A Note on Forecasting with Adaptive Filtering

Adaptive filtering has been suggested as a short-term-forecasting technique that is superior to other time series analysis methods. This note discusses several aspects of adaptive filtering and indicates its equivalence to an autoregressive process. The performance of adaptive filtering and two other forecasting techniques are compared for a particular time series.     

The use of localized molecular orbitals and the polarization propagator to identify transmission mechanisms in nuclear spin-spin couplings

An extension of the IPPP (inner projections of the polarization propagator) method to theoretically analyze transmission mechanisms of indirect nuclear spin-spin couplings is presented. The localization technique used is modified so that all the canonical molecular orbitals of a compound may be localized to represent chemical bonds, lone pairs, and the corresponding antibonding molecular orbitals. These localized molecular orbitals, together with the polarization propagator, are used to obtain an intuitive picture of how a coupling is generated as a sum of terms, each one consisting of two particle-hole single excitations. This picture can be used to identify underlying transmission mechanisms and quantitatively evaluate their importance toward the total coupling. The paramagnetic spin-orbit and the spin-dipole interactions are studied in detail.     

On the capriciousness of the FCCF Karplus curve

Numerous well-behaved Karplus curves correlating dihedral angle (phi) and NMR coupling constants (3JXY) exist for X-C-Z-Y fragments with X or Y = H, C, F, and P. Absent is the enigmatic F-C-C-F moiety. By calculating the four Ramsey contributions to 3JFF for F-CH2-CH2-F, a pleasing phi/3JFF curve with both positive and negative regions arises. Unlike the H-C-C-H curve, F-C-C-F is PSO vs FC dominated. The latter and the F lone electron pairs cause both the negative J values and the substituent-induced J-leveling effect.     

Low-temperature ozone treatment for carbon nanotube template removal: improving the template-based ALD method

This work addresses the production of stand-alone ceramic nanotubes by the template-based ALD method at low temperature. Nitrogen-doped multiwalled carbon nanotubes (CNTs) were coated with ZnO. Afterward, the template removal was evaluated by two different approaches: using oxidation in dry air or in an ozone-rich atmosphere. The samples treated by the two different methods were analyzed by XRD, TEM, SAED, and Raman spectroscopy. The dry air atmosphere requires high temperatures (~?700 °C) for a complete CNT removal; at that temperature, the ZnO tubular shape is completely collapsed due to recrystallization. Under ozone atmosphere, the template can be removed at temperatures as low as 85 °C; this temperature is lower than the ALD preparation temperature (120 °C). The ozone treatment maintains the tubular shape of the ZnO nanostructures. Photocatalytic activity of the ZnO samples was evaluated using the photo-oxidation of Amaranth as probe reaction, showing a higher activity the ZnO nanotubes obtained from the low-temperature ozone treatment than the high-temperature processed materials. The use of ozone for the template removal reinforces the template-based ALD method to produce inorganic nanotubes.     

Synthesis of Dienals by Condensation of Carbonyl Compounds with a New Reagent,the 4-Lithio-1-trimethylsiloxybutadiene

Carbonyl compounds 2 are converted into conjugated dienals 3. in a one pot reaction, by a condensation with lithio-4 trimethylsiloxybutadiene, followed by a mild acidic hydrolysis.     

Isomerization Energy Decomposition Analysis for Highly Ionic Systems: Case Study of Starlike E5Li7+ Clusters

The most stable forms of E₅Li₇⁺ (E=Ge, Sn, and Pb) have been explored by means of a stochastic search of their potential‐energy surfaces by using the gradient embedded genetic algorithm (GEGA). The preferred isomer of the Ge₅Li₇⁺ ion is a slightly distorted analogue of the D_5h three‐dimensional seven‐pointed starlike structure adopted by the lighter C₅Li₇⁺ and Si₅Li₇⁺ clusters. In contrast, the preferred structures for Sn₅Li₇⁺ and Pb₅Li₇⁺ are quite different. By starting from the starlike arrangement, corresponding lowest‐energy structures are generated by migration of one of the E atoms out of the plane with the a corresponding rearrangement of the Li atoms. To understand these structural preferences, we propose a new energy decomposition analysis based on isomerizations (isomerization energy decomposition analysis (IEDA)), which enable us to extract energetic information from isomerization between structures, mainly from highly charged fragments.