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Seasonal changes in the physical state of crown water associated with freezing tolerance in winter wheat The relationship between freezing tolerance (expressed as LTjj, the lethal freezing temperature for 50% of plants) and the amount and physical state (as determined by spin-lattice [TJ and spin-spin [Tj] relaxation times of protons) of water in crown tissue was examined in contrasting winter wheat (Triticum aestivum L.) varieties grown under field conditions from 1992 to 1994. During acclimation, the U^ values decreased from around -7 to -17, -20 and -27°C in PI 173438, Chihokukomugi and Valuevskaya, respectively. Tissue water content decreased continuously through autumn to reach a plateau around 3 g HjO (g dry weight)' in early winter when LTio was still decreasing, and then gradually increased under snow cover. A significant negative correlation was found between mean minimum air temperattires and fi-eezing tolerance prior to the estahlishment of continuous snow cover. In contrast, a positive association between mean mitiimum temperatures and crown tissue water content was significant only when air temperatures were above 0°C, as water content did not decrease further at sub-zero temperatures. Seasonal changes in T, were closely related to changes in freezing tolerance. Ti decreased until January even though water content stopped decreasing. Further tests on 15 field-grown varieties confirmed a strong negative association between freezing tolerance and T,. The results suggest that cold hardening is comprised of two stages, with the transition occurring at ca 0°C. Development of hardiness was related to (1) a reduction in water content in the first stage (at minimum temperatures > 0°C), and (2) a change in physical state of water without much reduction in water content in the second stage. Varietal differences in hardiness thus arise due to changes in both water content and physical state of water.

The temperature effect on the atomic hydrogen-induced surface processes on Ge(100) has been studied from a desorption point of view. The experiments are carried out for temperature-programmed-desorption (TPD) of H2 and D2 and collision-induced desorption (CID) of D2 and abstraction of HD in the reaction system H(g)+D/Ge(100). The D2 and H2 TPD spectra exhibit two clear peaks, assigned as β1 and β2 TPD arising from a monohydride and a dihydride phase, respectively. There are isotope effects on the TPD spectra; D2 TPD peaks shift to higher surface temperature (Ts) compared to the peaks of H2, and the ratio of the β2 to the β1 TPD peak intensity is smaller for H2 than for D2. It is found that the kinetics of the abstraction and CID reactions are similar to those on Si(100), indicating that the mechanism for the abstraction and CID on Ge(100) is same to that on Si(100). The observed D2 rate curves show up a strong Ts dependence. The CID of D2 versus Ts curve exhibits a peak at Ts≃480 K corresponding to the leading edge of the β2TPD spectra. For Ts⩾530 K, CID of D2 is fully replaced by the spontaneous desorption ascribed to the β1 TPD. This fact suggests that the mechanism of CID is same to that of the β2 TPD. For Ts∼480 K, the D2 rate curves can be fitted with a fourth-order kinetics in a momentary D adatom coverage. The transiently created dihydride species that are considered to be mobile across the surface via a dihydride–monohydride isomerization reaction to exchange their sites, are invoked to explain the observed fourth-order kinetics. Probing H atoms reveals that the thermal desorption from the isolated dideuterides is not allowed, suggesting that for the β1 TPD the concerted desorption from hydrogen-prepared Ge dimers is preferred to the desorption from isolated dihydrides.

This is a report of two patients in whom a pontine venous congestion occurred with a dural carotid-cavernous fistula (CCF), an extremely rare complication. This is the first such report. We underscore the importance of early diagnosis and treatment of dural CCFs.