| 1. |
- Bongi, M, et al.
(författare)
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PAMELA : A satellite experiment for antiparticles measurement in cosmic rays
- 2004
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Ingår i: IEEE Transactions on Nuclear Science. - 0018-9499 .- 1558-1578. ; 51:3, s. 854-859
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Tidskriftsartikel (refereegranskat)abstract
- PAMELA is a satellite-borne experiment that will study the antiproton and positron fluxes in cosmic rays in a wide range of energy (from 80 MeV up to 190 GeV for antiprotons and from 50 MeV up to 270 GeV for positrons) and with high statistics, and that will measure the antihelium/helium ratio with a sensitivity of the order of 10(-8). The detector will fly on-board a polar orbiting Resurs DK1 satellite, which will be launched into space by a Soyuz rocket in 2004 from Baikonur cosmodrome in Kazakhstan, for a 3-year-long mission. Particle identification and energy measurements are performed in the PAMELA apparatus using the following subdetectors: a magnetic spectrometer made up of a permanent magnet equipped with double-sided microstrip silicon detectors, an electromagnetic imaging calorimeter composed of layers of tungsten absorber and silicon detectors planes, a transition radiation detector made of straw tubes interleaved with carbon fiber radiators, a plastic scintillator time-of-flight and trigger system, a set of anticounter plastic scintillator detectors, and a neutron detector. The features of the detectors and the main results obtained in beam test sessions are presented.
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| 2. |
- Galembo, A., et al.
(författare)
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Effects of relative phases on pitch and timbre in the piano bass range
- 2001
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Ingår i: Journal of the Acoustical Society of America. - : Acoustical Society of America (ASA). - 0001-4966 .- 1520-8524. ; 110:3, s. 1649-1666
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Tidskriftsartikel (refereegranskat)abstract
- Piano bass tones raise questions related to the perception of multicomponent, inharmonic tones. In this study, the influence of the relative phases among partials on pitch and timbre was investigated for synthesized bass tones with piano-like inharmonicity. Three sets of bass tones (A0 = 27.5 Hz, 100 partials, flat spectral envelope) were generated; harmonic, low inharmonic, and high inharmonic. For each set, five starting phase relations among partials were applied; sine phases, alternate (sine/cosine) phases, random phases, Schroeder phases, and negative Schroeder phases. The pitch and timbre of the tones were influenced markedly by the starting phases. Listening tests showed that listeners are able to discriminate between tones having different starting phase relations, and also that the pitch could be changed by manipulating the relative phases (octave, fifth, major third). A piano-like inharmonicity gives a characteristic randomizing effect of the phase relations over time in tones starting with nonrandom phase relations. A measure of the regularity of the phase differences between adjacent partials is suggested for quantifying this randomization process. The observed phase effects might be of importance in synthesizing, recording, and reproducing piano music.
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| 3. |
- Galembo, A., et al.
(författare)
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Perceptual relevance of inharmonicity and spectral envelope in the piano bass range
- 2004
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Ingår i: Acta Acoustica united with Acustica. - 1610-1928 .- 1861-9959. ; 90:3, s. 528-536
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Tidskriftsartikel (refereegranskat)abstract
- Professionals consider the differences in the timbre of bass tones between large grand pianos and small uprights as significant. By tradition this difference has been attributed mainly to lower inharmonicity in grand pianos, due to longer bass strings. In this study, the importance of the spectral envelope, representing the dynamic balance between high-frequency and low-frequency energy in the spectrum, is contrasted against the importance of the level of inharmonicity. Results from two listening tests indicate that the inharmonicity is less important than the spectrum bandwidth in determining the timbre of piano bass tones.
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| 4. |
- Goldstein, S., et al.
(författare)
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The role of oxoammonium cation in the SOD-Mimic activity of cyclic nitroxides
- 2003
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 125:3, s. 789-795
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Tidskriftsartikel (refereegranskat)abstract
- Cyclic nitroxides (RNO.) mimic the activity of superoxide dismutase (SOD) and demonstrate antioxidant properties in numerous in vitro and in vivo models. Their broad antioxidant activity may involve the participation of their reduced and oxidized forms, that is, hydroxylamine (RNO-H) and oxoammonium cation (RNO+). To examine this possibility we studied the reactions of RNO+ and RNO+ with HO2./O-2(.-) and with several reductants by pulse radiolysis and rapid-mixing stopped-flow techniques. The oxoammonium cations were generated by electrochemical and radiolytic oxidation of 2,2,6,6-tetramethylpiperidinoxyl (TPO) and 3-carbamoyl-2,2,5,5-tetramethylpyrrolidinoxyl (3-CP). The rate constant for the reaction of RNO. with HO2. to form RNO+ was determined to be (1.2 +/- 0.1) x 10(8) for TPO and (1.3 +/- 0.1) x 10(6) M-1 s(-1) for 3-CP. The kinetics results demonstrate that the reaction of RNO. with HO2. proceeds via an inner-sphere electron-transfer mechanism. The rate constant for the reaction of RNO. with O-2(.-) is lower than 1 x 10(3) M-1 s(-1). The rate constant for the reaction of RNO+ with O-2(.-) was determined to be (3.4 +/- 0.2) x 10(9) for TPO+ and (5.0 +/- 0.2) x 10(9) M-1 s(-1) for 3-CP+. Hence, both nitroxides catalyze the dismutation of superoxide through the RNO./RNO+ redox couple, and the dependence of the catalytic rate constant, k(cat), on pH displayed a bell-shaped curve having a maximum around pH 4. The oxoammonium cation oxidized ferrocyanide and HO2- by a one-electron transfer, whereas the oxidation of methanol, formate, and NADH proceeded through a two-electron-transfer reaction. The redox potential of RNO./RNO+ couple was calculated to be 0.75 and 0.89 V for 3-CP and TPO, respectively. The elucidated mechanism provides a clearer insight into the biological antioxidant properties of cyclic nitroxides that should permit design of even more effective antioxidants.
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