37 research outputs found
Isolation and Monitoring of the Endohedral Metallofullerenes Y@C82 and Sc3@C82:On-Line Chromatographic Separation with EPR Detection
The direct coupling of high-performance liquid chromatography (HPLC) with on-line electron paramagnetic resonance (EPR) detection is demonstrated for monitoring separations of endohedral metallofullerenes (M@C2n). The HPLC-EPR approach readily permits detection of the paramagnetic species, such as Y@C82 and Sc3@C82, in the presence of the dominant empty-cage fullerenes (C60, C70) and diamagnetic metallofullerenes (e.g., M2@C2n). The results indicate that on-line EPR provides a noninvasive, selective detector for HPLC metallofullerene separations that is readily adaptable to air-sensitive and/or labile compounds. Specifically, the âEPR-activeâ metallofullerenes, Y@C82 and Sc3@C82, are selectively monitored on-line for an initial separation of the metallofullerene fraction from the dominant empty-cage fullerenes utilizing a combination of polystyrene columns. This preparative âcleanupâ procedure is followed by HPLC-EPR separation and monitoring of Y@C82 and Sc3@C82 species using a selective tripodal Ï-acidic-phase column (Trident-Tri-DNP) for the final stages of isolation
Development and application of analytical techniques to chemistry of donor solvent liquefaction. Final report, August 31, 1977-December 31, 1979
The scope of this project was to develop and apply analytical techniques for the characterization of coal conversion products. Solvent-refined coal served as the coal-derived material for the duration of the study. The investigation has focused primarily in the areas of separations and nuclear magnetic resonance spectroscopy. Highlights of the twenty-eight month study are listed and followed by a brief synopsis of the major findings
KLauS â A charge readout and fast discrimination chip for silicon photomultipliers
KLauS is an application specific integrated circuit (ASIC) for the readout of silicon
photomultipliers. The chip has been designed for the application in the analog hadronic calorimeter developed by the CALICE collaboration for the next linear collider experiment . To address the severe power constraints introduced by the highly granular design of the calorimeter, the chip has been designed for low power consumption while maintaining the high dynamic range and timing precision required by the experiment. In addition, a power gating scheme has been implemented to further decrease the average power consumption. For a duty cycle of 1% a value of 25”W per channel is achieved without affecting the readout capabilities of the chip. The chip has been designed in the 0.35”m SiGe technology and provides a low power readout channel for SiPMs with low gain for the input stage of the existing readout chip SPIROC. The analog channel of KLauS will be implemented in a future version of the SPIROC chip
KLauS: an ASIC for silicon photomultiplier readout and its application in a setup for production testing of scintillating tiles
KLauS is an ASIC produced in the AMS 0.35 mm SiGe process to read out the charge
signals from silicon photomultipliers. Developed as an analog front-end for future calorimeters with high granularity as pursued by the AHCAL concept in the CALICE collaboration, the ASIC is designed to measure the charge signal of the sensors in a large dynamic range and with low electronic noise contributions. In order to tune the operation voltage of each sensor individually, an 8-bit DAC to tune the voltage at the input terminal within a range of 2V is implemented. Using an integrated fast comparator with low jitter, the time information can be measured with subnanosecond resolution. The low power consumption of the ASIC can be further decreased using power gating techniques. Future versions of KLauS are under development and will incorporate an ADC with a resolution of up to 12-bits and blocks for digital data transmission. The chip is used in a setup for mass testing and characterization of scintillator tiles for the AHCAL test beam program
Characterization results and first applications of KLauS - an ASIC for SiPM charge and fast discrimination readout
KLauS is an ASIC produced in the AMS 0.35ÎŒm
SiGe technology to read out the charge signals from silicon
photomultipliers. Developed as an analog front end for future
calorimeters with high granularity as pursued by the AHCAL
concept in the CALICE collaboration, the ASIC is supposed to
measure the charge signal of the sensors in a large dynamic
range and with a high precision. In order to compensate bias
and temperature fluctuations of each sensor individually, an 8-bit
DAC to tune the voltage at the input terminal is implemented.
Using an integrated fast comparator with low jitter, the time
information can be measured with sub-nanosecond resolution.
The low power consumption of the ASIC can be further decreased
using power gating techniques. Future versions of KLauS
are under development and will incorporate an ADC with a
resolution of up to 12 bit together with blocks for digital data
transmission. Most recent characterization results for the KLauS
chip are presented as well as results from a KLauS-based test
setup developed for mass characterization of scintillator tiles used
in the AHCAL test beam program
Orientational Dynamics of the Sc3 Trimer in C82: An EPR Study
Electron paramagnetic resonance experiments on endohedral Sc3 in C82 show 22 hyperfine coupling split transitions with unusually large linewidths. Both the nuclear hyperfine coupling and the linewidths are found to be strongly temperature dependent. The data show that the three Sc ions are equivalent, and strongly suggest that they form a trimer which rapidly reorients within the C82 cage. A simple model is proposed which is in good agreement with the data.
Novel Structures from Arc-Vaporized Carbon and Metals: Single-Layer Carbon Nanotubes and Metallofullerenes
Far infrared transmittance of Sc2@C84 and Er2@C82
We have measured the far infrared transmittance of Sc2@C84 and Er2@C82 at 1.5 K between 30 and 200 cm-1. Both materials are observed to have a large primary absorption feature centered at 95 cm-1 with a width of approximately 50 cm-1, as well as a number of secondary absorption features which are different in the two materials. This is the first study of the far infrared properties of metallofullerenes and may help in the determination of the structural and electronic properties of these materials.