Donald Hebb (19041985) was the first to come up with a way to tell the difference between short-term and long-term memory. When the brain receives an input, like something that is seen or heard, a sensory memory keeps a copy of what is seen or heard, but this memory lasts for only about a few seconds. Anything that is kept in the brain longer depends on our selective attention. Things that we "notice" are kept in short-term memory for up to a few minutes. This memory is thought to be dependent on electrical activity in the brain and is easily destroyed by interruption or interference. Short-term memory includes iconic memory as well, which holds visual images; acoustic memory, to hold sounds; and working memory, which is an active process to keep a memory until it is put to use.
Memories which are stored for longer than this are called long-term memory. Hebb had a theory of long-term memory as a change in the strength of connections between the neurons. Long-term memory is relatively permanent storage and the process involves the creation of new proteins.
Whether or not the information is stored in long-term memory depends on its importance. Usually for animals memories that are made during times of stress and discomfort are important for adaptive values. In the future they help avoid anything that will bring them stress.
Short-term memory has a limited duration, and the contents decay over time. The decay idea is usually paired by the idea of repeating the memory over and over. In order to overcome the limitation of short-term memory, and retain information for a longer amount of time, it has to be repeated either by saying it out loud of by saying it mentally repeatedly. By doing this the information will re-enter the short-term process and be kept for a further period.
Forgetting greatly limits the information that can be kept over a short period of time. The capacity of short-term memory is finite, but there is no clear unit of measurement for what that is. Memory span is the term used to describe this, where there is only a certain amount of information that can be memorized over a short period until it is lost.
The capacity of short-term memory leads to the question of the capacity of short-term memory as a whole. At present there is no way of telling whether a piece of information will be stored as short-term memory or not. In an experiment done to determine the capacity of short-term memory individuals had to memory a list of items and recall it, and it was suggested that the span of their short-term memory was reached when they could no longer remember the list in order.
There are many conditions that can affect short-term memory. They range from simple distractions to serious disorders. The loss of memory is natural and is expected with ageing. By the age of 55 it is found experimentally that the loss of memory starts to occur which usually occurs more often with long-term memory loss. Age very much affects the short-term memory as well.
There are many other things which affect memory loss beside advanced age. There are disorders such as Alzheimer’s disease, aphasia, schizophrenia, advanced age, and posttraumatic stress disorder. These are all linked to the loss of memory.
Celestial equator
The celestial equator is a term in observational astronomy. It is a great circle on the imaginary celestial sphere, in the same plane as the Earth's equator. In other words, it is a projection of the terrestrial equator out into space. As a result of the Earth's axial tilt, the celestial equator is inclined by 23.4° with respect to the ecliptic plane.
An observer standing on the Earth's equator visualizes the celestial equator as a semicircle passing directly overhead through the zenith. As the observer moves north (or south), the celestial equator tilts towards the southern (or northern) horizon. At the poles, the celestial equator is parallel to the horizon.
The observer always sees the ends of the semicircle disappear over the horizon exactly due east and due west, regardless of the observer's position on Earth.
Epictetus
Epictetus was an Ancient Greek philosopher. He was born in Hierapolis, Phrygia around 55 AD. The name his parents gave him is unknown; the word "epíktetos" (επίκτητος) in Greek simply means "acquired." He spent his youth as a slave in Rome to Epaphroditos, a rich freedman and secretary to Nero. The city was near the modern-day town of Pamukkale in Turkey. He died around 135 AD in Nikopolis in Epirus, in Greece. He was one of the most influential philosophers of the late Stoa. Epictetus founded a school of philosophy, where he also taught. None of his writings survive, but one of his pupils, Arrian, wrote what Epictetus taught.
Philosophy, Epictetus taught, is a way of life and not just a theoretical discipline. To Epictetus, all external events are determined by fate, and so are beyond our control; we should accept whatever happens calmly and dispassionately. However, individuals are responsible for their own actions, which they can examine and control through rigorous self-discipline.
Suffering occurs from trying to control what is uncontrollable, or from neglecting what is within our power. As part of the universal city that is the universe, it is our duty to care for all our fellow men. Those who follow these precepts will achieve happiness and peace of mind.
Data type
In computer science, a data type is the combination of a value range with permissible operations.
"Data type" is frequently shortened to "type".
Data types in programming allow the programmer to perform operations on a date.
Every date has an associated data type.
In the Pascal programming language, the date 42 has the data type integer.
A data type forms a unit:
"Together", the specific permissible range and legal operations, are referred to as a concrete data type.
When a programmer or the compiler read the word integer in the source code, they automatically understand which values and operations are allowed.
Data types are an abstract concept.
This concept primarily appears in high-level programming languages.
Virtually all high-level programming language explicitly include the notion of data type.
Common basic data types may include:
Usually, these and other basic data types can be combined to "custom" data types using structure concepts like:
The notion of data type as presented above is unknown in assembly language, a "low-level" programming language.
All computers know integer number values.
Modern computers also know real numbers in binary.
But there is no rigid enforcement of proper “data type” use.
Assembly language does not prevent using an integer as if it was a real number.
This is intentional, because assembly language is the basis of all (high-level) programming languages.
Yet, the processor’s machine code sets the limits.
Usually, the only “data types” are:
All of which may be further differentiated by their size, how many Bytes each of those occupy, or—in the case of memory address—how many Bytes the referenced object occupies.
Interstellar travel
Interstellar space travel is manned or unmanned travel between stars. Interstellar travel is much more difficult than travel within the Solar System, though travel in starships is a staple of science fiction. Actually, there is no suitable technology at present. However, the idea of a probe with an ion engine has been studied. The energy would come through a laser base station.
Given sufficient travel time and engineering work, both unmanned and sleeper ship interstellar travel seem possible. Both present considerable technological and economic challenges which are unlikely to be met in the near future, particularly for manned probes. NASA, ESA and other space agencies have done research into these topics for several years, and have worked out some theoretical approaches.