|
I went to the National Gallery of Art in Washington D.C. and saw an artwork by Jack Whitten entitled Ascension I. This interesting piece was made by applying a tool to generate wavy lines in a background of acrylic paint to create the diagonal interlace pattern that you see in some baskets. Apart from the art itself, one of the things that caught my attention is that when I moved, the pattern of the art piece seemed to pulsate, displaying changes in color and giving off a glare. I was able to capture this with my phone camera in the video below. These optical effects are an example of what is called spatial aliasing. The most well-known example of spatial aliasing is when two grates or meshes are placed on top of each other and one of them is moved. A series of banding patterns appear, which are called interference patterns or Moiré patterns. Spatial aliasing occurs when a signal is not sampled often enough along an axis in space. Our eye and the camera do not monitor reality in a continuous fashion, instead they take samples and then put them together much in the same way that the sensation of movement is generated in a film by playing individual frames one after the other. Spatial aliasing is a problem in any branch of technology that involves waves, such as when playing or recording sounds or generating or producing light. Many industries, ranging from computer graphics to recording studios, implement anti-aliasing techniques to improve the quality of the images or the sound. Another modality of aliasing, called temporal aliasing, is produced when the sampling rate for the signal is insufficient over time. A classic example is the apparent change in rotation speed and direction of the spokes of a wheel. I have previously made a video of the phenomenon of temporal aliasing I observed when shooting a video of the railroad tracks from a moving train. The photos belong to the author and can only be used with permission.
0 Comments
I recently went to Left Fork Rocks in Frederick Municipal Forest in Maryland, and while climbing around I saw a snake. The snake was slithering into a cavity in the rocks, so I could not see its head, but I was able to identify it due to the presence of a rattle at the end of its tail. This is a specimen of the timber rattlesnake (Crotalus horridus). I have posted in general about rattlesnakes before, so in this post I will talk about the structure that makes them unique among snakes: the rattle. Many people find similarities between the noise made by the rattle of rattlesnakes and the noise made by maracas. However, unlike the maracas, the rattle does not have tiny balls inside banging against the wall that contains them. Rather, the rattle is composed of hollow segments made of keratin (the same stuff that makes up your fingernails). When the snake shakes its tail 50 – 100 times per second, the segments strike each other and produce the rattling sound. Every time a snake sheds its skin, it adds an additional segment to its rattle, but because the segments of the rattle can become damaged and fall off, the number of segments in a rattle are not a measure of the age of the rattlesnake or of the total number of times it has shed its skin.  The function of the rattle is to protect the snake against animals that may inadvertently harm the snake and which are too large for the snake to eat. But how did rattlesnakes get their rattles? One hypothesis is based on the fact that many snakes shake their tails when threatened. Scientists have found that those snakes which are closely related to rattlesnakes shake their tails in a manner that is similar to that of the rattlesnake. Thus, it is suggested that this behavior was a signal precursor that allowed for the selection of snake rattles once they developed. One last interesting fact about the rattle of rattlesnakes is that the snake can’t hear the sound they make with their rattles! Rattlesnakes have inner ear structures which are attached to the lower jaw (they don’t have an eardrum or an external ear like we do) and can sense vibrations transmitted through the ground. Rattlesnakes can perceive airborne sounds that produce vibrations in their bodies, but their overall ability to hear sounds is limited compared to humans. The photograph belongs to the author and can only be used with permission. |
Categories
All
Archives
August 2024
|
RSS Feed