Observations by human subjects on radiation- induced light flashes in fast-neutron, X-ray, and positive-pion beams

Exposure of human subjects to fast neutron beam to determine cause of light flashes observed by astronauts on lunar mission

Human visual response to nuclear particle exposures

Experiments with accelerated helium ions were performed in an effort to localize the site of initial radiation interactions in the eye that lead to light flash observations by astronauts during spaceflight. The character and efficiency of helium ion induction of visual sensations depended on the state of dark adaptation of the retina; also, the same events were seen with different efficiencies and details when particle flux density changed. It was concluded that fast particles cause interactions in the retina, particularly in the receptor layer, and thus give rise to the sensations of light flashes, streaks, and supernovae

Observations of cosmic ray induced phosphenes

Phosphene observations by astronauts on flights near and far from earth atmosphere are discussed. It was concluded that phosphenes could be observed by the naked eye. Further investigation is proposed to determine realistic human tolerance levels for extended missions and to evaluate the need to provide special spacecraft shielding

Light flash phenomenon seen by astronauts

The results from experiments conducted to characterize and elucidate light flashes seen by astronauts on Apollo 11, 12, 13, and 14 during transluna or transearth orbit are presented. The data show cosmic nuclei interacting with the visual apparatus causes the light flash phenomenon. The data also suggest that slow protons and helium ions with a stopping power greater than 10 KeV/micron will cause light flashes and streaks in the partially dark adapted eye. The effects of galactic cosmic nuclei interacting with man during long term missions are discussed

Enhancement of T1 and T2 relaxation by paramagnetic silica-coated nanocrystals

We present the first comprehensive investigation on water-soluble nanoparticles embedded into a paramagnetic shell and their properties as an MRI contrast agent. The nanoprobes are constructed with an inorganic core embedded into an ultra-thin silica shell covalently linked to chelated Gd{sup 3+} paramagnetic ions that act as an MRI contrast agent. The chelator contains the molecule DOTA and the inorganic core contains a fluorescent CdSe/ZnS qdots in Au nanoparticles. Optical properties of the cores (fluorescence emission or plasmon position) are not affected by the neither the silica shell nor the presence of the chelated paramagnetic ions. The resulting complex is a MRI/fluorescence probe with a diameter of 8 to 15 nm. This probe is highly soluble in high ionic strength buffers at pH ranging from {approx}4 to 11. In MRI experiments at clinical field strengths of 60 MHz, the QDs probes posses spin-lattice (T{sub 1}) and a spin-spin (T{sub 2}) relaxivities of 1018.6 +/- 19.4 mM{sup -1} s{sup -1} and 2438.1 +/- 46.3 mM{sup -1} s{sup -1} respectively for probes having {approx}8 nm. This increase in relaxivity has been correlated to the number of paramagnetic ions covalently linked to the silica shell, ranging from approximately 45 to over 320. We found that each bound chelated paramagnetic species contributes by over 23 mM{sup -1} s{sup -1} to the total T{sub 1} and by over 54 mM{sup -1} s{sup -1} to the total T{sub 2} relaxivity respectively. The contrast power is modulated by the number of paramagnetic moieties linked to the silica shell and is only limited by the number of chelated paramagnetic species that can be packed on the surface. So far, the sensitivity of our probes is in the 100 nM range for 8-10 nm particles and reaches 10 nM for particles with approximately 15-18 nm in diameter. The sensitivities values in solutions are equivalent of those obtained with small superparamagnetic iron oxide nanoparticles of 7 nm diameter clustered into a 100 nm polymeric shell. A thin paramagnetic silica shell as interface with the bioworld presents several advantages over polymeric coating or dendrimers in terms of in vivo biocompatibility and ease of functionalization with targeting biomolecules. Theoretically, these relaxivity values are high enough to be detected by MRI of a single cell labeled with 10{sup 5} probes. We briefly discuss the importance of probes coated with a paramagnetic silica shell for the detection and treatment of diseases in vivo

Enhancement of T1 and T2 relaxation by paramagnetic silica-coated nanocrystals

We present the first comprehensive investigation on water-soluble nanoparticles embedded into a paramagnetic shell and their properties as an MRI contrast agent. The nanoprobes are constructed with an inorganic core embedded into an ultra-thin silica shell covalently linked to chelated Gd{sup 3+} paramagnetic ions that act as an MRI contrast agent. The chelator contains the molecule DOTA and the inorganic core contains a fluorescent CdSe/ZnS qdots in Au nanoparticles. Optical properties of the cores (fluorescence emission or plasmon position) are not affected by the neither the silica shell nor the presence of the chelated paramagnetic ions. The resulting complex is a MRI/fluorescence probe with a diameter of 8 to 15 nm. This probe is highly soluble in high ionic strength buffers at pH ranging from {approx}4 to 11. In MRI experiments at clinical field strengths of 60 MHz, the QDs probes posses spin-lattice (T{sub 1}) and a spin-spin (T{sub 2}) relaxivities of 1018.6 +/- 19.4 mM{sup -1} s{sup -1} and 2438.1 +/- 46.3 mM{sup -1} s{sup -1} respectively for probes having {approx}8 nm. This increase in relaxivity has been correlated to the number of paramagnetic ions covalently linked to the silica shell, ranging from approximately 45 to over 320. We found that each bound chelated paramagnetic species contributes by over 23 mM{sup -1} s{sup -1} to the total T{sub 1} and by over 54 mM{sup -1} s{sup -1} to the total T{sub 2} relaxivity respectively. The contrast power is modulated by the number of paramagnetic moieties linked to the silica shell and is only limited by the number of chelated paramagnetic species that can be packed on the surface. So far, the sensitivity of our probes is in the 100 nM range for 8-10 nm particles and reaches 10 nM for particles with approximately 15-18 nm in diameter. The sensitivities values in solutions are equivalent of those obtained with small superparamagnetic iron oxide nanoparticles of 7 nm diameter clustered into a 100 nm polymeric shell. A thin paramagnetic silica shell as interface with the bioworld presents several advantages over polymeric coating or dendrimers in terms of in vivo biocompatibility and ease of functionalization with targeting biomolecules. Theoretically, these relaxivity values are high enough to be detected by MRI of a single cell labeled with 10{sup 5} probes. We briefly discuss the importance of probes coated with a paramagnetic silica shell for the detection and treatment of diseases in vivo

Quadrupolar Order Shimming of Permanent Magnets Using Harmonic Corrector Rings

Shimming systems are required to provide sufficient field homogeneity for high resolution NMR. In certain specialized applications, such as rotating-field NMR and portable (ex-situ) NMR, permanent magnet-based shimming systems can provide considerable advantages. We present a simple two-dimensional shimming method based on harmonic corrector rings which can provide arbitrary multipole order shimming corrections. Results demonstrate, for example, that quadrupolar order shimming improves the linewidth by up to an order of magnitude. An additional order of magnitude reduction is in princliple achievable by ultilizing this shimming method for z-gradient correction and higher order xy gradients

Detecting small low emission radiating sources

The article addresses the possibility of robust detection of geometrically small, low emission sources on a significantly stronger background. This problem is important for homeland security. A technique of detecting such sources using Compton type cameras is developed, which is shown on numerical examples to have high sensitivity and specificity and also allows to assign confidence probabilities of the detection. 2D case is considered in detail

Mangiferin Decreases Plasma Free Fatty Acids through Promoting Its Catabolism in Liver by Activation of AMPK

Mangiferin has been shown to have the effect of improving dyslipidemia. Plasma free fatty acids (FFA) are closely associated with blood lipid metabolism as well as many diseases including metabolic syndrome. This study is to investigate whether mangiferin has effects on FFA metabolism in hyperlipidemic rats. Wistar rats were fed a high-fat diet and administered mangiferin simultaneously for 6 weeks. Mangiferin (50, 100, 150 mg/kg BW) decreased dose-dependently FFA and triglycerides (TG) levels in plasma, and their accumulations in liver, but increased the β-hydroxybutyrate levels in both plasma and liver of hyperlipidemic rats. HepG2 cells were treated with oleic acid (OA, 0.2 mmol/L) to simulate the condition of high level of plasma FFA in vitro, and were treated with different concentrations of mangiferin simultaneously for 24 h. We found that mangiferin significantly increased FFA uptake, significantly decreased intracellular FFA and TG accumulations in HepG2 cells. Mangiferin significantly increased AMP-activated protein kinase (AMPK) phosphorylation and its downstream proteins involved in fatty acid translocase (CD36) and carnitine palmitoyltransferase 1 (CPT1), but significantly decreased acyl-CoA: diacylgycerol acyltransferase 2 (DGAT2) expression and acetyl-CoA carboxylase (ACC) activity by increasing its phosphorylation level in both in vivo and in vitro studies. Furthermore, these effects were reversed by Compound C, an AMPK inhibitor in HepG2 cells. For upstream of AMPK, mangiferin increased AMP/ATP ratio, but had no effect on LKB1 phosphorylation. In conclusion, mangiferin decreased plasma FFA levels through promoting FFA uptake and oxidation, inhibiting FFA and TG accumulations by regulating the key enzymes expression in liver through AMPK pathway. Therefore, mangiferin is a possible beneficial natural compound for metabolic syndrome by improving FFA metabolism