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[show abstract]
[hide abstract]
ABSTRACT: Mit Rhodium beschichtete Katalysatoren ermöglichen durch katalytische Partialoxidation (CPOX) die Darstellung großer Mengen Wasserstoff aus höheren Kohlenwasserstoffen wie Benzin oder Diesel innerhalb weniger Millisekunden Kontaktzeit. Die Reaktionsenthalpie erzeugt Temperaturen von bis zu 1300 °C und erlaubt den autothermen Betrieb von kom-pakten CPOX Reaktoren in Fahrzeugen, die einen neuen Weg zur Versorgung von APUs (auxiliary power unit) mit Wasserstoff bzw. Synthesegas aus bereits bestehenden Versor-gungsnetzen aufzeigen. Zur Evaluierung von Modellen und der Aufklärung wichtiger Ein-zelprozesse der Reaktion wurde eine Versuchsanlage entwickelt, an der die katalytische Par-tialoxidation von Modellkraftstoffen unter definierten Randbedingungen erforscht werden kann. Dabei realisiert die Verwendung kombinierter Messverfahren (Prozess-Infrarot-Spek-trometerie, Sektorfeld-Massenspektrometerie, paramagnetische Sauerstoffdetektion) die zeitaufgelöste Untersuchung der Reaktionsprodukte mit geschlossenen Bilanzen bei allen technisch relevanten Betriebspunkten. Eine detaillierte Analyse der Kohlenwasserstoffe er-folgt mit Hilfe eines Gaschromatographen. Beispielhaft werden Selektivität und Umsatz für die CPOX von i-Oktan im stationären wie instationären Betrieb diskutiert.
Chemie Ingenieur Technik 06/2009; 81(7):909 - 919. · 0.59 Impact Factor
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Advanced Materials 11/2004; 16(20):1817 - 1821. · 13.88 Impact Factor
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V. Komarov,
S. Dymov,
A. Kacharava,
A. Kulikov,
G. Macharashvili,
A. Petrus,
F. Rathmann,
H. Seyfarth,
H. Ströher,
Yu. Uzikov, [......],
M. Nioradze,
H. Ohm,
D. Prasuhn,
R. Santo,
H. Paetz gen. Schieck,
R. Schleichert,
H.J. Stein,
K. Watzlawik,
N. Zhuravlev,
K. Zwoll
[show abstract]
[hide abstract]
ABSTRACT: A study of the deuteron breakup reaction pd→(pp)n with forward emission of a fast proton pair with small excitation energy Epp< 3 MeV has been performed using the ANKE spectrometer at COSY-Jülich. An exclusive measurement was carried out at six proton-beam energies Tp= 0.6, 0.7, 0.8, 0.95, 1.35 and 1.9 GeV by reconstructing the momenta of the two protons. The differential cross section of the breakup reaction, averaged up to 8° over the cm polar angle of the total momentum of the pp pairs, has been obtained. Since the kinematics of this process is quite similar to that of backward elastic pd→dp scattering, the results are compared to calculations based on a theoretical model previously applied to the pd→dp process.
Physics Letters B. 10/2002;
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05/2002;
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U Hink,
H Li,
H Mollnau,
M Oelze,
E Matheis, M Hartmann,
M Skatchkov,
F Thaiss,
R A Stahl,
A Warnholtz,
T Meinertz,
K Griendling,
D G Harrison,
U Forstermann,
T Munzel
[show abstract]
[hide abstract]
ABSTRACT: Incubation of endothelial cells in vitro with high concentrations of glucose activates protein kinase C (PKC) and increases nitric oxide synthase (NOS III) gene expression as well as superoxide production. The underlying mechanisms remain unknown. To address this issue in an in vivo model, diabetes was induced with streptozotocin in rats. Streptozotocin treatment led to endothelial dysfunction and increased vascular superoxide production, as assessed by lucigenin- and coelenterazine-derived chemiluminescence. The bioavailability of vascular nitric oxide (as measured by electron spin resonance) was reduced in diabetic aortas, although expression of endothelial NOS III (mRNA and protein) was markedly increased. NOS inhibition with N:(G)-nitro-L-arginine increased superoxide levels in control vessels but reduced them in diabetic vessels, identifying NOS as a superoxide source. Similarly, we found an activation of the NADPH oxidase and a 7-fold increase in gp91(phox) mRNA in diabetic vessels. In vitro PKC inhibition with chelerythrine reduced vascular superoxide in diabetic vessels, whereas it had no effect on superoxide levels in normal vessels. In vivo PKC inhibition with N:-benzoyl-staurosporine did not affect glucose levels in diabetic rats but prevented NOS III gene upregulation and NOS-mediated superoxide production, thereby restoring vascular nitric oxide bioavailability and endothelial function. The reduction of superoxide in vitro by chelerythrine and the normalization of NOS III gene expression and reduction of superoxide in vivo by N:-benzoyl-staurosporine point to a decisive role of PKC in mediating these phenomena and suggest a therapeutic potential of PKC inhibitors in the prevention or treatment of vascular complications of diabetes mellitus. The full text of this article is available at http://www.circresaha.org.
Circulation Research 03/2001; 88(2):E14-22. · 9.49 Impact Factor
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S. Barsov,
U. Bechstedt,
G. Borchert,
W. Borgs,
M. Buescher,
M. Debowski,
W. Erven,
R. Esser,
P. Fedorets,
D. Gotta, [......],
Z. Rudy,
R. Schleichert,
Ch. Schneider,
H. Schneider,
O. W. B. Schult,
H. Seyfarth,
K. Sistemich,
H. J. Stein,
H. Stroeher,
I. Zychor
[show abstract]
[hide abstract]
ABSTRACT: The magnetic spectrometer ANKE has been put into operation in spring
1998 at the cooler synchrotron COSY-Juelich. ANKE allows to momentum
analyze ejectiles emitted from an internal target at forward angles
\vartheta ≈ 0° with high angular acceptance Δ Ω ≈
50 msr. A primary goal of the physics program with ANKE is the
investigation of K+ production in proton-nucleus collisions
at energies around and far below the free nucleon-nucleon threshold at
T=1.58 GeV. The measurements have been performed with C, Cu and Au
targets at various energies in the range T=1.0, ..., 2.3 GeV. The major
experimental challenge is that the kaon-to-background ratio is as low as
˜ 10-6 at the lowest energy. Data on the target-mass
dependence of the production cross sections for kaon momenta
pK+ = 150, ..., 510 MeV/c at beam energies of
T=1.0 and 2.3 GeV are presented.
Acta Physica Polonica Series B 09/2000; 31:2159. · 0.90 Impact Factor
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P. Kulessa,
Z. Rudy,
W. Cassing, M. Hartmann,
L. Jarczyk,
B. Kamys,
H. R. Koch,
H. Ohm,
K. Pysz,
H. Stroeher,
A. Strzalkowski
[show abstract]
[hide abstract]
ABSTRACT: The interaction of the strange particles (Λ, K+) with
nucleons is investigated. A comparison of calculated (within CBUU model)
and measured K+ spectra in proton--nucleus reactions is made
and shows good agreement. Experimentally determined production cross
sections of heavy Λ hypernuclei in collisions of protons with Bi
and U targets, obtained at COSY-Juelich, are compared with calculated
values and agreement is obtained if rescattering of the Λ
particles on nucleons is taken into account. The lifetimes of heavy
Λ hypernuclei produced on Bi and U targets were measured. The
value obtained for Bi (161 ± 7 ± 14) ps (the most precise
value in literature) and the new value of the lifetime obtained for U
(152 ± 10 ± 25)ps are consistent with possibility of the
violation of Δ I=1/2 rule for nonmesonic Λ decay.
Acta Physica Polonica Series B 09/2000; 31:2243. · 0.90 Impact Factor
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[show abstract]
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ABSTRACT: In the present study, we tested whether a nitrate-free interval is able to prevent increases in vascular superoxide (O2*-) and the development of hypersensitivity to vasoconstrictors and whether this may result in restoration of vascular nitroglycerin (NTG) sensitivity.
Intermittent NTG-patch treatment (12 h patch on/patch-off) has been shown to increase ischemic periods in patients with stable coronary arteries, suggesting a rebound-like situation during the patch-off period. Recently, we demonstrated that long-term treatment with NTG induces tolerance, which was in part related to increases in vascular O2*- and increased vasoconstrictor sensitivity.
New Zealand white rabbits received a continuous application of NTG patches (0.4 mg/h) or an intermittent application of NTG patches (12 h patch on, 12 h patch off) for three days. Isometric tension studies were performed with aortic rings, and vascular O2*- was estimated using lucigenin-derived chemiluminescence (5 micromol/liter). Expression of the copper/zinc (Cu/Zn) superoxide dismutase (SOD) was assessed by Western blotting, and SOD activity was measured by autooxidation of 6-hydroxydopamine.
Continuous treatment with NTG caused tolerance to NTG, cross-tolerance to the endothelium-dependent vasodilator acetylcholine, increased vascular O2*-, reduced Cu/Zn SOD expression and increased sensitivity to vasoconstrictors such as phenylephrine, serotonin and angiotensin II. On/off treatment with NTG improved tolerance, corrected endothelial dysfunction and decreased vascular O2*-. In addition the reduction in SOD expression was less pronounced, whereas increases in the sensitivity to vasoconstrictors such as phenylephrine and serotonin remained nearly unchanged.
Enhanced vasoconstrictor sensitivity may explain, at least in part, the rebound phenomena observed in patients during a 12-h NTG patch-off period.
Journal of the American College of Cardiology 09/2000; 36(2):628-34. · 14.16 Impact Factor
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S. Barsov,
U. Bechstedt,
G. Borchert,
W. Borgs,
M. Büscher,
M. Debowski,
M. Drochner,
W. Erven,
R. Eßer,
P. Fedorets, [......],
Z. Rudy,
R. Schleichert,
Chr. Schneider,
H. Schneider,
O. W. B. Schult,
H. Seyfarth,
K. Sistemich,
H. J. Stein,
H. Ströher,
P. Wüstner
[show abstract]
[hide abstract]
ABSTRACT: ANKE is a second generation experimental facility at the internal beam of the accelerator COSY at the Forschungszentrum Jülich (Germany). It has recently (May 1998) been installed in the ring, commissioned and immediately after this been exploited for first experiments. Using circulating beams of protons with energies between 1.0 and 2.3 GeV, sub- and near threshold production of K+ mesons in collisions with carbon-strip targets has been investigated. The detection system of ANKE used for the first measurements is capable of detecting positively charged ejectiles in the momentum range between about 100 and 600 MeV/c. In particular, it has been optimized for K+ identification in the presence of an intense background of protons and pions. The final results of the experiments (cross sections and momentum spectra) will be used to obtain more detailed information on the subthreshold production mechanism. © 2000 American Institute of Physics.
AIP Conference Proceedings. 05/2000; 512(1):138-142.
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T Münzel,
H Li,
H Mollnau,
U Hink,
E Matheis, M Hartmann,
M Oelze,
M Skatchkov,
A Warnholtz,
L Duncker,
T Meinertz,
U Förstermann
[show abstract]
[hide abstract]
ABSTRACT: Long-term nitroglycerin (NTG) treatment has been shown to be associated with cross-tolerance to endothelium-dependent vasodilators. It may involve increased production of reactive oxygen species (such as superoxide, O(2)(.-)) that rapidly inactivate the nitric oxide (NO) released from the endothelial cells. It remains to be elucidated, however, whether long-term treatment with NTG alters the activity and expression of the endothelial NO synthase (NOS III) and whether this enzyme can contribute to O(2)(.-) formation. We studied the influence of long-term NTG treatment on the expression of NOS III as assessed by RNase protection assay and Western blot. Tolerance was measured ex vivo in organ chamber experiments with rat aortic rings. O(2)(.-) and NO formation were quantified using lucigenin- and Cypridina luciferin analog-enhanced chemiluminescence as well as electron spin resonance (ESR) spectroscopy. Treatment of Wistar rats with NTG (Alzet osmotic minipumps, NTG concentration 10 microg x kg(-1) x min(-1)) for 3 days caused marked tolerance, cross-tolerance to the endothelium-dependent vasodilator acetylcholine, and a significant increase in O(2)(.-)-induced chemiluminescence. Tolerance was associated with a significant increase in NOS III mRNA to 236+/-28% and NOS III protein to 239+/-17%. In control vessels, the NOS inhibitor N(G)-nitro-L-arginine (L-NNA) increased the O(2)(.-)-mediated chemiluminescence, indicating that basal production of endothelium-derived NO depresses the baseline chemiluminescence signal. In the setting of tolerance, however, L-NNA decreased steady-state O(2)(.-) levels, indicating the involvement of NOS III in O(2)(.-) formation. Likewise, A23187-induced, NOS III-mediated O(2)(.-) production was more pronounced in tolerant than in control vessels. Vascular NO bioavailability as assessed with ESR spectroscopy using iron-thiocarbamate as a trap for NO was significantly reduced in tolerant vessels. Pretreatment of tolerant tissue in vitro with the protein kinase C (PKC) inhibitors reduced basal and stimulated NOS III-mediated O(2)(.-) production and partially reversed vascular tolerance. These findings suggest that NTG treatment increases the expression of a dysfunctional NOS III gene, leading to increased formation of O(2)(.-) and decreased vascular NO bioavailability. Normalization of NOS III-mediated O(2)(. -) production and improvement of tolerance with PKC inhibition suggests an important role for PKC isoforms in mediating vascular dysfunction caused by long-term NTG treatment.
Circulation Research 02/2000; 86(1):E7-E12. · 9.49 Impact Factor
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S. Barsov,
U. Bechstedt,
G. Borchert,
W. Borgs,
M. Büscher,
M. Debowski,
W. Erven,
R. Eßer,
P. Fedorets,
D. Gotta, [......],
B. Rimarzig,
Z. Rudy,
R. Schleichert,
Chr. Schneider,
H. Schneider,
O. W. B. Schult,
H. Seyfarth,
K. Sistemich,
H. J. Stein,
H. Ströher
[show abstract]
[hide abstract]
ABSTRACT: The new spectrometer ANKE has been put into operation at the accelerator
COSY of the Forschungszentrum Jülich. It enables the study of
forward going ejectiles from proton-induced reactions at internal
targets in COSY. First measurements of the double differential cross
sections for the subthreshold K+-production in pA collisions
have been performed at projectile energies as low as 1.0 GeV, i.e. 0.58
GeV below the free nucleon-nucleon threshold.
Nuclear Physics A 12/1999; 663:1107-1107. · 1.54 Impact Factor
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NACHRICHTEN AUS CHEMIE TECHNIK UND LABORATORIUM. 01/1997; 45(11):1098-&.
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[show abstract]
[hide abstract]
ABSTRACT: A beam of liquid He
N
droplets (N≈5000) is prepared by a cryogenic free jet expansion, doped with single molecules and studied via laser spectroscopy.
The spectra consist of sharp lines (Δν≅0.003–0.1 cm−1) and show rotational structure (for SF6), providing the first information on the droplet temperature, which is 0.37 K for4He
N
and 0.14 K for3He
N
. The rotational constants give information on the microscopic interaction of the molecule with the He environment. Each of
the sharp vibronic lines of the elecronic S1←S0 transition in glyoxal (C2O2H2) is accompanied by a phonon sideband, showing a distinct gap followed by a sharp peak at the roton energy (8.1 K) and a second
weaker maxon peak followed by a broad multiphonon wing. These provide the first evidence for superfluidity in4He
N
predicted theoretically.
Czechoslovak Journal of Physics 05/1996; 46:2951-2956. · 0.42 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: We give an upper bound on the number of vertices ofP
I
, the integer hull of a polyhedronP, in terms of the dimensionn of the space, the numberm of inequalities required to describeP, and the size of these inequalities. For fixedn the bound isO(m
n
n–
). We also describe an algorithm which determines the number of integer points in a polyhedron to within a multiplicative factor of 1+ in time polynomial inm, and 1/ when the dimensionn is fixed.
Combinatorica 02/1992; 12(1):27-37. · 0.67 Impact Factor
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S Barsov,
U Bechstedt,
W Bothe,
N Bongers,
G Borchert,
W Borgs,
W Bräutigam,
M Büscher,
W Cassing,
V Chernyshev, [......],
A Strzalkowski,
K.-H Watzlawik,
P Wüstner,
S Yashenko,
B Zalikhanov,
N Zhuravlev,
K Zwoll,
I Zychor,
O.W B. Schult,
H Ströher
[show abstract]
[hide abstract]
ABSTRACT: ANKE is a new experimental facility for the spectroscopy of products from proton-induced reactions on internal targets. It has recently been implemented in the accelerator ring of the cooler synchrotron COSY of the Forschungszentrum Jülich (FZ-Jülich), Germany. The device consists of three dipole magnets, various target installations and dedicated detection systems. It will enable a variety of hadron-physics experiments like meson production in elementary proton–nucleon processes and studies of medium modifications in proton–nucleus interactions.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment.
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I. Zychor,
M. Büscher, M. Hartmann,
A. Kacharava,
I. Keshelashvili,
A. Khoukaz,
V. Kleber,
V. Koptev,
Y. Maeda,
T. Mersmann,
S. Mikirtychiants,
R. Schleichert,
H. Ströher,
Yu. Valdau,
C. Wilkin
[show abstract]
[hide abstract]
ABSTRACT: The pp→pK+Y0 reaction has been studied for hyperon masses m(Y0)⩽1540 MeV/c2 at COSY-Jülich by using a 3.65 GeV/c circulating proton beam incident on an internal hydrogen target. Final states comprising two protons, one positively charged kaon and one negatively charged pion have been identified with the ANKE spectrometer. Such configurations are sensitive to the production of the ground state Λ and Σ0 hyperons as well as the Σ0(1385) and Λ(1405) resonances. Applying invariant- and missing-mass techniques, the two overlapping excited states could be well separated, though with limited statistics. The shape and position of the Λ(1405) distribution, reconstructed cleanly in the Σ0π0 channel, are similar to those found from other decay modes and there is no obvious mass shift. This finding constitutes a challenging test for models that predict Λ(1405) to be a two-state resonance.
Physics Letters B.
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[show abstract]
[hide abstract]
ABSTRACT: Let f0 be the conformal mapping of a given simply connected region R onto a disk D. It is known that f0 is the unique minimizer of φ(f)=‖f‖∞, where f varies in a set H1 of holomorphic functions defined on R and ‖ ‖∞ is the uniform (Chebyshev) norm. In this paper approximations to f0 are computed numerically with the aid of approximation and optimization techniques. The essential feature is the incorporation of the geometry of R into the numerical part of this problem. Several numerical examples are given, with figures. In addition, it has been shown in another paper by one of the authors that by changing ‖ ‖∞ slightly, one can also produce conformal mappings of R onto prescribed regions other than D. An example of this kind involving a triangle is also given.
Journal of Computational and Applied Mathematics.
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[show abstract]
[hide abstract]
ABSTRACT: Gomory's cutting-plane technique can be viewed as a recursive procedure for proving the validity of linear inequalities over the set of all integer vectors in a prescribed polyhedron. The number of rounds of cutting planes needed to obtain all valid linear inequalities is known as the rank of the polyhedron. We prove that polyhedra featured in popular formulations of the stable-set problem, the set-covering problem, the set-partitioning problem, the knapsack problem, the bipartite-subgraph problem, the maximum-cut problem, the acyclic-subdigraph problem, the asymmetric traveling-salesman problem, and the traveling-salesman problem have arbitrarily high rank. In particular, we prove conjectures of Barahona, Grötschel, and Mahjoub; Chvátal; Grötschel and Pulleyblank; and Jünger.
Linear Algebra and its Applications.
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P. Kulessa,
K. Pysza,
I. Zychor,
Z. Rudy,
H. Ohm,
B. Kamys, M. Hartmann,
W. Cassing,
H.R. Koch,
A. Strzalkowski,
H. Hodde,
W. Borgs,
R. Maiera,
D. Prasuhn,
M. Matoba,
O.W.B. Schult
[show abstract]
[hide abstract]
ABSTRACT: A very thin Bi target has been installed at the internal beam of COSY-Jülich and 1.0 and 1.9 GeV protons have been bumped onto it for determination of the background and production of hypernuclei, respectively. With the recoil-shadow method the position distribution of fission fragments was measured with two multi-wire proportional counters operated in coincidence. From the distribution recorded in the shadow region and the hypernucleus recoil momenta obtained through BUU calculations, a preliminary value of ∼ 145 ± 7 (stat) ± 23 (sys) ps was obtained for the lifetime of the heavy hypernuclei.
Nuclear Physics A.
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[show abstract]
[hide abstract]
ABSTRACT: Catalytic partial oxidation of iso-octane over a rhodium/alumina coated honeycomb monolith is experimentally and numerically studied at short-contact times for varying fuel-to-oxygen ratios. A new experimental set-up with well-defined inlet and boundary conditions is presented. The conversion on the catalyst and in the gas-phase is modeled by detailed reaction mechanisms including 857 gas-phase and 17 adsorbed species. Elementary-step based heterogeneous and homogeneous reaction mechanisms are implemented into two-dimensional flow field description of a single monolith channel. Experiment and simulation provide new insights into the complex reaction network leading to varying product distribution as function of fuel-to-oxygen ratio. At fuel rich conditions, the formation of by-products that can serve as coke precursors is observed and interpreted.
Combustion and Flame.
