Polarizable colloids are expected to form crystalline equilibrium phases when exposed to a steady, uniform field. However, when colloids become localized this field-induced phase transition arrests and the suspension persists indefinitely as a kinetically trapped, percolated structure. We anneal such gels formed from magnetorheological fluids by toggling the field strength at varied frequencies. This processing allows the arrested structure to relax periodically to equilibrium-colloid-rich, cylindrical columns. Two distinct growth regimes are observed: one in which particle domains ripen through diffusive relaxation of the gel, and the other where the system-spanning structure collapses and columnar domains coalesce apparently through field-driven interactions. There is a stark boundary as a function of magnetic field strength and toggle frequency distinguishing the two regimes. These results demonstrate how kinetic barriers to a colloidal phase transition are subverted through measured, periodic variation of driving forces. Such directed assembly may be harnessed to create unique materials from dispersions of colloids.magneto-rheological fluid | microgravity science | complex fluids S mart fluids, colloidal dispersions actuated by external magnetic or electric fields, have diverse applications. In buildings, magneto-rheological (MR) dampers are used to absorb the energy of earthquakes, automobiles and trucks are equipped with active MR shock absorbers, and electro-rheological (ER) fluids enable haptic controllers and tactile displays in microelectronics devices. It is the ability to rapidly and reversibly change the rheological properties of smart fluids that makes them so attractive. Understanding the mechanisms that govern the formation and dissolution of structures in such materials is essential (1, 2). Fieldinduced interactions between particles is the primary mechanism of ER and MR fluids, and is driven chiefly by the mutual attraction or repulsion of induced dipoles.Upon application of a steady field, ER and MR fluids respond by forming particulate chains along the field direction, imparting enhanced viscosity and the ability to resist transverse mechanical stresses. Following chain formation, thermal fluctuations create lateral attractive forces between neighboring chains and cause microstructural coarsening (3-5). Continued cross-linking between chains eventually damps the thermal fluctuations that drive coarsening in a self-retarding fashion. A kinetically arrested percolated structure results. However, investigations of the equilibrium thermodynamic properties of dipolar fluids show that the coarsened state is actually an arrested phase transition. Such dipolar fluids are predicted to form two coexisting phases: a particle rich, body-centered-tetragonal crystalline phase and a dilute fluid phase (6, 7). This contradiction with experimental observation is due to kinetic limitations; at typical field strengths (tens to hundreds of times stronger than the Boltzmann energy) the time scales over which the ...

Investigative procedures were approved by Henry Ford Human Investigation Committee and NASA Johnson Space Center Committee for Protection of Human Subjects. Informed consent was obtained. Authors evaluated ability of nonphysician crewmember to obtain diagnostic-quality musculoskeletal ultrasonographic (US) data of the shoulder by following a just-in-time training algorithm and using real-time remote guidance aboard the International Space Station (ISS). ISS Expedition-9 crewmembers attended a 2.5-hour didactic and hands-on US training session 4 months before launch. Aboard the ISS, they completed a 1-hour computer-based Onboard Proficiency Enhancement program 7 days before examination. Crewmembers did not receive specific training in shoulder anatomy or shoulder US techniques. Evaluation of astronaut shoulder integrity was done by using a Human Research Facility US system. Crew used special positioning techniques for subject and operator to facilitate US in microgravity environment. Common anatomic reference points aided initial probe placement. Real-time US video of shoulder was transmitted to remote experienced sonologists in Telescience Center at Johnson Space Center. Probe manipulation and equipment adjustments were guided with verbal commands from remote sonologists to astronaut operators to complete rotator cuff evaluation. Comprehensive US of crewmember's shoulder included transverse and longitudinal images of biceps and supraspinatus tendons and articular cartilage surface. Total examination time required to guide astronaut operator to acquire necessary images was approximately 15 minutes. Multiple arm and probe positions were used to acquire dynamic video images that were of excellent quality to allow evaluation of shoulder integrity. Postsession download and analysis of high-fidelity US images collected onboard demonstrated additional anatomic detail that could be used to exclude subtle injury. Musculoskeletal US can be performed in space by minimally trained operators by using remote guidance. This technique can be used to evaluate shoulder integrity in symptomatic crewmembers after strenuous extravehicular activities or to monitor microgravity-associated changes in musculoskeletal anatomy. Just-in-time training, combined with remote experienced physician guidance, may provide a useful approach to complex medical tasks performed by nonexperienced personnel in a variety of remote settings, including current and future space programs.

We implement image correlation, a fundamental component of many real-time imaging and tracking systems, on a graphics processing unit (GPU) using NVI-DIA's CUDA platform. We use our code to analyze images of liquid-gas phase separation in a model colloid-polymer system, photographed in the absence of gravity aboard the International Space Station (ISS). Our GPU code is 4,000 times faster than simple MATLAB code performing the same calculation on a central processing unit (CPU), 130 times faster than simple C code, and 30 times faster than optimized C?? code using single-instruction, multipledata (SIMD) extensions. The speed increases from these parallel algorithms enable us to analyze images downlinked from the ISS in a rapid fashion and send feedback to astronauts on orbit while the experiments are still being run.

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