Sputtering of adsorbed layers by ion bombardment

Sputtering of adsorbed species by particle bombardment is a major source of contamination in present-day thermonuclear devices. Nevertheless, there have been very few systematic studies of the sputtering processes which produce this contamination. These questions were investigated, both experimentally and numerically, for systems with various projectile and target mass ratios. We studied the sputtering of S and O from Ni (111) and Ni (110) surfaces by Ar⁺, Ne⁺ and He⁺ ions between 100 and 1600 eV. The sputtering cross-sections increase with ion mass and energy from 10^?16 to 10^?14 cm² for S in the observed range of parameters and are lower for oxygen. There is a maximum for an impact angle of about 30° relative to the surface. These results are generally confirmed by numerical studies with a modification of the computer program MARLOWE. Also the influence of various parameters, such as surface binding energy, surface geometry, impact angle, etc. will be discussed. The theoretical estimates of Winters and Sigmund are applied to the system under investigation. These calculations yield the right order of magnitude for the sputtering cross-sections. According to these results the main contributions to sputtering are from direct knock-off effects and from backscattered primaries, with a smaller contribution arising from the sputtering of the base material.     

A carbohydrate-rich diet reduces LDL size in QQ homozygotes for the Gln192Arg polymorphism of the paraoxonase 1 gene

Paraoxonase 1 (PON 1) is an esterase with antioxidant properties that is present in HDL. Gln192Arg polymorphism (also named Q192R or Q/R) of the PON 1 gene that encodes this protein defines two alleles (Q and R). The R allele has been associated with higher cardiovascular risk. LDL size and susceptibility to oxidation also have been identified as cardiovascular risk factors. Our objective was to determine whether genetic variations in the Gln192Arg polymorphism influence LDL size and susceptibility to oxidation after the consumption of diets with different fat content. In our experiments, the participants (n=98), underwent three 4-wk diets—one, saturated fat-enriched (SAT); another, monounsaturated fat-enriched (MONO); and a third, carbohydrate-enriched (CHO). We observed that LDL were smaller in the QQ group after the CHO diet vs. the SAT (P<0.01) and MONO diets (P<0.03). No differences in LDL size were found in QR/RR subjects. When we analyzed lag time of oxidation of LDL, we found that when carriers of the R allele (QR/RR) received the MONO diet, the lag period of LDL oxidation was longer as compared with the CHO diet. Otherwise, we found no differences in QQ homozygotes when we evaluated the lag time of oxidation of LDL after the three diets. These results suggest that the Gln192Arg polymorphism of the paraoxonase gene influences LDL size and susceptibility to oxidation in response to diet.     

Regional distribution of neuritic plaques in the nondemented elderly and subjects with very mild Alzheimer disease

BACKGROUND: Identification of the neuropathological lesions that are most closely associated with the earliest symptoms of Alzheimer disease (AD) is crucial to the understanding of the disease process and the development of treatment strategies to affect its progress. Do the classical neuropathological lesions of AD precede, follow, or occur in synchrony with the earliest signs of cognitive deterioration? DESIGN AND OUTCOME MEASURES: We examined the extent of neuritic plaque (NP) formation in 5 neocortical regions and the hippocampus, entorhinal cortex, and amygdala in 66 elderly subjects with no dementia, questionable dementia, or mild dementia as assessed using the Clinical Dementia Rating Scale (CDR). SETTING AND PATIENTS: Postmortem study of nursing home residents. RESULTS: Even questionable dementia (CDR, 0.5) was associated with a significant (P = .04) increase in neocortical NP density. The density of NPs increased further with increasing dementia severity in all brain regions examined. However, subjects with questionable dementia or definite but mild dementia did not differ significantly from each other. Density of NPs was nearly maximal in subjects with moderate dementia (CDR = 2.0), suggesting that other neuropathological changes may be responsible for cognitive deficits beyond this level. Dementia severity correlated significantly with the density of NPs in all brain regions examined (r range, 0.47-0.56; P < .001), even when subjects with a CDR of 0 were excluded. CONCLUSIONS: These findings are consistent with the hypothesis that NPs are among the earliest neuropathological lesions in AD. Even very mild or questionable dementia is associated with increased density of neocortical NPs that do not distinguish between clinically questionable vs definite dementia.     

On the spuriousness of the symbolic/subsymbolic distinction

The article criticises the attempt to establish connectionism as an alternative theory of human cognitive architecture through the introduction of thesymbolic/subsymbolic distinction (Smolensky, 1988). The reasons for the introduction of this distinction are discussed and found to be unconvincing. It is shown that thebrittleness problem has been solved for a large class ofsymbolic learning systems, e.g. the class oftop-down induction of decision-trees (TDIDT) learning systems. Also, the process of articulating expert knowledge in rules seems quite practical for many important domains, including common sense knowledge.The article discusses several experimental comparisons betweenTDIDT systems and artificial neural networks using the error backpropagation algorithm (ANNs usingBP). The properties of one of theTDIDT systemsID3 (Quinlan, 1986a) are examined in detail. It is argued that the differences in performance betweenANNs usingBP andTDIDT systems reflect slightly different inductive biases but are not systematic; these differences do not support the view that symbolic and subsymbolic systems are fundamentally incompatible. It is concluded, that thesymbolic/subsymbolic distinction is spurious. It cannot establish connectionism as an alternative cognitive architecture.     

Coupled simulation of the flue gas and process gas side of a steam cracker convection section

A coupled simulation of the flue gas and process gas side of the convection section of a steam cracker is performed, making use of the CFD software package Fluent. A detailed overview of the operating mode of the different heat exchangers suspended in the convection section is obtained. The asymmetric inlet flow field of the flue gas in the convection section, and the radiation from the convection section walls leads to large differences in outlet temperatures of the tubes located in the same row. The flow fields and temperature fields in the tubes of a single heat exchanger differ significantly with e.g., outlet temperatures of the hydrocarbon‐steam mixture ranging from 820 K to 852 K. Moreover, the simulations reveal the presence of hot spots on the lowest tube row, possibly causing fouling. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Functional Perovskites – From Epitaxial Films to Nanostructured Arrays

Functional perovskite materials gain increasing significance due to their wide spectrum of attractive properties, including ferroelectric, ferromagnetic, conducting and multiferroic properties. Due to the developments of recent years, materials of this type can conveniently be grown, mainly by pulsed laser deposition, in the form of epitaxial films, multilayers, superlattices, and well‐ordered arrays of nanoislands. These structures allow for investigations of preparation–microstructure–property relations. A wide variation of the properties is possible, determined by strain, composition, defect contents, dimensional effects, and crystallographic orientation. An overview of our corresponding work of recent years is given, particularly focusing on epitaxial films, superlattices and nanoisland arrays of (anti)ferroelectric and multiferroic functional perovskites.     

Effect of high-power nanosecond and femtosecond laser pulses on silicon nanostructures

The effect of high-power nanosecond (20 ns) and femtosecond (120 fs) laser pulses on silicon nanostructures produced by ion-beam-assisted synthesis in SiO₂ layers or by deposition onto glassy substrates is studied. Nanosecond annealing brings about a photoluminescence band at about 500 mn, with the intensity increasing with the energy and number of laser pulses. The source of the emission is thought to be the clusters of Si atoms segregated from the oxide. In addition, the nanosecond pulses allow crystallization of amorphous silicon nanoprecipitates in SiO₂. Heavy doping promotes crystallization. The duration of femtosecond pulses is too short for excess Si to be segregated from SiO₂. At the same time, such short pulses induce crystallization of Thin a-Si films on glassy substrates. The energy region in which crystallization is observed for both types of pulses allows short-term melting of the surface layer.     

Cesaro means in thermoelasticity of dipolar bodies

Summary Our study is concerned with the thermoelasticity of dipolar bodies. We prove that the Cesaro means of the kinetic and strain energies of a solution with finite energy become asymptotically equal as time tends to infinity.     

Evaluation of the addition of wheat residues in the production of Pinus oocarpa agglomerated panels

Clean Technologies and Environmental Policy - The aim of this research was to evaluate the physical and mechanical properties of Pinus oocarpa wood agglomerated panels produced with the addition of...