Neutron powder diffraction of metal-organic frameworks for hydrogen storage

We review recent structural studies that we have undertaken aimed at elucidating the fundamental properties of metal-organic framework materials and their interactions with hydrogen. We have shown that exposing coordinatively unsaturated metal centers can greatly enhance the hydrogen binding energy and that they result in a significant increase of the surface packing density of adsorbed hydrogen molecules on materials’ surface. We will review some of the structural aspects of these materials, especially the adsorbed hydrogen molecule surface packing density in one type of metal-organic framework, MOF-74, which can be packed even denser than that in solid hydrogen.      

Probabilistic signatures of spatiotemporal intermittency in the coupled sine circle map lattice

The phase diagram of the coupled sine circle map system exhibits a variety of interesting phenomena including spreading regions with spatiotemporal intermittency, non-spreading regions with spatial intermittency, and coherent structures termed solitons. A spreading to non-spreading transition is seen in the system. A cellular automaton version of the coupled system maps the spreading to non-spreading transition to a transition from a probabilistic to a deterministic cellular automaton. The solitonic sector of the system shows spatiotemporal intermittency with soliton creation, propagation and absorption. A probabilistic cellular automaton mapping is set up for this sector which can identify each one of these phenomena.      

Controlled synthesis of CeO<Subscript>2</Subscript> nanoparticles using novel amphiphilic cerium complex precursors

Maleic anhydride was grafted by long-chain alcohols (1-hexadecanol, 1-octadecanol) to amphiphilic mono-L cis-butene dicarboxylates (L = hexadecyl, octadecyl), i.e., MAH, MAO, respectively. Subsequently, corresponding amphiphilic cerium complexes with these two mono-L cis-butene dicarboxylate ligands (Ce(L')₃, L'= MAH, MAO) were synthesized and behaved as the precursors to prepare CeO₂ nanoparticles for both of which can form nanosized micelle-like aggregates by special self-assembly in the wet chemical process. The nanoparticles were further characterized by Fourier transform-infrared spectroscopy (FTIR), Diffuse reflectance ultraviolet-visible spectra (DRUVS), scanning electron microscope (SEM), transmission electron microscope (TEM), and x-ray diffraction (XRD). Both the CeO₂ nanoparticles are in a cubic fluorite structure and present regular and well-dispersion club-like morphology with average particle size in the range of 40–70 nm. Besides, the strong ultraviolet–visible absorption for these CeO₂ nanoparticles can be found at the long-wavelength ultraviolet to visible region of 200–500 nm.     

Evidences dominating the formation of ZnO nanostructures via in-situ study in an environmental scanning electron microscope

In order to well understand the growth mechanism of the diverse morphology of the ZnO nanostructures, in situ analysis of the formation of different ZnO nanostructures, such as nanowires, nanocombs, and nanosheets, has been conducted in an environmental scanning electron microscope (ESEM). It is found that both nanocombs and nanosheets grew in two-stage heating processes on parent nanowires. The difference is that the nanocombs were synthesized in extremely high pressure of zinc vapor via a self-catalyzed vapor-liquid-solid process, while the ZnO nanosheets were grown in relatively low pressure of zinc vapor. All the growth processes were revealed in real time imaging. It is demonstrated that the change in the growth environments can influence the thickness of the ZnO polycrystalline surface of the zinc powder, which alters the pressure of the zinc vapor and in turn determines the morphology of the final nanostructures.     

Continuously coupled parametric generators and their quantum statistics

In this paper the quantum-statistical properties of light beams propagating in a directional nonlinear coupler are investigated. This device is composed of a pair of linearly coupled nonlinear waveguides operating by means of degenerate parametric downconversion. The possibility of generation of nonclassical states of light in single and compound modes, using the short-length approximation, is discussed. Influence of linear and nonlinear mismatches for generation of nonclassical light is taken into account. This work was supported by Project LN00A015, Research Project No. CEZ: J14/98 and the COST project OC P11.003 of the Czech Ministry of Education.     

A polarised SUSANS facility to study magnetic systems

Using a right-angled magnetic air prism, we have achieved a separation of ～10 arcsec between ～2 arcsec wide up and down-spin peaks of 5.4 Å neutrons. The polarised neutron option has thus been introduced into the SUSANS instrument. Strongly spindependent SUSANS spectra have been observed over ±1.3 × 10^?4 Å^?1 range for several magnetic alloy samples. Spatial pair-distribution functions for the up and down-spins as well as the nuclear and magnetic scattering length density distributions in the micrometer domain, have been deduced from these spectra.     

Higgs bosons in the standard model,the MSSM and beyond

I summarize the basic theory and selected phenomenology for the Higgs boson(s) of the standard model, the minimal supersymmetric model and some extensions thereof, including the next-to-minimal supersymmetric model.     

Non-linear polarization and chiral effects in birefringent solitons

Novel effects resulting from joint action of chirality and non-linearity are discussed using a basic equation describing the temporal evolution of fields in a chiral medium with Kerr non-linearity. The spatial chirality effect is characterized through the Born-Fedorov formalism. Our simulations are based on the split-step Fourier method and the solution of the Stokes parameters. The numerical results show the chiral effect on solitons with circular polarization and mixed polarization spatial solitons.     

Numerical calculation of cutoff frequencies of optical fibers by a variational technique

A numerical method for calculating cutoff frequencies of modes of weakly guiding optical fibers is described. Starting from a properly constructed field representation, the method follows a variational approach to obtain an eigenvalue problem for the cutoff frequencies which can be easily solved by a standard numerical routine. The field representation uses an expansion in terms of the Laguerre–Gauss functions in the fiber core and limiting form for small arguments of modified Bessel functions in the fiber cladding. Fibers with power-law refractive index profiles and fibers with a profile showing a dip on the axis are analyzed. Results obtained for modes of arbitrary order (both azimuthal and radial) show that our method is very efficient and accurate.     

Phenomenological applications of<Emphasis Type="Italic">k</Emphasis><Subscript>T</Subscript>factorization

We discuss applications of the perturbative QCD approach in the exclusive non-leptonic two-bodyB-meson decays. We briefly review its ingredients and some important theoretical issues on the factorization approach. PQCD results are compatible with present experimental data for charmless B-meson decays. We predict the possibility of large direct CP asymmetry in B⁰ → π⁺π⁻ (23 +7%) and B⁰ →K ⁺π⁻ (− 17 ± 5%). We also investigate the branching ratios, CP asymmetry and isospin symmetry breaking in radiativeB →(K*/ρ)γ decays.