ALBERT

Notizen: The self-consistent radial electric field shear generated by a drift-thermal turbulence is studied in some detail. A set of new dynamical equations is derived. In this model, there exist three kinds of equilibrium states. The first is the zero shear state of the radial electric field; the second is the positive shear state of the radial electric field; and the third is the negative shear state of the radial electric field. But only the negative shear state may be stable. Two kinds of stable states with the negative shear radial electric field are relevant to the behavior such as that exhibited by high (H) mode and by edge localized modes (ELMs), respectively. © 1997 American Institute of Physics.

Notizen: Profile effects of the radiation, temperature, and the effect of atomic processes on thermal condensation instability in the tokamak edge are considered. The most important influence comes from a strong condensation effect due to the atomic processes and particle transport. © 1996 American Institute of Physics.

Notizen: Thermal broadening of Cl+ electron stimulated desorption ion angular distribution (ESDIAD) patterns, related to the vibrational motion of the adsorbate, has been investigated by subtraction of patterns measured at different temperatures. In the case of Cl on Si(100), the observed difference pattern between 130 and 305 K indicates that azimuthally isotropic motion of Cl occurs about the most probable Si–Cl bond direction. Equal distributions from the in-plane and out-of-plane bending motions are observed, correlating with the ∼200 cm−1 frequencies associated with these motions.

Notizen: A combination of experimental methods has been employed for the study of Cl2 adsorption and reaction on Si(100)–(2×1). At 100 K, Cl2 adsorption occurs rapidly to a coverage of ∼0.7 Cl/Si. This is followed by slower adsorption kinetics with further Cl2 exposure. Two Cl adsorption states are observed experimentally. One of the adsorption states is terminally bonded Cl on the inclined dangling bond of the symmetric Si2 dimer sites, with a vibrational frequency, ν(SiCl) of 550∼600 cm−1. These bonded Cl atoms give four off-normal Cl+ ESDIAD emission beams from the orthogonal domains of silicon dimer sites. The Si–Cl bond angle for this adsorption configuration is estimated to be inclined 25°±4° off-normal. The second Cl adsorption state, a minority species, is bridge bonded Cl with ν(Si2Cl) of ∼295 cm−1 which produces Cl+ ion emission along the surface normal direction. Both adsorption states are present at low temperatures. Irreversible conversion from bridge bonded Cl to terminally bonded Cl begins to occur near 300 K; the conversion is complete near ∼673 K. LEED studies indicate that the (2×1) reconstruction for the substrate is preserved for all Cl coverages. The most probable Cl+ kinetic energy in electron stimulated desorption, ESD, is 1.1−+0.30.6 eV. A significant adsorbate-adsorbate quenching effect reducing the Cl+ ion yield in ESD occurs above a Cl(a) coverage of ∼0.5 ML (monolayer) due to interadsorbate interactions. The maximum Cl+ yield is about 4×10−7 Cl+/e at an electron energy of 120 eV. Temperature programmed desorption results show that SiCl2 is the major etching product which desorbs at about 840 K.

Notizen: Characteristic chlorine bonding sites have been detected on a vicinal Si(100) single crystal surface exposing Si(100) terraces, 7–8 Si atoms in width. These terraces are separated by two-atom layer height steps. Following annealing to 673 K, three Cl+ beams are observed by the electron stimulated desorption ion angular distribution method. Two of the Cl+ beams originate from silicon-dimer dangling bond sites on the Si(100) terraces. The third Cl+ beam is associated with the Si–Cl bond on the step sites, and under zero field conditions it emits Cl+ at a polar angle of 24±2° with respect to the 〈100〉 direction, in the downstairs direction. The direction of Cl+ emission from the step site is qualitatively consistent with the theoretical model of the step reconstruction proposed by Chadi. © 1995 American Institute of Physics.

Notizen: The thermal behavior of NO on (flat) Pd(111) and (stepped) Pd(112) has been investigated by temperature programmed desorption (TPD), high resolution electron energy loss spectroscopy (HREELS), and Auger electron spectroscopy (AES) techniques. NO is shown to adsorb molecularly on both Pd(111) and Pd(112) in the temperature range 300–373 K. NO desorbs molecularly from Pd(111) near 500 K with evidence for slight NO dissociation. In contrast, on Pd(112), in addition to NO, relatively large amounts of N2(7x) and N2O(15x) are observed to desorb near 500 K, compared to Pd(111). This result indicates that the influence of the step sites on Pd(112) is to catalyze the decomposition of NO upon heating. This is a surprising result in light of the fact that NO molecules preferentially bind to terrace sites, instead of step sites, on Pd(112). HREELS measurements indicate the presence of small amounts of surface-bound O (resulting from NO thermal decomposition) coadsorbed with NO on both Pd(111) and Pd(112) after NO adsorption at 373 K, followed by 490 K annealing. In addition, HREELS provides evidence for the existence of subsurface O formed only on Pd(112) during this procedure. The presence of steps on Pd(112) presumably offers an efficient pathway for O incorporation within the outermost Pd layers, as no spectroscopic evidence for subsurface O exists for Pd(111). Annealing both surfaces to 550 K induces the diffusion of both surface O and subsurface O into the Pd bulk.

Notizen: The infra- and component communities of intestinal helminths of carp Cyprinus carpio were investigated in six lakes in the flood plain of the lower and middle reaches of the Yangtze River, China. Eight species of helminth parasites were recorded. The intestinal helminth communities were species rich in Niushan and Tonghu lakes where the digenean Asymphylodora japonica was the dominant species, whereas in Qinggang and Yanglan lakes a species-poor helminth community had only one species, Khawia sinensis. The degree of similarity within localities was highest in Qinggang and Yanglan lakes, and was high between communities where K. sinensis was the dominant species. The rich composition of these helminth communities may be because China is the heartland for carp while the poor helminth composition of those in Qinggang and Yanglan lakes may reflect the poor fauna there. It is suggested that species compositions of intestinal helminth communities of carp may be diversified in lakes in the flood plain of the Yangtze River.

Notizen: The density and size of short cracks on the surface of 1Cr18Ni9Ti stainless steel smooth specimens during low cycle fatigue are investigated using a replica technique. The density and size data are analysed from two different observation policies, i.e. Policy I pays attention to the whole specimen test piece and Policy II is related to an ‘effective short fatigue crack criterion’, which pays attention to the dominant crack (DC) initiation zone and the zones ahead of the DC tips. The results reveal that both the crack density and crack size evolution exhibit a specific character during the microstructural short crack (MSC) and physical short crack (PSC) stages. The Policy I-based observations exhibit an increasing density and little scatter of the density data. The increasing density violates the general test observation of decreasing collective crack effects in the PSC stage. The little scatter is too small to reflect the intrinsic scatter of fatigue properties. Both the crack density and crack size evolution from this policy show little relationship with the intrinsic localization of fatigue damage. However, Policy II-based observations show an increasing crack density and an increasing density scatter in the MSC stage. The density and scatter reach their maximum values at the transition point between the MSC and PSC stages. Then, they decrease with fatigue cycling in the PSC stage and tend to their saturation values when the DC size is above about 500 μm. This behaviour shows a good agreement with the general test observations of decreasing collective crack effects and growth rate scatter in the PSC stage. Further, both approaches exhibit an evolutionary positively skewed crack size distribution, and an increasing difference between the average crack length and the DC length in the PSC stage, indicative of decreasing collective crack effects. A three-parameter Weibull distribution (3-PWD) is appropriately used to describe the crack sizes and a 6.5 to 7.6 μm value of location parameter of the distribution is obtained to reflect a minimum value for the initial cracks. It is worth noting that Policy I-based observations show an increasing positively skewed crack size distribution, an increasing scatter of the size data and a decreasing shape parameter of the 3-PWD. This represents an increasing collective crack effect and an increasing irregularity of interactive cracks, which violates the general test observations. In contrast, Policy II-based observations exhibit a decreasing positively skewed size distribution shape and an increasing (from 〈1 gradually to 〉1) shape parameter of the 3-PWD that is in agreement with the general test observations. The increasing shape parameter indicates that the collective crack effects act as an evolutionary process from an initial non-ordered (chaotic) random state gradually to an independent random state at the transition point between the MSC and PSC stages and then, to a loading history-dependent random state. This behaviour is in accordance with the evolutionary DC growth behaviour. Therefore, the evolutionary short crack behaviour associated with the intrinsic localization of fatigue damage should be appropriately revealed from the ‘effective short fatigue crack criterion’-based observations.