Cold-hardening

Novolac and resol cold hardening oligomers habe been used 19-75-99). In the case of resol foams the process technology is not different from that used for epoxy foams. Glass, phenolic resins, carbon, polystyrene, polyacrylonitrile and poly(vinylidene chloride) microspheres have been used as fillers ... 

The novolac foams are made by mixing the solid (powdered) oligomer (70 parts), carbon filler (30 parts), and hardener (hexamethylenetetramine) in a vibromixer and then press-molding the mixture for one hour at 150 °C, at a compression of 30-40% of the initial volume39). Casting compositions curable at room temperature are made from resol cold hardening oligomers 83). 

Many physiological studies established a correlation between cold acclimation and increasing ABA levels in plant tissues (Chen etal., 1983). Furthermore, exogenous ABA application can induce cold-hardening to the same degree as a low temperature treatment does (Chen Gusta, 1983) while plant species which do not show a hardening capacity at low temperature do not harden even after ABA treatment. 

Guy, C.L. Carter, J.V. (1984). Characterization of partially purified glutathione reductase from cold-hardened and nonhardened spinach leaf tissue. Cryobiology 21, 454-64. 

Riov, J. Brown, G.N. (1976). Comparative studies of activity and properties of ferrodoxin-NADP+ reductase during cold hardening of wheat. Candian Journal of Botany 54, 1896-902. 

Swaaij, van A.C., Jacobsen, E. Feenstra, W.J. (1985). Effect of cold hardening, wilting and exogenously applied proline on leaf proline content and frost tolerance of several genotypes of Solanum. Physio-logia Plantarum 64, 230-6. 

During the cold hardening of material the dislocation density rises from 1010 m nr3 to values of 1014 m nr3. The stored strain energy is released during re-crystallization. 

The first series of experiments was devoted to determination of the effect scale on the slit temperature. In the second series of experiments we used the slits formed by massive plates of gold-silver alloy and pure palladium, varying considerably their microstructure. Namely, they were initially highly cold-hardened samples and later on the ones annealed at the recrystallisation temperature. In other words, we deal with either fine-grained or coarse-grained metal surfaces. 

As a preliminary step in the manufacture of unsaturated polyester thermoset plastic one uses low molecular weight linear polyester (Mr 10,000) obtained by a polycondensation of polyglycols with saturated and unsaturated dicarboxylic acids. The precondensate can then be dissolved and stored in the stabilized comonomer, e.g. styrene, with which it will be crosslinked later. The crosslinking polymerization reaction between the polyester chains and the styrene bridges is initiated with the help of organic peroxides which are added dispersed in plasticizers. The reaction begins at 60-90 °C and then proceeds exothermally. In addition to this a cold hardening reaction can also be carried out. For this reaction cold accelerators are necessary, e.g. tertiary amines or cobalt naphthenate. 

One can further divide lacquers according to their drying processes into oxidative drying, cold hardening, irradiation hardening and oven drying. 

In making a repair of the membrane, either after an injury to the lining in service, or after removal of unsound (blistered) membrane material, always flash the cold hardened asphalt around the repair with a torch to warm and soften it up before placing new hot material, so that the new may blend in with the old. 

For efficient curing of urea-formaldehyde (UF) resins at low temperatures, strong acids are needed as cold hardeners. A drawback of such use of strong acids is that the acid attacks wood. Water-soluble organic acids like citric or tartaric acids reduce the danger of attack on wood. Hot hardeners are ammonium salts of strong acids like ammonium chloride or ammonium sulfate that liberate the acid at high temperatures. 

Shaov A.Kh., Kushhov M.I., Kushhov E.M. Polymeric composite materials cold hardened for orthopedic stomatology IIAbstr. VI Russian scientific forum Stomatology 2004 .-2004.-P. 194-195. 

One may speculate that a cold-induced tightening of the thylakoid membrane may be important e.g. for reducing proton leakage (see Gilmore, 1997), and that the cold-hardening process lowers the temperature threshold for this event considerably. 

Hurry VM, Krol M, Oquist G and HunerNPA (1992) Effect of long-term photoinhibition on growth and photosynthesis of cold-hardened spring and winter wheat. Planta 188 369-375 Hurry VM, Keerberg 0, Parnik T, Gardestrdm P and Oquist G... 

Cold-hardening results in increased activity of enzymes involved in carbon metabolism in leaves of winter rye (Secale cereale L). Planta 195 554-562... 

To induce photoinhibition of photosynthesis non hardened and cold hardened plants were, unless otherwise specified, exposed to a continuous photosynthetic photon flux density (PPFD) of 400 umol m s (metal halogen lamps Osram HQI-T 400W/DH) at 5 °C. Since vertically oriented cereal leaves were not very much affected by photoinhibitory light coming from above, we positioned the leaves horizontally during photoinhibition. 

To induce photoinhibition of photosynthesis cold hardened and non hardened winter rye, spring barley and Scots pine were exposed to a stepwise increase of the PPFD at 5 (Rgure 1 A>D). Fully expanded, secondary leaves of rye and barley developed under the two growth regimes were used. For pine both primary and secondary needles were considered. It appears that leaves of winter rye developed at 5 had acquired an increased resistance to photoinhibition, whereas neither spring barley nor Scots pine did show any significant increase in resistance to photoinhibition upon cold acclimation. 

Figure 1. Time dependent photoinhibition of photosynthesis measured as the decrease of the chlorophyll fluorescence Fv/Fm ratio in non hardened (Q) and cold hardened (f)...

Figure 2. Time dependent photoinhibition of photosynthesis measured as the decrease of the chlorophyll fluorescence Fv/Fm ratio in non hardened and cold hardened ( ) seedlings of Scots pine grown and cold hardened under a photoperiod of 17 h and a PPFD of 50 umol m s . PPFD and temperature of phoitoinhibitory conditions were 400 umol m s and 5 °C, respectively. Standard deviations are given for n = 10.

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