Theory of zeolite catalysis

The reactivity of acidic zeolites to the activation of hydrocarbons is used to illustrate different modeling approaches applied to catalysis. Quantum-chemical calculations of transition-state and ground-state energies can be used to determine elementary rate constants. But to predict overall kinetics, quantum-mechanical studies have to be complemented with statistical methods to compute adsorption isotherms and diffusion constants as a function of micropore occupation. The relatively low turnover frequencies of zeolite-catalyzed reactions compared to superacid-catalyzed reactions are due mainly to high activation energies of the elementary rate constants of the proton-activated reactions. These high values are counteracted by the significant interaction energies of hydrocarbons with the zeolite micro pore wall dominated by van der Waals interactions

Jet formation in BL Lacertae objects with different accretion modes

We estimate the masses of massive black holes in BL Lac objects from their host galaxy luminosity. The power of jets and central optical ionizing luminosity for a sample of BL Lac objects are derived from their extended radio emission and the narrow-line emission, respectively. The maximal jet power can be extracted from a standard thin accretion disk/spinning black hole is calculated as a function of dimensionless accretion rate $\dot{m}$ ($\dot{m}=\dot{M}/\dot{M}_{\rm Edd}$). Comparing with the derived jet power, we find that the accretion disks in most BL Lac objects should not be standard accretion disks. For a pure advection dominated accretion flow (ADAF), there is an upper limit on its optical continuum luminosity due to the existence of an upper limit $\dot{m}_{\rm crit}$ on the accretion rate. It is found that a pure ADAF is too faint to produce the optical ionizing luminosity of BL Lac objects derived from their narrow-line luminosity. We propose that an ADAF is present in the inner region of the disk and it becomes a standard thin disk in the outer region in most BL Lac objects, i.e., ADAF+SD(standard disk) scenario. This ADAF+SD scenario can explain both the jet power and optical ionizing continuum emission of these BL Lac objects. The inferred transition radii between the inner ADAF and outer SD are in the range of $40-150 GM_{bh}/c^2$, if the disks are accreting at the rate $\dot{m}=0.01$.Comment: accepted by Ap

Evidence for the evolutionary sequence of blazars: different types of accretion flows in BL Lac objects

The limits on the mass of the black hole in 23 BL Lac objects are obtained from their luminosities of the broad emission line H\beta on the assumption that broad emission lines are emitted from clouds ionized by the radiation of the accretion disk surrounding a black hole. The distribution of line luminosity L_{H\beta} of all these BL Lac objects suggests a bimodal nature, although this cannot be statistically proven on the basis of the present, rather small sample. We found that standard thin disks are probably in the sources with L_{H\beta}>10^{41} erg s^{-1}. The central black holes in these sources have masses of 10^{8-10} M_\odot, if the matter is accreting at the rate of 0.025 {\dot M}_{\rm Edd}. For the sources with L_{H\beta}<10^{41} erg s^{-1}, the accretion flows have transited from standard thin disk type to the ADAF type. The lower limits on the mass of the black hole in these sources are in the range of 1.66-24.5\times 10^{8} M_\odot. The results support the evolutionary sequence of blazars: FSRQ\to LBL\to HBL.Comment: 5 pages, accepted for publication in ApJ Letter

The COSPIX mission: focusing on the energetic and obscured Universe

Tracing the formation and evolution of all supermassive black holes, including the obscured ones, understanding how black holes influence their surroundings and how matter behaves under extreme conditions, are recognized as key science objectives to be addressed by the next generation of instruments. These are the main goals of the COSPIX proposal, made to ESA in December 2010 in the context of its call for selection of the M3 mission. In addition, COSPIX, will also provide key measurements on the non thermal Universe, particularly in relation to the question of the acceleration of particles, as well as on many other fundamental questions as for example the energetic particle content of clusters of galaxies. COSPIX is proposed as an observatory operating from 0.3 to more than 100 keV. The payload features a single long focal length focusing telescope offering an effective area close to ten times larger than any scheduled focusing mission at 30 keV, an angular resolution better than 20 arcseconds in hard X-rays, and polarimetric capabilities within the same focal plane instrumentation. In this paper, we describe the science objectives of the mission, its baseline design, and its performances, as proposed to ESA.Comment: 7 pages, accepted for publication in Proceedings of Science, for the 25th Texas Symposium on Relativistic Astrophysics (eds. F. Rieger &amp; C. van Eldik), PoS(Texas 2010)25

Accurate ab initio spin densities

We present an approach for the calculation of spin density distributions for molecules that require very large active spaces for a qualitatively correct description of their electronic structure. Our approach is based on the density-matrix renormalization group (DMRG) algorithm to calculate the spin density matrix elements as basic quantity for the spatially resolved spin density distribution. The spin density matrix elements are directly determined from the second-quantized elementary operators optimized by the DMRG algorithm. As an analytic convergence criterion for the spin density distribution, we employ our recently developed sampling-reconstruction scheme [J. Chem. Phys. 2011, 134, 224101] to build an accurate complete-active-space configuration-interaction (CASCI) wave function from the optimized matrix product states. The spin density matrix elements can then also be determined as an expectation value employing the reconstructed wave function expansion. Furthermore, the explicit reconstruction of a CASCI-type wave function provides insights into chemically interesting features of the molecule under study such as the distribution of $\alpha$- and $\beta$-electrons in terms of Slater determinants, CI coefficients, and natural orbitals. The methodology is applied to an iron nitrosyl complex which we have identified as a challenging system for standard approaches [J. Chem. Theory Comput. 2011, 7, 2740].Comment: 37 pages, 13 figure

Magnetic Properties of Monomer and Dimer Tetrahedral VOx Entities Dispersed on Amorphous Silica-based Materials: Prediction of EPR Parameters from Relativistic DFT Calculations and Broken Symmetry Approach to Exchange Couplings

Molecular structures of the isolated tetrahedral oxovanadium(IV) and bridged μ-oxo-divanadium(IV) complexes hosted by the clusters mimicking surfaces of amorphous silica-based materials were investigated using density functional theory (DFT) calculations. Principal values of the g and A tensors for the monomer vanadyl species were obtained using the coupled-perturbed DFT level of theory and the spin–orbit mean-field approximation (SOMF). Magnetic exchange interaction for the μ-oxo bridged vanadium(IV) dimer was investigated within the broken symmetry approach. An antiferromagnetic coupling of the individual magnetic moments of the vanadium(IV) centers in the [VO–O–VO]2+ bridges was revealed and discussed in detail. The coupling explains pronounced decrease of the electron paramagnetic resonance signal (EPR) intensity, observed for the reduced VOx/SiO2 samples with the increasing coverage of vanadia, in terms of transformation of the paramagnetic monomer species into the dimers with S = 0 ground state

Semi-inclusive studies of semileptonic BsB_s decays at Belle

We present an analysis of the semi-inclusive decays $B_s \to D_s^- X \ell^+ \nu$ and $B_s \to D_s^{*-} X \ell^+ \nu$, where $X$ denotes a final state that may consist of additional hadrons or photons and $\ell$ is an electron or muon. The studied $B_s$ decays are contained in the $121.4~{\rm fb}^{-1}$ $\Upsilon(5S)$ data sample collected by the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. The branching fractions of the decays are measured to be $\mathcal{B}(B_s \to D_s^- X \ell^+ \nu) = [8.2 \pm 0.2 (\text{stat}) \pm 0.6 (\text{syst}) \pm 1.4 (\text{ext})]\%$ and $\mathcal{B}(B_s \to D_s^{*-} X \ell^+ \nu) = [5.4 \pm 0.4 (\text{stat}) \pm 0.4 (\text{syst}) \pm 0.9 (\text{ext})]\%$, where the first two uncertainties are statistical and systematic and the last is due to external parameters. The measurement also provides an estimate of the $B_s^{(*)}\bar{B}_s^{(*)}$ production cross-section, $\sigma(e^+e^- \to B_s^{(*)}\bar{B}_s^{(*)}) = (53.8 \pm 1.4 (\text{stat}) \pm 4.0 (\text{syst}) \pm 3.4 (\text{ext}))\,{\rm pb}$, at the center-of-mass energy $\sqrt{s} = 10.86\,{\rm GeV}$.Comment: 13 pages, 2 figures, submitted to Phys. Rev.

Measurements of CP Violation in B0→D∗−π+B^0 \to D^{*-}\pi^+ and B0→D−π+B^0 \to D^- \pi^+ Decays

We report measurements of time dependent decay rates for $B^0 \to D^{(*)-}\pi^+$ decays and extraction of CP violation parameters that depend on $\phi_3$. Using fully reconstructed $D^{(*)}\pi$ events and partially reconstructed $D^{*}\pi$ events from a data sample that contains 386 million $B\bar{B}$ pairs that was collected near the $\Upsilon(4S)$ resonance, with the Belle detector at the KEKB asymmetric energy $e^+ e^-$ collider, we obtain the CP violation parameters $S^+ (D^{(*)}\pi)$ and $S^- (D^{(*)}\pi)$. We obtain $S^+ (D^* \pi) = 0.049 \pm 0.020(\mathrm{stat}) \pm 0.011(\mathrm{sys})$, $S^- (D^* \pi) = 0.031 \pm 0.019(\mathrm{stat}) \pm 0.011(\mathrm{sys})$, and $S^+ (D \pi) = 0.031 \pm 0.030(\mathrm{stat}) \pm 0.012(\mathrm{sys})$, $S^- (D \pi) = 0.068 \pm 0.029(\mathrm{stat}) \pm 0.012(\mathrm{sys})$. These results are an indication of CP violation in $B^0 \to D^{*-}\pi^+$ and $B^0 \to D^- \pi^+$ decays at the $2.5 \sigma$ and $2.2 \sigma$ levels, respectively. If we use the values of $R_{D^{(*)}\pi}$ that are derived using assumptions of factorization and SU(3) symmetry, the branching fraction measurements for the $D_s^{(*)} \pi$ modes, and lattice QCD calculations, we can restrict the allowed region of $|\sin (2\phi_1 + \phi_3)|$ to be above 0.44 and 0.52 at 68% confidence level from the $D^* \pi$ and $D \pi$ modes, respectively.Comment: 14 pages, 12 figures, submitted to Physical Review

Measurement of the branching fractions for B- --> D(*)+ pi- l- nu-bar and B0bar --> D(*)0 pi+ l- nu-bar

We report on a measurement of the branching fractions for B- --> D(*)+ pi- l- nu-bar and B0bar --> D(*)0 pi+ l- nu-bar with 275 million BBbar events collected at the Upsilon(4S) resonance with the Belle detector at KEKB. Events are tagged by fully reconstructing one of the B mesons in hadronic modes. We obtain Br(B- --> D+ pi- l- nu-bar) = (0.54 +/- 0.07(stat) +/- 0.07(syst) +/- 0.06(BR)) x 10^-2, Br(B- --> D*+ pi- l- nu-bar) = (0.67 +/- 0.11(stat) +/- 0.09(syst) +/- 0.03(BR)) x 10^-2, Br(B0bar --> D0 pi+ l- nu-bar) = (0.33 +/- 0.06(stat) +/- 0.06(syst) +/- 0.03(BR)) x 10^-2, Br(B0bar --> D*0 pi+ l- nu-bar) = (0.65 +/- 0.12(stat) +/- 0.08(syst) +/- 0.05(BR)) x 10^-2, where the third error comes from the error on Bbar --> D(*) l- nu-bar decays. Contributions from B0bar --> D*+ l- nu-bar decays are excluded in the measurement of B0bar --> D0 pi+ l- nu-bar.Comment: 6 pages, 10 figures, submitted to Physical Review D (Rapid Communication), the Lepton-Photon 2005 Conference (Uppsala, Sweden) and the HEP2005 Europhysics Conference (Lisboa, Portugal

Observation of B0 to p pbar K*0 with a large K*0 polarization

We observe the decay B0 to p pbar K*0 with a branching fraction of (1.18^{+0.29}_{-0.25} (stat.) \pm 0.11 (syst.)) \times 10^{-6}. The statistical significance is 7.2 sigma for the signal in the low ppbar mass region. We study the decay dynamics of B0 to p pbar K*0 and compare it with B+ to p pbar K*+. The K*0 meson is found to be almost 100% polarized (with a fraction of (101 \pm 13 \pm 3)% in the helicity zero state), while the K*+ meson has a (32 \pm 17 \pm 9)% fraction in the helicity zero state. The direct CP asymmetries for B0 to p pbar K*0 and B+ to p pbar K*+ are measured to be -0.08\pm 0.20\pm 0.02 and -0.01\pm 0.19\pm 0.02, respectively. We also study the characteristics of the low mass ppbar enhancements near threshold and the associated angular distributions. In addition, we report improved measurements of the branching fractions BF(B+ to p pbar K*+) = (3.38^{+0.73}_{-0.60} \pm 0.39) \times 10^{-6} and BF(B0 to p pbar K0) = (2.51^{+0.35}_{-0.29} \pm 0.21) \times 10^{-6}, which supersede our previous measurements. These results are obtained from a 492 fb^{-1} data sample collected near the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e^+ e^- collider.Comment: 11 pages, 4 figures (8 figure files), submitted to Phys.Rev.Let