four discrete isomerization steps activated by ultraviolet light or a change in the temperature of the system. We find that axial chirality and the presence of two chiral centres are essential for the observed monodirectional behaviour of the molecular motor. Two light-induced cis-trans isomerizations are each associated with a 180° rotation around the carbon–carbon double bond and are each followed by thermally controlled helicity inversions, which effectively block reverse rotation and thus ensure that the four individual steps add up to one full rotation in one direction only. As the energy barriers of the helicity inversion steps can be adjusted by structural modifications, chiral alkenes based on our system may find use as basic components for ‘molecular machinery’ driven by light.
1,494 citations
TL;DR: The nature of p53 modifications, the enzymes that bring them about, and how changes in p53 modification lead to p53 activation are discussed are discussed.
Abstract: Activation of p53 can occur in response to a number of cellular stresses, including DNA damage, hypoxia and nucleotide deprivation. Several forms of DNA damage have been shown to activate p53, including those generated by ionising radiation (IR), radio-mimetic drugs, ultraviolet light (UV) and chemicals such as methyl methane sulfonate (MMS). Under normal conditions, p53 levels are maintained at a low state by virtue of the extremely short-half life of the polypeptide. In addition to this, p53 normally exists in an largely inactive state that is relatively inefficient at binding to DNA and activating transcription. Activation of p53 in response to DNA damage is associated with a rapid increase in its levels and with an increased ability of p53 to bind DNA and mediate transcriptional activation. This then leads to the activation of a number of genes whose products trigger cell-cycle arrest, apoptosis, or DNA repair. Recent work has suggested that this regulation is brought about largely through DNA damage triggering a series of phosphorylation, de-phosphorylation and acetylation events on the p53 polypeptide. Here, we discuss the nature of these modifications, the enzymes that bring them about, and how changes in p53 modification lead to p53 activation.
945 citations
TL;DR: The dramatic protective effects of celecoxib suggests that specific COX‐2 inhibitors may offer a way to safely reduce the risk of skin cancer in humans.
Abstract: Epidemiological and dietary studies suggest that nonsteroidal anti-inflammatory drugs (NSAIDs) reduce the risk of colon cancer, possibly through a mechanism involving inhibition of cyclooxygenase (COX)-2, which is overexpressed in premalignant adenomatous polyps and colon cancer. Because ultraviolet light (UV) can induce COX-2 and nonspecific NSAIDs can decrease UV-induced skin cancer, we evaluated the ability of two compounds, celecoxib (a specific COX-2 inhibitor) and indomethacin (a nonspecific NSAID), to block UV-induced skin tumor development in SKH:HR-1-hrBr hairless mice. Mice fed 150 or 500 ppm celecoxib showed a dose-dependent reduction (60% and 89%, respectively) in tumor yield. Indomethacin (4ppm) reduced tumor yield by 78%. Although both acute and chronic UV exposure increased cell proliferation and edema, neither compound reduced these parameters. In contrast, UV-induced prostaglandin synthesis in the epidermis was effectively blocked by both compounds. UV-induced increases in COX-2 expression in skin were also not altered in any of the treatment groups. Similarly, tumors that constitutively express high levels of COX-2 displayed no reduction by treatment with celecoxib or indomethacin. The dramatic protective effects of celecoxib suggests that specific COX-2 inhibitors may offer a way to safely reduce the risk of skin cancer in humans.
407 citations
TL;DR: In addition, it is estimated that standard gas and particulate absorbers and scatterers accounted for only about 52-62% of the observed UV reductions at Claremont and Riverside as discussed by the authors.
Abstract: Measurements in 1973 and 1987 showed that downward ultraviolet (UV) irradiances within the boundary layer in Los Angeles were up to 50% less than those above the boundary layer. Downward total solar irradiances were reduced by less than 14% in both studies. It is estimated that standard gas and particulate absorbers and scatterers accounted for only about 52–62% of the observed UV reductions at Claremont and Riverside. It is hypothesized that absorption by nitrated and aromatic aerosol components and nitrated aromatic gases caused at least 25–30% of the reductions (with aerosols accounting for about 4/5 of this percent). The remaining reductions are still unaccounted for. Absorbing aerosol components include nitrated aromatics, benzaldehydes, benzoic acids, aromatic polycarboxylic acids, phenols, polycyclic aromatic hydrocarbons, and nitrated inorganics. Many of these species have been observed to date in atmospheric particles, and absorption coefficient data indicate many are strong absorbers at long UV wavelengths. Since aerosols containing nitrated or aromatic aerosols have been observed widely in many areas aside from Los Angeles the finding may account for a portion of UV extinction in those regions as well. In Los Angeles, the finding may be important for predicting smog evolution, since UV reductions associated with high aerosol loadings were estimated to cause a 5–8% decrease in ozone mixing ratios in August 1987. Further laboratory and field studies are needed to quantify better the extent of UV absorption due to nitrated and aromatic aerosols and nitrated aromatic gases.
356 citations
TL;DR: Water-repellent surfaces have been prepared by exposing Si substrates with a hydroxylated surface oxide to fluoroalkyl silane (FAS) vapor as mentioned in this paper.
Abstract: Water-repellent surfaces have been prepared by exposing Si substrates with a hydroxylated surface oxide to fluoroalkyl silane (FAS) vapor. Since this chemical vapor surface modification (CVSM) is based on the chemical reaction between organosilane molecules and hydroxyl groups at the oxide surface, prior to CVSM, the substrate surface was completely hydroxylated by irradiating in air with a 172-nm ultraviolet light until the water contact angle of the surface became almost 0°. Under atmospheric pressure, the substrate was then exposed to vapor of an FAS precursor, that is, one of three types of FAS having different perfluoroalkyl chain lengths [CF3(CF2)nCH2CH2Si(OCH3)3, where n = 0, 5, or 7, referred to as FAS-3, FAS-13, and FAS-17, respectively]. The FAS molecules chemically reacted with the hydroxyl groups on the substrate surface and adsorbed onto it, forming a thin layer of less than 2 nm in thickness. The water repellency of the substrate surface increased with an increase in perfluoroalkyl chain len...
299 citations
TL;DR: A novel function for U2AF35 is revealed, a critical role for the 3′ splice site AG at the earliest steps of spliceosome assembly and the need for a weakened U2 AF35–AG interaction to regulate intron removal is revealed.
Abstract: The protein Sex-lethal (SXL) controls dosage compensation in Drosophila by inhibiting the splicing and translation of male-specific-lethal-2 (msl-2) transcripts1,2,3,4,5,6. Here we report that splicing inhibition of msl-2 requires a binding site for SXL at the polypyrimidine (poly(Y)) tract associated with the 3′ splice site, and an unusually long distance between the poly(Y) tract and the conserved AG dinucleotide at the 3′ end of the intron. Only this combination allows efficient blockage of U2 small nuclear ribonucleoprotein particle binding and displacement of the large subunit of the U2 auxiliary factor (U2AF65) from the poly(Y) tract by SXL. Crosslinking experiments with ultraviolet light indicate that the small subunit of U2AF (U2AF35) contacts the AG dinucleotide only when located in proximity to the poly(Y) tract. This interaction stabilizes U2AF65 binding such that SXL can no longer displace it from the poly(Y) tract. Our results reveal a novel function for U2AF35, a critical role for the 3′ splice site AG at the earliest steps of spliceosome assembly and the need for a weakened U2AF35–AG interaction to regulate intron removal.
294 citations
TL;DR: The results suggest that the induction of the p53 response by certain toxic agents is not triggered by DNA strand breaks but rather, may be linked to inhibition of mRNA synthesis either directly by the poisoning of RNA polymerase II or indirectly byThe induction of elongation-blocking DNA lesions.
Abstract: The mechanisms by which the p53 response is triggered following exposure to DNA-damaging agents have not yet been clearly elucidated. We and others have previously suggested that blockage of RNA polymerase II may be the trigger for induction of the p53 response following exposure to ultraviolet light. Here we report on the correlation between inhibition of mRNA synthesis and the induction of p53, p21 WAF1 and apoptosis in diploid human fibroblasts treated with either UV light, cisplatin or the RNA synthesis inhibitors actinomycin D, DRB, H7 and a-amanitin. Exposure to ionizing radiation or the proteasome inhibitor LLnL, however, induced p53 and p21 WAF1 without aAecting mRNA synthesis. Importantly, induction of p53 by the RNA synthesis or proteasome inhibitors did not correlate with the induction of DNA strand breaks. Furthermore, cisplatin-induced accumulation of active p53 in repair-deficient XP-A cells occurred despite the lack of DNA strand break induction. Our results suggest that the induction of the p53 response by certain toxic agents is not triggered by DNA strand breaks but rather, may be linked to inhibition of mRNA synthesis either directly by the poisoning of RNA polymerase II or indirectly by the induction of elongation-blocking DNA lesions.
286 citations
TL;DR: In this article, photolysis using ultraviolet light and graft polymerization of hydrophilic monomers onto the membrane surface was used to create more hyrophilic and lower fouling membrane surfaces.
273 citations
Patent•
19 Oct 1999TL;DR: In this article, a system for detecting substantially transparent injection molding material is described. But the system is not suitable for the case of fluorescent colorants. And it is not a system that is suitable for injection moldings with fluorescent colorant.
Abstract: A system is provided for detecting a substantially transparent injection molding material. The injection molding material contains a fluorescent colorant, which is invisible when not exposed to ultraviolet light, but becomes visible when exposed to ultraviolet light. A method of detecting the injection molding material involves exposing the injection molding material to ultraviolet light and examining the material during exposure.
261 citations
TL;DR: In this paper, a long-lifetime violet InGaN multi-quantum-well/GaN/AlGaN separate-confinement heterostructure laser diodes (LDs) were successfully fabricated using epitaxially laterally overgrown GaN by reducing a large number of threading dislocations originating from the interface between GaN and sapphire substrate.
Abstract: High-efficiency light-emitting diodes emitting amber, green, blue and ultraviolet light have been obtained through the use of InGaN active layers instead of GaN active layers. The localized energy states caused by In composition fluctuation in the InGaN active layer seem to be related to the high efficiency of the InGaN-based emitting devices. Long-lifetime violet InGaN multi-quantum-well/GaN/AlGaN separate-confinement heterostructure laser diodes (LDs) were successfully fabricated using epitaxially laterally overgrown GaN by reducing a large number of threading dislocations originating from the interface between GaN and sapphire substrate. The threading dislocations shorten the lifetime of the LDs through an increase of the threshold current density. The LDs with cleaved mirror facets showed an output power as high as 30 mW under room-temperature continuous-wave (CW) operation with a stable fundamental transverse mode. The lifetime of the LDs at a constant output power of 5 mW was estimated to be approximately 3000 h under CW operation at an ambient temperature of 50 °C. These results indicate that these LDs already can be used for many real applications, such as digital versatile disks, laser printers, sensors and exciting light sources as a commercial product with a high output power and a high reliability.
TL;DR: A competitive nature of GCG with this enzyme for the L-tyrosine binding at the active site of tyrosinase is revealed, which indicates that the consumption of green tea may help prevent cancers in humans and also reduce several free radicals including peroxynitrite.
TL;DR: In this paper, a single crystalline phase of 1,2-Bis (2,5-dimethyl-3-thienyl) perfluorocyclopentene (1a) was found to undergo photochromism.
Abstract: 1,2-Bis(2,5-dimethyl-3-thienyl)perfluorocyclopentene (1a) was found to undergo photochromism in a single crystalline phase. Upon irradiation with ultraviolet light the colorless crystal turned red with keeping the crystal shape. The red color is due to the closed-ring form 1b. The red color was bleached by irradiation with visible light (λ > 450 nm). The intensity of the red color observed under polarized light dramatically changed by rotating the crystal sample, and the order parameter was as high as 0.84. The high order parameter confirmed that the molecules undergo photochromism in the crystalline lattice. The direction of the electronic transition moment of 1b estimated from the absorption anisotropy at 535 nm agreed with the long axis of 1a packed in the crystal, which was determined by X-ray crystallographic analysis. The movement of each atom of the molecule in the crystal during the cyclization reaction was estimated by comparing the structures of 1a and 1b, both of which were determined by X-ray ...
TL;DR: In this article, a side reaction to produce a photostable byproduct took place when 1,2-bis(2-methyl-5-phenyl-3-thienyl)perfluorocyclopentene was irradiated in deaerated hexane with ultraviolet light.
TL;DR: The therapy met with unprecedented success from the outset, leaving little perceived need to understand underlying science, but in recent years there has been a new found interest in the basic aspects of psoralen photobiology and molecular mechanistic events contributing to therapeutic responses as well as to the development of skin cancers in PUVA patients.
TL;DR: In this paper, an improved electric-field poling technique, which incorporates spontaneous backswitching and leads to uniform short-pitch domain structures, was introduced, and the total volume of backswitched material, and hence the duty cycle of the back-switched domain grating, can be accurately controlled.
Abstract: In nonlinear optics applications employing quasiphase matching, short-pitch domain gratings are generally required for the efficient generation of visible and ultraviolet light. Here we introduce an improved electric-field poling technique, which incorporates spontaneous backswitching and leads to uniform short-pitch domain structures. The total volume of backswitched material, and hence the duty cycle of the backswitched domain grating, can be accurately controlled. First-order single-pass continuous-wave second harmonic generation of 60 mW at 460 nm is achieved at 6.1%/W efficiency in 0.5-mm-thick 4-μm-period backswitch-poled lithium niobate.
TL;DR: In this paper, two new design configurations for efficient photocatalytic reactors have been discussed that not only address the solution to both of the above problems but also have scale-up potential.
Abstract: Semiconductor photocatalysis is a newly emerging technology for the elimination of harmful chemical compounds from air and water. It couples low-energy ultraviolet light with semiconductors acting as photocatalysts overcoming many of the drawbacks that exist for the traditional water treatment methods. Recent literature has established the potential of this powerful technology to destroy toxic pollutants dissolved or dispersed in water. However, to date no viable pilot plant exists using this technology. In this paper, the challenges that need to be addressed for the scale-up of multiphase photocatalytic reactors are discussed. A new reactor design concept is necessary that must be able to address the two most important parameters, namely, uniform light distribution inside the reactor through the absorbing and scattering liquid to the catalyst, and providing high surface areas for catalyst coating per unit of reactor volume. Two new design configurations for efficient photocatalytic reactors have been discussed that not only address the solution to both of the above problems but also have scale-up potential.
TL;DR: The effect of hormic dosage of ultraviolet radiation in delaying the senescence of tomato was investigated in this paper, where mature-green tomato fruit (var. Capello) were irradiated with ultraviolet light (UV-C, 200-280 nm) corresponding to 0, UV-3.7×103 J m−2 and UV-24.4×103J m −2, and were stored at 16°C, under high relative humidity for a period of 35 days.
TL;DR: High-strength, surface-eroding polymers were synthesized from methacrylated anhydride monomers of sebacic acid and 1,6-bis(carboxyphenoxy) hexane to produce highly crosslinked polyanhydride networks that maintained >70% of their tensile modulus with 50% mass degradation.
Abstract: High-strength, surface-eroding polymers were synthesized from methacrylated anhydride monomers of sebacic acid (MSA) and 1,6-bis(carboxyphenoxy) hexane (MCPH). These multifunctional monomers were photopolymerized using ultraviolet light to produce highly crosslinked polyanhydride networks. Through this approach, the crosslinking density of the resulting polymer network was used to control the final mechanical properties, while the degradation time scale was controlled by the chemical composition of the network. The combined hydrophobicity of the polymer backbone with the hydrolytically labile anhydride linkages led to surface-eroding networks, as confirmed by linear cumulative mass loss profiles as a function of degradation time for crosslinked polymer disks. By copolymerizing varying amounts of MSA and MCPH, the degradation rate of the final network was controlled from 2 days to 1 year. The tensile modulus of crosslinked poly(MSA) (1.4 GPa) was nearly an order of magnitude larger than that of linear poly(sebacic acid). In general, the mechanical properties of the crosslinked polyanhydrides networks were within ranges of those reported for cortical and trabecular bone. However, unlike bulk degrading polyesters such as poly(lactic acid), these surface eroding networks maintained >70% of their tensile modulus with 50% mass degradation.
TL;DR: In this paper, the activation of protooncogenes and inactivation of tumor suppressor genes in affected cells are considered as the core events that provide a selective growth advantage and clonal expansion during the multistep process of carcinogenesis.
Abstract: The activation of protooncogenes and inactivation of tumor suppressor genes in affected cells are considered as the core events that provide a selective growth advantage and clonal expansion during the multistep process of carcinogenesis. Somatic mutations, induced by exogenous or endogenous mechanisms, were found to alter the normal functions of the p53 tumor suppressor gene. p53 is the most prominent example of tumor suppressor genes because it is mutated in about half of all human cancer. In contrast to other tumor suppressor genes (like APC and RB ), about 80% of p53 mutations are missense mutations that lead to amino acid substitutions in proteins and can alter the protein conformation and increase the stability of p53 . These changes can also alter the sequence-specific DNA binding and transcription factor activity of p53 . These abnormalities can abrogate p53 dependent pathways involved in important cellular functions like cell-cycle control, DNA repair, differentiation, genomic plasticity and programmed cell death. A number of different carcinogens have been found to cause different characteristic mutations in the p53 gene. For example, exposure to ultraviolet light is correlated with transition mutations at dipyrimidine sites; aflatoxin B 1 exposure is correlated with a G:C to T:A transversion that leads to a serine substitution at residue 249 of p53 in hepatocellular carcinoma; and exposure to cigarette smoke is correlated with G:C to T:A transversions in lung carcinoma. Therefore, measuring the characteristic p53 mutation load or frequency of mutated alleles in nontumorous tissue (before the clonal expansion of mutated cells), can generate hypotheses, e.g., providing a molecular linkage between exposure to a particular carcinogen and cancer, and identifying individuals at increased cancer risk.
TL;DR: SYPRO Ruby protein blot stain provides a sensitive, gentle, fluorescence-based method for detecting proteins on nitrocellulose or polyvinylidene difluoride membranes and is fully compatible with subsequent biochemical applications including colorimetric and chemiluminescent immunoblotting, Edman-based sequencing and mass spectrometry.
TL;DR: Results indicate that the photocurable glues developed here may serve as a biodegradable tissue adhesive glue usable in cardiovascular surgery and endoscopic surgery.
Abstract: This article presents a novel photochemically driven surgical tissue adhesive technology using photoreactive gelatins and a water-soluble difunctional macromer (poly(ethylene glycol) diacrylate: PEGDA).The gelatins were partially derivatized with photoreactive groups, such as ultraviolet light (UV)-reactive benzophenone and visible light-reactive xanthene dye (e.g., fluorescein sodium salt, eosin Y, and rose bengal). A series of the prepared photocurable tissue adhesive glues, consisting of the photoreactive gelatin, PEGDA, and a saline solution with or without ascorbic acid as a reducing agent, were viscous solutions under warming, and their effectiveness was evaluated as hemostasis- and anastomosis-aid in cardiovascular surgery. Regardless of the type of photoreactive groups, the irradiation of the photocurable tissue adhesive glues by UV or visible light within 1 min produced water-swollen gels, which had a high adhesive strength to wet collagen film. These were due to the synergistic action of photoreactive group-initiated photo-cross-linking and photograft polymerization. An increase in the irradiation time resulted in increased gel yield and reduced water swellability. A decrease in the molecular weight of PEGDA and an increase in concentration of both gelatin and PEGDA resulted in reduced water swellability and increased tensile and burst strengths of the resultant gels. In rats whose livers were injured with a trephine in laparotomy, the bleeding spots were coated with the photocurable adhesive glue and irradiated through an optical fiber. The coated solution was immediately converted to a swollen gel. The gel was tightly adhered to the liver tissue presumably by interpenetration, and concomitantly hemostasis was completed. The anastomosis treatment with the photocurable glue in the canine abdominal or thoracic aortas incised with a knife resulted in little bleeding under pulsatile flow after declamping. Histological examination showed that the glues photocured on rat liver surfaces were gradually degraded with time in vivo with infiltration of inflammatory cells and connective tissues without necrotic sign in surrounding tissue. In addition, in the laparoscopic surgery, percutaneous delivery of the glue and its in situ photogelation on rat liver surfaces were demonstrated using a specially designed fiberscope. These results indicate that the photocurable glues developed here may serve as a biodegradable tissue adhesive glue usable in cardiovascular surgery and endoscopic surgery.
TL;DR: Addition of (-)-epigallocatechin gallate (EGCG), an ingredient of green tea extract, to low concentration of green and black tea extracts substantially enhanced the scavenging of H2O2 and quenching of 8-OHdG, suggesting the important role of EGCG in the antioxidant activities of tea extracts.
Patent•
27 Oct 1999
TL;DR: An authentication system combines a source of ultraviolet light (and optionally a scanning mechanism) with apparatus for capturing and recognizing either graphic images or characters or both, where the graphic images and characters have been previously made with fluorescent substances that may be invisible under ordinary visible light, but are rendered detectable by the ultraviolet light as mentioned in this paper.
Abstract: An authentication system combines a source of ultraviolet light (and optionally a scanning mechanism) with apparatus for capturing and recognizing either graphic images or characters or both, where the graphic images and/or characters have been previously made with fluorescent substances that may be invisible under ordinary visible light, but are rendered detectable by the ultraviolet light. As in conventional optical character recognition (OCR), the characters may be conventional alphanumeric characters readable by human readers once they are made visible. The authentication system has a housing enclosing its optical path, a source of UV light, a detector for detecting graphic images or characters, conversion of the detector signal to digital form, a memory storing predetermined indicia, recognition logic, and indicating means. The system may also include a scanning mechanism and optical filters to select predetermined wavelengths of fluorescent light. The detector may be capable of detecting both fluorescent images and normal visible images, and the authentication system may incorporate switching mechanisms to allow multiplexed acquisition of fluorescent and normally visible images. The authentication system can operate in conjunction with a process for marking articles with indicia selected from a predetermined set of graphic images and characters readable by optical character recognition and/or by image comparison. That process can include printing fluorescent graphic images or characters in registration with (or with predetermined offset from) visible images or characters or indicia printed with substances fluorescent at different wavelengths. The recognition logic of the authentication system can include comparison of fluorescent and visible images or two different fluorescent images with each other. Pairs of indicia to be recognized and/or compared may be arranged to constitute a stereogram or other arrangement for first-order authentication by a human observer.
TL;DR: The characteristics of the green fluorescent proteins that make them useful for FRET imaging studies are described and the important characteristics of an imaging system suitable for detecting FRET signals are outlined.
Abstract: Publisher Summary This chapter reviews the theoretical basis of fluorescence resonance energy transfer (FRET) microscopy, with emphasis on its application to the living cell. It describes the characteristics of the green fluorescent proteins (GFPs) that make them useful for FRET imaging studies and outlines the important characteristics of an imaging system suitable for detecting FRET signals. The factors that limit the detection of the weak fluorescent signals associated with FRET include the contribution of autofluorescence, photobleaching, light scattering, and fluctuation in excitation light intensity relative to the image background. These factors can be especially significant for the acquisition of images using ultraviolet light excitation of BFP. The contribution of these factors could be considerably reduced by using two-photon excitation fluorescence imaging microscopy. The chapter uses the expression of genetic vectors encoding protein fusions to GFP and BFP to demonstrate the practical implementation of FRET imaging. It also describes the future direction of FRET imaging technology in biological applications.
TL;DR: UV-B has greater intensity in summer than in winter, at midday than in morning or late afternoon, in places closer to the equator, and at high altitudes, while UVR is absorbed by stratospheric ozone.
Abstract: BACKGROUND Sunlight is subdivided into visible light, ranging from 400 nm (violet) to 700 nm (red); longer infrared, “above red” or .700 nm, also called heat; and shorter ultraviolet radiation (UVR), “below violet” or ,400 nm. UVR is further subdivided into UV-A (320–400 nm), also called black (invisible) light; UV-B (290–320 nm), which is more skin-penetrating; and UV-C (,290 nm). UV-B constitutes ,0.5% of sunlight reaching the earth’s surface, but is responsible for most of the acute and chronic sunrelated damage to normal skin.1 Most UVR is absorbed by stratospheric ozone. UV-B has greater intensity in summer than in winter, at midday than in morning or late afternoon, in places closer to the equator, and at high altitudes. Sand, snow, concrete, and water can reflect up to 85% of sunlight, thus intensifying exposure.1
TL;DR: In this article, an optically addressed ultraviolet light modulator was demonstrated which exploits the optical anisotropy in a ZnO film epitaxially grown on (0112) sapphire.
Abstract: An optically addressed ultraviolet light modulator has been demonstrated which exploits the optical anisotropy in a ZnO film epitaxially grown on (0112) sapphire. This device achieves both high contrast and high speed by exploiting the anisotropic bleaching of the anisotropic absorption and concomitant ultrafast polarization rotation near the lowest exciton resonances produced by femtosecond ultraviolet pulses. The resultant modulation is characterized by a contrast ratio of 70:1, corresponding to a dynamic polarization rotation of 12°, and it decays to a quasiequilibrium value within 100 ps.
TL;DR: In this paper, a pulsed dielectric barrier discharge (DBD) was used to measure the OH radical potential for pollutant oxidation in argon-water vapor gas mixtures.
Abstract: Good understanding of the different phases of the plasma-chemistry involved is essential for the development of nonthermal plasma technologies for pollution control. These techniques are often based on the dissociation of parent gases to produce radicals that, in turn, decompose the toxic compounds. Our research concerns OH radical production in a pulsed dielectric barrier discharge (DBD). OH[A 2Σ+–X 2Π(0,0)] emission in argon-water vapor gas mixtures has been studied. Particular attention has been paid to the influence of water vapor partial pressure on the lifetime and intensity of emitted fluorescence in order to develop a pulsed DBD ultraviolet light source for spectroscopic investigation. This source was used to perform OH(X 2Π) time-resolved average absolute density measurements in other DBD discharges based on resonant absorption spectroscopy. This diagnostic has been validated in argon and air-water vapor mixtures. The temporal behavior of the density OH(X 2Π) radicals after a pulse discharge has been studied in argon and air with and without 500 ppm of trichloroethylene. This simple and inexpensive tool, compared to more sophisticated laser absorption or laser-induced fluorescence measurements for plasma investigation, is very useful for characterizing the OH radical potential for pollutant oxidation.
TL;DR: Data indicate that PCT is an effective alternative to gamma irradiation for prevention of TA-GVHD, and inactivating high levels of pathogenic viruses and bacteria in PC.
01 Sep 1999
TL;DR: The basic mechanisms underlying UV-induced immunosuppression will be discussed and a link between UV- induces apoptosis and apoptosis was recognized.
Abstract: Ultraviolet light (UV) represents one of the most relevant environmental factors influencing humans, especially with regard to its hazardous health effects, which include premature skin aging, skin cancer, and exacerbation of infectious diseases. Several of these effects are mediated by the immunosuppressive properties of UV. UV can compromise the immune system in several ways, e.g., by affecting the function of antigen-presenting cells, inducing the release of cytokines, and modulating the expression of surface molecules. Recently a link between UV-induced immunosuppression and apoptosis was recognized. In the following, the basic mechanisms underlying UV-induced immunosuppression will be discussed.