Memory mechanism

The immune system in vertebrates provides a defense mechanism against foreign parasites such as viruses and bacteria. Three main properties are essential to its successful operation specific recognition of foreign molecules, the ability to destroy the foreign parasite, and a memory mechanism that allows a more rapid response to a second infection by the same microorganism. 

Addiction may result from inappropriate neuronal plasticity. As discussed in earlier sections of this chapter, drugs of abuse activate the same neuronal pathways as natural reinforcers. However, they do so in a strong and unregulated manner that is hypothesized to lead to abnormal engagement of learning and memory mechanisms, ultimately producing abnormal plasticity in neuronal circuits involved in motivation and decision-making. As a result, the addict becomes narrowly focused on compulsive, habitual behaviors associated with the addictive... 

Shah, P. A. Miyake (1999). In A. Miyake 8c R Shah (Eds.), Models of working memory Mechanisms of active maintenance and executive control (1-27). Cambridge Cambridge University Press. 

The first building block is the robust memory mechanism called priming. We know that a word—and if a word why not a sentence—can prime subsequent recall so that associated words are more easily recognized. And we know that sleep, especially REM, may even enhance this priming, especially for weak primes. The explanation offered for priming is that the neuronal networks underlying associated words are activated by the prime word (or sentence). 

Thus, the latent psi function is accessible only through the intermediary of Memory. The precise nature of the Memory mechanisms involved is still unknown. It is an interesting theory and seems to fit some experimental data [42]. 

Because the brain s memory mechanisms are so seriously disrupted during sleep we cannot escape bizarre mental experiences that would otherwise occur only during madness. ... 

One question that has not yet been considered and that unfortunately has been discussed only very sparingly in the literature is that of whether neural DNA, as well as RNA, could be involved in neurotransmission or memory mechanisms, and of what possible function it might have. The following observation with regard to DNA is suggestive ... 

It may be relevant to mention here the commonplace within the discipline of genetics—that only 2 to 5 percent of the genome is active at any one time, that these inactive areas can be activated by external (i.e., extracellular) factors such as hormones, and that large populations of similar nucleotide sequences exist in the DNA complements of higher organisms. It is possible to speculate on a memory mechanism, based on an interaction of intercalating amines and neural DNA, that would function on principles similar to the intercalator/RNA interaction that may be involved in neural transmission. The remainder of this chapter is concerned with a discussion of such a speculation. 

Rowan MJ et al (2007) Synaptic memory mechanisms Alzheimer s disease amyloid beta-peptide-induced dysfunction. Biochem Soc Trans 35(Pt 5) 1219-1223... 

Fig. 5.2 Schematic figures of the shape memory mechanism of LLDPE/PP/LLDPE-PP blends [12]...

Schematic figures of the shape memory mechanism of the styrene-butadiene-styrene (SBS) triblock copolymer/poly(e-caprolactone) (PCL) blend in (a)-(d). (Adapted from Zhang, H., Wang, H., Zhong, W, and Du, Q. 2009. A novel type of shape memory polymer blend and the shape memory mechanism. Polymer 50 1596-1601. Copyright Elsevier Ltd. Reproduced with permission.)...

Zhang, H., Wang, H., Zhong, W., and Du, Q. 2009. A novel type of shape memory polymer blend and the shape memory mechanism. Polymer 50 1596-1601. 

Fig. 26 Left Shape-memory response curve of an elastomer containing 2 mol% of UPy pendant side groups. Right Proposed shape-memory mechanism (states 1—5) involving thennoieveisible H-bonding. Colored side groups represent H-bonding groups in the hot (red) and cold (blue) states darker lines represent the lightly cross-linked covalent netwoik. Adopted with pennissirai liom [144]. Copyright 2(X)7, John Wiley Sons, Inc.

Figure 3.49 Schematic showing the shape memory mechanism involved in the two-stage biaxial programming and recovery. Note the contribution of the compression programming to the further segmental alignment along the tension direction. Source [59] Reproduced with permission from the American Society of Civil Engineers...

Like other polymeric materials, rheological modeling was first attempted to predict the constitutive behavior of SMPs. Although earher efforts [5-8] using rheological models were able to describe the characteristic thermomechanical behavior of SMPs, loss of the strain storage and release mechanisms usually led to limited prediction accuracy. Also, the models were 1-D and could only predict the behavior under a uniaxial stress condition, such as 1-D tension. Furthermore, these models can oidy work for a small strain. They cannot predict the thermomechanical behavior of SMPs with finite strain, which is the case for most SMPs. Later, meso-scale models [9,10] were developed to predict the constitutive behavior of SMPs. However, one limitation is that a meso-scale model cannot understand the shape memory mechanisms in detail because the mechanisms controlling the shape memory are in a molecular... 

In Section 5.2, we treated the SMPF as a microphase segregated structure and, based on their chemical composition and shape memory mechanisms, these phases are classified as soft phase and hard domain, and both may be semicrystalline. From the point of view of micromechanics modeling, however, this is not convenient because the RVE, which is made of a semicrystalline soft phase and a semicrystalline hard domain, will be difficult to analyze. Therefore, in the following, we will treat the SMPF as a two-phase composite with a crystalline phase and an amorphous phase that is, the RVE will be a two-phase element. Clearly, both the soft phase and hard domain contribute to the amorphous phase and crystalline phase. Selection of the RVE in such way makes it easier to utilize existing constitutive relations for both amorphous polymer and crystalline polymer. 

In fact, not only alloys have shape memory properties, some polymers, ceramics and even biological systems also possess such properties. For example, bacteriophages can use the shape memory mechanism to enter into host cells. However, to date, only SMAs are widely used in microvalve fabrication. We will focus on the introduction of SMA microvalves. 

Shape memory ceramics (SMCs) have also been studied. The principal drawback of the SMC materials is their small recovery strain, much smaller than those of metal alloys, due to the intrinsic fragile behaviour and the microfractures that ceramics tend to produce in their structure. However, it is possible to classify these materials in terms of their shape memory mechanisms (Wei et al, 1998) ... 

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