Otto Julius Zobel (October 20, 1887 – January 1970) was a design engineer who worked for the American Telephone & Telegraph Company (AT&T) in the early part of the 20th century. Zobel's work on filter design was revolutionary and led, in conjunction with the work of John R. Carson, to significant commercial advances for AT&T in the field of frequency division multiplex (FDM) telephone transmissions.

Zobel invented the m-derived filter and the constant-resistance filter, which remains in use today. With Carson he helped to establish the nature of noise in electric circuits, concluding that—contrary to mainstream belief—it is not even theoretically possible to filter out noise entirely and that noise will always be a limiting factor in what it is possible to transmit. Thus, they anticipated the later work of Claude Shannon, who showed how the theoretical information rate of a channel is related to the noise of the channel.

Analogue filters are a basic building block of signal processing much used in electronics. Amongst their many applications are the separation of an audio signal before application to bass, mid-range and tweeter loudspeakers; the combining and later separation of multiple telephone conversations onto a single channel; the selection of a chosen radio station in a radio receiver and rejection of others.

Analogue filters have played an important part in the development of electronics. Especially in the field of telecommunications, filters have been of crucial importance in a number of technological breakthroughs and have been the source of enormous profits for telecommunications companies. It should come as no surprise, therefore, that the early development of filters was intimately connected with transmission lines. Transmission line theory gave rise to filter theory, which initially took a very similar form, and the main application of filters was for use on telecommunication transmission lines. However, the arrival of network synthesis techniques greatly enhanced the degree of control of the designer.

Zobel networks are a type of filter section based on the image impedance design principle. They are named after Otto Zobel of Bell Labs who published a much referenced paper on image filters in 1923. The distinguishing feature of Zobel networks is that the input impedance is fixed in the design independently of the transfer function. This characteristic is achieved at the expense of a much higher component count compared to other types of filter sections.

Zobel networks were formerly widely used in telecommunications to flatten and widen the frequency response of copper land lines, producing a higher quality line from one originally intended for ordinary telephone use. However, as analogue technology has given way to digital they are now little used.

Minimum orbit intersection distance, abbreviated MOID, is a measure used in astronomy to assess collision risk between astronomical objects. It is defined as the distance between the closest points of the osculating orbits of the two bodies in question. Of greatest interest is the risk of a collision with Earth; the MOID between an object and Earth is called Earth MOID. Earth MOID is often listed on comet and asteroid databases such as the Jet Propulsion Laboratory's Small-body Database. However, MOID can be defined with respect to other bodies as well: Jupiter MOID, Venus MOID and so on.

An object is classified as a Potentially Hazardous Object (PHO) – that is, posing a possible risk to Earth – if, among other conditions, its Earth MOID is less than 0.05 AU.

A mechanical filter is a signal processing filter that is used in place of an electronic filter but for the same task, usually at radio frequencies. At the input and output of the filter there are transducers which convert the electrical signal into, and back from, a mechanical vibration.

The components of a mechanical filter are all directly analogous to the various elements of an electrical circuit. It is therefore possible use electrical network analysis and filter design techniques on mechanical filters which is a great convenience for electrical engineers in the design of these circuits. Any of the classic frequency responses can be obtained with the right choice of component values.

A Murphy drip is a rectal infusion apparatus to administer the medical procedure of proctoclysis, also known as rectoclysis. During the procedure, an end of the Murphy drip is inserted into the rectum and large quantities of liquid are infused into the rectum drop-by-drop. Prior to fluids or medicines being given intravenously, the Murphy drip and hypodermoclysis were the prime routes to administer fluids such as for replacement when patients could not be fed by mouth. Wisconsin surgeon John Benjamin Murphy introduced the drip method of saline infusion per rectum in the treatment of peritonitis.