Image synthesis for SAR system, calibration and processor design

The Point Scattering Method of simulating radar imagery rigorously models all aspects of the imaging radar phenomena. Its computational algorithms operate on a symbolic representation of the terrain test site to calculate such parameters as range, angle of incidence, resolution cell size, etc. Empirical backscatter data and elevation data are utilized to model the terrain. Additionally, the important geometrical/propagation effects such as shadow, foreshortening, layover, and local angle of incidence are rigorously treated. Applications of radar image simulation to a proposed calibrated SAR system are highlighted: soil moisture detection and vegetation discrimination

Evaluation of SIR-A space radar for geologic interpretation: United States, Panama, Colombia, and New Guinea

Comparisons between LANDSAT MSS imagery, and aircraft and space radar imagery from different geologic environments in the United States, Panama, Colombia, and New Guinea demonstrate the interdependence of radar system geometry and terrain configuration for optimum retrieval of geologic information. Illustrations suggest that in the case of space radars (SIR-A in particular), the ability to acquire multiple look-angle/look-direction radar images of a given area is more valuable for landform mapping than further improvements in spatial resolution. Radar look-angle is concluded to be one of the most important system parameters of a space radar designed to be used for geologic reconnaissance mapping. The optimum set of system parameters must be determined for imaging different classes of landform features and tailoring the look-angle to local topography

Deterministically entangling distant nitrogen-vacancy centers by a nanomechanical cantilever

We present a practical scheme by global addressing to deterministically entangle negatively charged nitrogen-vacancy (N-V) centers in distant diamonds using a nano-mechanical cantilever with the magnetic tips strongly coupled to the N-V electron spins. Symmetric Dicke states are generated as an example, and the experimental feasibility and challenge of our scheme are discussed.Comment: 5 pages, 4 figure

Vorrichtung zur Beobachtung der dreidimensionalen Bewegung von Objekten, die in einer Flüssigkeit gehalten sind

Vorrichtung zur Beobachtung der dreidimensionalen Bewegung von Objekten (2), die in einer Flüssigkeit gehalten sind und deren Bewegung abhängig ist von den in der Flüssigkeit herrschenden örtlichen Eigenschaften wie der Temperatur, der chemischen Zusammensetzung oder den Lichtverhältnissen, wobei die Vorrichtung umfasst:- eine Beobachtungkammer (5) zur Aufnahme der mit den Objekten (2) versehenen Flüssigkeit,- eine erste Belichtungseinrichtung (6) mit einer Lichtquelle (7), eingerichtet zur lokalen Änderung der Eigenschaften in der Flüssigkeit,- eine optische Aufnahmeeinheit (12), eingerichtet zur optischen Erfassung der Objekte (2) in der Flüssigkeit, dadurch gekennzeichnet,dass die erste Belichtungseinrichtung (6) eingerichtet ist, gezielt eine Lichtmenge in einer gewünschten dreidimensionalen Verteilung in die Flüssigkeit der Beobachtungskammer (5) einzubringen, wobei die Flüssigkeit Bestandteile aufweist, die bei Einwirkung von optischen Lichtstrahlen einer bestimmten Wellenlänge ihre Eigenschaften ändern unddass die optische Aufnahmeeinheit eingerichtet ist, die Bewegung der Objekte (2) räumlich zu erfassen und in entsprechende elektronische Signale umzuwandeln

The steering gaits of sperm

Sperm are highly specialized cells, which have been subject to substantial evolutionary pressure. Whereas some sperm features are highly conserved, others have undergone major modifications. Some of these variations are driven by adaptation to mating behaviours or fitness at the organismic level. Others represent alternative solutions to the same task. Sperm must find the egg for fertilization. During this task, sperm rely on long slender appendages termed flagella that serve as sensory antennas, propellers and steering rudders. The beat of the flagellum is periodic. The resulting travelling wave generates the necessary thrust for propulsion in the fluid. Recent studies reveal that, for steering, different species rely on different fundamental features of the beat wave. Here, we discuss some examples of unity and diversity across sperm from different species with a particular emphasis on the steering mechanisms. This article is part of the Theo Murphy meeting issue ‘Unity and diversity of cilia in locomotion and transport’

The future of higher education (HE) hangs on innovating our assessment – but are we ready, willing and able?

Graduates are entering a sociotechnological world, with teaching and assessment needing to reflect that, by shifting from a ‘recall-on-paper’ to ‘do-it-for-real’. With increasing student numbers, it is not feasible to have staff-student ratios and round-the-clock availability required to provide instant feedback and ever-more interactive teaching sessions, so digital solutions are the only option. There is already growing comfort with using computers in formal assessment; however, more work is required to extend beyond performance indicators enabling digital assessments, to addressing how students apply their learning to relevant work-based scenarios. This opinion piece discusses the issues HE currently face to ensure students develop the employability skills that equip them to be proficient in the skills directly related to their degree subject but also transferable to other graduate careers. It raises possible solutions to current technological problems in developing more computer-based assessment, to enable academics to design assessments that develop the capabilities students need

A stable chemokine gradient controls directional persistence of migrating dendritic cells

Navigation of dendritic cells (DCs) from the site of infection to lymphoid organs is guided by concentration gradients of CCR7 ligands. How cells interpret chemokine gradients and how they couple directional sensing to polarization and persistent chemotaxis has remained largely elusive. Previous experimental systems were limited in the ability to control fast de novo formation of the final gradient slope, long-lasting stability of the gradient and to expose cells to dynamic stimulation. Here, we used a combination of microfluidics and quantitative in vitro live cell imaging to elucidate the chemotactic sensing strategy of DCs. The microfluidic approach allows us to generate soluble gradients with high spatio-temporal precision and to analyze actin dynamics, cell polarization, and persistent directional migration in both static and dynamic environments. We demonstrate that directional persistence of DC migration requires steady-state characteristics of the soluble gradient instead of temporally rising CCL19 concentration, implying that spatial sensing mechanisms control chemotaxis of DCs. Kymograph analysis of actin dynamics revealed that the presence of the CCL19 gradient is essential to stabilize leading edge protrusions in DCs and to determine directionality, since both cytoskeletal polarization and persistent chemotaxis are abrogated in the range of seconds when steady-state gradients are perturbed. In contrast to Dictyostelium amoeba, DCs are unable to decode oscillatory stimulation of soluble chemokine traveling waves into a directional response toward the wave source. These findings are consistent with the notion that DCs do not employ adaptive temporal sensing strategies that discriminate temporally increasing and decreasing chemoattractant concentrations in our setting. Taken together, in our experimental system DCs do not depend on increasing absolute chemokine concentration over time to induce persistent migration and do not integrate oscillatory stimulation. The observed capability of DCs to migrate with high directional persistence in stable gradients but not when subjected to periodic temporal cues, identifies spatial sensing as a key requirement for persistent chemotaxis of DCs

Ab-initio theory of NMR chemical shifts in solids and liquids

We present a theory for the ab-initio computation of NMR chemical shifts (sigma) in condensed matter systems, using periodic boundary conditions. Our approach can be applied to periodic systems such as crystals, surfaces, or polymers and, with a super-cell technique, to non-periodic systems such as amorphous materials, liquids, or solids with defects. We have computed the hydrogen sigma for a set of free molecules, for an ionic crystal, LiH, and for a H-bonded crystal, HF, using density functional theory in the local density approximation. The results are in excellent agreement with experimental data.Comment: to appear in Physical Review Letter