Showing papers by "Technical University of Dortmund published in 1987"

Exclusive non-leptonic decays ofD-,D s - andB-mesons

Abstract: Recent experimental results onD-,Ds- andB-decays are interpreted on the basis of the valence quark model. For nonleptonic decays generally good results are obtained using factorization with little direct annihilation. Final state interaction causes corrections, however: small bare amplitudes can be fed by stronger amplitudes through channel mixing. This effect can simulate or enhance weak annihilation processes in particular if high lying resonances contribute. A comparison of\(D^0 \to \bar K^0 \phi \) withDs→ϱπ decays will clarify this issue. The effective QCD coefficients obtained in the analysis are discussed and used to estimate the contribution of two-body decays to the total widths. The result reflects already the lifetime differences betweenD0 andD+ mesons. Predictions for numerousB-decay branching rations allow for further tests and for a determination of so far unknown decay constants. A first bound on |Vub| from nonleptonic decays is found from the experimental limit on\(\bar B^0 \to \pi ^ + \pi ^ - \).

Localization, quantum interference, and the metal-insulator transition

Abstract: The density of states, and the phase diagram of localization in a three-dimensional disordered tight binding model with box, Gaussian, and Lorentzian distribution of the site energies is numerically determined. The influence of the behaviour of the spectral density on the position of the mobility edge is discussed. Extended states are found outside the unperturbed band for the box and the Gaussian distribution. This implies the existence of two metal-insulator transitions at certain energies which may be attributed to the breakdown of potential localization, and the breakdown of quantum interference localization, respectively. The general validity of the scaling hypothesis in the localization theory is discussed in view of these results.

Experimental toxicology of formaldehyde

Abstract: Formaldehyde is a reactive chemical which undergoes spontaneous reactions with various cellular constituents. Mutagenicity data may be interpreted on the background of this behavior. Mice are better able to reduce the irritating effect of formaldehyde than rats and to reduce their ventilation rate when formaldehyde acts on the respiratory tract. Subacute exposure of rats to concentrations higher than 2 ppm inhibits mucociliary clearance of the nasal epithelium and leads to progressive histological and ultrastructural lesions at this site. The occurrence of squamous cell carcinomas of the nasal epithelium of rats after 2 years inhalation of 14.3 ppm formaldehyde (CIIT study) is probably the result of chronic and recurrent local toxicity; this is supported by species differences in susceptibility to the tissue damaging and carcinogenic effect of formaldehyde (rat, mouse, hamster). Data on formaldehyde-DNA interaction further support the argument that a direct risk extrapolation from the formaldehyde effects in rats to those expected for man is not possible.

Organotin compounds: Toxicology and biomedicinal applications

Abstract: The toxicology and biomedical aspects and applications of organotin compounds are discussed. Factors affecting toxicity are considered first and then the mechanisms of toxicity are described and assessed. A review of the main biomedical applications then follows, covering biochemical, agricultural and other biocidal uses, and recent developments in the field of anticarcinogenesis.

Optical quantum-confined Stark effect in GaAs quantum wells.

Abstract: The dynamical coupling of the first two conduction-band sublevels in an 84.5-A\r{} GaAs multiple-quantum-well structure by an intense ${\mathrm{CO}}_{2}$ laser pulse leads to drastic changes in the absorption spectrum of the lowest excitons. In order to observe this new effect, the polarization of the pump laser has to be perpendicular to the plane of the layers. From the analysis of the experimental results in terms of a three-level nonlinear susceptibility the energy difference of the first two conduction-band sublevels and their transition dipole moment are determined to be 110.3 meV and 14 e\ensuremath{\cdot}A\r{}, respectively.

Direct Identification of the Carbon Skeleton of Organic Compounds using Double Quantum Coherence 13C‐NMR Spectroscopy. The INADEQUATE Pulse Sequence

Abstract: NMR spectroscopy plays an important part in the determination of the structures of organic compounds. The parameters of importance here are the chemical shifts of the 1H and 13C nuclei and the spin-spin interactions both between 1H nuclei and between 1H and 13C nuclei. Couplings between 13C nuclei were almost completely neglected until a few years ago, since they were extremely difficult to observe because of the low natural abundance of 13C. However, it is these couplings which afford information directly on the carbon-carbon connectivities in the molecule. It is now possible to use a special NMR pulse sequence to make these couplings more readily visible: the result of using this sequence is a 13C-NMR spectrum from which the carbon skeleton concerned can be directly read off. Two-dimensional spectra in particular are very easy to evaluate. The pulse sequence involved, which bears the somewhat puzzling name INADEQUATE, produces double-quantum coherences from which the NMR signals of the coupled carbon nuclei can be obtained. In this article the principle of double-quantum coherence is described and a number of examples for the application of the INADEQUATE pulse sequences to problems in synthetic organic chemistry, biosynthesis and natural products chemistry are presented; in addition, the possibility of applying the INADEQUATE method to other nuclei is considered.

Total neutrino and antineutrino charged current cross section measurements in 100, 160, and 200 GeV narrow band beams

Abstract: Neutrino and antineutrino total charged current cross sections on iron were measured in the 100, 160, and 200 GeV narrow band beams at the CERN SPS in the energy range 10 to 200 GeV. Assuming σ/E to be constant, the values corrected for non-isoscalarity are σv/E = (0.686 ± 0.019) * 10−38 cm2/ (GeV · nucleon) and σv/E = (0.339 ± 0.010) * 10−38 cm2/ (GeV·nucleon). Between 50 and 150 GeV no energy dependence of σ/E was observed within ±3% for neutrino and ±4% for antineutrino interactions.

The relevance of 4,5-dihydroxy-2-hexanone in the excretion kinetics of n-hexane metabolites in rat and man.

Abstract: Male Wistar rats were exposed ton-hexane concentrations between 50 and 3000 ppm for 8 h, and urinary excretion kinetics of then-hexane metabolites 1-hexanol, 2-hexanol, 3-hexanol, 2-hexanone, 2,5-hexanedione, and 4,5-dihydroxy-2-hexanone were assessed. The amounts of metabolites excreted were linearly dependent on then-hexane exposure concentration, up to an exposure of about 300 ppm. Above 300 ppm exposure the metabolite excretion indicated saturation kinetics in the metabolism ofn-hexane. In its quantity, the newly described 4,5-dihydroxy-2-hexanone was the second metabolite, its amount in the urine being about ten times higher than that of excreted 2,5-hexanedione. Using gas chromatography-mass spectrometry the occurrence of 4,5-dihydroxy-2-hexanone as ann-hexane metabolite in urine of man was confirmed after exposure of a male volunteer to a mean of 217 ppmn-hexane for 4 h (laboratory exposure). Twenty-six hours after starting this exposure the excretion of 4,5-dihydroxy-2-hexanone (as a result of then-hexane exposure) reached a level which was four times higher than the excretion of 2,5-hexanedione. The results in both rat and man indicate the relevance of 4,5-dihydroxy-2-hexanone as a metabolite ofn-hexane metabolism. Formation of this metabolite may be viewed as a route of detoxification.

Proof of the nonexistence of (formal) phase transitions in polaron systems. I

Abstract: In recent literature it was frequently claimed that free polarons should undergo a (formal) phase transition from a mobile to a localized state, if the electron-phonon coupling constant \ensuremath{\alpha} exceeds some critical value ${\ensuremath{\alpha}}_{c}$. For \ensuremath{\alpha}=${\ensuremath{\alpha}}_{c}$, the formal free energy should be nonanalytic in \ensuremath{\alpha}. In this paper we prove that for optical polarons no such transition exists for finite temperatures. To do so, we use functional-integration techniques and discuss perturbation theory in \ensuremath{\alpha} to infinite order.

Ground Term Confluence in Parametric Conditional Equational Specifications

Abstract: We consider the problem of Knuth-Bendix-like completion for specifications with conditional equations for the particular case of achieving ground confluence. Inductive theorems of the given specification will be used for proving the convergence of critical pairs. The theorems may have the form of arbitrary first-order formulas, allowing for expressing properties of the theory that could otherwise not be specified equationally. A completion procedure will be given and demonstrated to be useful on examples which previous approaches fail to handle. Finally, an application of these ideas to parameterized specifications will be indicated.

Ground state properties of a spinless Falicov-Kimball model; additional features

Abstract: We have studied some energetic and structural ground state properties of a spinless Falicov-Kimball model. Using a method based on “Tchebycheff-Markoff inequalities”, we have calculated sharp upper and lower bounds for the ground state energy. These calculations lead to rigorous results for a special range of parameters, where we are able to give the exactf-level occupation pattern for a square lattice. The results for the “symmetric” case, where a superstructure occurs leading to a metal-insulator transition, have already been published. In this paper we present some additional results also for the “unsymmetric case” and study valence-transitions for fixed particle-number.

Kinetics and disposition in toxicology. Example: carcinogenic risk estimate for ethylene.

Abstract: Pharmacokinetic analysis of the behaviour of xenobiotics in living organisms is the basis for the understanding of dose (concentration-) response relationships. Risk estimates may lead to erroneous results if pharmacokinetic principles are neglected. The pharmacokinetic behaviour of a xenobiotic should be known before planning long-term experiments on toxicity and carcinogenicity. This is demonstrated using ethylene as an example. On the basis of the pharmacokinetics in rats of ethylene and ethylene oxide, its carcinogenic metabolite, we estimated the theoretical risk for the carcinogenic potential of ethylene. Our results demonstrate that exposure of rats to ethylene concentrations higher than 1000 ppm correspond to a (theoretical) exposure to 5.6 ppm ethylene oxide: exposures to ethylene at 40 ppm are equivalent to ethylene oxide exposures of 1 ppm, which is the (new) TLV for ethylene oxide.

Differential effect of N-acetylcysteine on excretion of the metals Hg, Cd, Pb and Au.

Abstract: Male Wistar rats were subacutely treated with sublethal doses of HgCl2, CdCl2, Pb(NO3)2, or Na-aurothiomalate. The metal preparations contained trace doses of radioactive nuclide. Based on the doses given and on the radioactivity excretion in urine and faeces the body burden was determined. After the metal treatment periods, some of the animals received N-acetylcysteine (up to 100 mg/kg daily, on 6 consecutive days, i.p.), and the effect of this potential chelator on metal excretion was monitored. The excretion of Hg (after dosing with HgCl2) was not influenced by N-acetylcysteine. The elimination of Cd in urine (after dosing with CdCl2) was increased by a factor of four. Also, the elimination of Pb [after dosing with Pb(NO3)2] was gradually increased (in faeces and urine) by increasing doses of N-acetylcysteine. After dosing with Na-aurothiomalate, the excretion of Au in urine was increased to about 30%. The data suggest some activity of N-acetylcysteine in facilitating excretion of Pb, Cd or Au, but not of Hg.

Inhalation pharmacokinetics of 1,2-epoxybutene-3 reveal species differences between rats and mice sensitive to butadiene-induced carcinogenesis.

Abstract: Comparative investigations of inhalation pharmacokinetics of 1,2-epoxybutene-3 (vinyl oxirane, the primary reactive intermediate of butadiene) revealed major differences in metabolism of this compound between rats and mice. Whereas in rats no indication of saturation kinetics of epoxybutene metabolism could be observed up to exposure concentrations of 5000 ppm, in mice saturation of epoxybutene metabolism becomes apparent at atmospheric concentrations of about 500 ppm. The estimated maximal metabolic rate (Vmax) in mice for epoxybutene was only 350 μmol×h−1×kg−1 (rats: >2600 μmol× h−1×kg−1). In the lower concentration range where first order metabolism applies (up to about 500 ppm) epoxybutene is metabolized by mice at higher rates compared to rats (metabolic clearance per kg body weight, mice: 24900 ml×h−1, rats: 13400 ml×h−1). Under these conditions the steady state concentration of epoxybutene in the mouse is about 10 times that in the rat. When mice are exposed to high concentrations of butadiene (>2000 ppm; conditions of saturation of butadiene metabolism; closed exposure system) epoxybutene is exhaled by the animals, and its concentration in the gas phase increases with exposure time. At about 10 ppm epoxybutene signs of acute toxicity are observed. When rats are exposed to butadiene under similar conditions, the epoxybutene concentration reaches a plateau at about 4 ppm. Under these conditions hepatic non-protein sulfhydryl compounds are virtually depleted in mice but not in rats. We conclude that in addition to the higher rate of metabolism of butadiene in mice, limited detoxification and consequently accumulation of its primary reactive intermediate epoxybutene may be a major determinant for the higher susceptibility of mice to butadiene-induced carcinogenesis.

Nearly All Convex Bodies Are Smooth and Strictly Convex.

Abstract: By an old result of Klee, those convex bodies which are not smooth or not strictly convex form a set of first Baire category. It is proved here that they are “even fewer”: they only form a σ-porous set.

Pharmacokinetics of the neurotoxin n-hexane in rat and man.

Abstract: The pharmacokinetics of inhaled n-hexane in rat and man were compared. In the rat metabolism was saturable. Up to 300 ppm, the metabolic rate was directly proportional to the concentration in the atmosphere, reaching 47 mumol/(h X kg). Only 17% of n-hexane was exhaled unchanged. Above 300 ppm, the amount of n-hexane in the body rose with increasing atmospheric concentrations from 1.6 up to a limiting value of 9.6, which corresponded to the thermodynamic distribution coefficient of n-hexane between the organism and the atmosphere. Up to 3000 ppm, the rate of metabolism increased to 245 mumol/(h X kg); only a slow further increase was found up to 7000 ppm (285 mumol/(h X kg]. In man the steady-state concentrations of n-hexane were about 1 ppm. The metabolic clearance was 132 1/h, and n-hexane accumulated to a factor of 2.3 in the organism. The thermodynamic distribution coefficient was calculated to be 12. Twenty per cent of n-hexane in the body was exhaled unchanged. At low concentrations the rate of metabolism of n-hexane is limited in both species by transport to the enzyme system. Under these conditions the rate of metabolism of n-hexane should not be influenced by xenobiotics which induce the n-hexane metabolizing enzyme system.

Diagonalizing over Deterministic Polynomial Time

Abstract: Though some of our concepts will be defined for arbitrary complexity classes, we are only interested in diagonalizing over deterministic polynomial time. (In particular, we do not consider the polynomially bounded classes for other complexity measures like nondeterministic time (NP), (bounded) alternating time (PH), or space (PSPACE).) We say that a diagonalization concept D pertains to deterministic polynomial time (or P) if the following holds. First, the concept is sufficiently strong to diagonalize over P, i.e., to construct a recursive set D~ P. Second, we obtain diagonals of (essentially) arbitrarily low hyperpolynomial deterministic time complexity, i.e., any property Q which can be enforced by a diagionalization of type D is shared by some set in DTIME(f(n)), f any "natural" hyperpolynomial function. Our interest was in finding as powerful as possible diagonalization concepts which still pertain to P. From the concepts discussed here, only some will pertain to P. Other ones will be too powerful, that is they will also allow certain diagonalizations over deterministic exponential time or nondeterministic polynomial time.

Multiplicity dependence of the average transverse momentum and of the particle source size inp−p interactions at $$\sqrt s $$ =62, 44 and 31 GeV

Abstract: The average transverse momentum and the size of the particle emitting source (measured via Bose-Einstein correlations) have been studied as functions of the charged particle density in the central region inp-p interactions at\(\sqrt s \)=62, 44 and 31 GeV. Both the average transverse momentum and the source size increase with increasing density at all three energies. This effect, very weak at\(\sqrt s \)=31 GeV, becomes stronger with increasing energy.