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Lattice Boltzmann methods are of limited applicability for direct numerical simulation of turbulent flow due to instabilities in the zero viscosity limit. We observe that this is caused by an insufficient degree of Galilean invariance of the relaxation-type Lattice Boltzmann collision operator. The cascaded digital lattice Boltzmann automata described here, provides a method with which to achieve stable collision operators down to the limit of zero viscosity.

Objectives The paper presents a novel and more generalized concept for spatial encoding by non-unidirectional, nonbijective spatial encoding magnetic fields (SEMs). In combination with parallel local receiver coils these fields allow one to overcome the current limitations of neuronal nerve stimulation. Additionally the geometry of such fields can be adapted to anatomy. Materials and methods As an example of such a parallel imaging technique using localized gradients (PatLoc)-system, we present a polar gradient system consisting of 2×8 rectangular current loops in octagonal arrangement, which generates a radial magnetic field gradient. By inverting the direction of current in alternating loops, a near sinusoidal field variation in the circumferential direction is produced. Ambiguities in spatial assignment are resolved by use of multiple receiver coils and parallel reconstruction. Simulations demonstrate the potential advantages and limitations of this approach. Results and conclusionsThe exact behaviour of PatLoc fields with respect to peripheral nerve stimulation needs to be tested in practice. Based on geometrical considerations SEMs of radial geometry allow for about three times faster gradient switching compared to conventional head gradient inserts and even more compared to whole body gradients. The strong nonlinear geometry of the fields needs to be considered for practical applications.

Nuclear magnetic resonance spectroscopy and imaging (MRI) play an indispensable role in science and healthcare but use only a tiny fraction of their potential. No more than ≈10 p.p.m. of all 1H nuclei are effectively detected in a 3-Tesla clinical MRI system. Thus, a vast array of new applications lays dormant, awaiting improved sensitivity. Here we demonstrate the continuous polarization of small molecules in solution to a level that cannot be achieved in a viable magnet. The magnetization does not decay and is effectively reinitialized within seconds after being measured. This effect depends on the long-lived, entangled spin-order of parahydrogen and an exchange reaction in a low magnetic field of 10−3 Tesla. We demonstrate the potential of this method by fast MRI and envision the catalysis of new applications such as cancer screening or indeed low-field MRI for routine use and remote application.

Bacterial phototaxis was first recognized over a century ago, but the method by which such small cells can sense the direction of illumination has remained puzzling. The unicellular cyanobacterium Synechocystis sp. PCC 6803 moves with Type IV pili and measures light intensity and color with a range of photoreceptors. Here, we show that individual Synechocystis cells do not respond to a spatiotemporal gradient in light intensity, but rather they directly and accurately sense the position of a light source. We show that directional light sensing is possible because Synechocystis cells act as spherical microlenses, allowing the cell to see a light source and move towards it. A high-resolution image of the light source is focused on the edge of the cell opposite to the source, triggering movement away from the focused spot. Spherical cyanobacteria are probably the world’s smallest and oldest example of a camera eye. DOI: http://dx.doi.org/10.7554/eLife.12620.001

We report the fabrication of 3D micro coils made with an automatic wire bonder. Using standard MEMS processes such as spin coating and UV lithography on silicon and Pyrex R wafers results in high aspect ratio SU-8 posts with diameters down to 100 μm that serve as mechanical stabilization yokes for the coils. The wire bonder is employed to wind 25 μm insulated gold wire around the posts in an arbitrary (e.g. solenoidal) path, yielding arrays of micro coils. Each micro coil is bonded directly on-chip, so that loose wire ends are avoided and, compared to other winding methods, coil re-soldering is unnecessary. The manufacturing time for a single coil is about 200 ms, and although the process is serial, it is batch fabrication compatible due to the high throughput of the machine. Despite the speed of manufacture we obtain high manufacturing precision and reliability. The micro air-core solenoids show an RF quality factor of over 50 when tested at 400 MHz. We present a flexible coil making method where the number of windings is only limited by the post height. The coil diameter is restricted by limits defined by lithography and the mechanical strength of the posts. Based on this technique we present coils ranging from 100 μm diameter and 1 winding up to 1000 μm diameter and 20 windings.

Nuclear magnetic resonance spectroscopy (NMR) and imaging (MRI) are important non-destructive investigative techniques for soft matter research. Continuous advancements have not only lead to more sensitive detection, and new applications, but have also enabled the shrinking of the detectable volume of sample, and a reduction in time needed to acquire a spectrum or image. At the same time, advances in microstructuring and on-chip laboratories have also continued unabated. In recent years these two broad areas have been productively joined into what we term micro nuclear magnetic resonance (mMR), an exciting development that includes miniaturized detectors and hyphenation with other laboratory techniques, for it opens up a range of new possibilities for the soft matter scientist. In this paper we review the available miniaturization technologies for NMR and MRI detection, and also suggest a way to compare the performance of the detectors. The paper also takes a close look at chiplaboratory augmented mMR, and applications within the broad soft matter area. The review aims to contribute to a better understanding of both the scientific potential and the actual limits of mMR tools in the various interdisciplinary soft matter research fields.

Despite the existence of numerous motion correction methods, head motion during MRI continues to be a major source of artifacts and can greatly reduce image quality. This applies particularly to diffusion weighted imaging, where strong gradients are applied during long encoding periods. These are necessary to encode microscopic movements. However, they also make the technique highly sensitive to bulk motion. In this work, we present a prospective motion correction method where all applied gradients are adjusted continuously to compensate for changes of the object position and ensure the desired phase evolution in the image coordinate frame. In magnetic resonance imaging of the human brain, patient motion remains problematic for both clinical routine and research. For an average patient, it is difficult to stay completely immobile for the duration of an MRI scan. Breathing motion, cardiac pulsation, and involuntary head movements are common especially during the long image acquisitions used for high resolution scanning and diffusion weighted imaging (DWI; (1)). To reduce artifacts from pulsative blood flow and breathing motion, cardiac and respiratory gating of the experiment is possible (2,3).DWI is a noninvasive means to image the microscopic movements of water in living tissue and has become an essential part of clinical routine, especially due to its sensitivity to early stages of brain ischemia (4,5). However, its sensitivity to microscopic movements makes the technique extremely vulnerable to bulk motion (6,7). Imaging after stroke often involves patients unable to cooperate, which exacerbates the problem. To understand the limitations of different correction methods, a distinction between motion during the acquisition of a single diffusion-encoded image (intrascan) and movements in between these images (interscan) as well as between in-plane and through-plane motion must be made (6,7). In-plane intrascan motion can be corrected retrospectively by realigning the data, correcting the phase shift, and applying a b-matrix rotation (8-13). In most cases this is achieved by including additional navigators. For through-plane motion, retrospective methods fail, as the measured slice data are inconsistent. Rotations during diffusion encoding can shift the k-space center sufficiently to preclude retrospective correction. Additionally, position inconsistencies during slice encoding and the refocusing pulses can result in signal loss at the edges of the imaged object, which are not correctable retrospectively.It has been shown that prospective motion correction can compensate for both types of interscan motion (in-plane and through-plane) using external tracking devices (14,15), navigators (16,17), or position information obtained by comparison of the current volume with previous image acquisitions (18). The acquired position information is used to update the orientation of the imaging volume and is applied to the calculation of the subsequent gradients. However, intrascan motion remains problematic for all currently ...