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At least 685 records · Page 38Linked to original sources
PubMed1986

Idiopathic sub-retinal neovascular membranes in the macula (hemorrhagic macular choroidopathy of young adults). Clinical report and effectiveness of laser treatment.

Twenty-six patients with idiopathic sub-retinal neovascular membranes (INVMs) located within the posterior pole were examined. Clinical and fluorescein angiographic features of these patients are described. Follow-up ranged from 2 to 96 months (mean 16.5 months). Laser treatment was performed according to the location of the neovascular membrane: 7 out of 9 eyes (77%) increased their final visual acuity or stabilized after Argon blue-green laser photocoagulation (INVMs further than 200 microns from the center of the fovea). Krypton red light laser treatment was performed in 13 eyes with juxta-foveal and sub-foveal INVMs: following treatment 10 eyes (77%) improved by 2 or more Snellen lines or maintained their pre-treatment visual acuity. Because of the fact that the Krypton laser was not yet available, 5 patients were not treated: all of them had sub-foveal (3) or juxta-foveal INVMs (2). The natural history of 4 cases (80%) showed an increase in the final visual acuity in 3 eyes and a steady state in one eye. Pathogenesis and treatment outcome of the disease are finally discussed.

Adolescent↗
PubMed1981

A model approach to laser coagulation of dermal vascular lesions.

The quantitative absorption of light by blood and by human skin is discussed in relation to laser coagulation therapy of dermal vascular lesions. The skin is represented by epidermis and dermis. Both layers are assumed to be planparallel. Absorption and scattering of light by turbid materials was accounted for by the Kubelka theory. Reflection and transmission data of blood and of skin were taken from the literature. This model shows that, firstly, argon-laser coagulation at 488/514.5 nm of dermal vascular lesions is a selective method because vascular absorption exceeds non-vascular dermal absorption by a factor of 10. Secondly, a coagulation depth of about 1 mm is predicted in agreement with the literature. Thirdly, the epidermis absorbs the 488/514.5 nm wavelengths about half as strong as blood and is therefore non-transparent. The consequences of this have been discussed in relations to the final cosmetic result. Fourthly, there is theoretical evidence that better cosmetic results may be expected when coagulation is performed at either 420 nm, 540 nm, or 575 nm. This suggests application of the krypton-laser with lines at 407, 413, and 415 nm (violet), at 531 nm, or at 568 nm. The krypton 647 nm line and the ruby 694 nm line are of little value for this purpose.

Absorption↗
PubMed1991

Hereditary hemorrhagic macular dystrophy.

We treated two brothers who had a hemorrhagic macular lesion in one eye; a similar problem affected the fellow eye of both patients within eight months. Generalized fine granularity of the retinal pigment epithelium and peripheral iris transillumination defects were observed in both siblings. A study of the family suggested that the disorder was dominantly inherited and probably was Sorsby's pseudoinflammatory macular dystrophy. The macular lesions in one brother were treated by argon green laser photocoagulation and in the other brother by krypton red laser photocoagulation. Although the brother treated by krypton red laser photocoagulation attained better final visual function, additional differences in treatment methods also may have contributed to the final outcome.

Adult↗
PubMed1982

Macular photocoagulation. Optimal wavelength selection.

Relative merits of different laser wavelengths for macular photocoagulation are analyzed in terms of light scattering and light absorption in hemoglobin, melanin, and macular xanthophyll. Disadvantages of inner retinal damage in the macula caused by the blue-green argon photocoagulators in standard clinical use are discussed, along with advantages of argon green and krypton yellow light. Results of treatment of subretinal neovascularization in disciform macular degeneration are presented. A repetitive treatment, close follow-up protocol was employed with the objectives of closing neovasculature and preserving central visual field. In 74 successive patients treated with monochromatic argon green radiation, neovasculature was closed in 93%, central visual field loss was reduced or stabilized in 76%, and visual acuity was improved or stabilized in 70%. Results were analyzed in terms of location and size of the neovascular membrane, and it was found that best results were obtained with neovascularization farther than 600 microns from the foveola and smaller than 2 mm2. In 17 patients with neovascular membranes more than 600 microns from the foveola, neovasculature was closed in 100%, central visual field loss was reduced or stabilized in 94%, and visual acuity was improved or stabilized in 88%. Similar results were obtained with monochromatic krypton yellow radiation.

Humans↗
PubMed1983

Photocoagulation for choroidal neovascularization.

Nearly 90% of severe visual loss among patients with senile macular degeneration can be ascribed to the neovascular form of the disease. The Senile Macular Degeneration Study demonstrated that argon laser photocoagulation can reduce the risk of severe visual loss by more than 60% among patients with choroidal new vessel membranes 200 microns or greater from the center of the foveal avascular zone (FAZ). The Krypton Photocoagulation Study, also supported by the National Eye Institute, is evaluating whether krypton red laser photocoagulation can reduce the risk of visual loss in SMD patients with new vessels within 200 microns of the center of the FAZ.

Blindness↗
PubMed1988

Modified grid laser photocoagulation for diabetic macular edema. The effect on the central visual field.

Modified grid laser photocoagulation has been shown to stabilize visual acuity in patients with diabetic macular edema, but the effect on extrafoveal visual function is uncertain. Automated static threshold perimetry was performed on 64 eyes of 36 patients before and after modified grid therapy with the argon green or krypton red laser. Twenty-eight eyes underwent two grid treatments for persistent macular edema. For all eyes tested, average threshold sensitivity in the central 5 degrees dropped 3.44 dB (standard deviation [SD], 3.79 dB) after the first treatment and 6.86 dB (SD, 5.02 dB) cumulatively after the second treatment. Qualitatively, the grayscale displays of the central visual field were darker after treatment, but the scotomata from laser photocoagulation could not be distinguished from those due to macular edema. The foveal threshold showed no significant change. In a subgroup of patients tested, color vision was not significantly improved and nearly all patients exhibited a tritan defect before and after treatment. No difference was detected between the argon and krypton groups. This suggests that with modified grid laser photocoagulation visual acuity and foveal threshold are preserved at the expense of generalized loss of threshold sensitivity across the central 10 degrees of the visual field.

Color Perception↗
PubMed1999

Clinical significance of postlaser indocyanine green angiographic hot spots in age-related macular degeneration.

OBJECTIVE: To report the natural history and clinical significance of indocyanine green (ICG) angiographic hot spots in age-related macular degeneration (ARMD) after laser photocoagulation. DESIGN: Retrospective noncomparative case series. PARTICIPANTS: Two hundred thirty consecutive patients with exudative ARMD who underwent krypton laser treatment between March 1993 and December 1996. INTERVENTION: Krypton laser photocoagulation was performed on all patients. Digital videoangiograms, including both fluorescein angiography and ICG angiography, were obtained at 2 weeks, 4 weeks, 6 weeks, and 3 months postlaser treatment on each patient and repeated if clinical changes were noted. MAIN OUTCOME MEASURES: Detection by ICG of hyperfluorescent spots (hot spots) within the hypofluorescent laser-treated area. RESULTS: Forty patients (18%) developed ICG hot spots 2 weeks after laser treatment. The hot spots disappeared spontaneously without recurrent choroidal neovascular (CNV) membrane in 31 patients (78%). Recurrent CNV was discovered at the hot spot in four patients and away from the hot spot in five patients. CONCLUSION: The postlaser ICG angiographic hot spot is not rare. These spots tend to disappear spontaneously and do not necessarily represent a recurrent CNV. The presence of a hot spot on ICG angiography is not an indication for immediate laser retreatment.

Aged↗
PubMed2001

The intrinsic stability of the noble gas-coordinated transition-metal complex ions.

Density-functional-theory and high-level ab initio calculations have been performed on the [AuXe4]2+ ion and some other hypothetical xenon-, krypton-, and argon-coordinated transition-metal complex cations in the gas phase. Geometry optimization at the QCISD(T) level using a (6s7p4d2f1g) basis set for Au and a (4s4p2d1f) set for Xe predicted Au-Xe bond lengths in good agreement with the AuXe4(2+)(Sb2F11-)2 crystal structure. The ligand-binding energies of the [AuXe4]2+, [AuXe4]3+, and [PtXe4]2+ ions were predicted to be 229, 565, and 233 kcal/mol, respectively, at the CCSD(T) level. It is found that higher-level correlation effects are important to obtain accurate geometry parameters. The calculated results also indicated that various trivalent, tetravalent, and hexavalent transition-metal complexes of xenon or krypton might also be intrinsically stable.

Drug Stability↗
PubMed2003

A gate to organokrypton chemistry: HKrCCH.

An organic molecule containing krypton, HKrCCH, is reported. The preparation of HKrCCH includes 193-nm photolysis of H2C2/Kr solid mixtures at 8 K and subsequent thermal mobilization of hydrogen atoms at >/=30 K. The identification is based on infrared absorption spectroscopy and supported by ab initio calculations which show ionic and covalent contributions to the bonding. We believe that a series of similar organokrypton molecules can be prepared as computationally demonstrated for HKrC4H and HKrC3H3. These results feature a generally novel way for activating chemically the H-CC- group, which can find practical applications of the krypton catalysis.

Journal Article↗
PubMed2005

Generic van der Waals equation of state, modified free volume theory of diffusion, and viscosity of simple liquids.

The shear viscosity formula derived by the density fluctuation theory in previous papers is computed for argon, krypton, and methane by using the self-diffusion coefficients derived in the modified free volume theory with the help of the generic van der Waals equation of state. In the temperature regime near or above the critical temperature, the density dependence of the shear viscosity can be accounted for by ab initio calculations with the self-diffusion coefficients provided by the modified free volume theory if the minimum (critical) free volume is set equal to the molecular volume and the volume overlap parameter (alpha) is taken about unity in the expression for the self-diffusion coefficient. In the subcritical temperature regime, if the density fluctuation range parameter is chosen appropriately at a temperature, then the resulting expression for the shear viscosity can well account for its density and temperature dependence over the ranges of density and temperature experimentally studied. In the sense that once the density fluctuation range is fixed at a temperature, the theory can account for the experimental data at other subcritical temperatures on the basis of the intermolecular force only; the theory is predictive even in the subcritical regime of temperature. Theory is successfully tested in comparison with experimental data for self-diffusion coefficients and shear viscosity for argon, krypton, and methane.

Journal Article↗
PubMed2005

Coordination of ScO+ and YO+ by multiple Ar, Kr, and Xe atoms in noble gas matrixes: a matrix isolation infrared spectroscopic and theoretical study.

The combination of matrix isolation infrared spectroscopic and quantum chemical calculation results provide strong evidence that scandium and yttrium monoxide cations, ScO+ and YO+, coordinate multiple noble gas atoms in forming noble gas complexes. The results showed that ScO+ coordinates five Ar, Kr, or Xe atoms, and YO+ coordinates six Ar or Kr and five Xe atoms in solid noble gas matrixes. Hence, the ScO+ and YO+ cations trapped in solid noble gas matrixes should be regarded as the [ScO(Ng)5]+ (Ng = Ar, Kr, or Xe), [YO(Ng)6]+ (Ng = Ar or Kr) or [YO(Xe)5]+ complexes. Experiments with dilute krypton or xenon in argon or krypton in xenon produced new IR bands, which are due to the stepwise formation of the [ScO(Ar)(5-n)(Kr)n]+, [ScO(Kr)(5-n)(Xe)n]+ (n = 1-5), [YO(Ar)(6-n)(Kr)n]+ (n = 1-6), and [YO(Ar)(6-n)(Xe)n]+ (n = 1-4) complexes.

Journal Article↗
PubMed2000

A stable argon compound

The noble gases have a particularly stable electronic configuration, comprising fully filled s and p valence orbitals. This makes these elements relatively non-reactive, and they exist at room temperature as monatomic gases. Pauling predicted in 1933 that the heavier noble gases, whose valence electrons are screened by core electrons and thus less strongly bound, could form stable molecules. This prediction was verified in 1962 by the preparation of xenon hexafluoroplatinate, XePtF6, the first compound to contain a noble-gas atom. Since then, a range of different compounds containing radon, xenon and krypton have been theoretically anticipated and prepared. Although the lighter noble gases neon, helium and argon are also expected to be reactive under suitable conditions, they remain the last three long-lived elements of the periodic table for which no stable compound is known. Here we report that the photolysis of hydrogen fluoride in a solid argon matrix leads to the formation of argon fluorohydride (HArF), which we have identified by probing the shift in the position of vibrational bands on isotopic substitution using infrared spectroscopy. Extensive ab initio calculations indicate that HArF is intrinsically stable, owing to significant ionic and covalent contributions to its bonding, thus confirming computational predictions that argon should form a stable hydride species with properties similar to those of the analogous xenon and krypton compounds reported before.

Journal Article↗
PubMed2001

History of trace gases in presolar diamonds inferred from ion-implantation experiments.

Diamond grains are the most abundant presolar grains found in primitive meteorites. They formed before the Solar System, and therefore provide a record of nuclear and chemical processes in stars and in the interstellar medium. Their origins are inferred from the unusual isotopic compositions of trace elements-mainly xenon-which suggest that they came from supernovae. But the exact nature of the sources has been enigmatic, as has the method by which noble gases were incorporated into the grains. One observation is that different isotopic components are released at different temperatures when the grains are heated, and it has been suggested that these components have different origins. Here we report results of a laboratory study that shows that ion implantation (previously suggested on other grounds) is a viable mechanism for trapping noble gases. Moreover, we find that ion implantation of a single isotopic composition can produce both low- and high-temperature release peaks from the same grains. We conclude that both isotopically normal and anomalous gases may have been implanted by multiple events separated in space and/or time, with thermal processing producing an apparent enrichment of the anomalous component in the high-temperature release peak. The previous assumption that the low- and high-temperature components were not correlated may therefore have led to an overestimate of the abundance of anomalous argon and krypton, while obscuring an enhancement of the light-in addition to the heavy-krypton isotopes.

Journal Article↗
PubMed2006

Seawater subduction controls the heavy noble gas composition of the mantle.

The relationship between solar volatiles and those now in the Earth's atmosphere and mantle reservoirs provides insight into the processes controlling the acquisition of volatiles during planetary accretion and their subsequent evolution. Whereas the light noble gases (helium and neon) in the Earth's mantle preserve a solar-like isotopic composition, heavy noble gases (argon, krypton and xenon) have an isotopic composition very similar to that of the modern atmosphere, with radiogenic and (in the case of xenon) solar contributions. Mantle noble gases in a magmatic CO2 natural gas field have been previously corrected for shallow atmosphere/groundwater and crustal additions. Here we analyse new data from this field and show that the elemental composition of non-radiogenic heavy noble gases in the mantle is remarkably similar to that of sea water. We challenge the popular concept of a noble gas 'subduction barrier'--the convecting mantle noble gas isotopic and elemental composition is explained by subduction of sediment and seawater-dominated pore fluids. This accounts for approximately 100% of the non-radiogenic argon and krypton and 80% of the xenon. Approximately 50% of the convecting mantle water concentration can then be explained by this mechanism. Enhanced recycling of subducted material to the mantle plume source region then accounts for the lower ratio of radiogenic to non-radiogenic heavy noble gas isotopes and higher water content of plume-derived basalts.

Journal Article↗
PubMed2004

Raman under nitrogen. The high-resolution Raman spectroscopy of crystalline uranocene, thorocene, and ferrocene.

The utility of recording Raman spectroscopy under liquid nitrogen, a technique we call Raman under nitrogen (RUN), is demonstrated for ferrocene, uranocene, and thorocene. Using RUN, low-temperature (liquid nitrogen cooled) Raman spectra for these compounds exhibit higher resolution than previous studies, and new vibrational features are reported. The first Raman spectra of crystalline uranocene at 77 K are reported using excitation from argon (5145 A) and krypton (6764 A) ion lasers. The spectra obtained showed bands corresponding to vibrational transitions at 212, 236, 259, 379, 753, 897, 1500, and 3042 cm(-1), assigned to ring-metal-ring stretching, ring-metal tilting, out-of-plane CCC bending, in-plane CCC bending, ring-breathing, C-H bending, CC stretching and CH stretching, respectively. The assigned vibrational bands are compared to those of uranocene in THF, (COT)2-, and thorocene. All vibrational frequencies of the ligands, except the 259 cm(-1) out-of-plane CCC bending mode, were found to increase upon coordination. A broad, polarizable band centered about approximately 460 cm(-1) was also observed. The 460 cm(-1) band is greatly enhanced relative to the vibrational Raman transitions with excitations from the krypton ion laser, which is indicative of an electronic resonance Raman process as has been shown previously. The electronic resonance Raman band is observed to split into three distinct bands at 450, 461, and 474 cm(-1) with 6764 A excitation. Relativistic density functional theory is used to provide theoretical interpretations of the measured spectra.

Journal Article↗
PubMed2005

High resolution infrared spectra of H2-Kr and D2-Kr van der Waals complexes.

Infrared spectra of weakly bound hydrogen-krypton complexes have been studied at high spectral resolution (0.04 cm(-1)) using a long-path (154 m) low temperature (100 K) absorption cell and a Fourier transform spectrometer. In addition to spectra from the regions of the H(2) and D(2) fundamental vibrational bands in the midinfrared, the results also include the region of the pure rotational S(0)(0) transition of H(2) in the far infrared. A total of 219 measured line positions from these spectra have been fully assigned to specific quantum transitions and form the basis for determining a greatly improved semiempirical three-dimensional intermolecular potential energy surface for hydrogen-krypton in an accompanying paper.

Journal Article↗
PubMed2006

Exploring hyperpolarized 83Kr by remotely detected NMR relaxometry.

For the first time, a hyperpolarized (hp) noble gas with a nuclear electric quadrupole moment is available for high-field nuclear-magnetic-resonance (NMR) spectroscopy and magnetic-resonance imaging. Hp (83)Kr (I=92) is generated by spin-exchange optical pumping and separated from the rubidium vapor used in the pumping process. Optical pumping occurs under the previously unstudied condition of high krypton gas densities. Signal enhancements of more than three orders of magnitude compared to the thermal equilibrium (83)Kr signal at 9.4 T magnetic-field strength are obtained. The spin-lattice relaxation of (83)Kr is caused primarily by quadrupolar couplings during the brief adsorption periods of the krypton atoms on the surrounding container walls and significantly limits the currently obtained spin polarization. Measurements in macroscopic glass containers and in desiccated canine lung tissue at field strengths between 0.05 and 3 T using remotely detected hp (83)Kr NMR spectroscopy reveal that the longitudinal relaxation dramatically accelerates as the magnetic-field strength decreases.

Journal Article↗
PubMed2001

Characterization of formaldehyde by gas chromatography using multiple pulsed-discharge photoionization detectors and a flame ionization detector.

Formaldehyde, water, methanol, butanal, and butanone are characterized by gas chromatography using three pulsed-discharge photoionization detectors (PDPIDs) and a flame ionization detector (FID). One of the PDPIDs is operated in helium mode, and the other two are operated in argon and krypton modes. The FID is included for comparison. The PDPIDs are used to efficiently differentiate between and quantitatively identify formaldehyde and the other three compounds in a sample mixture. This is accomplished by using butanone as the internal standard and correlating the relative responses of the four organic compounds in the helium-, argon-, and krypton-mode PDPIDs with their relative retention times.

Journal Article↗