Search Results - (Author, Cooperation:J. Huber)

2018-02-03

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Geosciences

Computer Science

Medicine

Natural Sciences in General

Physics

Biochemistry, Microbiology

2018-05-05

The American Society for Biochemistry and Molecular Biology (ASBMB)

0021-9258

1083-351X

Biology

Chemistry and Pharmacology

2018-10-06

American Physical Society (APS)

0556-2821

1089-4918

Physics

String theory, quantum gravity, gauge/gravity duality

2016-03-05

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

2018-09-07

Nature Publishing Group (NPG)

2044-5385

Medicine

2012-10-19

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

Animals ; *Cell Transformation, Neoplastic ; Colitis/complications/metabolism/pathology ; Colon/metabolism/pathology ; Colonic Neoplasms/complications/metabolism/pathology ; Disease Models, Animal ; Down-Regulation ; Epithelial Cells/metabolism/pathology ; Genes, APC ; Inflammasomes/*metabolism ; Interleukin-18/metabolism ; Interleukins/deficiency/genetics/metabolism ; Intestines/*metabolism/*pathology ; Mice ; Mice, Knockout ; Receptors, Interleukin/deficiency/genetics/*metabolism ; Time Factors ; Weight Loss

1432-0711

Springer Online Journal Archives 1860-2000

Medicine

Electronic Resource

article

1985

Kreativität ; Sachinformation ; Basteln ; Freizeit

Behinderten-Zeitschrift, Bd. 22 (1985) H. 1, S. 20-21, 0175-5854

German

1089-7550

AIP Digital Archive

Physics

We describe some attempts to observe magnetic structure in various actinide (5f-electron) materials. Our experimental technique is neutron powder diffraction as practiced at a spallation (pulsed) neutron source. We will discuss our investigations of α-Pu, δ-Pu, α-UD3, and β-UD3. β-UD3 is a simple ferromagnet: Surprisingly, the moments on the two nonequivalent uranium atoms are the same within experimental error. α-UD3, α-Pu, and δ-Pu are nonmagnetic, within the limits of our observations. Our work with pulsed neutron diffraction shows that it is a useful technique for research on magnetic materials.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

The intermetallic compound CePt orders ferromagnetically at a Curie temperature (θC) of 5.8 K.1 The earliest measurement of CePt to identify its ferromagnetism and to determine its θC was actually that of magnetization under pressure up to 7 kbar. Reference has been made to the results,1,2 but the data are only now being presented. Additionally, we are reporting measurement on CePt of low-field ac susceptibility (χac) under pressure up to 16 kbar. Magnetization and χac data both yield plots of θC versus pressure (p); and while measurement of χac gives only a qualitative indication of the pressure dependence of the saturation moment, it is by far the easier experiment. We find d(ln θC)/dp = 1.3 × 10−2 kbar−1, in accord with other studies.3,4 Kappler et al. have reported that CePd (isostructural with CePt) and Ce3Pd5 also order ferromagnetically at 6.5 and 1.5 K, respectively.5 Our measurements of χac under pressure show that d(ln θC)/dp equals 0.6×10−2 kbar−1 for CePd but that it is essentially zero for Ce3Pd5.

Electronic Resource

1089-7690

AIP Digital Archive

Physics

Chemistry and Pharmacology

The magnetic properties of the evsB2 spin component of the 3A2 state in the molecule CS2 have been investigated with a resolution of ∼100 kHz by quantum beat spectroscopy in a supersonic jet. Zeeman-level tuning in 12CS2 and 13CS2, providing Landé g factors, and measurements of the 13CS2 nuclear hyperfine structure were carried out, particularly to investigate their J dependence. Based on these results, it is proposed that both the magnetic moment and the hyperfine splitting are dominated by spin-uncoupling interactions, described in the rotational Hamiltonian by B(J−S).2 In addition, the g factors and rotational state lifetimes were used to provide spectroscopic assignments and to elucidate details of the state mixing.

Electronic Resource

1089-7690

AIP Digital Archive

Physics

Chemistry and Pharmacology

We investigate final rotational state distributions following the decay of long-lived resonance states with k*=0, 1, and 2 quanta of internal bending excitation. The calculations are related to the photodissociation of HONO on the S1 electronic state surface, truncated to two degrees of freedom namely the HO–NO dissociation bond and the ONO bending angle. The decay of the k*=0 resonance yields a smooth Gaussian-type distribution, in very good agreement with recent measurements. The distributions following the decay of the excited bending states show a bimodal behavior with the main maxima at high rotational states. The final angular momentum distributions reflect the coordinate-dependence of the dissociation wave function in the region of the transition state, mediated by the dynamics in the exit channel when the wave packet slides down the steep potential slope. A qualitative interpretation of the rotational state distributions is provided by a simple classical model which applies the transition-state wave function as a weighting for trajectories starting on a line that separates the intermediate complex from the product channel.

Electronic Resource

1089-7690

AIP Digital Archive

Physics

Chemistry and Pharmacology

The laser-induced fluorescence spectrum of propynal (S1←S0) (A˜ 1A‘←X˜ 1A') has been investigated and a series of perturbations due to singlet–triplet coupling resolved. The singlet–triplet interaction matrix elements are of the order of 280 MHz. Fluorescence decays for both the mixed singlet–triplet eigenstates have been measured and are shown to contain quantum beats due to coherent excitation of nuclear hyperfine levels. This Doppler-free measurement in the time domain leads to an accurate determination of the nuclear hyperfine splittings produced by the two nonequivalent hydrogen atoms. The hyperfine structure has been analyzed for two rotational levels in the 91 vibrational state and gives the following values for combinations of the Fermi contact constants and dipole–dipole constants of the two protons in the pure triplet state: T1(a˜ 3A‘): A(1)FC+ 1/2 (T(1)xx−T(1)yy) ∼46 MHz; A(2)FC+ 1/2 (T(2)xx−T(2)yy) −4 MHz; T(1)zz∼T(2)zz ∼0 MHz. A simple model for the spin distribution in propynal predicts that the Fermi contact constant should be positive for the aldehydic proton and smaller and negative for the acetylenic proton and suggests that the Fermi contact constants make the dominant contribution to the effective hyperfine constants.

Electronic Resource

1089-7690

AIP Digital Archive

Physics

Chemistry and Pharmacology

The photodissociation dynamics of difluorodiiodomethane CF2I2 following 248 nm excitation were studied using the time-of-flight crossed laser-molecular beam technique. There is clear evidence that CF2I2 undergoes exclusively a simultaneous three-body dissociation. Two different reaction channels are observed: the dominant one (86%) yields CF2+I(2P1/2)+I(2P3/2) while the less efficient one (14%) produces the same fragments but in the ground state CF2+I(2P3/2)+I(2P3/2). The angle I–C–I between the recoil velocity vectors of the two departing I atoms was determined to be 120 °. The measured anisotropy parameters of βCF2=−0.8 for the CF2 fragments and βI=+1.1 for the I atoms (in both reaction channels) imply that the excited state symmetry of CF2I@B|2 is B1 (molecular symmetry C2v) and also indicate that the excited state lifetime is significantly shorter than a rotational period. Furthermore, the dissociation energy for the rupture of both C–I bonds was determined to be D0≤53 kcal/mol. Based on this dissociation energy a heat of formation for CF2I2 of ΔH0f, 0 K=−46 kcal/mol was calculated.

Electronic Resource

1089-7690

AIP Digital Archive

Physics

Chemistry and Pharmacology

We investigated the photodissociation of ClNO via the S1 electronic state using a three-dimensional (3D) ab initio potential-energy surface (PES). The dissociation is found to be fast and direct. In the Franck–Condon (FC) region the slope of the potential along the dissociation path is relatively small giving rise to narrow partial absorption peaks. The total absorption spectrum therefore exhibits a broad vibrational structure which is in perfect agreement with recent measurements. The vibrational excitation of the NO fragment is small and can be qualitatively described within the adiabatic approximation. It is found to be very sensitive to the vibrational FC factor in the transition region. The rotational state distribution of NO is highly inverted with a peak around j=30. It is readily explained by the rotational reflection principle. The experimental results are satisfactorily reproduced by our calculations which underlines the overall quality of the calculated PES. Minor adjustments are necessary, however, to quantitatively reproduce the vibrational branching ratio.

Electronic Resource

1089-7690

AIP Digital Archive

Physics

Chemistry and Pharmacology

We investigated the photodissociation of methyl nitrite (CH3 ONO) and methyl thionitrite (CH3 SNO) within the first absorption band (S1 ←S0 ). The calculations were based on a two-dimensional model including the O–NO/S–NO and N=O bond distances as active coordinates. The S1 -potential energy surfaces were calculated with quantum chemical methods and the dynamical calculations were performed exactly within the time-independent approach. The main emphasis is on the origin of diffuse vibrational structure in the photoabsorption spectrum of both molecules. A low potential barrier of 0.086 eV along the O–NO dissociation coordinate in CH3 ONO prevents immediate dissociation and leads to an initial state dependent lifetime for the excited complex of 100–250 fs corresponding to 3–8 NO vibrational periods. CH3 ONO decays nonadiabatically via vibrational predissociation. The absorption spectrum of CH3 ONO is dominated by narrow Feshbach-like scattering resonances which can be characterized by two quantum numbers, m and n*: m=0 and 1 specifies the quanta of excitation in the O–NO bond and n*=0,1,2,... specifies the excited vibrational level of the N=O bond. The potential barrier is absent in CH3 SNO and the dissociation is direct on the time scale of about 10 fs corresponding to only one third of a NO vibrational period. Nevertheless, the absorption spectrum exhibits diffuse vibrational structures. The shape of the individual absorption peaks is determined by the classical Franck–Condon reflection principle. The dissociation of CH3 SNO is primarily adiabatic which leads to a pronounced energy dependence of the final NO vibrational state distribution. The diffuse structures originate in both cases from excitation of the NO stretching vibration. In order to make contact with time-dependent theory we calculated the autocorrelation function of the time-dependent wave function by inverse Fourier transformation of the energy-dependent spectra. The agreement with available experimental data for both molecules is quite satisfactory. This includes the energy spacing of the vibrational structure, the overall shape of the absorption spectrum, and thelifetime of the excited complex.

Electronic Resource

1089-7690

AIP Digital Archive

Physics

Chemistry and Pharmacology

The photodissociation of cis-CH3 ONO following excitation into the first absorption band near 350 nm is investigated by means of classical trajectories and an ab initio potential energy surface. The calculations include the O–N coordinate, the N=O coordinate, and the ONO bending angle as variables whilst the internal degrees of freedom of the CH3 O moiety are kept fixed. The calculated lifetimes range from 120 to 410 femtoseconds for excitation of the n*=4 to n*=0 vibrational states of the terminal NO group in the intermediate complex. They agree well with the lifetimes estimated from the anisotropy parameter β. The ONO bending degree of freedom has only a small effect on the lifetime of the complex. The final vibrational state (n) distribution of the NO fragment exhibits a systematic energy dependence which manifests itself in a propensity for the excitation of level n=n*−1 that is in excellent agreement with the measurement. Two-dimensional calculations for a fixed ONO bending angle cannot satisfactorily reproduce these experimental findings. The rotational state distributions are highly inverted with maxima around j∼30–35 depending slightly on the initial state (n*) and the final state (n) of NO. The overall agreement with the measured distributions is satisfactory. The results of this study emphasize the importance of the bending degree of freedom in the dissociation of CH3 ONO and by revealing the interplay of the three active vibrational modes they provide a detailed picture of the predissociation mechanism in a polyatomic molecule.

Electronic Resource

1089-7690

AIP Digital Archive

Physics

Chemistry and Pharmacology

We have investigated the photodissociation of FNO in the first absorption band (S0→S1) by a two-dimensional wave packet study based on an ab initio potential energy surface. The quantum chemical calculations were performed in the multiconfiguration self-consistent field (MCSCF) approach including the N–O and the F–NO bond distances with the FNO bond angle being fixed. The most striking feature of the time-dependent dynamical analysis is a bifurcation of the wave packet near the Franck–Condon point: while one part of the wave packet leaves the inner region of the potential energy surface very rapidly, a second part remains trapped for several periods in an extremely shallow well at short F–NO distances. The direct part leads to a broad background in the absorption spectrum while the trapped portion of the wave packet gives rise to relatively narrow resonances, i.e., well resolved diffuse vibrational structures. The bandwidth decreases with the degree of internal excitation. The calculated spectrum agrees well with the measured one.

Electronic Resource

1089-7690

AIP Digital Archive

Physics

Chemistry and Pharmacology

We study experimentally and theoretically reflection-type structures in the rotational distributions of NO following the photodissociation of FNO via excitation of the S1 state. Exciting quasibound states with zero quanta of bending vibration in the FNO(S1) state yields Gaussian-type rotational distributions, while excitation of states with one bending quantum leads to bimodal distributions. In the latter case, the ratio of the two intensity maxima depends on the number of NO stretching quanta in the S1 state. The accompanying calculations employing a three-dimensional ab initio potential energy surface for the S1 state of FNO are performed in the time-dependent wave packet approach. They reproduce the main features of the experimental distributions, especially the bimodality. The analysis of two-dimensional calculations for a frozen NO bond distance shows that the final rotational state distributions can be explained as the result of a dynamical mapping of the stationary wave function on the transition line onto the fragment rotational quantum number axis. Here the transition line is defined as the line which separates the inner part of the FNO(S1) potential energy surface from the strongly repulsive F+NO product channel.

Electronic Resource

1089-7690

AIP Digital Archive

Physics

Chemistry and Pharmacology

The rotational state dependence of the radiationless processes of S1 propynal, HC≡CCHO, was investigated in three selected vibronic bands located at an excess energy of about 3000 cm−1 in a molecular beam using molecular quantum beat spectroscopy. The number of quantum beat frequencies counted in single rovibronic fluorescence decays shows a clear dependence on the rotational quantum number N of the excited rovibronic singlet state, reflecting an increase of the number of coupling triplet states nT by a factor of 4, from N=0 to 14. This increase is accompanied by a lengthening of the decay lifetimes by a factor of 3. Given eigenstate resolution, the effect of magnetic interactions in the triplet state is discussed and it is concluded that the N dependence is predominantly due to mixing of K states resulting in a symmetry breakdown. This mixing is proposed to be mainly induced by hyperfine interaction via the dipole–dipole term.

Electronic Resource