High-Speed Monitoring of Surface Defects in Rail Tracks Using Ultrasonic Doppler Effect

Railroads provide both efficiency and economy in passenger and freight transportation. Like other transportation modes, however, they are prone to various problems. Statistics show that over the course of this century, the average carload and trainload tonnage has increased significantly. There is also an increasing concentration of traffic on fewer main line tracks. The average length of haul has also risen [1,2]. Unfortunately, these trends have not been offset with a proportional increase in the amount of new rail laid. Consequently, the stress on rails and fatigue related failures may continue to increase. With the new demands, it is important to assess the rail integrity by detecting rail defects nondestructively and speedily

Real-Time Processing of Continuous Doppler Signals for High-Speed Monitoring of Rail Tracks

In the rail industry, existing railroad tracks are carrying heavier and heavier train loads, instead of constructing new rails and distributing trainload tonnage [1,2]. As the average load per track increases, there is a growing concern about the critical flaws in the rail. Consequently, it is necessary to assess the rail integrity by means of rapid nondestructive detection of rail defects

Graduate Student Recital: Jung-Min Wooh, Violin; Tong-Sook Han, Piano; April 23, 1974

Hayden AuditoriumTuesday EveningApril 23, 19748:15 p.m

Spontaneous jumping, bouncing and trampolining of hydrogel drops on a heated plate

Drops of liquid on a hot surface can exhibit fascinating behaviour such as the Leidenfrost effect in which drops hover on a vapour layer. Here Pham et al. show that when hydrogel drops are placed on a rapidly heated plate they bounce to increasing heights even if they were initially at rest

Cylindrical chains of water drops condensing on microstructured lubricant-infused surfaces

We studied the condensation of water drops on a micro-structured lubricant-infused surfaces. Hierarchical micro-prism surfaces were fabricated by soft imprinting with wet TiO2 nanoparticle paste. After hydrophobization, the patterned surfaces were infused with silicone oil as a lubricant. When cooling at high humidity (over 80%), water drops nucleate and start growing on the surface. Once they have reached a certain size, the drops at neighboring channels of the micro-prisms attract each other and spontaneously form cylindrical chains. These chains of drops align perpendicular to the prism array. The morphology and the length-to-width ratio of the chains of drops depend on the thickness of the lubricant layer. This new concept of water drop alignment on lubricant-infused surfaces offers a new route for pattern formation with condensed drops.N

Tuning static drop friction

The friction force opposing the onset of motion of a drop on a solid surface is typically considered to be a material property for a fixed drop volume on a given surface. However, here we show that even for a fixed drop volume, the static friction force can be tuned by over 30% by preshaping the drop. The static friction usually exceeds the kinetic friction that the drop experiences when moving in a steady state. Both forces converge when the drop is prestretched in the direction of motion or when the drop shows low contact angle hysteresis. In contrast to static friction, kinetic friction is independent of preshaping the drop, that is, the drop history. Kinetic friction forces reflect the material properties

Nanoporous Substrate-Infiltrated Hydrogels: a Bioinspired Regenerable Surface for High Load Bearing and Tunable Friction

Nature has successfully combined soft matter and hydration lubrication to achieve ultralow friction even at relatively high contact pressure (e.g., articular cartilage). Inspired by this, hydrogels are used to mimic natural aqueous lubricating systems. However, hydrogels usually cannot bear high load because of solvation in water environments and are, therefore, not adopted in real applications. Here, a novel composite surface of ordered hydrogel nanofiber arrays confined in anodic aluminum oxide (AAO) nanoporous template based on a soft/hard combination strategy is developed. The synergy between the soft hydrogel fibers, which provide excellent aqueous lubrication, and the hard phase AAO, which gives high load bearing capacity, is shown to be capable of attaining very low coeffcient of friction (0.3) and superlubrication (≈10−3) when their state is changed from contracted to swollen by means of acidic and basic actuation. The mechanisms governing ultralow and tunable friction are theoretically explained via an in-depth study of the chemomechanical interactions responsible for the behavior of these substrate-infiltrated hydrogels. These findings open a promising route for the design of ultra-slippery and smart surface/interface materials