| 1851. |
- Khromova, A., et al.
(author)
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Report on recent results of the PERCIVAL soft X-ray imager
- 2016
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In: Journal of Instrumentation. - : IOP. - 1748-0221. ; 11:November
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Journal article (peer-reviewed)abstract
- The PERCIVAL (Pixelated Energy Resolving CMOS Imager, Versatile And Large) soft X-ray 2D imaging detector is based on stitched, wafer-scale sensors possessing a thick epi-layer, which together with back-thinning and back-side illumination yields elevated quantum efficiency in the photon energy range of 125–1000 eV. Main application fields of PERCIVAL are foreseen in photon science with FELs and synchrotron radiation. This requires high dynamic range up to 105 ph @ 250 eV paired with single photon sensitivity with high confidence at moderate frame rates in the range of 10–120 Hz. These figures imply the availability of dynamic gain switching on a pixel-by-pixel basis and a highly parallel, low noise analog and digital readout, which has been realized in the PERCIVAL sensor layout. Different aspects of the detector performance have been assessed using prototype sensors with different pixel and ADC types. This work will report on the recent test results performed on the newest chip prototypes with the improved pixel and ADC architecture. For the target frame rates in the 10–120 Hz range an average noise floor of 14e− has been determined, indicating the ability of detecting single photons with energies above 250 eV. Owing to the successfully implemented adaptive 3-stage multiple-gain switching, the integrated charge level exceeds 4 centerdot 106 e− or 57000 X-ray photons at 250 eV per frame at 120 Hz. For all gains the noise level remains below the Poisson limit also in high-flux conditions. Additionally, a short overview over the updates on an oncoming 2 Mpixel (P2M) detector system (expected at the end of 2016) will be reported.
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| 1852. |
- Kim, Beom Jun, et al.
(author)
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Dynamic instabilities induced by asymmetric influence : Prisoners' dilemma game in small-world networks
- 2002
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In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics. - 1063-651X .- 1095-3787. ; 66:2, s. 021907-
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Journal article (peer-reviewed)abstract
- A two-dimensional small-world-type network, subject to spatial prisoners' dilemma dynamics and containing an influential node defined as a special node, with a finite density of directed random links to the other nodes in the network, is numerically investigated. It is shown that the degree of cooperation does not remain at a steady state level but displays a punctuated equilibrium-type behavior manifested by the existence of sudden breakdowns of cooperation. The breakdown of cooperation is linked to an imitation of a successful selfish strategy of the influential node. It is also found that while the breakdown of cooperation occurs suddenly, its recovery requires longer time. This recovery time may, depending on the degree of steady state cooperation, either increase or decrease with an increasing number of long-range connections.
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| 1853. |
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| 1854. |
- Kim, Beom Jun, et al.
(author)
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XY model in small-world networks
- 2001
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In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics. - 1063-651X .- 1095-3787. ; 64:5, s. 056135-
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Journal article (peer-reviewed)abstract
- The phase transition in the XY model on one-dimensional small-world networks is investigated by means of Monte Carlo simulations. It is found that long-range order is present at finite temperatures, even for very small values of the rewiring probability, suggesting a finite-temperature transition for any nonzero rewiring probability. Nature of the phase transition is discussed in comparison with the globally coupled XY model.
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| 1855. |
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| 1856. |
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| 1857. |
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| 1858. |
- Kim, D. K., et al.
(author)
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Characterization and MRI study of surfactant-coated superparamagnetic nanoparticles administered into the rat brain
- 2001
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In: Journal of Magnetism and Magnetic Materials. - 0304-8853 .- 1873-4766. ; 225:02-jan, s. 256-261
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Journal article (peer-reviewed)abstract
- A pre-clinical study has been carried out for the utilization of magnetite (Fe-3 O-4) nanoparticles as a diagnostic tracer for MRI. Surfactant-coated Fe3O4 nanoparticles have been synthesized by a chemical coprecipitation method with a narrow particle size of around 6 nm. Preliminary experiments demonstrated the feasibility of using superparamagnetic Fe-3 O-4 nanoparticles as contrast agents in MR imaging.
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| 1859. |
- Kim, Do Kyung, et al.
(author)
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Energy absorption of superparamagnetic iron oxide nanoparticies by microwave irradiation
- 2005
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In: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 97:10, s. 10J510-
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Journal article (peer-reviewed)abstract
- The main complexity in hyperthermia is generating and controlling the temperature distribution within tumor cells without damaging the normal tissue. Superparamagnetic iron oxide nanoparticles (SPIONs) with a diameter of 11 nm were prepared by controlled coprecipitation and coated with oleic acid to prevent agglomeration and flocculation in the solvent. In situ monitoring of the temperature increment was performed to interpret the microwave absorption rate of the SPION dispersed in appropriate host media (polar or nonpolar solvents) during microwave irradiation. This approach allowed for the prediction of heating mechanisms as a result of the excitation of unpaired electrons of iron, effects of coating agents, particle size, and volume fraction (phi). The conversion efficiency from microwave irradiation to thermal energy was predicted by applying the conservation of energy to a differential volume. The rates of heat loss and energy absorption were obtained by nonlinear fitting of the experimental data.
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| 1860. |
- Kim, D. K., et al.
(author)
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Protective coating of superparamagnetic iron oxide nanoparticles
- 2003
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In: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 15:8, s. 1617-1627
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Journal article (peer-reviewed)abstract
- Magnetic nanoparticles are becoming increasingly important for several biomedical applications. For example, superparamagnetic magnetite nanoparticles with suitable biocompatible coatings are useful in magnetic resonance imaging, tissue engineering, and drug delivery, etc. In this study we report the synthesis of magnetite nanoparticles and the further coating of these particles by several types of protective layers. Thermodynamic modeling of the chemical system has been adopted as a rational approach to establish routes to better synthesis conditions for pure phase magnetite. Quantitative analysis of different reaction equilibria involved in the precipitation of magnetite from aqueous solutions has been used to determine optimum synthesis conditions. Superparamagnetic magnetite nanoparticles (SPION) with diameters of 6 and 12 nm have been prepared by controlled chemical coprecipitation of magnetite phase from aqueous solutions containing suitable salts of Fe2+ and Fe3+ under inert atmosphere. Pure magnetite phase SPION could be observed from X-ray diffraction. Magnetic colloid suspensions containing particles with three different types of coatings (sodium oleate (NaOl), starch, and methoxypoly(ethylene glycol) (MPEG)) have been prepared by using different stabilization methods. SPION coatings were studied by determining the change of the surface charge by electrokinetic sonic amplitude (ESA) measurements, as a function of varying NaOl in the solution, where the amount of NaOl needed to form a stable suspension was determined. For stable suspension, the optimum concentration of sodium oleate (NaOl) chemisorbed at 2.5 g of SPION surface is 5.2 x 10(-7) M NaOl which shows maximum ESA value of 0.034 mPa(.)M/V. SPION coating by starch results in the formation of agglomerate. The agglomeration size of starch-coated SPION can be decreased by introducing H2O2 as an oxidizing agent; the resulting particle size is 42 nm as determined by dynamic light scattering (DLS). For the modification of SPION surfaces with MPEG, the surface was first silanized by 3-aminopropyltrimethoxy silane (APTMS) as a coupling agent with a thickness of two or three molecular layers. AFM image shows that each cluster includes several magnetite single particles with the cluster size around 120 nm. SPION, both coated and uncoated, have been characterized by several techniques. AFM was used to image the MPEG-coated SPION. FTIR study indicated that the different coating agents cover the SPION surface. Magnetic characterization was carried out using SQUID and Mossbauer spectroscopy.
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