960 research outputs found
Controlling colloidal phase transitions with critical Casimir forces
The critical Casimir effect provides a thermodynamic analogue of the
well-known quantum mechanical Casimir effect. It acts between two surfaces
immersed in a critical binary liquid mixture, and results from the confinement
of concentration fluctuations of the solvent. Unlike the quantum mechanical
effect, the magnitude and range of this attraction can be adjusted with
temperature via the solvent correlation length, thus offering new opportunities
for the assembly of nano and micron-scale structures. Here, we demonstrate the
active assembly control of equilibrium phases using critical Casimir forces. We
guide colloidal particles into analogues of molecular liquid and solid phases
via exquisite control over their interactions. By measuring the critical
Casimir particle pair potential directly from density fluctuations in the
colloidal gas, we obtain insight into liquefaction at small scales: We apply
the Van der Waals model of molecular liquefaction and show that the colloidal
gas-liquid condensation is accurately described by the Van der Waals theory,
even on the scale of a few particles. These results open up new possibilities
in the active assembly control of micro and nanostructures
Fiber-Optic Network Architectures for Onboard Avionics Applications Investigated
This project is part of a study within the Advanced Air Transportation Technologies program undertaken at the NASA Glenn Research Center. The main focus of the program is the improvement of air transportation, with particular emphasis on air transportation safety. Current and future advances in digital data communications between an aircraft and the outside world will require high-bandwidth onboard communication networks. Radiofrequency (RF) systems, with their interconnection network based on coaxial cables and waveguides, increase the complexity of communication systems onboard modern civil and military aircraft with respect to weight, power consumption, and safety. In addition, safety and reliability concerns from electromagnetic interference between the RF components embedded in these communication systems exist. A simple, reliable, and lightweight network that is free from the effects of electromagnetic interference and capable of supporting the broadband communications needs of future onboard digital avionics systems cannot be easily implemented using existing coaxial cable-based systems. Fiber-optical communication systems can meet all these challenges of modern avionics applications in an efficient, cost-effective manner. The objective of this project is to present a number of optical network architectures for onboard RF signal distribution. Because of the emergence of a number of digital avionics devices requiring high-bandwidth connectivity, fiber-optic RF networks onboard modern aircraft will play a vital role in ensuring a low-noise, highly reliable RF communication system. Two approaches are being used for network architectures for aircraft onboard fiber-optic distribution systems: a hybrid RF-optical network and an all-optical wavelength division multiplexing (WDM) network
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