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Wastewater treatment plants (WWTPs) are the hotspots for the spread of antibiotic resistance genes (ARGs) into the environment. Nevertheless, a comprehensive assessment of the city-level and short-term daily variations of ARG surveillance is still lacking in WWTPs. Here, 285 ARGs and ten mobile gene elements (MGEs) were monitored in seven WWTPs in Xiamen via high-throughput qPCR (HT-qPCR) for seven days. The average daily load of ARGs to WWTPs was about 1.21 × 1020copies/d, and a total of 1.44 × 1018copies/d was discharged to the environment across the entire city. Interestingly, no daily variations were observed in ARG richness, abundance, and community composition. Stochastic processes were the main force determining the assembly of ARG communities, with their relative importance ranked in the order of influent (INF) > effluent (EFF) > activated sludge (AS). Further analyses indicated that bacteria and ARGs from upstream treatment units played an increasingly dominant role in shaping ARG communities in AS and EFF, respectively, suggesting the importance of mass-immigration of bacteria and ARGs from the source on ARG transport in wastewater treatment units. This emphasizes the need to revise the way we mitigate ARG contamination but focus on the source of ARGs in urban wastewater.

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Dissolved organic matter (DOM), known as a key to the aquatic carbon cycle, is influenced by abiotic and biotic factors. However, the compositional variation and these factors' effects on fluorescence DOM (FDOM) in urban rivers undergoing different anthropogenic pressure are poorly investigated. Herein, using fluorescence excitation-emission matrix and parallel factor analysis (EEM-PARAFAC), four FDOM components (C1, C2, C3, and C4) were identified in a less urbanized north river (NR) and a more urbanized west river (WR) of Jiulong River Watershed in Fujian province, China. C1, C2, and C4 were related to humic-like substances (HLS) and C3 to protein-like substances (PLS). HLS (63.9% in WR and 36.4% in NR) and PLS (62.7% in WR and 37.3% in NR) exhibited higher fluorescence in the more urbanized river. We also found higher PLS in winter, but higher HLS in summer for both rivers. Although the coefficient of variation indicated a difference in FDOM components stability to some extent between the two rivers, the typhoon event that occurred in summer had a stronger disruptive impact on the CDOM and FDOM of a more urbanized river than that of a less urbanized river. We explore abiotic and biotic factors' effects on FDOM using the partial least squares path model (PLS-PM). PLS-PM results revealed higher significant influences of biotic factors on FDOM in the more urbanized river. This study enhances our understanding of FDOM dynamics of rivers with different anthropogenic pressure together with the abiotic and biotic factors driving them.

Bacteria communities, as key drivers of energy flow and nutrient recycling in rivers, usually consist of a few abundant taxa and many rare taxa. During the last decades, rivers on the Tibetan Plateau have experienced dramatic land surface changes under climate change and anthropogenic disturbances. However, the responses of abundant and rare taxa to such changes and disturbances still remains unclear. In this study, we explored the biogeography and drivers of the abundant and rare bacteria in Yarlung Tsangpo River sediments on the Tibetan Plateau. Our study demonstrated that changes in surrounding land-use patterns, especially in forest land, bare land and cropland, had profound influences on the distribution of the abundant and rare sediment bacteria in the Yarlung Tsangpo River. Although both communities exhibited significant distance-decay patterns, dispersal limitation was the dominant process in the abundant community, while the rare community was mainly driven by heterogeneous selection. Our results also revealed that the abundant bacteria exhibited stronger adaptation across environmental gradients than the rare bacteria. The similar biogeographic patterns but contrasting assembly processes in abundant and rare communities may result from the differences in their environmental adaptation processes. This work provides valuable insights into the importance of land surface changes in influencing the biogeographic patterns of bacteria in fluvial sediments, which helps to predict their activities and patterns in Tibetan rivers under future global climate change and anthropogenic disturbances.

Despite the growing awareness of antibiotic resistance genes (ARGs) spreading in the environment, there is a knowledge gap on the fate and transport of ARGs in particle-attached (PA) and free-living (FL) lifestyles in deep freshwater ecosystems experiencing seasonal hydrological changes. Here, we examined the ARG profiles using high-throughput quantitative PCR in PA and FL lifestyles at four seasons representing two hydrological seasons (i.e., vertical mixing and thermal stratification) in the Shuikou Reservoir (SR), Southern China. The results indicated that seasonal hydrological dynamics were critical for influencing ARGs in PA and FL fractions, and the transition of ARGs between the two lifestyles. Although both PA and FL ARG profiles were likely to be shaped by horizontal gene transfer, PA and FL ARGs had different responses to the changes in physico-chemicals (e.g., nutrients and dissolved oxygen) caused by seasonal hydrological dynamics. The particle-associated niche (PAN) index revealed that there were 94 non-conservative ARGs (i.e., no preferences for PA and FL), 23 conservative ARGs that preferred PA lifestyle, and 16 conservative ARGs for FL lifestyle. A sharp decline in the number of conservative ARGs in stratified seasons suggests a hydrological dynamics-dependent transition of ARGs between two lifestyles. Remarkably, the conservative ARGs (in PA or FL lifestyle) were more closely related to bacterial OTUs in their preferred lifestyle compared to their counterpart lifestyle, suggesting a lifestyle-dependent ARG enrichment. Altogether, these findings enhance our understanding of the role of seasonal hydrological changes in the dissemination of ARGs in different size fractions in deep aquatic ecosystems.

Antibiotic resistance genes (ARGs) are a well-known environmental concern. Yet, limited knowledge exists on the fate and transport of ARGs in deep freshwater reservoirs experiencing seasonal hydrological changes, especially in the context of particle-attached (PA) and free-living (FL) lifestyles. Here, the ARG profiles were examined using high-throughput quantitative PCR in PA and FL lifestyles during four seasons representing two hydrological phenomena (vertical mixing and thermal stratification) in the Shuikou Reservoir (SR), Southern China. The results indicated that seasonal hydrological dynamics were critical for influencing the ARGs in PA and FL and the transition of ARGs between the two lifestyles. ARG profiles both in PA and FL were likely to be shaped by horizontal gene transfer. However, they exhibited distinct responses to the physicochemical (e.g., nutrients and dissolved oxygen) changes under seasonal hydrological dynamics. The particle-association niche (PAN) index revealed 94 non-conservative ARGs (i.e., no preferences for PA and FL) and 23 and 16 conservative ARGs preferring PA and FL lifestyles, respectively. A sharp decline in conservative ARGs under stratified hydrologic suggested seasonal influence on the ARGs transition between PA and FL lifestyles. Remarkably, the conservative ARGs (in PA or FL lifestyle) were more closely related to bacterial OTUs in their preferred lifestyle than their counterparts, indicating lifestyle-dependent ARG enrichment. Altogether, these findings enhanced our understanding of the ARG lifestyles and the role of seasonal hydrological changes in governing the ARG transition between the lifestyles in a typical deep freshwater ecosystem.

Antibiotic resistance genes (ARGs) became an emerging contaminant, and were found to accumulate in natural and man-made environments. A comprehensive understanding of the diversity and abundance of ARGs in pristine environments is critical for defining the baseline levels of environmental ARGs. However, there is limited information available on the ARG profiles of pristine environments, especially for shallow-sea hydrothermal vents ecosystems. Here, we combined 16S rRNA gene full-length amplicon sequencing and high-throughput quantitative PCR (HT-qPCR) to study the bacterial communities, and ARG abundance and diversity in the shallow-sea hydrothermal vent ecosystem of the Kueishantao Islet. The results of the 16S rRNA gene amplicon sequencing showed that several sulfur-cycling related bacterial genera, including Thiomicrorhabdus, Thioreductor, Sulfurovum, Sulfurimonas and Lebetimonas, dominated in the water column of the shallow-sea system. Temperature was the significant factor shaping the bacterial communities. The results of HT-qPCR analysis showed that the Kueishantao shallow-sea system harbored the lowest diversity (average 10 ARG subtypes) and abundance (average 1.0 × 10−3 copy per bacterial cell) of ARGs compared with other pristine (i.e., Tibet lake sediments, marine water and sediments) and anthropogenic-disturbed (i.e., drinking water reservoirs, urban ponds and wastewater treatment plants) environments. Procrustes analysis demonstrated a concordant pattern between the compositions of bacterial communities and ARGs in the shallow-sea system, while variation partition analysis revealed that the shared effects of physicochemical and bacterial communities explained >80% of the variation in the composition of ARGs. These results suggest that the vent bacterial communities and local environmental factors played an important role in shaping the distribution of the ARG profiles. Our study provides the first comprehensive overview of the background level of ARGs in a shallow-sea hydrothermal vent ecosystem.

In this article, we report the discovery of a series of pyrimidopyridones as inhibitors of IRAK4 kinase. From a previously disclosed 5-azaquinazoline series, we found that switching the pyridine ring for an N-substituted pyridone gave a novel hinge binding scaffold which retained potency against IRAK4. Importantly, introduction of the carbonyl established an internal hydrogen bond with the 4-NH, establishing a conformational lock and allowing truncation of the large basic substituent to a 1-methylcyclopyl group. Subsequent optimisation, facilitated by X-ray crystal structures, allowed identification of preferred substituents at both the pyridone core and pyrazole. Subsequent combinations of optimal groups allowed control of lipophilicity and identification of potent and selective inhibitors of IRAK4 with better in vitro permeability and lower clearance.

Microeukaryotes play a significant role in biogeochemical cycling and can serve as bioindicators of water quality in freshwater ecosystems. However, there is a knowledge gap on how freshwater microeukaryotic communities are assembled, especially that how terrestrial microeukaryotes influence freshwater microeukaryotic assemblages. Here, we used a combination of 18S rRNA gene amplicon sequencing and community-based microbial source tracking (MST) approaches (i.e., SourceTracker and FEAST) to assess the contribution of microeukaryotes from surrounding environments (i.e., soils, river sediments, swine wastewater, influents and effluents of decentralized wastewater treatment plants) to planktonic microeukaryotes in the main channel, tributaries and reservoir of a peri-urban watershed, China in wet and dry seasons. The results indicated that SAR (~ 49% of the total communities), Opithokonta (~ 34%), Archaeplastida (~ 9%), and Amoebozoa (~ 2%) were dominant taxa in the watershed. The community-based MST analysis revealed that sewage effluents (7.96 – 21.84%), influents (2.23 – 13.97%), and river sediments (2.56 – 11.71%) were the major exogenous sources of riverine microeukaryotes. At the spatial scale, the downstream of the watershed (i.e., main channel and tributaries) received higher proportions of exogenous microeukaryotic OTUs compared to the upstream reservoirs, while at the seasonal scale, the sewage effluents and influents contributed higher exogenous microeukaryotes to river water in wet season than in dry season. Moreover, the swine and domestic wastewater led to the presence of Apicomplexa in wet season only, implying rainfall runoff may enhance the spread of parasitic microeukaryotes. Taken together, our study provides novel insights into the immigration patterns of microeukaryotes and their dominant supergroups between terrestrial and riverine habitats.

Sales forecasting plays an important role in guiding the sales and marketing of e-commerce enterprises, and warehousing department planning warehouse location. At the same time, sales data can better reflect future sales trends. This paper establishes a sales forecasting and analysis model for commodities with common characteristics using their historical sales data through time series model, and forecasts the sales inventory of a certain kind of products from a quantitative point of view. In order to improve the predictive reliability, this paper introduces external observable data and qualitative analysis of historical data prediction model by using hidden Markov model to predict the characteristics of hidden values, so as to further improve the reliability of prediction model.

Excessive quantities of nitrates in the aquatic environment can cause eutrophication and raise water safety concerns. Therefore, identification of the sources of nitrate is crucial to mitigate nitrate pollution and for better management of the water resources. Here, the spatiotemporal variations and sources of nitrate were investigated by stable isotopes (δ

We researched the external cavity spectral beam combination (SBC) of laser diode (LD) with pigtail output. Two laser diodes with pigtail output, center wavelength of 976nm, and about 45% of electric-to-optical (e-o) conversion efficiency was employed to achieve spectral beam combination. This method demonstrated the feasibility of closed loop SBC of LD with pigtail. The free running spectrum, single laser spectrum with locked wavelength, after combination spectrum were measured. It showed that the spectral width of free running and tunnel range of single laser locked is about 12nm, 6nm respectively. The feedback efficiency of external cavity is about 1.55% when the transmission of cavity output mirror is about 30%. The combination power of 1.63W was obtained, the o-o(optical-to-optical) transferable efficiency is about 25%. The deterioration factor beam quality is about 1.2×, meanwhile, the efficiency loss of SBC and the reason of deterioration of beam quality were analyzed due to the internal loss of external cavity, the transmission loss of grating. In this way, the space stitching, configuration of single chip can transfer to fiber arrangement and organization, due to flexibility and miniaturization of fiber, that will provide a novel thinking for SBC of LD in high power direct application.

Rapid urbanization has resulted in pervasive occurrence of antibiotic resistance genes (ARGs) in urban aquatic ecosystems. However, limited information is available concerning the ARG profiles and the forces responsible for their assembly in urban landscape lagoon systems. Here, we employed high-throughput quantitative PCR (HT-qPCR) to characterize the spatial variations of ARGs in surface and core sediments of Yundang Lagoon, China. The results indicated that the average richness and absolute abundance of ARGs were 11 and 53 times higher in the lagoon sediments as compared to pristine reference Tibetan lake sediments, highlighting the role of anthropogenic activities in ARG pollution. Co-occurrence network analysis indicated that various anaerobic prokaryotic genera belonging to Alpha-, Deltaproteobacteria, Bacteroidetes, Euryarchaeota, Firmicutes and Synergistetes were the potential hosts of ARGs. The partial least squares-path modeling (PLS-PM) analysis revealed positive and negative indirect effects of physicochemical factors and heavy metals on the lagoon ARG profiles, via biotic factors, respectively. The horizontal (mediated by mobile genetic elements) and vertical (mediated by prokaryotic communities) gene transfer may directly contribute the most to drive the abundance and composition of ARGs, respectively. Furthermore, the neutral community model demonstrated that the assembly of sediment ARG communities was jointly governed by deterministic and stochastic processes. Overall, this study provides novel insights into the diversity and distribution of ARGs in the benthic habitat of urban lagoon systems and underlying mechanisms for the spread and proliferation of ARGs.

The occurrence, dissemination and assembly processes of antibiotic resistance genes (ARGs) in urban water ecosystems are far from being understood. Here, we examined the diversity and abundance of ARGs in urban water ecosystems including landscape ponds, drinking water reservoirs, influents (IFs) and effluents (EFs) of wastewater treatment plants of a coastal city, China through high-throughput quantitative PCR. A total of 237 ARGs were identified, where multidrug, aminoglycoside and beta-lactamase resistance genes were the most abundant. Urban ponds had a comparatively high diversity and large numbers of shared ARGs with IFs and EFs. The average absolute abundance of ARGs (1.38 × 107 copies/mL) and mobile genetic elements (MGEs) (4.19 × 106 copies/mL) in ponds were only one order of magnitude lower than those of IFs, but higher than those of EFs and reservoirs. Stochastic processes dominated the ARG community assembly in IFs and ponds due to the random horizontal gene transfer caused by MGEs. These results imply that urban ponds are hotspots of ARGs. We further identified 25, 3, and 11 indicator ARGs for tracing the ARG contamination from IFs, EFs and ponds, respectively. Our study represents the first to highlight the role of urban ponds in the dissemination of ARGs.

Micropollutants have become of great concern, because of their disrupting effects on the structure and function of microbial communities. However, little is known about the relative importance of trace micropollutants on the aquatic prokaryotic communities as compared to the traditional physico-chemical characteristics, especially at different spatial dimensions. Here, we investigated free-living (FL) and particle-associated (PA) prokaryotic communities in a subtropical water reservoir, China, across seasons at horizontal (surface water) and vertical (depth-profile) scales by using 16S rRNA gene amplicon sequencing. Our results showed that the shared variances of physico-chemicals and micropollutants explained majority of the spatial variations in prokaryotic communities, suggesting a strong joint effect of the two abiotic categories on reservoir prokaryotic communities. Micropollutants appeared to exert strong independent influence on the core sub-communities (i.e., abundant and wide-spread taxa) than on the satellite (i.e., less abundant and narrow-range taxa) counterparts. The pure effect of micropollutants on both core and satellite sub-communities from FL and PA fractions was ~1.5 folds greater than that of physico-chemical factors at the horizontal scale, whereas an opposite effect was observed at the vertical scale. Moreover, eight micropollutants including anti-fungal agents, antibiotics, bisphenol analogues, stimulant and UV-filter were identified as the major disrupting compounds with strong associations with core taxa of typical freshwater prokaryotes. Altogether, we concluded that the ecological disrupting effects of micropollutants on prokaryotic communities may vary along horizontal and vertical dimensions in freshwater ecosystems.

The urban water ecosystems, such as the landscape ponds are commonly considered under the influence of anthropogenic disturbances, which can lead to the deterioration of the water quality. The prokaryotic communities are considered as one of the best indicators of the water quality. However, there are significant gaps in understanding the ecological processes that shape the composition and function of prokaryotic communities in the urban water ecosystems. Here, we investigated the biogeographic distribution of prokaryotic assemblages in water environments including landscape ponds, drinking water reservoirs, influents (IFs) and effluents (EFs) of wastewater treatment plants of a coastal city (Xiamen), China, by using 16S rDNA amplicon sequencing. Our results indicated that the ponds had higher α-diversity of prokaryotic communities than those in the reservoirs, while there were significant variations in the community compositions among ponds, reservoirs, IFs and EFs. Moreover, ponds harbored a significantly higher proportion of sewage- and fecal-indicator taxa than those in the reservoirs, suggesting the occurrence of exogenous pollution in the urban ponds. Null model analysis revealed that dispersal limitation was the main ecological processes resulting in the divergence of prokaryotic community compositions between ponds and other environments, while dispersal limitation and variable selection played an essential role in the formation of unique prokaryotic assemblages in the reservoirs. Function predication analysis demonstrated that the ponds shared more similar functional profiles with IFs or EFs (e.g., chemoheterotrophy, fermentation, chlorate reducers, nitrate reduction and respiration) than the reservoirs, whereas dominance of photoautotrophy was observed in the reservoirs. Overall, this study provides a profound insight of the ecological mechanisms underlying the responses of prokaryotic communities in the urban landscape ponds to the anthropogenic disturbances.

A new synthetic approach for α-ketoamides was achieved by copper-catalyzed coupling reactions between N,N-dialkylformamides and phenylacetic acids. A variety of substrates were well tolerated to give yields of 46–87% (17 examples). A 13C-labeling experiment revealed that the carbonyl group of the products came from the phenylacetic acid.

Liu, J.; Liu, C.-L.; Zhang, L.-P., and Xu, Y., 2019.Evaluating marine economic bearing capacity: a network analysis. In: Gong, D.; Zhu, H., and Liu, R. (eds.), Selected Topics in Coastal Research: Engineering, Industry, Economy, and Sustainable Development. Journal of Coastal Research, Special Issue No. 94, pp. 597–600. Coconut Creek (Florida), ISSN 0749-0208.Because of the approximate characteristics of network analysis method, it has been used by many researchers to solve the evaluation of marine economic carrying capacity. In this paper, a method of evaluating and contributing factors of marine economic carrying capacity based on network analysis method is proposed. Based on the evaluation and contribution factors of marine economic carrying capacity, the evaluation and contribution factors of marine economic carrying capacity (MEBC), evaluation of bearing capacity (EBC) and control factors of marine economy (CFME) are established. The experimental results show that this method has wide applicability, and it is also a useful exploration for the evaluation of marine economic carrying capacity in the new period.

A new synthetic approach for α-ketoamides was achieved by copper-catalyzed coupling reactions between N,N-dialkylformamides and phenylacetic acids. A variety of substrates were well tolerated to give yields of 46–87% (17 examples). A 13C-labeling experiment revealed that the carbonyl group of the products came from the phenylacetic acid.

A self-organized nanostructure has been observed on the Cr/Pt(111) system. Cr overlayers with various coverages were deposited on a Pt(111) surface. Upon annealing to different temperatures, metastable surface alloys characteristic for a miscible metallic system have been observed. For a limited coverage range from 1.5 to 3.0 ML and an annealing temperature of 800 K, a spatial self-organization takes place on the bimetallic surface, forming a highly ordered hexagonal superstructure. The scanning tunnel microscope contrast of the superstructure is sensitive to the bias voltage, resulting in different patterns: either a mosaic structure and/or a network consisting of one-atom-wide lines. Relative to the Pt(111) surface, the superstructure has a $(\sqrt{39}\ifmmode\times\else\texttimes\fi{}\sqrt{39})R16.1\ifmmode^\circ\else\textdegree\fi{}$ unit cell with a dimension of 17.3 \AA{}. We propose that the network consists of Pt dislocation lines, and is caused by a stress-induced reconstruction of the top Pt(111) layer. The mosaic pattern is related to a two-dimensional array of Cr clusters containing only ten atoms.

TiO 2 (110) single crystals with trace amounts of Ca impurities were investigated by ISS, XPS, LEED, and STM. After initial cleaning and with increasing annealing temperature, ISS and XPS clearly show the segregation of Ca to the surface of fresh TiO 2 (110) crystals. As revealed by LEED and STM, a [ 60 ] structure is formed as an overlayer, with row-like features along the substrate [001] direction. In line with the Ca 2p 3/2 peak position of 347.4 eV, we propose the formation of a CaTiO 3 -like compound, oriented with its (110) face parallel to the substrate. © 1998 Elsevier Science B.V. All rights reserved.

Nanostructured Ag (polycrystalline Ag with nanometre-sized grains), synthesized by inert-gas condensation plus in situ vacuum compaction, has been investigated by positron lifetime spectroscopy (PLS). The results indicate that there is a common character, i.e. only three lifetime components (, and ) are resolvable from the lifetime spectrum on each of the specimens synthesized under the whole compacting pressure range investigated (from 0.15 to 1.50 GPa). Corresponding to the three lifetime components, there are three types of defect (traps) in nanostructured Ag: (a) vacancy-like (VL) defects, (b) vacancy-cluster (VC) defects and (c) larger voids. Compacting pressure and annealing treatment has great influences on the positron annihilating behaviour. The lifetimes and corresponding intensities decreased irreversibly with compacting pressure and annealing temperature, indicating that the VL defects and VC defects are both mechanically and thermally unstable, and so it is inappropriate to consider them as structural elements in nanostructured Ag. Moreover, the interfaces in n-Ag can be considered as superpositions of VL defects on the normal ordered boundaries, and since the number and size of the VL defects change with external conditions, the interfaces in n-Ag can stay in various metastable states, which implies that its interfacial structures may range from total random states (gaslike) to complete ordered structures, depending on the number and size of the VL defects contained. The forming process of bulk nanostructured Ag revealed by PLS can be roughly divided into three stages: (1) formation stage of interfaces (compacting pressure GPa); (2) rapid elimination of the three types of defect (0.6 GPa 1.1 GPa). Based on these results obtained on nanostructured Ag, a density criterion that of the polycrystalline counterpart is proposed for the formation of bulk nanostructured materials.

The dc resistance and the temperature coefficient of resistance (TCR) of bulk nanostructured silver (n-Ag), synthesized by inert gas condensation and in situ vacuum compaction as well as by the sol-gel method, was investigated in the temperature range from 4.2 to 300 K. The results indicated that for all of the n-Ag specimens with larger grain sizes (d>20 nm) and higher densities (relative density D>88%) investigated, their resistivity decreased with decreasing temperature, showing metallic behavior; however, it was found that for the n-Ag with smaller grain sizes and lower density (D=45–50 %), the resistance increased with decreasing temperature (negative TCR) as its mean size d

The thermal stability of ultrathin chromium films on Pt(111) has been studied using low-energy He+ ion scattering spectroscopy, X-ray photoelectron spectroscopy, low-energy electron diffraction, and scanning tunneling microscopy. At room temperature, Cr grows on Pt(111) with a modified Stranski−Krastanov growth mode (almost complete wetting of the first two layers with subsequent three-dimensional island growth). Upon annealing, chromium diffuses into the Pt lattice. This causes a smoothening of the surface features. A flat Pt(111) surface, devoid of Cr, is regained after prolonged annealing above 770 K. At lower temperatures, metastable Cr−Pt surface alloys are formed. The apparent composition and stability of these surface alloys are dependent upon the amount of Cr deposited initially. Both the Cr adlayer and Pt surface atoms were found to be perturbed at the interface. Experimental and theoretical results indicate that a redistribution of charge between Pt and Cr occurs upon alloy formation with the gr...

The growth of vapor-deposited Cr and chromium oxide on Pt(111) has been studied by ion scattering spectroscopy, x-ray photoelectron spectroscopy, low energy electron diffraction, and scanning tunneling microscopy. Both metal Cr film and its oxide nucleate at Pt(111) step edges, and grow in a step-flow mode. The metal Cr film is pseudomorphic to the Pt(111) substrate within the first two monolayers. At higher coverages, the chromium overlayer adopts a bcc(110) surface structure and forms three-dimensional elongated islands oriented along the three close-packed directions of the Pt(111) surface. For the chromium oxide, a well ordered p(2×2) structure is observed within the first two monolayers and attributed to the epitaxial growth of metastable Cr3O4. At higher coverages, a (√3×√3)R30° structure appears, due to the formation of the stable Cr2O3 phase.

We have prepared chromium oxide films on Pt(111) with thicknesses ranging from less than a monolayer to more than eight monolayers. The films were grown by Cr vapor deposition under an oxygen background pressure of 2 × 10 −6 mbar and a sample temperature of 600 K. The growth, structure and thermal properties of the resulting overlayers have been studied using a combination of ISS, XPS, LEED and STM. During the initial stage of growth, the film nucleates at Pt step edges, and grows in a step-flow mode. For the first two monolayers, a well-ordered p(2 × 2) structure is observed and attributed to the epitaxial growth of metastable Cr 3 O 4 . At higher coverage, a (√3 × √3)R30° structure appears, due to the formation of the stable Cr 2 O 3 phase. After heating in vacuum to about 700 K, the p(2 × 2) film begins to decompose and agglomerate, and finally becomes a (√3 × √3)R30° overlayer. The latter is stable up to the highest temperature used in these studies (1000 K), although at this temperature it also shows dewetting and further clustering.

The growth and structure of ultrathin chromium films on Pt(111) have been studied using low-energy He+ ion scattering spectroscopy, X-ray photoelectron spectroscopy, low energy electron diffraction and scanning tunneling microscopy. Upon initial deposition at room temperature, the Cr atoms migrate along the Pt terraces and populate the step edges. Further growth results in two-dimensional islands of chromium developing from the step edges and across the Pt terraces. The film is pseudomorphic to the Pt(111) substrate. At coverages above 3 ML, chromium forms three-dimensional elongated islands oriented along the three closepacked directions of the Pt(111) surface. The chromium overlayer adopts a bcc (110) surface structure with the close-packed overlayer directions, 〈111〉, aligned with the close-packed Pt(111) directions, 〈110〉. The presence of the Cr overlayer was found to electronically perturb the Pt surface atoms leading to a redistribution of charge between Pt and Cr.

We present a study of an ultrathin surface layer of platinum silicide formed on a Pt(111) crystal as a result of surface segregation of Si and Ca trace impurities. The structure and composition of this surface compound is investigated with low energy He+ ion scattering, (LEIS), x‐ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED), and scanning tunneling microscopy (STM). Si surface segregation onto Pt(111) is thermally activated; annealing at temperatures between 750 and 1100 K results in the formation of a surface silicide. The highest Si coverage that can be reached is 0.4 monolayers; the Ca coverage at saturation is below 0.02 monolayers. The enthalpy of Si segregation is found to be −(105±30) kJ/mole. A well‐ordered (√19×√19)R23.41° or |−23 25| structure is observed by LEED and STM; the amount of surface area covered with this structure is proportional to the Si coverage measured with LEIS. At low annealing temperatures up to 800 K, two domains coexist with |−23 25| and |−32 ...

Colloidal SiO 2 particles with diameters from 10 to 20 nm were deposited onto HOPG and investigated in air by STM. Both single particles and aggregates could be imaged clearly. In some cases, the aggregates were more than 30 nm thick. These results show that, in spite of the insulating character of its bulk solid, the SiO 2 material in form of nanometer-particles could have a good conductivity under the STM conditions. This work will also give us an understanding of conductivities of DNA and other biomolecules.

The glycoproteins and glycolipids from membranes of virulent strain Z and avirulent strain M ofMycoplasma hyopneumoniae have been compared. The proteins and the glycoproteins were identified by SDS-polyacrylamide gel electrophoresis and concanavalin A-biotin labeling, respectively. The membrane preparation contained approximately 34 protein bands with molecular weights between 20 KD and 100 KD. The concanavalin A-biotin system reacted with a glycoprotein of a molecular weight of approximately 28,000 from avirulent strain M and did not react with the correspondent band from virulent strain Z. The membrane glycolipids of both strains consisted of monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG), and the percentages of 16∶0, 18∶0, and 18∶1 fatty acids comprised more than 80% of the total fatty acids of membrane glycolipids. The 18∶0 fatty acid of MGDG in avirulent strain M was twofold higher than that of virulent strain Z.

Using scanning tunnelling microscopy, we have directly observed parallel stranded DNA helixes of 43 nucleotides in length. Th double delix is righ-handded and has an average spacing, 17.43 A (± 1S.D.:2.30 A), and an average apparent depth, 4.79 A(±1S.D.: 1.04 A) for each groove. The average pitch of the helical turn is 34 A(±1S.D.: 3.35 A) and consists of no more than ten base pairs. The diameter of the helix is approx. 17–20A. Our results provide direct evidence for the existence of a parallel structure of DNA in vitro and some details of its fine structure.

Sphingomyelin liposomes and brain microsomes were oxidized by exposure to hydrogen peroxide and ferrous ion. Lipid peroxidation were measured by the formation of thiobarbituric acid- reactive substances (TBAR). Hydroxyl radical was detected using the spin- trapping technique. Incubation of sphingomyelin liposomes with H2O2-Fe2+ resulted in an increase in the formation of TBAR. Na(+)-K(+)-ATPase activity was markedly inhibited and the SH group content decreased during incubation of microsomes in the presence of H2O2-Fe2+. Sodium ferulate effectively inhibited TBAR formation, protected Na(+)-K(+)-ATPase activity and prevented the oxidative modification of SH groups. Spin-trapping experiments showed that sodium ferulate effectively scavenged the hydroxyl radicals.