Memory reversibility

Memory Reversible capacity loss found on NiCd and to a lesser extent on NiMH batteries. The modem definition of memory refers to crystalline formation of the cell plates. 

For two-photon memories, a number of media types and reading mechanisms have been used (165). Generally, media comprise two photon-absorbing chromophores dissolved within a soHd polymer matrix. Suitable reversible photochromic dyes are, for example, spiropyrans. Although photochromic materials often suffer from photobleaching, as well as from instability leading to self-erasure, new materials and host environments are under development (172). Bacteriorhodopsin (BR) also has been proposed as a two-photon memory material. 

Cholinergic mechanisms have long been studied with respect to memory and learning. An interesting study demonstrated that the age-related decline in memory observed in laboratory rodents can be reversed by administration of choline [62-49-7] (13). 

The MOSEET has three regions of operation. The cutoff region occurs for V g < Up. In this region, the drain-to-source current is the reverse saturation current of the back-to-back source and drain junctions. This leakage current is small but nonzero and allows charge to leak off capacitors which are isolated by cutoff MOSFETs. Because this is how bits are stored in dynamic memory (DRAM) ceUs, DRAMs must be regularly refreshed to retain their memory. 

Fig. 1. Schematic of the hysteresis loop associated with a shape-memory alloy transformation, where M. and Afp correspond to the martensite start and finish temperatures, respectively, and and correspond to the start and finish of the reverse transformation of martensite, respectively. The physical property can be volume, length, electrical resistance, etc. On cooling the body-centered cubic (bcc) austenite (parent) transforms to an ordered B2 or E)02...

Fig. 2. The shape-memory process, where Tis temperature, (a) The cycle where the parent phase undergoes a self-accommodating martensite transformation on cooling to the 24 variants of martensite. No macroscopic shape change occurs. The variants coalesce under stress to a single martensite variant, resulting in deformation. Then, upon heating, they revert back to the original austenite crystallographic orientation, and reverse transformation, undergoing complete recovery to complete the cycle, (b) Shape deformation. Strain recovery is typically ca 7%.

The term electrochromism was apparently coined to describe absorption line shifts induced in dyes by strong electric fields (1). This definition of electrocbromism does not, however, fit within the modem sense of the word. Electrochromism is a reversible and visible change in transmittance and/or reflectance that is associated with an electrochemicaHy induced oxidation—reduction reaction. This optical change is effected by a small electric current at low d-c potential. The potential is usually on the order of 1 V, and the electrochromic material sometimes exhibits good open-circuit memory. Unlike the well-known electrolytic coloration in alkaU haUde crystals, the electrochromic optical density change is often appreciable at ordinary temperatures. 

Infrared Spectrophotometry. The isotope effect on the vibrational spectmm of D2O makes infrared spectrophotometry the method of choice for deuterium analysis. It is as rapid as mass spectrometry, does not suffer from memory effects, and requites less expensive laboratory equipment. Measurement at either the O—H fundamental vibration at 2.94 p.m (O—H) or 3.82 p.m (O—D) can be used. This method is equally appticable to low concentrations of D2O in H2O, or the reverse (86,87). Absorption in the near infrared can also be used (88,89) and this procedure is particularly useful (see Infrared and raman spectroscopy Spectroscopy). The D/H ratio in the nonexchangeable positions in organic compounds can be determined by a combination of exchange and spectrophotometric methods (90). 

In recent years increasing attention has been paid to the possibility of delaying or even reversing the memory loss that accompanies old age or the more tragic loss of human capabilities associated with premature senility - Alzheimer s disease. Progress is hampered by the difficulty of identifying suitable animal tests, and there is presently no reliable therapy. 

In previous chapters, we have examined a variety of generalized CA models, including reversible CA, coupled-map lattices, reaction-diffusion models, random Boolean networks, structurally dynamic CA and lattice gases. This chapter covers an important field that overlaps with CA neural networks. Beginning with a short historical survey, chapter 10 discusses zissociative memory and the Hopfield model, stocheistic nets, Boltzman machines, and multi-layered perceptrons. 

Wernicke s syndrome is a serious consequence of alcoholism and thiamine (vitamin Bx) deficiency. Certain characteristic signs of this disease, notably ophtalmoplegia, nystagmus, and ataxia, respond rapidly to the administration of thiamine but to no other-vitamin. Wernicke s syndrome may be accompanied by an acute global confusional state that may also respond to thiamine. Left untreated, Wernicke s syndrome frequently leads to a chronic disorder in which learning and memory are strongly impaired. This so-called Korsakoff s psychosis is characterized by confabulation, and is less likely to be reversible once established. 

The main disturbance in inhalant intoxication delirium is a reversible decrease in the level of consciousness and awareness of the environment, which includes an inability to focus, sustain, or shift attention. The intoxicated person is confused and easily distracted by irrelevant stimuli and difficult to engage in a meaningful conversation. He or she may also exhibit prominent disorientation, short- and long-term memory deficits, language disturbances, and perceptual disturbances that may include illusions and hallucinations. Other prominent features associated with inhalant intoxication delirium are... 

Howard, M. A., Gross, A., Grady, M. S., Langer, R., Mathiowitz, E., Winn, H. R., and Mayberg, M. R., Intracerebral drug delivery in rats reverses lesion-induced memory deficits,... 

The phase relationship between the most commonly known tetragonal phase CaC2-I and phase(s) II (or III) is still in question. CaC2-I transforms reversibly into the cubic phase IV, as does the phase (II -r) III. It is interesting to note that the cubic phase IV seems to have a memory for its respective precursor phase (III or I) that is regained after cooling down phase IV. The synthesis of... 

True. Excessive alcohol use can lead to serious damage to mental health. Depression, anxiety, delusions and negative changes in personality can occur. Korsakoff s psychosis occurs in some excessive users of alcohol. This form of dementia results in disorientation, loss of memory and lowered intellectual abilities. It is reversible in some sufferers through the administration of thiamine (vitamin Bj. 

In contrast to the nicotinic antagonists and indeed both nicotinic and muscarinic agonists, there are a number of muscarinic antagonists, like atropine, hyoscine (scopolamine) and benztropine, that readily cross the blood-brain barrier to produce central effects. Somewhat surprisingly, atropine is a central stimulant while hyoscine is sedative, as least in reasonable doses. This would be the expected effect of a drug that is blocking the excitatory effects of ACh on neurons but since the stimulant action of atropine can be reversed by an anticholinesterase it is still presumed to involve ACh in some way. Generally these compounds are effective in the control of motion but not other forms of sickness (especially hyoscine), tend to impair memory (Chapter 18) and reduce some of the symptoms of Parkinsonism (Chapter 15). 

ACh is metabolised extraneuronally by the enzyme acetylcholinesterase, to reform precursor choline and acetate. Blocking its activity with various anticholinesterases has been widely investigated and some improvement in memory noted. Such studies have invariably used reversible inhibition because of the toxicity associated with long-term irreversible inhibition of the enzyme. Physostigmine was the pilot drug. It is known to improve memory in animals and some small effects have been seen in humans (reduces number of mistakes in word-recall tests rather than number of words recalled), but it really needs to be given intravenously and has a very short half-life (30 min). 

Nevertheless NGF from mouse mandibular gland has been infused into the right lateral ventricle of two patients (67 and 57 years) for three months at a rate of 75 pg/h. The younger showed no change in memory performance the older some improvement after one month, which ceased after the infusion was stopped. Both patients had various reversible side-effects such as back pain and weight loss. 

Carney, J.M., Starke-Reed, P.E., Oliver, C.N., Landrum, R.W., Cheng, M.S. and Wu, J.F. (1991). Reversal of age-related increase in brain protein oxidation, decrease in enzyme activity, and loss in temporal and spatial memory by chronic administration of the spin-trapping compound N-tert-butyl-cr-phenylnitrone. Proc. Natl Acad. Sci. USA 88, 3633-3636. 

---