Experimental and theoretical investigations of tellurium(IV) diimides and imidotelluroxanes: X-ray structures of B(C6F5)3 adducts of OTe(mu-NtBu)2TeNtBu, [OTe(mu-NtBu)2Te(mu-O)]2 and tBuNH2

The hydrolysis of (t)BuNTe(mu-N(t)Bu)(2)TeN(t)Bu (1) with 1 or 2 equiv of (C(6)F(5))(3)B.H(2)O results in the successive replacement of terminal imido groups by oxo ligands to give the telluroxane-Lewis acid adducts (C(6)F(5))(3)B.OTe(mu-N(t)Bu)(2)TeN(t)Bu (2) and [(C(6)F(5))(3)B.OTe(mu-N(t)Bu)(2)Te(mu-O)](2) (3), which were characterized by multinuclear NMR spectroscopy and X-ray crystallography. The Te=O distance in 2 is 1.870(2) A. The di-adduct 3 involves the association of four (t)()BuNTeO monomers to give a tetramer in which both terminal Te=O groups [d(TeO) = 1.866(3) A] are coordinated to B(C(6)F(5))(3). The central Te(2)O(2) ring in 3 is distinctly unsymmetrical [d(TeO) = 1.912(3) and 2.088(2) A]. The X-ray structure of (C(6)F(5))(3)B.NH(2)(t)()Bu (4), the byproduct of these hydrolysis reactions, is also reported. The geometries and energies of tellurium(IV) diimides and imido telluroxanes were determined using quantum chemical calculations. The calculated energies for the reactions E(NR)(2) + Te(NR)(2) (E = S, Se, Te; R = H, Me, (t)Bu, SiMe(3)) confirm that cyclodimerization of tellurium(IV) diimides is strongly exothermic. In the mixed-chalcogen systems, the cycloaddition is energetically favorable for the Se/Te combination. The calculated energies for the further oligomerization of the dimers XE(mu-NMe)(2)EX (E = Se, Te; X = NMe, O) indicate that the formation of tetramers is strongly exothermic for the tellurium systems but endothermic (X = NMe) or thermoneutral (X = O) for the selenium systems, consistent with experimental observations.     

Mass spectrometric behaviour of simple oxazolidines under electron impact and chemical ionization

The 70 eV electron impact mass spectra of 33 differently substituted oxazolidines were studied to determine the effect of substituents and the existence of the ring—chain tautomeric equilibrium on the decomposition of the molecular ions. Most of the fragmentations can be rationalized to start as the cleavage initiated by the radical site at nitrogen. Isomeric compounds showed different spectra and were easily differentiated. The position of the ring—chain equilibrium could be located only roughly. The chemical ionization mass spectra of the compounds were also recorded, with ammonia, isobutane, acetone or methane as reagent gas. Methane was the only reagent gas that promoted extensive fragmentation of the protonated molecules. However, no information about the position of ring-chain tautomerism was obtained under these conditions. Analogously to other related five-membered heterocycles, the oxazolidines reacted under acetone chemical ionization conditions to afford [M + CH₃CO]⁺ adduct ions. These adducts were stable, however, and unlike those of 1,3-dioxolanes and 1,3-oxathiolanes, they did not decompose and form stable oxonium ions.     

Effect of the Solvent Flow Rate on the Ionization Efficiency in Atmospheric Pressure Photoionization-Mass Spectrometry

In the novel atmospheric pressure photoionization-mass spectrometry the ionization efficiency has been observed to decrease when the solvent flow rate is increased. The effect of the flow rate on the ionization efficiency was studied by comparing the behavior of two analytes, one of which is ionized through charge exchange, the other through proton transfer. Additional information about the ion loss mechanisms was obtained by comparing results obtained with two different APPI ion sources: a Sciex prototype and the Agilent/Syagen APPI source. In addition to the measurements done by using the mass analyzer, the total ion current in the ion source was obtained by measuring the currents of the ions arriving at curtain/end plate and orifice/capillary of the two mass spectrometers. The total ion current measurements showed a significant decrease at high solvent flow rates. Loss of dopant radical cations was thought to be the reason for the signal decrease of the analytes formed through charge exchange. Analytes formed through proton transfer were not as seriously ected by the high solvent flow rates, but some saturation of their signal was nevertheless observed. Loss of photons through absorption by solvent vapor is another mechanism that can be held responsible for a reduction of the total number of ions produced by the APPI source.     

Infrared spectrum of CO2 in the region of the bending fundamental ν2

The infrared spectrum of CO₂ in the region 540–830 cm^?1 has been studied with a Fourier spectrometer at a resolution of 0.010 cm^?1. In addition to the fundamental ν₂, more than 10 “hot” band transitions of ¹²C¹⁶O₂ have been identified. The rotational constants involved have been derived. Special care has been taken in obtaining accurate constants for the level 01¹0. The ν₂ fundamentals of the isotopic molecules ¹³C¹⁶O₂, ¹⁶O¹²C¹⁸O, and ¹⁶O¹²C¹⁷O have also been observed in a natural sample.     

Coupling Element-Based Dual-Antenna Structures for Mobile Terminal with Hand Effects

This paper presents a comprehensive simulation study on the performance of coupling element-based dual-antenna structures on a mobile terminal at the 2,000 MHz Universal Mobile Telecommunications System (UMTS) frequency band with varying two significant hand effects; vertical position of hand along terminal chassis, and distance between hand palm and terminal chassis. The results reveal that in uniformly distributed isotropic environment, there exists a gain imbalance between antenna elements due to hand effects and it is shown that a gain imbalance of 3.7 dB lead to a reduction of 1.9 dB in diversity gain at 99% reliability level using maximal ratio combining (MRC) technique. For a dual-antenna configuration, the impact of gain imbalance on diversity gain is more significant when only one antenna element is in close proximity to the hand, compared to when both antenna elements are in the presence of the hand. It is also shown that a dual-antenna structure with elements vertically oriented along the edges of a small 100 mm × 40 mm mobile terminal chassis achieves better performance in port-to-port isolation, gain imbalance and diversity gain compared to other studied dual-antenna configurations when the user’s hand is present.     

Performance Analysis of Maximum SNR Scheduling with an Infrastructure Relay Link

We consider infrastructure-based amplify-and-forward (AF) relaying for extending downlink and uplink coverage areas of a cellular base station. The base station serves multiple mobile users via a multi-hop backhaul relay link by sharing out access link channel resources with maximum signal-to-noise ratio (SNR) scheduling. We analyze the performance of the system by deriving closed-form expressions for outage probability, outage capacity, ergodic capacity, average end-to-end SNR and amount of fading (AoF). These measures show that maximum SNR scheduling of multiple users in a cellular relay link offers significant diversity, capacity and SNR improvement over single-user transmission and round robin scheduling. We also relate performance of the relay link to that of a distributed antenna system (DAS), and show that the noisy wireless backhaul relay link induces tolerable performance deterioration compared to deploying a cable-connected distributed antenna.     

Mechanisms of postsynthesis doping of boron nitride nanostructures with carbon from first-principles simulations

Electron-beam-mediated postsynthesis doping of boron-nitride nanostructures with carbon atoms [Nature (London) 464, 571 (2010); J. Am. Chem. Soc. 132, 13?692 (2010)] was recently demonstrated, thus opening a new way to control the electronic properties of these systems. Using density-functional theory static and dynamic calculations, we show that the substitution process is governed not only by the response of such systems to irradiation, but also by the energetics of the atomic configurations, especially when the system is electrically charged. We suggest using spatially localized electron irradiation for making carbon islands and ribbons embedded into BN sheets. We further study the magnetic and electronic properties of such hybrid nanostructures and show that triangular carbon islands embedded into BN sheets possess magnetic moments, which can be switched on and off by electrically charging the structure.     

Stability considerations of a high-temperature superconductor tape at different operating temperatures

Stability of a Bi-2223/Ag multifilamentary composite conductor against fast transport current ramps was studied by using a numerical model. The model was based on the two-dimensional magnetic diffusion and heat conduction equations. Calculations were carried out both in an adiabatic mode and pool boiling modes in liquid helium, hydrogen and nitrogen. When estimating the heat load (AC losses), real temperature dependent current density–electric field characteristics were used. The results computed by the finite element method are presented and discussed with special emphasis on differences of the stability considerations between high-temperature and low-temperature superconductors.     

Estimating a linear functional relationship under linear constraints for errors

Maximum likelihood estimates for parameters in a linear functional relationship are derived when the errors are also linearly related for each observation. This is approximately the case, for example, when both variables are smooth functions of time and their values are recorded as an experimental unit reaches a certain state. This kind of model specification was needed to describe how the timing of growth cessation of trees depends on night length and temperature sum. If the slope in the constraint equation for errors varies, then an iterative estimation procedure is needed. The estimation method is extended for a two-phase linear model.