Self-activation

Phosphors usually contain activator ions in addition to the host material. These ions are dehberately added in the proper proportion during the synthesis. The activators and their surrounding ions form the active optical centers. Table 1 Hsts some commonly used activator ions. Some soflds, made up of complexes such as calcium tungstate [7790-75-2] CaWO, are self-activated. Also in many photolurninescence phosphors, the primary activator does not efficiently absorb the exciting radiation and a second impurity ion is introduced known as the sensitizer. The sensitizer, which is an activator ion itself, absorbs the exciting radiation and transfers this energy to the primary activator. 

When properly designed, this type of valve arrangement conforms to the ASME code. It is a pilot operated pressure relief valve in which the major relieving device is combined with and is controlled by a self-activating auxiliary pressure relief valve. See Figures 7-5A and B. 

Zinc sulfide, with its wide band gap of 3.66 eV, has been considered as an excellent electroluminescent (EL) material. The electroluminescence of ZnS has been used as a probe for unraveling the energetics at the ZnS/electrolyte interface and for possible application to display devices. Fan and Bard [127] examined the effect of temperature on EL of Al-doped self-activated ZnS single crystals in a persulfate-butyronitrile solution, as well as the time-resolved photoluminescence (PL) of the compound. Further [128], they investigated the PL and EL from single-crystal Mn-doped ZnS (ZnS Mn) centered at 580 nm. The PL was quenched by surface modification with U-treated poly(vinylferrocene). The effect of pH and temperature on the EL of ZnS Mn in aqueous and butyronitrile solutions upon reduction of per-oxydisulfate ion was also studied. EL of polycrystalline chemical vapor deposited (CVD) ZnS doped with Al, Cu-Al, and Mn was also observed with peaks at 430, 475, and 565 nm, respectively. High EL efficiency, comparable to that of singlecrystal ZnS, was found for the doped CVD polycrystalline ZnS. In all cases, the EL efficiency was about 0.2-0.3%. 

Pan ERE, Bard AJ (1985) Semiconductor Electrodes. 58. The effect of temperature on photo- and electroluminescence in Al-doped self-activated ZnS crystals. J Phys Chem 89 1232-1236... 

The self-activating process for converting an inactive catalyst, I, to its active form, A. Such processes typically display a discernible lag-phase followed by accelerated conversion of I to A. Zymogen activation can display autocatalysis, as exemplified by the conversion of pepsinogen to active pepsin at low pH. Many growth processes can also be described via an autocatalysis curve. 

SELENOPHOSPHATE SYNTHETASE SELENOPHOSPHATE SYNTHETASE SELF-ABSORPTION Self-activating process,... 

As described above, aUylic boron reagents are self-activating. Type I reagents where the allylation is effected by coordination of the aldehyde carbonyl oxygen... 

A second example of protease inhibitor design that properly illustrates the peptide scaffold-based approach is that of thrombin inhibitors. Work with these compounds led to the identification of highly potent, selective, and in vivo-effective lead compounds. A member of the serine protease family, thrombin cleaves a number of substrates (e.g., fibrinogen) and activates its platelet receptor (a G-protein-coupled receptor) by proteolysis of the extracellular N-terminal domain which results in self-activation (for a review see Reference 66). Initial lead inhibitors of thrombin were substrate-based, including the fibrinogen P3-Pi Phe-Pro-Arg sequence [67] and simple Arg derivatives such as Tos-Arg-OMe [68]. 

When caspase 8, an initiator caspase, is activated by an apoptotic signal carried through FADD, it further self-activates by cleaving its own proenzyme form. Mitochondria are one target of active caspase 8. The protease causes the release of certain proteins contained between the inner and outer mitochondrial membranes ... 

Self-Activation. Although pure substances do not normally luminesce, zinc sulfide that has been fired in the presence of a halogen luminesces bright blue [5.311], [5.312], The luminescence center is assumed to be a cation vacancy. The charge compensation occurs through exchange of S2- by Cl-. 

Cation holes can also be created by coactivation with trivalent metal ions or by incorporation of oxygen [5.313]. The luminescence band of self-activated zinc sulfide with the zinc-blende structure exhibits a maximum at 470 nm. On transition to the wurtzite structure, the maximum shifts to shorter wavelengths. In the mixed crystals zinc sulfide-cadmium sulfide and zinc sulfide-zinc selenide, the maximum shifts to longer wavelengths with increasing cadmium or selenium concentration. 

ZnO Zn is a typical example of a self-activated phosphor. In the case of zinc oxide, it is an excess of zinc which enables the phosphor to luminesce. The production is carried out by thermal oxidation of crystallized zinc sulfide in air at ca. 400 °C. The green luminescence, with a broad maximum at 505 nm, has a very short decay time of 10-6 s. As a phosphor for cathode-ray tubes, ZnO.Zn is classified in the TEPAC list as P 24 and in the WTDS system as GE. 

The production of self-activated CaW04 is more difficult than that of MgW04. Small deviations from stoichiometry in the composition have a marked effect on the efficiency. Also, traces of Pb2 + shift the emission peak from 415 nm to 439 nm (0.0006 mol % Pb2+). To bind excess CaO in the production process, a small proportion of sulfate is used. The precipitated CaW04 is washed until chloride-free, dried,... 

Self-activated molybdate phosphorus are described in [5.406]. The energy transfer that occurs in molybdates activated with Eu3+ is described in [5.388], [5.407],... 

How can each step in this complex assembly process set the stage for the next step Apparently the structure of each newly synthesized protein monomer is stable only until a specific interaction with another protein takes place. The binding energy of this interaction is sufficient to induce a conformational alteration that affects a distant part of the protein surface and generates complementarity toward a binding site on the next protein that is to be added. Every one of the baseplate proteins must have such self-activating properties Sometimes proteolytic cleavage of a subunit is required. If it occurs at an appropriate point in the sequence it provides thermodynamic drive for the assembly process. 

Stimulated platelets release arachidonic acid rapidly from their phospholipids, apparently as a result of activation of phospholipase A2. The released arachidonate can in turn be metabolized to endoperoxides and thromboxane A2 (Chapter 21). These compounds are also potent activators of platelets and cause a self-activating or autocrine effect.1) While PAF has a beneficial function, it can under some conditions contribute in a dangerous way to inflammation and to allergic responses including anaphylaxis,) asthmag and cold-induced urticaria.1 Although the effect of PAF is separate from those of histamine and of leukotrienes, these agents may act cooperatively to induce inflammation.1... 

The Srs(P04)3Cl crystals are hexagonal needles with lattice parameters ah = 9.953 A. and ch = 7.194 A. The needle axis corresponds to the crystallographic c axis. The europium(II) doped sample is a phosphor, readily excitable with electrons, x-rays, and both short and long ultraviolet light. It emits in the blue with a peak at 445 nm. Crystals of strontium chloride vanadate(V) are orthorhombic platelets with lattice constants a = 7.43 A., b = 11.36 A., and c = 6.54 A., with the b axis corresponding to the thin dimension of the flakes. Strontium chloride vanadate(V) is a self-activated phosphor giving broadband emission with a peak at 423 nm. when excited with 2537-A. radiation. All compounds are insulators, with resistivities >1012 ft-cm. 

Chlorine dioxide is almost never used in a concentrated liquid form, as the liquid is unstable and can explode. It is not stored in any significant quantity, although it is available in a stabilized solution form (typically 3 to 12% CIO2, with carbonate/bicarbonate or other stabilizers). The more concentrated solutions (>5%) require activation with acid, while the more dilute forms (<5%) become self-activating when diluted a further four to five times. 

IFN-y modulates a number of components of the immune response. This is the only type II IFN whereas there are more than 20 types of type I IFNs (IFN-a, IFN-(3, IFN-w and IFN-t). It is not related to type I IFNs, has separate receptors and is encoded by a different chromosomal locus. IFN-y is produced by activated T lymphocytes (THi and CD8+ cells), NK cells, B cells, NKT cells and professional APCs. It promotes the activity of cytolytic T lymphocytes, macrophages and NK cells. The cell self-activation and activation of nearby cells in part may result from IFN-y production by professional APCs, which include monocyte/macrophage and dendritic cells. The early host defense against infection is likely to utilize IFN-y secreted by NK and professional APCs. In acquired immune responses, T lymphocytes are the major source of IFN-y. 

Autoantigens with adjuvants. DNA also becomes more immunogenic if it is conjugated with either endogenous self-activator (natural adjuvant) or exogenous adjuvant from viral or bacterial peptides. 

Matrix-assisted laser desorption ionization is another ionization mode used for MS analysis. Enzymatically digested peptides have been studied using a 90-well microchip constmcted in a MALDI plate format (see Figure 7.41). Peptide digestion was initiated in the MALDI interface where the peptide hormone, adreno-corticotropin (ACTH) was mixed with the enzyme carboxypeptidase Y. The mixing process was self-activated in the vacuum conditions. Subsequent TOF MS analysis produced kinetic information of the peptide digestion reaction [820]. 

FIGURE 7.41 Picture of the microfabricated fluidic device integrated with a standard MALDI-TOF sample plate. Because of the self-activating character of the microfluidic device, the system can be introduced into the MALDI ionization chamber without any wire or tube for the sample introduction and the flow control [820]. Reprinted with permission from the American Chemical Society. 

Experiments with aspartic acid have shown that only a-aspartic acid dipeptides are formed [123], which is consistent with the transformation of the substrate into a pentacoordinated phosphorane mixed anhydride 17 [24] containing a five-membered ring through a self-activation process. 

The bleach in a dishwasher tablet or powder is percarbonate and this needs a bleach activator, but now it is possible to add a metal compound as a catalyst because there is no danger of the contents of the dishwasher suffering in the way that some fabrics can be affected. In some tablets a new self-activating bleaching agent, PAP (short for 6-(phthalimido)peroxyhexanoic acid) is used and this needs no activator or catalyst. 

In other words, evidence has been obtained that in this system also, the autowave self-activation of the reactant is due to the positive feedback between the chemical reaction and its brittle fracture. 

A few years ago the concept considered was introduced also in the low-temperature chemistry of the solid.31 Benderskii et al. have employed the idea of self-activation of a matrix due to the feedback between the chemical reaction and the state of stress in the frozen sample to explain the so called explosion during cooling observed by them in the photolyzed MCH + Cl2 system. The model proposed in refs. 31,48,49 is unfortunately not quite concrete, because it includes an abstract quantity called by the authors the excess free energy of internal stresses. No means of measuring this quantity or estimating its numerical values are proposed. Neither do the authors discuss the connection between this characteristic and the imperfections of a solid matrix. Moreover, they have to introduce into the model a heat-balance equation to specify the feedback, although they proceed from the nonthermal mechanisms of selfactivation of reactants at low temperatures. Nevertheless, the essence of their concept is clear and can be formulated phenomenologically as follows the... 

It is useful to point out the similarity between the YL in GaN and the so-called self-activated (SA) luminescence in II-VI compounds. Metal vacancies and their complexes with donor impurities are well known in II-VI compounds (e.g. ZnS, ZnSe). The metal vacancy complexes (the so-called SA centres) exhibit features which are strikingly similar to the YL recombination between a shallow donor-like state and a deep acceptor state, and a broad luminescence band of Gaussian shape [22,23]. 

Now the emphasis on the power of the formal approach to the study of dreaming should become clear even to those who still long for the mystique of fortune-cookie dream interpretation. We can see that, when the brain self-activates in sleep, it changes its chemical self-instructions. The mind has no choice but to go along with the programme. It sees, it moves, and it feels things intensely but it does not think, remember, or focus attention very well. This, in turn, shows clearly that our so-called minds are functional states of our brains. The mind is not something else - it is not a spirit, it is not an independent entity. It is the self-activated brain whose capacity for subjectivity remains to be explained but whose form of subjectivity can now be understood. 

We have already given our answer to the question of why we dream based on physiological mechanisms because the brain self-activates in sleep. We have already hinted that dreaming itself may be an epiphenomenon of brain self-activation, so dreaming may occur for reasons that are quite different from those that we would infer from the psychological study of REM sleep dreaming. 

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