The origin of the squeal acoustic emissions when a chalk is rubbed on a blackboard or better on a ceramic plate, and those when a wet finger is rubbed on a smooth surface, such as a glass surface, is sought in the stick-slip effect between the rubbing surfaces. In the case of the squealing chalk, the stick-slip effect is anchored by shear modes of vibration in about a 0. Furthermore, there are the interfacial bands at the contact areas that result in the decrease of the friction coefficient with relative velocity of slide, i. Such bands are basically composed of the asperities on the surface of the chalk band and of the epidermis ridges and the water layer, respectively. Keywords:
Dance of neurons: How brain cell vibrations could help treat diseases like Alzheimer's
Think of a squid's jet of water and ink. The nerve that powers this reflex is so huge that it looks like a blood vessel. When a British zoologist began experimenting with it in the s, the squid neuron transformed what we knew about the brain. The nerve, thick enough to clamp and to record electrical changes across its membrane, shed light on the wet circuits in our skulls. The squid's big brain cell started a revolution in neuroscience, ultimately yielding five Nobel Prizes to 13 scientists over 50 years. The model it led to inspired drugs like Prozac and Xanax. But the picture of neural signaling that emerged is more about chemistry and electricity than mechanics.
Vibrations or oscillations occur primarily in solid objects or assemblies of objects as a result of forces acting upon the objects from outside, or from forces originating inside the objects. An example of an outside force is wind acting upon a building or bridge. An example of an internal force is the cylinders in a gasoline car engine. Soft materials tend to damp out vibrations quickly while harder materials maintain vibrations longer.
Awareness of this problem has been rapidly growing in the industry, and it is now common to install sensors on the creping doctor to measure vibration during operation. Blade vibration measurement shares some similarities with conventional condition monitoring techniques, but there are also differences, especially when it comes to identifying the appropriate corrective actions required to solve the problem. This paper outlines the physics behind creping blade vibration, the basic measurements used to describe it, and some analysis methods that can be used to interpret the basic measurements and manage vibration with short- and long-term strategies.