Indicator Electrodes (312 hits)
Category: RomanceRating: -1.75 on 9 reviews (Rate this item) (V)
Submitted by redbarchetta (View user info) at 2007-03-22 15:29:33 EDT
In 4.1, we assumed that the indicator electrode was planar and sufficiently large that we could ignore edge effects in solving the diffusion problem. PRovided that the radius of curvature is large compared with the diffusion layer thickness, qualitatively similar results are obtained for cylindrical or spherical electrodes, indeed for any stationary electrode in an unstirred solution. Common designs for stationary electrodes include all three geometries: planar (metal disk electrodes), cylindrical (wires), and spherical (hanging mercury drop).
When the electrode is very small, edge effects dominate and steady-state currents are often obtained. Since the behavior of microelectrodes is qualitatively different, we will discuss them separately in 4.8.
Two other indicator electrodes are commonly used in electroanalytical and mechanistic work. The dropping mercury electrode (d.m.e.), shown in Figure 4.10, consists of a fine-bore capillary through which mercury flows, forming a drop at the end of the capillary which grows until its weight exceeds the force of surface tension holding it to the capillary. Depending on the length and bore of the capillary, the pressure of mercury above the capillary, and the Hg-solution interfacial tension, the lifetime of a mercury drop can be anywhere from 1 to 10 s. The factors governing the drop time were discussed in 2.5. The current through a d.m.e. is time dependent, but because the solution is stirred when a drop falls, each new drop starts the experiment anew. If the current is measured just before the drop falls, experiments using a d.m.e. are essentially at constant time. We will discuss the operation of the d.m.e. in greater detail in 4.5.
User Reviews
Submitted by ilikesteak (user info) at 2007-03-23 15:53:33 EDT (#)
Ranking: 0
Meh.
Submitted by DancingOtter (user info) at 2007-03-22 16:31:45 EDT (#)
Ranking: -2
WTF
Submitted by ih8u2man (user info) at 2007-03-22 16:18:51 EDT (#)
Ranking: -2
Aphasia (or aphemia) is a loss or impairment of the ability to produce and/or comprehend language, due to brain damage.
Depending on the area and extent of the damage, someone suffering from aphasia may be able to speak but not write, or vice versa, or display any of a wide variety of other deficiencies in reading, writing, and comprehension.
Aphasia may co-occur with speech disorders such as dysarthria or apraxia of speech, which also result from brain damage.
Usually, aphasias are a result of damage to the language centres of the brain (like Broca's area). These areas are almost always located in the left hemisphere, and in most people this is where the ability to produce and comprehend language is found. However, in a very small number of people language ability is found in the right hemisphere. In either case, damage to these language areas can be caused by a stroke, traumatic brain injury, or other head injury. Aphasia may also develop slowly, as in the case of a brain tumor or progressive neurological disease.
It is not a result of deafness or muscle paralysis, and it does not necessarily affect intelligence.
All these types of aphasia are classified as secondary; primary aphasia is a relatively rare condition with no known cause and often no other symptoms.
The brains of young children with brain damage sometimes restructure themselves to use different areas for speech processing, and regain lost function; adult brains are less adaptable and lack this ability.
Aphasia can be assessed in a variety of ways, from quick clinical screening at the bedside to several-hour-long batteries of tasks that examine the key components of language and communication.
Submitted by DirtyHarry (user info) at 2007-03-22 16:05:14 EDT (#)
Ranking: -2
Well this changes everything!
Submitted by sideshow (user info) at 2007-03-22 15:59:44 EDT (#)
Ranking: -2
WTF is this horseshit? Ghey....
Submitted by DesolateMisanthrope (user info) at 2007-03-22 15:38:18 EDT (#)
Ranking: -2
K, I'll keep that in mind
Submitted by Fartman (user info) at 2007-03-22 15:36:51 EDT (#)
Ranking: -2
We will discuss the operation of the d.m.e. in greater detail in 4.5.
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No, we won't.
Submitted by Alcoholocaust (user info) at 2007-03-22 15:32:15 EDT (#)
Ranking: -2
solid -4, but I'll give you 2 for the username
Submitted by MidnightToSix (user info) at 2007-03-22 15:30:52 EDT (#)
Ranking: -2
Thanks for letting me know.