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  • 14.60.Cd  (3)
  • Capillary, glass  (2)
  • Lactones  (2)
  • 1
    Digitale Medien
    Digitale Medien
    Systematic studies of positron production in heavy-ion collisions near the Coulomb barrier (1992)
    Springer
    The European physical journal 342 (1992), S. 79-94 
    Details
    ISSN: 1434-601X
    Schlagwort(e): 14.60.Cd ; 25.70.Cd ; 25.70.Ef
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract We present the results obtained from systematic studies of positron creation for a series of heavy-collision systems, with united chargeZ u =Z 1 +Z 2 ranging fromZ u =164 (Pb + Pb) toZ u =184 (U+U) at bombarding energies close to the Coulomb barrier, using the Orangeβ-spectrometer at GSI. For each collision system studied, the dominating continuous distributions due to quasiatomic and nuclear positron emission are determined accurately. This is essential in obtaining the characteristics of the still unexplained monoenergetic positron lines which appear in the energy range between 200 keV and 400 keV. Our results are compared with coupled-channels calculations for quasi-atomic positron creation. The latter describe quite well the global features of the measured spectra, but overestimate systematically their absolute values. From the comparison, a common normalization factor of about 0.75 can be established for the calculated spectra. In particular, the dependence onZ u of the measured emission probabilities was found to follow a power law (∝Z u 195±1), in fair agreement with the theoretical prediction.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01294492
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  • 2
    Digitale Medien
    Digitale Medien
    Investigations of correlated ρ+ e− emission in heavy-ion collisions near the Coulomb barrier (1993)
    Springer
    The European physical journal 346 (1993), S. 153-168 
    Details
    ISSN: 1434-601X
    Schlagwort(e): 14.60.Cd ; 25.70.Cd ; 25.70.Ef
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract We present the results obtained from a series of ρ+ρ−-coincidence measurements in heavy-ion collisions using the double-Orangeβ-spectrometer at GSI. The collision systems U+U, U+Pb, and U+Ta were investigated at bombarding energies close to and slightly above (U+Ta) the Coulomb barrier. For all systems studied, very narrow (FWHM−20 keV) ρ+ρ− lines were observed in the sum-energy spectra, with kinetic energies ranging from ∼555 keV to ∼810 keV, superimposed on a continuous distribution mainly due to uncorrelated ρ+ρ− emission. Particularly in the U+Ta system, a pronounced sum-energy line appears at ∼634 keV, predominantly in deep-inelastic collisions. In some cases (e.g. U+Pb) the line characteristics is consistent with a two-body decay mode of an emitter which moves with the c.m. velocity of the colliding ions. However, other lines, and in particular the 634 keV line (U+Ta), exhibit a rather isotropical opening-angle distribution whereas their energy is unequally shared between positrons and electrons, thus being in clear disagreement with this scenario. In general, the data preclude an emission from the separated (moving) nuclei, and, in the latter cases, provide evidence that the e+e−-pair decay occurs in the vicinity of the Coulomb field of a third heavy (positively charged) partner having only a small transverse velocity (|v|⊥〈0.02c)
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01294631
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  • 3
    Digitale Medien
    Digitale Medien
    Positron lines from subcritical heavy ion-atom collisions (1987)
    Springer
    The European physical journal 328 (1987), S. 129-145 
    Details
    ISSN: 1434-601X
    Schlagwort(e): 14.60.Cd ; 25.70.Cd ; 25.70.Ef
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract Positron lines were observed in heavy ion-atom collisions at bombarding energies close to the Coulomb barrier in subcritical systems with the sum of the atomic numbers of the colliding nucleiZ u =Z 1+Z 2 being smaller thanZ u =172. Each collision system, studied,208Pb +208Pb(Zu=164),238U+181Ta(Zu=165), and238Au(Zu=171), exhibits the emission of two positron lines withZ u -independent c.m. energies of ∼ 258 keV and ∼ 340 keV, and with widths of about 30 keV, superimposed on continuous positron spectra from nuclear pair decay and pair emission induced by the time changing Coulomb field of the collision. The production cross section of thee +-lines rises with a high power ofZ u (ocZ u 22), which is comparable to theZ u 20-dependence for the collision induced positrons.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01290655
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  • 4
    Digitale Medien
    Digitale Medien
    Gas chromatographic resolution of carbohydrate enantiomers. A new chiral phase for pentoses (1981)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 4 (1981), S. 553-556 
    Details
    ISSN: 0935-6304
    Schlagwort(e): Gas chromatography ; Capillary, glass ; Carbohydrate enantiomer separation ; New chiral stationary phases ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: New chiral polymers have been prepared by conversion of cyano groups of polysiloxanes XE-60 and OV-225 into carboxylic groups and subsequent coupling to give the respective S-valine-R-α-phenyl-ethyl amide. In contrast to the corresponding stationary phases with S-α-phenylethyl amide groups, which have been used for the resoultion of trifluoroacetylated hexose derivatives, the new phase show high enantioselectivity for pentose and 6-deoxyhexose derivatives.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jhrc.1240041103
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  • 5
    Digitale Medien
    Digitale Medien
    The use of glass capillary columns for the analysis of polar natural products (1979)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 2 (1979), S. 378-384 
    Details
    ISSN: 0935-6304
    Schlagwort(e): Gas chromatography ; Capillary, glass ; Glass capillaries for low volatile polar natural products analysis ; Application to N-TFA-dipeptide, TMS-ribose, TMS-manno-samin, peptide sequence analysis ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Two published procedures for glass capillary column production are applied to produce capillaries for chromatography of polar natural compounds. Soda lime glass capillaries, after leaching with aqueous HCL, are either treated with colloidal silicic acid or with barium carbonate and coated with either Silar 7CP or SE 52. A test mixture as well as polar carbohydrate and peptide mixtures are chromatographed on the different columns and their chromatographic properties are evaluated. Combined capillary gas chromatography-electron impact and chemical ionization mass spectrometry are used for identification of the peptide sequence.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jhrc.1240020622
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  • 6
    Digitale Medien
    Digitale Medien
    Cyclodextrins as chiral stationary phases in capillary gas chromatography. Part III: Hexakis(3-O-acetyl-2,6-di-O-pentyl)-α-cyclodextrinPart II: see ref. [4]. (1988)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 11 (1988), S. 621-625 
    Details
    ISSN: 0935-6304
    Schlagwort(e): Enantioselective gas chromatography ; α-Cyclodextrin ; Lactones ; O-Alkylglycerols ; Chiral pharmaceuticals ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The properties of hexakis(3-O-acetyl-2,6-di-O-pentyl)-α-cyclodextrin as a chiral stationary phase for capillary gas chromatography are described. For the first time the enantiomers of a series of different lactones are separated and their order of elution is assigned. Moreover, the enantiomers of trifluoroacetylated aldols and amino alcohols, the cyclic carbonates of 1,2-diols, 1,3-diols, O-alkylated glycerols, and some chiral pharmaceuticals are also separated on the new chiral phase. The modified α-cyclodextrin is stable above 200°C.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jhrc.1240110903
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  • 7
    Digitale Medien
    Digitale Medien
    Cyclodextrins as chiral stationary phases in capillary gas chromatography. Part V: Octakis(3-O-butyryl-2,6-di-O-pentyl)-γ-cyclodextrinPart IV: HRC 12 (1989) 35. (1989)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 12 (1989), S. 732-738 
    Details
    ISSN: 0935-6304
    Schlagwort(e): Enantioselective gas chromatography ; Cyclodextrin ; Amino acids ; Hydroxy acids ; Terpene alcohols ; Terpene ketones ; Lactones ; Cyclopropane derivatives ; Cyclic ethers ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: γ-Cyclodextrin with 3-O-butyryl and 2,6-di-O-pentyl residues is a very versatile chiral stationary phase for enantiomer separation. Most of the common and many uncommon amino acids can be separated as well as α- and β-hydroxy acids, chiral alcohols, diols, triols, ketones, bicyclic, and tricyclic acetals, amines, alkyl halides, lactones, and functionalized cyclopropane derivatives.
    Zusätzliches Material: 13 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jhrc.1240121108
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