Optical Anisotropy of Photonic Crystals of Cubic Symmetry Induced by Multiple Diffraction of Light

The optical spectra of Bragg reflection from opal-like photonic crystals under conditions of the resonant enhancement of the multiple diffraction of light have been studied experimentally and theoretically using the photonic crystal structures prepared of monodisperse polystyrene globules. It is shown that the reflection signal registered in mutually orthogonal configurations of the polarizer and analyzer is related to the intrinsic optical anisotropy of the crystals and is a specific manifestation of the multiple Bragg diffraction in three-dimensional photonic crystals.     

Interference of polariton waves in structures with wide GaAs/AlGaAs quantum wells

The optical reflection spectra of semiconductor GaAs/AlGaAs structures with wide quantum wells are studied experimentally. A theoretical analysis of the spectra is performed in terms of the exciton-polariton model in the approximation of quantum confinement of the exciton center of mass with regard to the contributions of both heavy and light excitons to the crystal polarization. The applicability range of the theory of the center-of-mass confinement for GaAs/AlGaAs heterostructures is estimated. It is established that, for quantum wells more than 180 nm wide, the interference effects observed in the reflection spectra of polariton waves are reproduced, to a good accuracy, by theoretical calculations based on the quantum confinement of the exciton center of mass. For quantum-well widths less than 150 nm, the experimental results are described better by the model of quantum confinement of electrons and holes.     

The energy localization problem and the renormalized vacuum energy in static Robertson-Walker universes

We calculate the renormalized quantum vacuum energy inside a spherical boundary for the massless conformal scalar field in curved background Robertson-Walker geometry. We use the mode sum method with an exponential cutoff. In our calculations we do not make assumptions about the exterior geometry or the global topology of the universe.     

Subspace-based MRS data quantitation of multiplets using prior knowledge

Accurate quantitation of Magnetic Resonance Spectroscopy (MRS) signals is an essential step before converting the estimated signal parameters, such as frequencies, damping factors, and amplitudes, into biochemical quantities (concentration, pH). Several subspace-based parameter estimators have been developed for this task, which are efficient and accurate time-domain algorithms. However, they suffer from a serious drawback: they allow only a limited inclusion of prior knowledge which is important for accuracy and resolution. In this paper, a new method is presented: KNOB-SVD and its improved variant KNOB-TLS. KNOB-SVD is a recently proposed method, based on the Singular Value Decomposition (SVD), which allows the use of more prior knowledge about the signal parameters than previously published subspace-based methods. We compare its performance in terms of robustness and accuracy with the performance of three commonly used methods for signal parameter estimation: HTLS, a subspace-based method which does not allow any inclusion of prior knowledge, except for the model order; HTLSPK(Delta fd(eq)), a subspace-based method obtained by incorporating in HTLS the prior information that the frequency differences between doublet components are known and the damping factors are equal; and AMARES, an interactive maximum likelihood method that allows the inclusion of a variety of prior knowledge. Extensive simulation and in vivo studies, using (31)P as well as proton MRS signals, show that the new method outperforms HTLS and HTLSPK(Delta fd(eq)) in robustness, accuracy, and resolution, and that it provides parameter estimates comparable to the AMARES ones.     

Joint spare parts inventory and reliability decisions under a service constraint

Reliability and inventory levels of spare parts are major factors that determine the service level for the maintenance of machines provided by original equipment manufacturers (OEMs). In general, decisions on reliability and stock levels are made separately in practice, and academic literature offers little guidance on how to jointly make these two decisions. In order to fill in the gap in the literature and provide guidance to OEMs, we jointly model reliability and inventory problems. We consider three different service measures: aggregate fill rate, average downtime per system per year and expected total number of long downs in a year. Our models minimize the sum of holding and emergency shipment costs subject to a limited reliability improvement budget and a target service level. We develop an algorithm that considers reliability and inventory decisions simultaneously, test our solution approach on real-life and randomly generated data sets and compare the results with an approach that considers reliability and inventory decisions sequentially. Numerical results show substantial benefits of integrating reliability and inventory decisions.     

Pore hierarchy in mesoporous silicas evidenced by in-situ SANS during nitrogen physisorption

The pore hierarchy of a hierarchical porous SiO2 with 14 nm spherical mesopores and 3 nm worm-like pores (KLE1C16) is studied by small-angle neutron scattering (SANS) in combination with in-situ nitrogen sorption at 77 K. A novel setup is used developed at Hahn-Meitner Institute, Berlin. It is demonstrated that in these materials indeed all of the large mesopores are connected through the smaller ones, thus providing invaluable insights into the general phenomenon of pore connectivity in mesoporous materials.     

On \mathfrak{F}-reachable subgroups of finite groups

The structure of $\mathfrak{F}$ -reachable subgroups in Θ-Frattini extensions is established.     

Experimental and theoretical study on the structure and vibrational spectra of β-2-aminopyridinium dihydrogenphosphate

Experimental and theoretical vibrational spectra of β-2-aminopyridinium dihydrogenphosphate (β-2APDP) have been investigated. The FT-IR spectrum of β-2APDP was recorded in the region 4000-400 cm(-1). The optimized molecular structure and theoretical vibrational frequencies of β-2APDP have been investigated using ab initio Hartree-Fock (HF) and density functional B3LYP method with 6-311++G(d,p) basis set. The optimized geometric parameters (bond lengths and bond angles) and theoretical frequencies have been compared with the corresponding experimental data and it is found that they agree well with each other. All the assignments of the theoretical frequencies were performed by potential energy distributions using VEDA 4 program. Furthermore, the used scale factors were obtained from the ratio of the frequency values of the strongest peaks in the experimental and theoretical IR spectra. From the results it was concluded that the B3LYP method is superior to the HF method for the vibrational frequencies.     

Amine-modified maleic anhydride containing terpolymers for the adsorption of uranyl ion in aqueous solutions

Maleic anhydride–styrene–methyl methacrylate (MA–S–MM) terpolymer was prepared. It was modified by ethylenediamine (EDA) and diethylenetriamine (DETA) in order to get cross-linked polymers bearing carboxyl and amine groups. Modified polymers used as an adsorbent for the removal of UO₂ ²⁺ from water. The characterizations of structures of all the polymers were performed by Fourier transform infrared. The adsorptive features of adsorbents were then investigated for UO₂ ²⁺ in view of dependency on ion concentration, pH, temperature and kinetics. Experimentally obtained isotherms were evaluated with reference to Langmuir, Freundlich and Dubinin–Radushkevich models. The maximum monolayer adsorption capacity for UO₂ ²⁺ was found to be 1.59 and 2.43 mol kg^?1 for EDA–MA–S–MM and DETA–MA–S–MM, respectively. It can be said that the new modified polymers prepared in our laboratory have been suggested as new adsorbents for uranyl ions.