## 3 Applications of Low Field Magnetic Resonance  
The first set of articles describe the characterization of industrially relevant materials with low field NMR. In [1], the amount of bound water and free water in heat-treated and untreated Chinese Fir heartwood were investigated using various NMR methods. Their results indicated that the heat treatment made it more difficult for the wood to be accessed by moisture, providing a scientific basis for assessing the application of heat-treated wood, especially for outdoor applications. In [2], the authors use low field relaxometry to monitor the change of the evaporable water content in the early hydration process of cement paste, with different water-to-cement ratios. Their results demonstrated that the first derivative curves of the transverse magnetization were in agreement with the known five stages of cement hydration process. In [3], the time-domain nuclear magnetic resonance (TD-NMR) technique was applied to determine the solid content of black liquor which is a by-product of paper pulp production and is used for the recovery of chemicals and serves as an energy source for pulp mills. Before entering the recovery unit, black liquor runs through several stages of evaporation, wherein the solids content can be used to control the evaporation effectiveness. In [4], changes in wettability with the TD-NMR T\({}_{2}\) distribution and diffusion coefficient have been used, starting with a well-controlled glass bead based porous system and then a model rock (Berea), in the presence of one phase, either oil or brine exclusively to investigate the influence of wettability on oil recovery. Another porous media application is presented in [5], where a simplified method for predicting permeability coefficients of clay-quartz mixtures based on NMR technology without centrifugal and evaporation experiments was proposed following the NMR testing of eight clay-quartz mixtures with different mineral compositions. The second set of articles cover more fundamental aspects of the development of low field techniques including image quality improvement and memory-saving in a Permanent-Magnet-Array-Based MRI Systems by approaches of compensating the uneven point population by increasing the numbers of sampling points or rotation angles [6]. In [7], a mini-review summarizes the progress that has been achieved in the coupling between TD-NMR (using low-field spectrometers) and electrochemistry and how the challenges that this coupling poses have been overcome over the years. In [8], advances in the development of a Field Programmable Gate Array (FPGA) based spectrometers for NMR relaxation is described along with applications in NMR cryoporometry. Performing the NMR measurement in the strong heteronuclear J-coupling regime is described in [9] and shows promise for the chemical analysis of small molecules. The results demonstrate that high resolution J-coupled spectra are quantitative, and the common NMR observables, including Larmor frequency, heteronuclear and homonuclear J-couplings, relative signs of the J-coupling, chemical shift and relaxation times, are all measurable and are differentiable between molecules at low magnetic fields. The mini-review in [10] discusses the theory and applications of the Continuous Wave Free Precession (CWFP) sequence in low-field, TD-NMR. CWFP is a special case of the often used Steady State Free Precession (SSFP) sequences and, unlike regular pulsed experiments, in the CWFP regime the amplitude is not dependent on T\({}_{1}\). In [11], TD-NMR is reviewed as a candidate for assisting product and process development in several applications throughout the rubber, plastics, composites, and adhesives industry. Several examples illustrate measurements such as crosslink density in vulcanized rubber and the monitoring of crystallization kinetics. In [12], the authors use hyperpolarized \({}^{13}\)C[1H] NMR to overcome the challenges of low sensitivity and significant peak overlap in \({}^{1}\)H NMR spectra associated with low magnetic fields.