MS-Xα study of the KCl: Cu− spectrum

We have interpreted the KCl:Cu^? spectrum in the context of the MS-X_α method. The results, considering only allowed electric-dipole transitions, are in good agreement with the experimental data. Four new absorption bands, peaking at 573, 390, ～324 and ～310nm, at room temperature, are reported.     

A graph theory approach to subcontracting, machine duplication and intercell moves in cellular manufacturing

We address in this paper the problem of finding an optimal strategy for dealing with bottleneck machines and bottleneck parts in the cell formation process in group technology. Three types of economic decisions are considered: subcontracting, machine duplication and intercell moves. The problem is formulated as a minimum weighted node covering problem in a hypergraph, and we show that it can be solved in polynomial time by finding a maximum weighted stable set in a bipartite graph. We extend this result to cellular manufacturing systems in which the sequence of operations of each part is known in advance.     

Reaction mechanism and rate constants of the CH+CH4 reaction: a theoretical study

Ab initio and density functional calculations have been performed to elucidate the mechanism of CH radical insertion into methane. The results show that the reaction can be viewed to occur via two stages. On the first stage, the CH radical approaches methane without large structural changes to acquire proper positioning for the subsequent stage, where H-migration occurs from CH₄ to CH, along with a C–C bond formation. Where the first stage ends and the second begins, a tight transition state was located using the B3LYP/6-311G(d,p) and MP4(SDQ)/6-311++G(d,p) methods. Using a rigid rotor – harmonic oscillator approach within transition state theory, we show that at the MP5/6-311++G(d,p)//MP4(SDQ)/6-311++G(d,p) level the calculated rate constants are in a reasonably good agreement with experiment in a broad temperature range of 145–581 K. Even at low temperatures, the insertion reaction bottleneck is found about the location of the tight transition state, rather than at long separations between the CH and CH₄ reactants. In addition, high level CCSD(T)-F12/CBS calculations of the remainder of the C₂H₅ potential energy surface predict the CH+CH₄ reaction to proceed via the initial insertion step to the ethyl radical which then can emit a hydrogen atom to form highly exothermic C₂H₄+H products.     

Nonlinear free vibrations of beams in space due to internal resonance

The geometrically nonlinear free vibrations of beams with rectangular cross section are investigated using a p-version finite element method. The beams may vibrate in space, hence they may experience longitudinal, torsional and non-planar bending deformations. The model is based on Timoshenko’s theory for bending and assumes that, under torsion, the cross section rotates as a rigid body and is free to warp in the longitudinal direction, as in Saint-Venant’s theory. The geometrical nonlinearity is taken into account by considering Green’s nonlinear strain tensor. Isotropic and elastic beams are investigated and generalised Hooke’s law is used. The equation of motion is derived by the principle of virtual work. Mostly clamped–clamped beams are investigated, although other boundary conditions are considered for validation purposes. Employing the harmonic balance method, the differential equations of motion are converted into a nonlinear algebraic form and then solved by a continuation method. One constant term, odd and even harmonics are assumed in the Fourier series and convergence with the number of harmonics is analysed. The variation of the amplitude of vibration with the frequency of vibration is determined and presented in the form of backbone curves. Coupling between modes is investigated, internal resonances are found and the ensuing multimodal oscillations are described. Some of the couplings discovered lead from planar oscillations to oscillations in the three dimensional space.     

Effect of glycine substitution on the ferroelectric phase of betaine arsenate [(CH3)3NCH2COO·H3AsO4]

The present work reports an experimental investigation on the influence of glycine (NH₂CH₂COOH) substitution in the polar properties and the critical dynamics of the molecular ferroelectric betaine arsenate, (CH₃)₃NCH₂COO·H₃AsO₄. The dielectric dispersion (20 Hz<ν<3 MHz) and the thermally induced displacement currents are investigated in detail over the extended Curie region of the system (130 K<T<100 K). The results obtained for a single crystal with nominal glycine content of 20% are analyzed, compared with those obtained for pure betaine arsenate and discussed within the scope of a phenomenological Landau model previously used to describe a system with competing ferroelectric and structural instabilities.     

Dark matter results from 100 live days of XENON100 data

We present results from the direct search for dark matter with the XENON100 detector, installed underground at the Laboratori Nazionali del Gran Sasso of INFN, Italy. XENON100 is a two-phase time-projection chamber with a 62 kg liquid xenon target. Interaction vertex reconstruction in three dimensions with millimeter precision allows the selection of only the innermost 48 kg as the ultralow background fiducial target. In 100.9 live days of data, acquired between January and June 2010, no evidence for dark matter is found. Three candidate events were observed in the signal region with an expected background of (1.8 ± 0.6) events. This leads to the most stringent limit on dark matter interactions today, excluding spin-independent elastic weakly interacting massive particle (WIMP) nucleon scattering cross sections above 7.0 × 10(-45) cm(2) for a WIMP mass of 50 GeV/c(2) at 90% confidence level.     

Comparative study of the influence of cavity preparation with high-speed rotation or Er:YAG laser on infiltration of aesthetic restorations

Laser Physics - The aim of the present study was to compare marginal infiltration in Class V cavities prepared on extracted human premolars with either high-speed rotation or a Er:YAG laser. Class...     

Hydrogen bonding in nitrofurantoin polymorphs: a computation‐assisted spectroscopic study

The importance of hydrogen‐bond formation in the molecular packing arrangements of two anhydrous forms of nitrofurantoin is investigated, combining computational methods and spectroscopic data. The overall results indicate, as expected, that the vibrational modes related to the CO, N H and C H groups are strongly affected by intermolecular hydrogen‐bond formation. Moreover, the importance of weak C‐H···O interactions in conferring additional stability to molecular associations in biological systems is evidenced in this study. The complete assignment of the Raman and infrared spectra of both polymorphs is accomplished by means of a computationally based methodology, which accounts for the effects of intermolecular interactions in the crystal. The vibrational shifts due to crystal packing interactions are evaluated from DFT calculations for a set of suitable molecular pairs, using the B3LYP/6‐31G* approach. This methodology provides an answer to the current demand for a reliable and complete assignment of the vibrational spectra of pharmaceutically active compounds such as nitrofurantoin. Copyright © 2009 John Wiley & Sons, Ltd.     

Integrable spin–boson models descending from rational six-vertex models

We construct commuting transfer matrices for models describing the interaction between a single quantum spin and a single bosonic mode using the quantum inverse scattering framework. The transfer matrices are obtained from certain inhomogeneous rational vertex models combining bosonic and spin representations of SU(2)$\mathit{SU}(2)$, subject to non-diagonal toroidal and open boundary conditions. Only open boundary conditions are found to lead to integrable Hamiltonians combining both rotating and counter-rotating terms in the interaction. If the boundary matrices can be brought to triangular form simultaneously, the spectrum of the model can be obtained by means of the algebraic Bethe ansatz after a suitable gauge transformation; the corresponding Hamiltonians are found to be non-Hermitian. Alternatively, a certain quasi-classical limit of the transfer matrix is considered where Hermitian Hamiltonians are obtained as members of a family of commuting operators; their diagonalization, however, remains an unsolved problem.