Low temperature far IR spectra of (CH34)N NiCl3, (CH3)4N NiBr3 and (CD3)4N NiBr3

The known phase transition in (CH₃)₄N NiCl₃, at 171 K, has been characterised by far IR spectroscopy. The transition is explained as due to a formation of weak labile C-H,…, Cl hydrogen bonds at low temperatures, restricting the “free” internal rotations of the methyl groups and perhaps at the same time ordering the orientations of the tetramethylammonium ions. No similar transition in (CH₃)₄N NiBr₃ was found.     

IVUS flow measurements: line spread function and decorrelation pattern

A method to measure transverse blood flow, based on correlation between consecutive radio frequency (RF) signals, has been developed. Currently, we are implementing the method for an intravascular (IVUS) array catheter. In this paper, the acoustical beam (line-spread function, LSF) was experimentally measured and compared with the simulated one. Next, the experimental LSF(E) was convolved with a matrix of white noise to produce RF(E) signals. Decorrelation pattern from the RF(E) signals was compared with the correspondent autoconvolution of the LSF(E) and a good agreement was found. We conclude that the transverse decorrelation pattern of the IVUS array catheter can be assessed from the properties of the acoustical beam.     

New Insights into the Diels–Alder Reaction of Graphene Oxide

Graphene oxide is regarded as a major precursor for graphene‐based materials. The development of graphene oxide based derivatives with new functionalities requires a thorough understanding of its chemical reactivity, especially for canonical synthetic methods such as the Diels–Alder cycloaddition. The Diels–Alder reaction has been successfully extended with graphene oxide as a source of diene by using maleic anhydride as a dienophile, thereby outlining the presence of the cis diene present in the graphene oxide framework. This reaction provides fundamental information for understanding the exact structure and chemical nature of graphene oxide. On the basis of high‐resolution ¹³C‐SS NMR spectra, we show evidence for the formation of new sp³ carbon centers covalently bonded to graphene oxide following hydrolysis of the reaction product. DFT calculations are also used to show that the presence of a cis dihydroxyl and C vacancy on the surface of graphene oxide are promoting the reaction with significant negative reaction enthalpies.     

Identification of Nonlinear Oscillator with Parametric White Noise Excitation

An identification technique is proposed for a nonlinear oscillator excited by response-dependent white noise. Stiffness, damping and excitation are estimated from records of the stationary stochastic response. The estimation of the stiffness is based on a nonparametric procedure in which the potential energy at the displacement extremes is obtained from the kinetic energy at the previous mean-level-crossing. A nonparametric estimate is obtained by an iterative averaging, in which the increased knowledge of the potential energy in each step is used to avoid bias. The second step in the procedure is to estimate the stationary probability potential in a nonparametric form from a histogram of the kinetic energy at mean-level-crossings. The damping is also estimated in a nonparametric way from approximate expressions of the covariance functions of a set of modified phase plane variables at a given energy level. Finally, the excitation is estimated from a relation between the stationary probability potential, the damping and the excitation. The separation of damping and excitation requires a parametric representation. The system identification technique is investigated by application to response records obtained by stochastic simulation. The stiffness estimation generally gives excellent results, while the damping and excitation estimation tend to be slightly biased for systems with strongly nonlinear stiffness.     

The measurement of magnetic susceptibilities with commercially available milli-oerstedmeters,III

In preceeding papers a method was described for measuring magnetic susceptibilities without the use of a balance. In the present paper the application of that method to low and high temperature measurements is reported. The measurement accuracy is some factor 30 smaller than in the earlier experiments, because of the necessary alterations in the set-up. Measurements on CuSO₄-5H₂O are in support of the data reported by Reekie.     

Gas‐Phase Spectroscopy of Ferric Heme?NO Complexes

Weakly bound complexes between ferric heme cations and NO were synthesised in the gas phase from ion–molecule reactions, and their absorption measured based on photodissociation yields. The Soret band, which serves as an important marker band for heme‐protein spectroscopy, is maximal at 357±5 nm and significantly blue‐shifted compared to ferric heme nitrosyl proteins (maxima between 408 and 422 nm). This is in stark contrast to the Q‐band absorption where the protein microenvironment is nearly innocent in perturbing the electronic structure of the porphyrin macrocycle. Photodissociation is primarily through loss of NO. In contrast to the Q‐band region, two‐photon absorption was seen in the Soret band despite NO loss only requiring ～1 eV. A model based on intersystem crossing to a long‐lived triplet state where a barrier has to be surmounted is suggested. Finally, we summarise the measured absorption maxima of heme and its complexes with amino acids and NO.