Vol 48, No 1 (2017)

Different nuclear magnetic resonance (NMR) methods such as spectroscopy, diffusometry and relaxometry are applied with the aim to monitor motor oil degradation. Chemical degradation is detected by ¹H NMR spectroscopy. With respect to quality control, low-field NMR is the established technique, which mostly uses relaxation and diffusion. Conventional methods such as mono-exponential data modeling lead to inadequate description of relaxation and diffusion data of complex fluids like motor oils. Inverse Laplace transform has difficulties in quantification, comparability and interpretation. Therefore, various data processing approaches are investigated to obtain the physico-chemically and numerically most correct description of the data. The gamma distribution model for diffusion and also for T₁ and T₂ relaxation data numerically describes the data with high accuracy. Three differently degraded motor oils were exemplarily investigated with regard to spectroscopic, relaxation and diffusion parameters.

Study of human pathologies and acquisition of anatomical images without any surgical intervention inside human body is possible because of magnetic resonance imaging (MRI), which is the keystone technique to characterize the psychology and neurochemistry of human body. However, for clinical trials, the study and cure of human diseases are followed by medical investigations of different animal anatomies. By employing different imaging techniques to animal anatomical models during their clinical trials yielded in exceptional image acquisition without any surgical invasion in the model, which resulted in noninvasive technique as compared to surgical invasion and opened the possibility to study human pathologies more precisely. This work exploits the notable properties of unique combination of multi-circular hybridized surface coils which can be used as hybridized magnetic metamaterial hat (HMMH). HMMH not only strengthens the uniformity of radio frequency (RF) rotational symmetry around its axis but also improves the signal-to-noise ratio (SNR) for rat’s brain imaging at 7-T MRI. We analyzed a periodic array of strongly coupled circular copper coils attached on circular coil shaped printed circuit board (PCB) substrate. In the design, some copper coils were inspired by the slot cavity loaded with parametric elements (capacitor and inductor). In addition, coils in the form of HMMH exploited the advantages of the hybrid modes which exhibited better and deeper RF sensitivity into the region of interest (ROI) as compared to single loop RF coil by exciting two Eigen modes simultaneously which resulted in homogenized magnetic field (B-field) and enhanced SNR at ROI. At resonance, the value of relative negative permeability, μ_r = −7 + j11 was achieved at 300 MHz for 7-T MRI. Furthermore, image quality at ROI was optimized by varying rat’s head position under magnetic resonance (MR) coil of MRI apparatus and in the presence or absence of HMMH. Design configuration and circuit model analysis were also done.

The Dy^III ions in the dimer [Dy₂(H₂tea)₂(O₂CPh)₄]·2H₂O (1) (H₃tea = triethanolamine) have the 9-coordinate monocapped square-antiprismatic ligand field environment. Compound 1 shows slow relaxation of magnetization which is observable only with applied magnetic fields. This is consistent with the idea that low-symmetry ligand fields allow for the quantum tunneling of magnetization. This is reflected by the fact that there are no observable maxima in the out-of-phase ac susceptibility above 1.8 K. The {g}-tensor of the Dy^III ions {g_x = 11, g_y = 8.2, g_z = 1} further underlying the reduced uniaxiality in this system was determined in electron paramagnetic resonance (X- and Q-band) studies of 1 at temperatures down to 4 K.