3.10 - Nitroxide-Mediated Polymerization

A novel method by C. Zhou and R. Betti [Bull. Am. Phys. Soc. 50, 140 (2005)] to assemble and ignite thermonuclear fuel is presented. Massive cryogenic shells are first imploded by direct laser light with a low implosion velocity and on a low adiabat leading to fuel assemblies with large areal densities. The assembled fuel is ignited from a central hot spot heated by the collision of a spherically convergent ignitor shock and the return shock. The resulting fuel assembly features a hot-spot pressure greater than the surrounding dense fuel pressure. Such a nonisobaric assembly requires a lower energy threshold for ignition than the conventional isobaric one. The ignitor shock can be launched by a spike in the laser power or by particle beams. The thermonuclear gain can be significantly larger than in conventional isobaric ignition for equal driver energy.

http://absimage.aps.org/image/DPP06/MWS_DPP06-2006-000513.pdf

Shock Ignition of Thermonuclear Fuel with High Areal Density

After three decades of developments, single particle tracking (SPT) has become a powerful tool to interrogate dynamics in a range of materials including live cells and novel catalytic supports because of its ability to reveal dynamics in the structure–function relationships underlying the heterogeneous nature of such systems In this review, we summarize the algorithms behind, and practical applications of, SPT We first cover the theoretical background including particle identification, localization, and trajectory reconstruction General instrumentation and recent developments to achieve two- and three-dimensional subdiffraction localization and SPT are discussed We then highlight some applications of SPT to study various biological and synthetic materials systems Finally, we provide our perspective regarding several directions for future advancements in the theory and application of SPT

Single Particle Tracking: From Theory to Biophysical Applications

Strong correlations—cooperative behavior due to many-particle interactions—are omnipresent in nature. They occur in electrolytic solutions, dense plasmas, ultracold ions and atomic gases in traps, complex (dusty) plasmas, electrons and excitons in quantum dots and the quark–gluon plasma. Correlation effects include the emergence of long-range order, of liquid-like or crystalline structures and collective dynamic properties (collective modes). The observation and experimental analysis of strong correlations are often difficult, requiring, in many cases, extreme conditions such as very low temperatures or high densities. An exception is complex plasmas where strong coupling can be easily achieved, even at room temperature. These systems feature the strongest correlations reported so far and experiments allow for an unprecedented precision and full single-particle resolution of the stationary and time-dependent many-particle behavior. The governing role of the interactions in strongly correlated systems gives rise to many universal properties observed in all of them. This makes the analysis of one particular system interesting for many others. This motivates the goal of this paper which is to give an overview on recent experimental and theoretical results in complex plasmas including liquid-like behavior, crystal formation, structural and dynamic properties. It is expected that many of these effects will be of interest also to researchers in other fields where strong correlations play a prominent role. (Some figures in this article are in colour only in the electronic version) This article was invited by Gordon Baym.

/pdf/complex-plasmas-a-laboratory-for-strong-correlations-1cwqbmx8sl.pdf

Complex plasmas: a laboratory for strong correlations

This review stands in the larger framework of functional materials by focussing on heterostructures of rare-earth nickelates, described by the chemical formula RNiO3 where R is a trivalent rare-earth R  =  La, Pr, Nd, Sm, …, Lu. Nickelates are characterized by a rich phase diagram of structural and physical properties and serve as a benchmark for the physics of phase transitions in correlated oxides where electron-lattice coupling plays a key role. Much of the recent interest in nickelates concerns heterostructures, that is single layers of thin film, multilayers or superlattices, with the general objective of modulating their physical properties through strain control, confinement or interface effects. We will discuss the extensive studies on nickelate heterostructures as well as outline different approaches to tuning and controlling their physical properties and, finally, review application concepts for future devices.

/pdf/rare-earth-nickelates-rnio3-thin-films-and-heterostructures-1c1v82me5q.pdf

Rare-earth nickelates RNiO3: thin films and heterostructures.

The moment method is an image analysis technique for subpixel estimation of particle positions. The total error in the calculated particle position includes effects of pixel locking and random noise in each pixel. Pixel locking, also known as peak locking, is an artifact where calculated particle positions are concentrated at certain locations relative to pixel edges. We report simulations to gain an understanding of the sources of error and their dependence on parameters the experimenter can control. We suggest an algorithm, and we find optimal parameters an experimenter can use to minimize total error and pixel locking. For a dusty plasma experiment, we find that a subpixel accuracy of 0.017 pixel or better can be attained. These results are also useful for improving particle position measurement and particle tracking velocimetry using video microscopy in fields including colloids, biology, and fluid mechanics.

/pdf/accurate-particle-position-measurement-from-images-zy5w7ors4a.pdf

Accurate particle position measurement from images.

The moment method is an image analysis technique for sub-pixel estimation of particle positions. The total error in the calculated particle position includes effects of pixel locking and random noise in each pixel. Pixel locking, also known as peak locking, is an artifact where calculated particle positions are concentrated at certain locations relative to pixel edges. We report simulations to gain an understanding of the sources of error and their dependence on parameters the experimenter can control. We suggest an algorithm, and we find optimal parameters an experimenter can use to minimize total error and pixel locking. Simulating a dusty plasma experiment, we find that a sub-pixel accuracy of 0.017 pixel or better can be attained. These results are also useful for improving particle position measurement and particle tracking velocimetry (PTV) using video microscopy, in fields including colloids, biology, and fluid mechanics.

Accurate particle position measurement from images

Velocity errors in particle tracking velocimetry (PTV) are studied. When using high-speed video cameras, the velocity error may increase at a high camera frame rate. This increase in velocity error is due to particle-position uncertainty, which is one of the two sources of velocity errors studied here. The other source of error is particle acceleration, which has the opposite trend of diminishing at higher frame rates. Both kinds of errors can propagate into quantities calculated from velocity, such as the kinetic temperature of particles or correlation functions. As demonstrated in a dusty plasma experiment, the kinetic temperature of particles has no unique value when measured using PTV, but depends on the sampling time interval or frame rate. It is also shown that an artifact appears in an autocorrelation function computed from particle positions and velocities, and it becomes more severe when a small sampling-time interval is used. Schemes to reduce these errors are demonstrated.

/pdf/errors-in-particle-tracking-velocimetry-with-high-speed-3gq7bm16u8.pdf

Errors in particle tracking velocimetry with high-speed cameras.

It is demonstrated experimentally that strongly coupled plasma exhibits solid superheating A 2D suspension of microspheres in dusty plasma, initially self-organized in a solid lattice, was heated and then cooled rapidly by turning laser heating on and off Particles were tracked using video microscopy, allowing atomistic-scale observation during melting and solidification During rapid heating, the suspension remained in a solid structure at temperatures above the melting point, demonstrating solid superheating Hysteresis diagrams did not indicate liquid supercooling in this 2D system

/pdf/solid-superheating-observed-in-two-dimensional-strongly-3bppbldlrp.pdf

Solid superheating observed in two-dimensional strongly coupled dusty plasma.

The viscoelasticity of two-dimensional liquids is quantified in an experiment using a dusty plasma. An experimental method is demonstrated for measuring the wave-number--dependent viscosity $\ensuremath{\eta}(k)$, which is a quantitative indicator of viscoelasticity. Using an expression generalized here to include friction, $\ensuremath{\eta}(k)$ is computed from the transverse current autocorrelation function, which is found by tracking random particle motion. The transverse current autocorrelation function exhibits an oscillation that is a signature of elastic contributions to viscoelasticity. Simulations of a Yukawa liquid are consistent with the experiment.

Yan Feng

Papers

Accurate particle position measurement from images.

Accurate particle position measurement from images

Errors in particle tracking velocimetry with high-speed cameras.

Solid superheating observed in two-dimensional strongly coupled dusty plasma.

Viscoelasticity of 2D liquids quantified in a dusty plasma experiment.