ALBERT — All Library Books, journals and Electronic Records Telegrafenberg

1

Electronic Resource

Climatological Ertel’s potential-vorticity flux and mean meridional circulation in the extratropical troposphere – lower stratosphere (1998)

Bartels, J. ; Peters, D. ; Schmitz, G.

Springer

Annales geophysicae 16 (1998), S. 250-265

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ISSN: 0992-7689

Keywords: Meteorology and atmospheric dynamics ; Climatology ; General circulation ; Middle atmosphere

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences , Physics

Notes: Abstract We investigated to what extent the isentropic, non-geostrophic formulation of zonally averaged circulation derived for stratospheric conditions is applicable to climatological transport in the extratropical troposphere and lower stratosphere. The study is based on 10 years of daily data of ECMWF analysis and on the ECHAM3 climate model of the German Climate Computing Centre. The main result is a scalar isentropic mixing coefficient, Kyy, and a mean meridional transport circulation consistently derived from the same data base. For both data sources, isentropic mean meridional circulation is derived from horizontal mass flow rate for 4 representative months. Alternatively, a mean meridional circulation is calculated from total diabatic heating rates of the ECHAM3 model. It is shown that only the latter is in good agreement with the ECMWF mean meridional circulation. Isentropic analysis also comprises the seasonal cycle of the climatological meridional gradient and flux of Ertel’s potential vorticity (PV). Application of Tung’s flux-gradient relation yields that for all seasons Kyy is positive in height-latitude regions where statistical significance is reached. Large Kyy values, marking regions of more efficient mixing, have been found in the subtropical vertical band of weak westerly wind and in mid-latitudes in regions of upward-propagating baroclinic wave activity in the middle and upper troposphere. Based on the ECMWF data and results of baroclinic-wave behaviour, strong indications are presented that positive zonally averaged PV flux polewards of the jet core in the NH is strengthened by stationary waves and nonlinear effects. Reduced eddy transport is apparent in winter and spring slightly below the subtropical tropopause jet. The seasonal cycle of Kyy from ECHAM3 data is to a great extent in agreement with the result based on ECMWF analysis. In the model, reduced interannual variability enlarges the height-latitude range where sign of Kyy is significant.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s00585-998-0250-3

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2

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Quark-antiquark-gluon jets in dis diffractive dissociation (1999)

Bartels, J. ; Jung, H. ; Wüsthoff, M.

Springer

The European physical journal 11 (1999), S. 111-125

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ISSN: 1434-6052

Source: Springer Online Journal Archives 1860-2000

Topics: Physics

Notes: Abstract. We study the diffractive production of $q\bar{q}g$ jets with large transverse momenta in the region of large diffractive masses (small $\beta$ ). Cross sections for transverse and longitudinal photons are obtained in the leading log $1/x_{{\mathbb{P}}}$ and log $1/\beta$ approximation, keeping all powers in log $k_t^2/Q^2$ . We perform a numerical study and illustrate the angular distribution of the three jets. We also estimate the integrated diffractive three jet cross section and compare with the dijet cross section obtained before.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s100529900081

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3

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Spin dependence of deep inelastic diffraction (1999)

Bartels, J. ; Gehrmann, T. ; Ryskin, M.G.

Springer

The European physical journal 11 (1999), S. 325-333

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ISSN: 1434-6052

Source: Springer Online Journal Archives 1860-2000

Topics: Physics

Notes: Abstract. Using a perturbative model for diffractive interactions, we derive an expression for the polarized diffractive structure function $g_1^D$ in the high energy limit. This structure function is given by the interference of diffractive amplitudes with polarized and unpolarized exchanges. For the polarized exchange we consider both two-gluon and quark-antiquark amplitudes. The polarized diffractive amplitude receives sizable contributions from non-strongly ordered regions in phase space, resulting in a double logarithmic enhancement at small x. The resummation of these double logarithmic terms is outlined. We also discuss the transition from our perturbative expression to the nonperturbative region. A first numerical estimate indicates that the perturbative contribution to the spin asymmetry is substantially larger than the nonperturbative one.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s100529900219

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4

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Incorporation of the transition metal Hf into GaN (1999)

Bartels, J. ; Freitag, K. ; Marques, J.G. ; [et al.]

Springer

Hyperfine interactions 120-121 (1999), S. 397-402

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ISSN: 1572-9540

Source: Springer Online Journal Archives 1860-2000

Topics: Physics

Notes: Abstract The perturbed angular correlation (PAC) technique was applied to study the incorporation of the transition metal Hf into GaN after implantation. To this end the PAC probe 181Hf(181Ta) was implanted into epitaxial Wurtzite GaN layers (1.3 μm on sapphire) with an energy of 160 keV and doses of 7× 1012 at/cm2. PAC spectra were recorded during an isochronal annealing programme, using rapid thermal annealing (RTA) and furnace annealing, in the 300–1000ºC temperature range. After implantation the spectra show a damped oscillation corresponding to a quadrupole interaction frequency (QIF) of νQ= 340 MHz for 30% of the probe nuclei. Annealing up to 600ºC reduces the damping of this frequency without an increase of the probe atom fraction fs in these sites. Above 600ºC fs grows rapidly until after the 900ºC RTA step more than 80% of the Hf probes experience a well defined QIF due to the incorporation of Hf on undisturbed sites of the hexagonal GaN wurtzite lattice. An interaction frequency of νQ= 340 MHz is derived. RTA and furnace annealing yield similar results for annealing up to 800ºC, where the undisturbed fraction reaches about 60%. Then RTA at higher temperatures increases this fraction, while furnace annealing leads to a decrease down to 22% after annealing at 1000ºC. To our knowledge this is the first time that a transition metal probe like Hf is incorporated to such a large extent into a semiconductor lattice.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1017080902893

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5

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Cavities in silicon investigated with the PAC-probe 111In (1999)

Bartels, J. ; Noll, C. ; Vianden, R.

Springer

Hyperfine interactions 120-121 (1999), S. 353-358

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ISSN: 1572-9540

Source: Springer Online Journal Archives 1860-2000

Topics: Physics

Notes: Abstract The perturbed angular correlation technique (PAC) was used to study the creation and development of He-induced cavities. In order to investigate the interaction of Indium atoms with cavities in Silicon the Bonn isotope separator was used to implant overlapping profiles of He (10 keV) and radioactive 111In (160 keV) into undoped FZ-silicon. To get insight into the cavity formation mechanism samples were prepared with various He-doses (0.6, 2 and 6× 1016 ions/cm2). The samples were measured directly after implantation and after different annealing steps (thold= 10 min, T = 500–1100ºC). Further, different implantation and annealing sequences were used. At higher He doses (2 and 6× 1016 ions/cm2) we find a large fraction of 111In probe atoms subjected to an electric field gradient (EFG) corresponding to a quadrupole interaction frequency (QIF) of νQ= 411(6) MHz with η= 0.25(4). The corresponding defect configuration is formed most effectively after He implantation into annealed, 111In doped Si. This and the affinity of In to vacancies leads us to the assumption that, similarly to the situation in metals, the Indium atoms act as nucleation centres for vacancy clusters (cavities) and are situated on the inner walls of the cavities.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1017016616097

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6

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The triple regge limit of diffractive dissociation in deep inelastic scattering (1995)

Bartels, J. ; Wüsthoff, M.

Springer

The European physical journal 66 (1995), S. 157-179

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ISSN: 1434-6052

Source: Springer Online Journal Archives 1860-2000

Topics: Physics

Notes: Abstract We derive, within perturbative QCD, a formula for the inclusive cross section of the diffractive dissociation of the deep inelastic photon γ*+q→X+q in the triple Regge limits≫M 2≫Q 2≫Λ 2. We use the leading ln(s/M 2, ln(M 2/Q 2) approximation and derive an, expression for the triple Pomeron vertex. The Pomeron above this vertex is found to be of higher order than the BFKL Pomeron. The resulting formula for the cross section is infrared finite. We show that the Abramovsky-Gribov-Kanchelli cutting rules are satisfied, and we discuss implications for the Pomeron structure function.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF01496591

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7

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An analysis of diffraction in deep-inelastic scattering (1999)

Bartels, J. ; Ellis, J. ; Kowalski, H. ; [et al.]

Springer

The European physical journal 7 (1999), S. 443-458

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ISSN: 1434-6052

Source: Springer Online Journal Archives 1860-2000

Topics: Physics

Notes: Abstract. We propose a simple parametrization for the deep-inelastic diffractive cross section. It contains the contribution of $q\bar{q}$ production to both the longitudinal and the transverse diffractive structure functions, and of the production of $q\bar{q}g$ final states from transverse photons. We start from the hard region and perform a suitable extrapolation into the soft region. We test our model on the 1994 ZEUS and H1 data, and confront it with the H1 conjecture of a singular gluon distribution.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s100529801022

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8

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The BFKL Pomeron in deep inelastic diffractive dissociation neart=0 (1995)

Bartels, J. ; Lotter, H. ; Wüsthoff, M.

Springer

The European physical journal 68 (1995), S. 121-136

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ISSN: 1434-6052

Source: Springer Online Journal Archives 1860-2000

Topics: Physics

Notes: Abstract The small-t behaviour of the deep inelastic diffractive dissociation cross section in the triple Regge region is investigated, using the BFKL approximation in perturbative QCD. We show that the cross section is finite att=0, but the diffusion in lnk t 2 leads to a large contribution of small momenta at the triple Pomeron vertex. We study the dependence upon the total energy and the invariant mass. Att=0, there is a decoupling of the three BFKL singularities which is a consequence of the conservation of the conformal dimension. For large invariant masses, the four gluon state in the uppert-channel plays an important role and cannot be neglected.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF01579811

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