NMR Imaging of Anisotropic Solid-State Chemical Reactions Using Multiple-Pulse Line-Narrowing Techniques and \u3csup\u3e1\u3c/sup\u3eH T\u3csub\u3e1\u3c/sub\u3e Weighting

The reactions of substituted benzoic acid crystals and powders with ammonia gas have been monitored using solid-state 1H NMR imaging techniques. The reactions are inherently (crystal) or by design (powder) spatially anisotropic: For a crystal of 4-bromobenzoic acid, the expected reaction anisotropy was not seen, either optically or with 1H NMR imaging, most likely due to poor crystal quality or an unexpected crystal morphology. Nevertheless, some anisotropy in the reaction was observed and the extent of reaction was obtained from the NMR images. For a deep bed of powdered toluic acid, an anisotropic reaction profile is found. The reaction of the more exposed top layers of the bed is rapid whereas there is a delay in the reaction of the bottom layers associated with the rate of diffusion of ammonia into the bed. The apparent reaction rate constant, k = 5 (2) × 10−4 mol−1 m3 s−1, and the effective diffusivity, De = 1.0 (4) × 10−5 m2 s−1, were obtained from a fit to a simultaneous diffusion with reaction model for a slab. This work is the first application of 1H NMR imaging, using multiple-pulse line-narrowing techniques, for monitoring a chemical reaction. For this work, the special advantage of line narrowing is that the images are weighted not by the 1H T2 but rather by the T1, relaxation time. Thus, for the materials studied herein, selection of an appropriate relaxation time in the NMR experiment enables observation of either the reaction product or the total sample. © 1992, American Chemical Society. All rights reserved

Remote sensing by nuclear quadrupole resonance

Detection of explosives has the flavor of those mathematical problems that are not invertible. It is easier to hide explosives than to find them. Many approaches have been proposed and executed for the remote detection of explosives, contraband materials, weapons of mass destruction, currency, etc. Most detection technologies suffer from a common problem: the features they look for, such as discontinuties in electrical conductivity, are not unique properties of the target but are contained, to some degree, in the more benign surroundings. Such a degeneracy leads to clutter in the response. For example, resolving the false alarms generated by this clutter can determine the rate of advance of a conventional electromagnetic metal detector employed as a landmine detector. One approach that provides a unique signature is nuclear quadrupole resonance (NQR) (the technique is also called QR, to avoid confusion with strictly nuclear techniques). This paper outlines the important physical principles behind the use of NQR for remote detection, indicates areas of applicability, and presents recent results of field trials of a prototype landmine detection system

Colorectal cancer screening by non-invasive metabolic biomarker fecal tumor M2-PK

As Earth’s climate rapidly changes, species range shifts are considered key to species persistence. However, some range-shifting species will alter community structure and ecosystem processes. By adapting existing invasion risk assessment frameworks, we can identify characteristics shared with high-impact introductions and thus predict potential impacts. There are fundamen- tal differences between introduced and range-shifting species, primarily shared evolutionary histories between range shifters and their new community. Nevertheless, impacts can occur via analogous mechanisms, such as wide dispersal, community disturbance and low biotic resistance. As ranges shift in response to climate change, we have an opportunity to develop plans to facilitate advantageous movements and limit those that are problematic