Crossword clues for activator
activator
The Collaborative International Dictionary
activator \activator\ n. 1. any agency bringing about activation; (Biol.) a molecule that increases the activity of an enzyme or a protein that increases the production of a gene product in DNA transcription.
Wiktionary
n. 1 One who, or that which, activates. 2 (context biology English) Any chemical or agent which regulates one or more genes by increasing the rate of transcription. 3 (context biology English) A type of effector that increases the rate of enzyme-mediated reactions. 4 A type of dopant used in phosphors and scintillators. 5 (context mining English) An agent that enables the flotation of a mineral or minerals.
WordNet
n. (biology) any agency bringing about activation; a molecule that increases the activity of an enzyme or a protein that increases the production of a gene product in DNA transcription [ant: inhibitor]
Wikipedia
Activator may refer to:
- Activator (genetics), a DNA-binding protein that regulates one or more genes by increasing the rate of transcription
- Activator (phosphor), a type of dopant used in phosphors and scintillators
- Enzyme activator, a type of effector that increases the rate of enzyme mediated reactions
- Sega Activator, a motion-sensing controller for the Sega Mega Drive/Genesis
- Activator technique, a method of spinal adjustment
A transcriptional activator is a protein ( transcription factor) that increases gene transcription of a gene or set of genes. Most activators are DNA-binding proteins that bind to enhancers or promoter-proximal elements.
Most activators function by binding sequence-specifically to a DNA site located in or near a promoter and making protein–protein interactions with the general transcription machinery ( RNA polymerase and general transcription factors), thereby facilitating the binding of the general transcription machinery to the promoter. The DNA site bound by the activator is referred to as an "activator site." The part of the activator that makes protein–protein interactions with the general transcription machinery is referred to as an "activating region." The part of the general transcription machinery that makes protein–protein interactions with the activator is referred to as an "activation target."
In phosphors and scintillators, the activator is the element added as dopant to the crystal of the material to create desired type of nonhomogeneities.
In luminescence, only a small fraction of atoms, called emission centers or luminescence centers, emit light. In inorganic phosphors, these inhomogeneities in the crystal structure are created usually by addition of a trace amount of dopants, impurities called activators. (In rare cases dislocations or other crystal defects can play the role of the impurity.) The wavelength emitted by the emission center is dependent on the atom itself, its electronic configuration, and on the surrounding crystal structure.
The activators prolong the emission time (afterglow). In turn, other materials (such as nickel) can be used to quench the afterglow and shorten the decay part of the phosphor emission characteristics.
The electronic configuration of the activator depends on its oxidation state and is crucial for the light emission. Oxidation of the activator is one of the common mechanisms of phosphor degradation. The distribution of the activator in the crystal is also of high importance. Diffusion of the ions can cause depletion of the crystal from the activators with resulting loss of efficiency. This is another mechanism of phosphor degradation.
The scintillation process in inorganic materials is due to the electronic band structure found in the crystals. An incoming particle can excite an electron from the valence band to either the conduction band or the exciton band (located just below the conduction band and separated from the valence band by an energy gap). This leaves an associated hole behind, in the valence band. Impurities create electronic levels in the forbidden gap. The excitons are loosely bound electron-hole pairs which wander through the crystal lattice until they are captured as a whole by impurity centers. The latter then rapidly de-excite by emitting scintillation light (fast component). In case of inorganic scintillators, the activator impurities are typically chosen so that the emitted light is in the visible range or near-UV where photomultipliers are effective. The holes associated with electrons in the conduction band are independent from the latter. Those holes and electrons are captured successively by impurity centers exciting certain metastable states not accessible to the excitons. The delayed de-excitation of those metastable impurity states, slowed down by reliance on the low-probability forbidden mechanism, again results in light emission (slow component).
The activator is the main factor determining the phosphor emission wavelength. The nature of the host crystal can however to some degree influence the wavelength as well.
More activators can be used simultaneously.
Common examples of activators are:
- Copper, added in concentration of 5 ppm to copper-activated zinc sulfide, used in glow in the dark materials and green CRT phosphors; long afterglow
- Silver, added to zinc sulfide to produce a phosphor/scintillator used in radium dials, spinthariscopes, and as a common blue phosphor in color CRTs, and to zinc sulfide- cadmium sulfide used as a phosphor in black-and-white CRTs (where the ZnS/(Zn,Cd)S ratio determines the blue/yellow balance of the resulting white); short afterglow
- Europium(II), added to strontium aluminate, used in high-performance glow in the dark materials, very long afterglow; with other host materials it is frequently used as the red emitter in color CRTs and fluorescent lights.
- Cerium, added to yttrium aluminium garnet used in white light emitting diodes, excited by blue light and emitting yellow
- Thallium, used in sodium iodide and caesium iodide scintillator crystals for detection of gamma radiation and for gamma spectroscopy
A newly discovered activator is Samarium(II), added to calcium fluoride. Sm(II) is one of the few materials reported which offers efficient scintillation in the red region of the spectrum, particularly when cooled by dry ice.
Usage examples of "activator".
Blood-steam misted the workings of a wing flap electrohydraulic activator, slowing its motion.
One last point, Alfred: I left temporary activators on the gates between my office and your bedroom door.
With her right foot she gently pushed down on the activator pedal and aligned her Elmeth with Sha's Rik Dom.
But, since the activator was still operating and the entrance was fairly narrow, it continued to function as a curtain of insulating negative force, a curtain which had holes in it through which one could occasionally "peek" by means of the anthropometer at the people imprisoned inside.
Fingering off the sonic activator to return the Aurite crystal's molecular bonds to their stable length, Polar tucked it into his black sash, then half smiled.
Have the lab start with chromosomes 6 and 7, and give me a count of the Hy-3 activators.
Among these activators are magnesium, manganous zinc, ferrous, cobaltous, and nickelous ions, as well as others.
Fanaticism is a prime activator of psychoenergies and the view of consequents is minimal.
The cell activators produced it in abundant amounts as if it were a by-product.
They had taken some retard muties and given them voice box activators that were controlled from within the complex.
Aflame with anger I whirled around and as I struck my holster release the weapon sprang ready into my hand while I simultaneously hit the wide activator buckle of my auto-defence system.
He sauntered to one of his own works, a three-meter-high arrangement of oscillating rods that ran the whole sound spectrum into the high kilohertzes, and passed two fingers over the activator eye.
Since accidental death affects the body from without and is not a result of any organic process, the cell activator is helpless in coping with the damage.
To make a monkey nervous all the time you put extra responders in those activator brain cells concerned with the fear response.
I would assume it was the activator for the range restrictors on the other robots.