bluuebunny/crossref_metadata_2025 huggingface dataset:
Establishment of Liebermannia dichroplusae n. comb. on the Basis of Molecular Characterization of Perezia dichroplusae Lange, 1987 (Microsporidia)
Authors: SOKOLOVA YULIYA Y. , LANGE CARLOS E. , FUXA JAMES R.
Published: May 2007

ABSTRACT. Perezia dichroplusae Lange, 1987 is a parasite of the Malpighian tubules of an Argentine grasshopper, Dichroplus elongatus (Orthoptera, Acrididae, Melanoplinae). In order to determine relationships of this microsporidium with Perezia nelsoni and with other microsporidia, we sequenced its small subunit ribosomal RNA gene (SSU rDNA) (GenBank Accession No. EF016249) and performed phylogenetic analysis of the novel sequence against 17 microsporidian SSU rDNA sequences from GenBank, using neighbor‐joining (NJ), maximum‐parsimony (MP), and maximum‐likelihood (ML) methods. This analysis revealed the highest similarity (96%) of the new sequence to Liebermannia patagonica, a parasite of gut epithelium cells of another grasshopper from Argentina, versus only 65% similarity to P. nelsoni, a parasite of muscles of paenaeid shrimps. In phylogenetic trees inferred from SSU rDNA sequences, the microsporidium from D. elongatus is sister taxon to L. patagonica and both cluster with Orthosomella operophterae. At the higher hierarchical level, the Liebermania–Orthosomella branch forms a clade with the Endoreticulatus–Cystosporogenus–Vittaforma group and with Enterocytozoon bieneusi. Perezia nelsoni falls into another large clade together with Nosema and Ameson species. We propose transferring P. dichroplusae to the genus Liebermannia and creating a new combination Liebermannia dichroplusae n. comb., based both on SSU rDNA sequence analysis and on common characters between P. dichroplusae and L. patagonica, which include the presence of elongated multinuclear sporonts, sporoblastogenesis by a similar process of sequentially splitting off sporoblasts, ovocylindrical spores of variable size, tissue tropism limited to epithelial cells, Orthoptera as hosts, and geographical distribution of hosts in the southern temperate region of Argentina. We argue that the condition of the nuclei in spores (i.e. diplokaryotic in L. patagonica or monokaryotic in L. dichroplusae) cannot be used to distinguish genera. Therefore, we remove the statement about the presence of diplokaryotic spores from the revised diagnosis of the genus Liebermannia.
Ultrastructure of Buddenbrockia allmani n. sp. (Myxozoa, Malacosporea), a Parasite of Lophopus crystallinus (Bryozoa, Phylactolaemata)
Authors: CANNING ELIZABETH U. , CURRY ALAN , HILL SAMANTHA L. L. , OKAMURA BETH
Published: May 2007

ABSTRACT. Development of a new species of malacosporean myxozoan (Buddenbrockia allmani n. sp.) in the bryozoan Lophopus crystallinus is described. Early stages, represented by isolated cells or small groups, were observed in the host's body wall or body cavity. Multiplication and rearrangement of cells gave an outer cell layer around a central mass. The outer cells made contact by filopodia and established adherens junctions. Sporoplasmosomes were a notable feature of early stages, but these were lost in subsequent development. Typical malacosporean sacs were formed from these groups by attachment of the inner (luminal) cells by a basal lamina to the outer layer (mural cells). Division of luminal cells gave rise to a population of cells that was liberated into the lumen of the sac. Mitotic spindles in open mitosis and prophase stages of meiosis were observed in luminal cells. Centrioles were absent. Detached luminal cells assembled to form spores with four polar capsules and several valve cells surrounding two sporoplasms with secondary cells. Restoration of sporoplasmosomes occurred in primary sporoplasms. A second type of sac was observed with highly irregular mural cells and stellate luminal cells. A radially striated layer and dense granules in the polar capsule wall, and previous data on 18 rDNA sequences enabled assignment of the species to the genus Buddenbrockia, while specific diagnosis relied on the rDNA data and on sac shape and size.
Chemokinesis by Tetrahymena in Response to Bacterial Oligopeptides
Authors: LEICK VAGN , LINDEMOSE SØREN
Published: May 2007

ABSTRACT. The ciliate Tetrahymena responds very efficiently by chemoattraction to a group of trichloroacetic acid‐soluble oligopeptides isolated from a commercial bioprotein from Methanococcus. When fractionated by reversed phase C18‐high‐pressure liquid chromatography, this group of very efficient chemoattractants turned out to consist of a heterogeneous group of oligopeptides with molecular weight ranging from 0.2 to 1.5 kDa. The peptides were very rich in the following amino acids: aspartic acid, alanine, glutamic acid, proline, glycine, lysine, and arginine. The term chemokinesis is used throughout to emphasise that chemoattraction does not necessarily include an element of orientation of cells.
Constrained Sintering of Alumina Thin Films: Comparison Between Experiment and Modeling
Authors: Guillon Olivier , Aulbach Emil , Rödel Jürgen , Bordia Rajendra K.
Published: May 2007

Alumina thin films deposited by dip coating on alumina substrates were sintered between 1150° and 1350°C. A new measuring system using a rocking arm as a mechanical amplifier allows in situ measurement of the shrinkage of the film. Comparison of experimental densification behavior with the predictions of the isotropic continuum mechanics model (using values of constitutive parameters determined by sinter forging) highlights the inadequacy of the isotropic models. These results, together with other published evidence, provide justification to consider anisotropic models.
Highly Aligned Porous Silicon Carbide Ceramics by Freezing Polycarbosilane/Camphene Solution
Authors: Yoon Byung‐Ho , Lee Eun‐Jung , Kim Hyoun‐Ee , Koh Young‐Hag
Published: May 2007

We fabricated highly aligned porous silicon carbide (SiC) ceramics with well‐defined pore structures by freezing a polycarbosilane (PCS)/camphene solution. In this method, the solution prepared at 60°C was cast into a mold at temperatures ranging from 20° to −196°C, which resulted in a bicontinuous structure, in which each phase (camphene or PCS) was interconnected in a regular pattern. After the removal of the frozen camphene network, the samples showed highly porous structures, in which long straight and short elongated pore channels were formed parallel and normal to the direction of freezing, respectively. Thereafter, porous SiC ceramics were produced by the pyrolysis of the porous PCS objects at 1400°C for 1 h in a flowing Ar atmosphere, while preserving their mother pore structures having aligned pore channels.
Microstructure and Piezoelectric Properties of 0.95(Na0.5K0.5)NbO3–0.05SrTiO3 Ceramics
Authors: Cho Kyung‐Hoon , Park Hwi‐Yeol , Ahn Cheol‐Woo , Nahm Sahn , Uchino Kenji , Park Seung‐Ho , Lee Hyeung‐Gyu , Lee Hwack‐Joo
Published: May 2007

The 0.95(Na0.5K0.5)NbO3–0.05SrTiO3 (0.95NKN–0.05ST) ceramics formed in this study had a porous microstructure with small grains and low piezoelectric properties due to their low density. However, when a small amount of Na2O was intentionally subtracted from the 0.95NKN–0.05ST ceramics, a liquid phase was formed, which led to increased density and grain size. Piezoelectric properties were also improved for the Na2O‐subtracted 0.95NKN–0.05ST ceramics. The increased density and grain size were responsible for the enhancement of the piezoelectric properties. In particular, the 0.95(Na0.49K0.5)NbO2.995–0.05ST ceramics showed high piezoelectric properties of d33=220, kp=0.4, Qm=72, and ɛ3T/ɛo=1447, thereby demonstrating their promising potential as a candidate material for application to lead‐free piezoelectric ceramics.
Fabrication of Patterned Inverse Opal Structure Through Physical Confinement Assembly and Selective Electrochemical Deposition
Authors: Kuo Cheng‐Yu , Lu Shih‐Yuan
Published: May 2007

We develop a chemical modification‐free process for fabrication of patterned photonic crystals (PhCs) of inverse opal structure. This process, involving photolithography, colloidal assembly, and electrochemical deposition, is potentially applicable for fabrication of practical optical devices. Polystyrene (PS) spheres were self‐assembled onto pre‐patterned substrates to serve as the sacrificial template. This template was then converted into a patterned inverse opal structure with selective electrochemical deposition. The thickness of the inverse opal structure can be easily controlled by adjusting the time of electrodeposition. We demonstrated the process with fabrication of a T‐shape structure surrounded by an inverse opal structure of titania. Titania was chosen here as a representative demonstration material, and the process can be readily applied to other materials of desired characteristics.
Synthesis, Properties, and Formation Mechanism of Zinc Ferrite Hollow Spheres
Authors: Xu Xin‐Jiang , Zhou Li‐Hua , Zhai Quan‐Guo , Lu Can‐Zhong
Published: May 2007

Hollow spheres of zinc ferrite were prepared via a surfactant‐assisted hydrothermal approach. The morphology and composition of the final products were characterized by X‐ray diffraction, transmission electron microscopy, and field emission scanning electron microscopy. It was observed from the microscope images that the final products were composed of spherical nanostructures about 70–100 nm in diameter. Anti‐ferromagnetic transition at the temperature of about 18.06 K was observed from the temperature–magnetic susceptibility curve of the ZnFe2O4 hollow spheres. Possible formation mechanism of the hollow sphere has been discussed. This work may provide us a new synthesis route for the preparation and fabrication of other ferrite nanostructures.
Plant phenology and seed predation: interactions between gorses and weevils in Brittany (France)
Authors: Barat Myriam , Tarayre Michèle , Atlan Anne
Published: May 2007

Exapion ulicis (Forster) and Exapion lemovicinum (Hoffmann) (Coleoptera: Curculionoidea: Apionidae) are seed predators of the three gorse species occurring in Brittany (France): Ulex europaeus L., Ulex gallii Planch., and Ulex minor Roth.(Fabaceae). Host‐plant phenology plays a major role in the relationship between apionid weevils and their gorse species, because larvae develop within gorse pods and adults have to wait for pod dehiscence to be released. We monitored flowering and fruiting phenology of gorse species, weevil reproductive behaviour, and egg‐laying patterns in six natural populations in the native area of these gorse species. At each site, U. europaeus, which flowers mainly in spring, was sympatric with one of two autumn flowering gorse species, U. gallii and U. minor. We noticed that E. ulicis laid eggs in spring and was restricted to U. europaeus whereas E. lemovicinum laid eggs in autumn and was restricted to the two autumn‐flowering species U. gallii and U. minor. Therefore, host specificity depended on gorse phenology, and not on geographic proximity. In addition, the infested pod content showed that E. ulicis laid several eggs per pod and suggested that females chose pods with the highest numbers of seeds. In contrast, E. lemovicinum laid a single egg per pod and showed no preference for pods with many seeds. Finally, the impact of seed predation by E. ulicis was higher than that of E. lemovicinum.
Evaluation of Napier grass (Pennisetum purpureum) varieties for use as trap plants for the management of African stemborer (Busseola fusca) in a push–pull strategy
Authors: Khan Zeyaur R. , Midega Charles A. O. , Wadhams Lester J. , Pickett John A. , Mumuni Abdulai
Published: May 2007

We evaluated eight Napier grass [Pennisetum purpureum Schumach (Poaceae)] varieties, used in various parts of eastern Africa as fodder, for their potential role as trap plants in the management of the African stemborer, Busseola fusca Füller (Lepidoptera: Noctuidae) through a push–pull strategy. Oviposition preference, larval orientation, settling, arrest and dispersal, feeding, mortality and survival, and development were determined for each of these varieties under laboratory and screen house conditions. Two‐choice tests showed that only two of the varieties tested (cv. Bana and cv. Uganda Hairless) were preferentially chosen by gravid female moths for oviposition over a susceptible maize variety, cv. Western Hybrid 502. Larval preference was, however, highly variable. Larval feeding by first instars on the maize leaves was more intense and significantly more than on leaves of all the Napier grass varieties evaluated. Food consumed and amounts assimilated by the third instars over a 24‐h period were not different among larvae fed on stems of maize and those fed on stems of the various Napier grass varieties. Larval survival was significantly lower on all the Napier grass varieties (below 3%) than on maize (about 44%). Similarly, larval development was about 2–3 weeks longer on majority of the Napier grass varieties. It was concluded that cv. Bana had potential for use as a trap plant in the management of B. fusca because it was more preferred by the moths for oviposition, equally preferred as maize by the larvae for orientation, settling, and arrest, and allowed minimal survival of the larvae. It can thus be used with such ‘push’ plants as Desmodium spp. (Fabaceae) in a ‘push–pull’ strategy, but the effectiveness of such a strategy would strictly depend on proper establishment and management of these companion plants.
Endophyte–grass complexes and the relationship between feeding preference and performance in a grass herbivore
Authors: Bourassa Steeve , Brodeur Jacques , Carrière Yves
Published: May 2007

Overseeding non‐endophytic turfgrass lawns with endophytic turfgrass is considered promising for the development of integrated pest management programs in urban landscapes. In this context, a better understanding of the variability in the preference–performance response of insect herbivores exposed to endophytic grasses could be useful to develop efficient practices. Specifically, while endophytic varieties that are strongly toxic and avoided could provide good control of mobile pests, varieties that are toxic but not avoided could be more suitable for the control of sedentary pests. In this laboratory study, we investigated how the infection of 10 grass varieties by Neotyphodium endophytes affected the feeding performance and preference of newly hatched nymphs of the hairy chinch bug, Blissus leucopterus hirtus Montandon (Heteroptera: Lygaeidae), a common turfgrass pest in north‐eastern USA. We found that endophytes generally induced a strong relationship between feeding performance and preference in this herbivore. However, two endophytic varieties did not conform to this relationship, with one variety being highly toxic but not avoided and the other less toxic but highly avoided. These results provide a solid basis to further explore the impacts of endophytic grasses on the dispersal and survival of insect pests in mixed stands of endophytic and non‐endophytic plants.
Bacterial colonization immediately after installation on oral titanium implants
Authors: Fürst Mirjam M. , Salvi Giovanni E. , Lang Niklaus P. , Persson G. Rutger
Published: May 2007

Background: Information on bacterial colonization immediately after dental implant insertion is limited.

Aims: (1) To assess the early colonization on titanium implants immediately after placement and throughout the first 12 post‐surgical weeks, (2) to compare the microbiota at interproximal subgingival implant and adjacent tooth sites.

Material and methods: Subgingival plaque samples from implant and neighbouring teeth were studied by checkerboard DNA–DNA hybridization before surgery, 30 min after implant placement, and 1, 2, 4, 8, and 12 weeks after surgery.

Results: Comparing bacterial loads at implant sites between 30 min after placement with 1‐week data showed that only the levels of Veillonella parvula (P<0.05) differed with higher loads at week 1 post‐surgically. Week 12 data demonstrated significantly higher bacterial loads for 15/40 species at tooth sites compared with pre‐surgery (P‐values varying between 0.05 and 0.01). Between the period immediately after surgery and 12 weeks at implant sites, 29/40 species was more commonly found at 12 weeks. Included among these bacteria at implant sites were Porphyromonas gingivalis (P<0.05), Tannerella forsythia, (P<0.01), and Treponema denticola (P<0.001). Immediately post‐surgery 5.9% of implants, and 26.2% of teeth, and at week 12, 15% of implants, and 39.1% of teeth harbored Staphylococcus aureus. Comparing tooth and implant sites, significantly higher bacterial loads were found at tooth sites for 27/40 species after 30 min following implant placement. This difference increased to 35/40 species at 12 weeks post‐surgically.

Conclusions: Bacterial colonization occurred within 30 min after implant placement. Early colonization patterns differed between implant and tooth surfaces.
The Tropical Ant Mosaic in a Primary Bornean Rain Forest
Authors: Davidson Diane W , Lessard Jean‐Philippe , Bernau Christopher R. , Cook Steven C.
Published: May 2007

In primary lowland rain forest in Brunei Darussalam, we studied arboreal ant communities to evaluate whether densities and spacing of spatially territorial taxa along 2.9 km of well‐studied trails are consistent with existence of a continuous mosaic of dominant ants. A median intercolony distance of 24.5 m, about twice or less distances over which colonies of most included species regularly ranged, suggested a relatively continuous mosaic. Despite relying on nesting sites in preformed plant cavities, carpenter ants contributed > 70 percent of mapped colonies. Most belonged to theCamponotus(Colobopsis)cylindricus(COCY) complex, including SE Asia's ‘exploding’ ants. Their lack of aggression against certainPolyrhachisspecies was associated with interspecific territory sharing by members of the two groups, and with a dominance‐discovery trade‐off. Experimental approaches yielded evidence for two putative contributors to positive association. Larger‐bodiedPolyrhachisparasitize food‐finding abilities of smaller, more populousCamponotusworkers, and the two taxa cooperate in territorial defense. Highly territorial and predatory weaver ants (Oecophylla smaragdina) were an important component of the ant mosaic in primary forest, second only to codominant COCY andPolyrhachistaxa. Members of the genusCrematogasterwere significantly associated withOecophyllain baiting censuses and regularly monopolized near‐nest baits to the exclusion of weaver ants. Litter ant abundances differed between territories ofOecophyllaand less predatory COCY species, but direction of difference was inconsistent over time. The densely packed mosaic of spatially territorial, and differentially predatory, taxa in Bornean rain forest likely contributes to spatial variation in ant effects on plant and arthropod communities.
Carrying Capacity and Potential Production of Ungulates for Human Use in a Mexican Tropical Dry Forest
Authors: Mandujano Salvador
Published: May 2007

Data are provided on the carrying capacity and potential production for sustainable human use of white‐tailed deer (Odocoileus virginianus) and collared peccary (Pecari tajacu) in a protected tropical dry forest at Chamela on the Pacific coast of Mexico. In this paper, the carrying capacity was defined as the equilibrium density plus the number of animals removed by predators. The equilibrium point was estimated from the density dependent relationship between the finite population growth rate and the current density according to a logistic model. Annual density was estimated using the line transect method. Carrying capacity estimates were 16.5 to 17.2 deer/km2 and 9.3–9.5 peccaries/km2, representing a combined biomass of 841–874 kg/km2. A potential production for human use of 2.1 deer/km2 and 4.4 peccaries/km2 was estimated employing the model of Robinson and Redford (1991). The data suggest that, in the protected tropical dry forest of Chamela, the density and biomass of wild ungulates can maintain a similar or greater density and biomass than other Neotropical forests. To obtain an accurate estimation of the maximum sustainable yield (MSY), it is necessary to consider predation. From a management point of view, it is important to consider that carrying capacity varies as a function of the rainfall pattern.
Environmental Control of Early Succession on a Large Landslide in a Tropical Dry Ecosystem (Casita Volcano, Nicaragua)
Authors: Velázquez Eduardo , Gómez‐Sal Antonio
Published: May 2007

We described the plant communities on a large landslide in a human‐dominated area of tropical dry forest landscape (Casita Volcano, Nicaragua) and in the adjacent forest, 3 yr after landslide occurrence. At both sites, we determined the relationships between spatial changes in environmental factors and the spatial distribution of species and plant traits. Subsequently, we tested the hypothesis that the compositional similarity between the landslide and the forest increased with a decrease in the distance from the forest edge and the width of the landslide. In the forest, the spatial distribution of species and plant traits was determined mainly by an elevational gradient that was associated with the amount of bare soil, whereas, on the landslide, there was no such gradient but species distributions were influenced mostly by the presence of residual agricultural and forest soils and human disturbance. We did not find an increase in compositional similarity between the landslide and the forest at the edge or in the narrow zones of the landslide. Compared to other landslides, the recovery process was strongly influenced by the extreme abiotic heterogeneity, climate seasonality, and human use in the area. The study of succession in tropical dry landslides located in densely populated zones should focus on understanding the response of regional ecosystems to a complex disturbance regime in which human‐induced disturbances play a major role.
Use of a Wetland Index to Evaluate Changes in Riparian Vegetation After Livestock Exclusion1
Authors: Coles‐Ritchie Marc C. , Roberts David W. , Kershner Jeffrey L. , Henderson Richard C.
Published: May 2007

Abstract: A method was developed to characterize ecological integrity of riparian sites based on the abundance of hydric species. This wetland index can be calculated with species data, or with community type data as performed here. Classified riparian community types were used to describe vegetation at 14 livestock exclosures and adjacent grazed areas. Community type wetland index values were generated and used to calculate site wetland index values. It was hypothesized that removal of livestock would result in higher wetland index values because of release from herbivory and decreased physical disturbance of vegetation, streambanks, and soil. The wetland index for exclosures was about 12% higher than grazed sites; differences were statistically significant (p < 0.01) based on pairedt‐tests. The increase in hydric vegetation after livestock exclusion may have contributed to the greater bank stability (p = 0.002) and smaller width‐to‐depth ratio (p = 0.005) in exclosures. Challenges were encountered in using community types to describe and compare site vegetation, which could be avoided with species data collection. The wetland index can be a tool to monitor sites over time, compare sites with similar environments, or compare sites for which environmental differences can be accounted.
Hydrograph Separation by Incorporating Climatological Factors: Application to Small Experimental Watersheds 1
Authors: Nejadhashemi Amir P. , Sheridan Joseph M. , Shirmohammadi Adel , Montas Hubert J.
Published: May 2007

Abstract:  Evaluating the relative amounts of water moving through the different components of the hydrological cycle is required for precise management and planning of water resources. An important aspect of this evaluation is the partitioning of streamflow into surface (quick flow) and base‐flow components. A prior study evaluated 40 different approaches for hydrograph‐partitioning on a field scale watershed in the Coastal Plain of the Southeastern United States and concluded that the Boughton’s method produced the most consistent and accurate results. However, its accuracy depends upon the proper estimation of: (1) the end of surface runoff, and (2) the fraction factor (α) that is function of many physical and hydrologic characteristics of a watershed. Proper identification of the end of surface runoff was accomplished by using a second derivative approach. Applying this approach to 12 years of separately measured surface and subsurface flow data from a field scale watershed (study area) proved to be accurate for 87% of the time. Estimation of the α value was accomplished in this study using two steps: (1) alpha was fitted to individual hydrographs: and, (2) a regression equation that determines these alpha values based on climatological factors (e.g., rainfall, evapotranspiration) was developed. Using these strategies improved the streamflow partitioning method’s performance significantly.
Quantitative evaluation of film thickness uniformity: Application to off-axis magnetron source onto a rotating substrate
Authors: Du X. S. , Jiang Y. D. , Yu J. S. , Li J. , Xie G. Z.
Published: May 2007

To predict the thin film thickness distribution in a quantitative way, a theoretical calculation was conducted according to the cosine law approach for off-axis sputtering. The numerical calculation was focused on the optimal geometry instead of the thickness distribution itself, which took into account several variables including the target-to-substrate distance, the off-axis displacement, the emission characteristic, the width of the erosion groove, and the film thickness requirement. The effects of these variables on the optimal geometry were analyzed individually and the subsequent combined equations for optimal geometry were summarized. Thus, the combined equations were multivariable functions. These equations were simple and general and could be applied directly. For many situations, these equations eliminate the need to perform the complex, detailed calculation otherwise needed for each deposition geometry variant.
Cryotrapping assisted mass spectrometry for the analysis of complex gas mixtures
Authors: Ferreira Jose A. , Tabarés Francisco L.
Published: May 2007

A simple method is described for the unambiguous identification of the individual components in a gas mixture showing strong overlapping of their mass spectrometric cracking patterns. The method, herein referred to as cryotrapping assisted mass spectrometry, takes advantage of the different vapor pressure values of the individual components at low temperature (78K for liquid nitrogen traps), and thus of the different depletion efficiencies and outgassing patterns during the fast cooling and slow warming up of the trap, respectively. Examples of the use of this technique for gas mixtures with application to plasma enhanced chemical vapor deposition of carbon and carbon-nitrogen hard films are shown. Detection of traces of specific C3 hydrocarbons (<50ppm of initial methane) in methane/hydrogen plasmas and the possible trapping of thermally unstable C–N compounds in N2 containing deposition plasmas are addressed as representative examples of specific applications of the technique.
Growth and electronic and magnetic properties of α-FeSe films on GaAs (001) substrates
Authors: Liu K. W. , Zhang J. Y. , Li Binghui , Li Bingsheng , Shan C. X. , Lu Youming , Shen Dezhen
Published: May 2007

FeSe films have been grown on GaAs (001) substrates by low-pressure metal organic vapor deposition at different temperatures. X-ray diffraction analysis indicated that the FeSe films grown at substrate temperatures (Ts) between 220 and 340°C were preferentially oriented with tetragonal structure. It was not possible to deposit films at Ts above 400°C. The atomic molar ratios of Se∕Fe increased with increasing the flow rate of H2Se∕Fe(CO)5 and the growth temperature. The electronic property results showed that the conductive type of FeSe could be adjusted by controlling the growth temperature. The coercivity of FeSe decreased with increasing the growth temperature from 220to300°C due to the improvement of crystal quality.
Sputtering yield measurements at glancing incidence using a quartz crystal microbalance
Authors: Kolasinski Robert D. , Polk James E. , Goebel Dan , Johnson Lee K.
Published: May 2007

Low energy sputtering yields at grazing incidence have been investigated experimentally using a quartz crystal microbalance (QCM) technique. This method involved precoating the QCM with a thin film of the desired target material and relating the resonance frequency shift directly to mass loss during ion bombardment. A highly focused, low divergence ion beam provided a well defined incidence angle. Focusing most of the ion current on the center of the target allowed for higher sensitivity by taking into account the radial mass sensitivity of the QCM. Measurements of Mo, Cu, and W sputtering yields were taken for low energy (80–1000eV) Xe+ and Ar+ to validate this experimental method. The target films ranged from 3.5to8.0μm in thickness and were deposited so that their crystal structure and density would match those of the bulk material as closely as possible. These properties were characterized using a combination of scanning electron microscope imagery, profilometry, and x-ray diffraction. At normal incidence, the sputtering yields demonstrated satisfactory agreement with previously published work. At angles of incidence up to 40° off normal, the data agreed well with predictions from existing theoretical models. Sputtering yields were found to increase by a factor of 1.6 over this range. The optimum angle for sputtering occurred at 55°, after which the yields rapidly decreased. Measurements were taken up to 80° from the surface normal.
Design and test of magnetic shields for quadrupole mass spectrometers
Authors: Gervasini G. , De Angeli M. , Gittini G.
Published: May 2007

The use of quadrupole mass spectrometers in plasma experiments with magnetic field confinement presents troublesome problems because of the presence of static magnetic fields. In mass spectrometers, the Lorentz force associated with the magnetic field deflects the ion trajectory in the analyzer section with a subsequent loss of instrument sensitivity. In order to reduce the effect of the externally applied magnetic field in the quadrupole, different magnetic materials have been considered as a shielding structure (iron Fe-37, soft iron Armco™, Amumetal™ sheets). The present work describes a solution to shielding quadrupole mass spectrometers against strong magnetic fields giving an introduction to magnetic shield design, by means of finite element calculations, taking into account many factors such as the material used, the length and thickness of the shield, and the effects of openings. To prove the efficiency of the shielding system, the hydrogen signal from the quadrupole instrument has been monitored. The intensity and the direction of the magnetic field with respect to the quadrupole head axes have been varied. Measurements of the magnetic field have been made in order to validate the calculations and an example of application of the shield design guidelines to a magnetic confined plasma device is presented and tested in situ. The principal aim of the present work is to indicate a possible approach to the problem and how to obtain a practical solution with a worthy compromise between costs and performances.
Inverted-magnetron cold-cathode gauge in hybrid-discharge mode
Authors: Mao Huiyong , Wang Yi
Published: May 2007

In high-vacuum measurement, cold-cathode ionization gauges have been widely used due to their unique advantages such as being simple and robust, low outgassing, x-ray effects, and so on. But during the measuring process, they show that a considerable pump effect, contamination buildup, and the heating and sputtering of the electrode surface from discharge can also become a serious problem at higher measured pressures. In such circumstances, pulsed operation is a good solution. However, the lowest measurable pressure of cold-cathode ionization gauges in pulsed operation is hard to extend, which limits its application. But if the measurable range of the cold-cathode gauge is divided into two regions, the low-pressure region where it is operated in dc discharge mode to ensure its lowest measurable pressure and the high-pressure region where it is operated in pulsed-discharge mode to reduce its above disadvantages at high pressures, the problem can be well solved. This article describes a pulsed high-voltage generating circuit controlled by a single-chip CPU to perform such a hybrid discharge in an inverted-magnetron gauge. With this circuit, the following problems of an inverted-magnetron gauge were investigated: the difference between pulsed-discharged mode and dc discharge mode, one method of extending the low measurable pressure limit in pulsed-discharge mode, the volt-current characteristics at different pressures, and constant-current pulsed-discharge measurement at pressures above 2×10−2Pa.
Oxidation suppression in ytterbium silicidation by Ti∕TiN bicapping layer
Authors: Jiang Yu-Long , Xie Qi , Detavernier Christophe , Van Meirhaeghe R. L. , Ru Guo-Ping , Qu Xin-Ping , Li Bing-Zong , Huang Anping , Chu Paul K.
Published: May 2007

Ytterbium (Yb) silicide is a promising contact material due to its low contact resistance and small Schottky barrier height in contact with n-type Si. However, as one of the rare earth metals, Yb is easily oxidized during physical vapor deposition and rapid thermal annealing. In this article, a bilayered Ti∕TiN cap is proposed and demonstrated to effectively suppress oxidation during Yb silicidation. The authors’ results reveal that diffusion of Ti atoms in the TiN layer plays a key role in oxidation suppression.
Sticking probability of Ti atoms in magnetron sputtering deposition evaluated from the spatial distribution of Ti atom density
Authors: Nafarizal N. , Sasaki K.
Published: May 2007

By comparing the spatial distribution of Ti atom density in front of a planar substrate with a diffusion model proposed by Chantry [P. J. Chantry, J. Appl. Phys. 62, 1141 (1987)], the authors evaluated the sticking probability of Ti atoms in magnetron sputtering deposition. The spatial distribution of Ti atom density was measured precisely by laser-induced fluorescence imaging spectroscopy. They found that the sticking probability of Ti atoms during the growth of Ti film was 0.9±0.2. This result suggests the possibility that the sticking probability is less than unity, which is widely assumed in many simulation studies. The sticking probability was almost unchanged when the discharge pressure and power were varied. In addition, heating the substrate at 250°C and biasing it at a self-bias voltage of −200V by a rf power had no significant influence on the sticking probability.
Competitive growth of Ta nanopillars during glancing angle deposition: Effect of surface diffusion
Authors: Zhou C. M. , Gall D.
Published: May 2007

Periodic arrays of Ta nanopillars were grown onto patterned substrates by glancing angle sputter deposition at growth temperatures Ts ranging from 200to900°C. The Si substrates were patterned using a colloidal suspension of 260-nm-diameter silica spheres that was dispersed to form a two-dimensional close-packed monolayer. At low growth temperatures, Ts⩽500°C, nanopillars exhibit regular hexagonal arrays. However, the arrays randomize with increasing Ts and completely degrade at Ts=900°C. The transition to a less ordered film morphology is attributed to strong interpillar competition caused by the increasing adatom diffusion length with increasing Ts. The competitive growth mode leads to a decrease in the pillar number density (by 48%) and pillar separation (from 65nm to negligible), an increase in the average pillar width from 200to260nm, the accelerated growth of some pillars at the cost of others which die out (25%), and an increased probability (20%) for the merging of neighboring pillars.
Voltage oxide removal for plating: A new method of electroplating oxide coated metals in situ
Authors: von Gutfeld R. J. , West A. C.
Published: May 2007

A novel in situ method for electroplating oxide coated metals is described. Termed VORP, for voltage oxide removal for plating, the process utilizes a voltage pulse ∼20–200V, ∼2ms in duration, applied between working and counterelectrodes while both are immersed in a copper electrolyte. The pulse is almost immediately followed by galvanostatic plate-up. Adherent copper deposits up to ∼4μm in height on stainless steel 316 coupons have been obtained. Temperature testing up to 260°C in air does not affect the copper adhesion. A preliminary model for oxide removal is proposed utilizing concepts of dielectric breakdown.
Thermal-desorption behavior of MoS2−xOx solid-lubricant films sputtered on bearing rollers
Authors: Koguma K. , Ikeda M. , Ota N. , Matsuda K. , Kaneta M.
Published: May 2007

Mo S 2 − x O x films were prepared on the rollers of a cross-roller bearing by the radio-frequency magnetron-sputtering method. Outgassing properties of these rollers at various temperatures were measured by the thermal-desorption method. For film with oxygen content of 2.8at.%, the unique gases of M∕e=32 (S+) and 34 (H2S+) were detected at about 370 and 420K, respectively. These gases were not detected until 500K after baking at 393K for 24h. In order to understand the outgassing mechanism of these gases, the chemical structure of film surface was analyzed by x-ray photoelectron spectroscopy before and after the thermal-desorption spectroscopy (TDS) measurement. An increase of MoO2 and a decrease of free sulfur in the film were confirmed after the TDS measurement. This result suggests that MoO2, S, and H2S are produced by the chemical reaction between adsorption water and MoS2. In addition, it has been found that the detection temperature and peak temperature of H2S become high with the increase in the oxygen content in the film.
Anisotropic resistivity of thin films due to quantum electron scattering from anisotropic surface roughness
Authors: Salvadori M. C. , Cattani M. , Teixeira F. S. , Wiederkehr R. S. , Brown I. G.
Published: May 2007

Platinum thin films with thickness in the range of 0.4–12nm were formed by filtered vacuum arc plasma deposition on a substrate with anisotropic roughness. The electrical resistivity was measured in directions parallel and perpendicular to the surface modulation as a function of film thickness, and the resistivity was found to be anisotropic with the degree of anisotropy increasing with decreasing film thickness. The very small thickness of the films calls for a quantum model for film resistivity, and it is shown that the measured resistivity can be interpreted as due to quantum electron scattering by the thin film anisotropic surface roughness.
Effect of arc suppression on the physical properties of low temperature dc magnetron sputtered tantalum thin films
Authors: Subrahmanyam A. , Valleti Krishna , Joshi Srikant V. , Sundararajan G.
Published: May 2007

Arcing is a common phenomenon in the sputtering process. Arcs and glow discharges emit electrons which may influence the physical properties of films. This article reports the properties of tantalum (Ta) thin films prepared by continuous dc magnetron sputtering in normal and arc-suppression modes. The substrate temperature was varied in the range of 300–673K. The tantalum films were ∼1.8μm thick and have good adherence to 316 stainless steel and single-crystal silicon substrates. The phase of the Ta thin film determines the electrical and tribological properties. The films deposited at 300K using both methods were crystallized in a tetragonal structure (β phase) with a smooth surface (grain size of ∼10nm) and exhibited an electrical resistivity of ∼194μΩcm and a hardness of ∼20GPa. When the substrate temperature was 473K and higher, the arc-suppression mode appears to influence the films to crystallize in the α phase with a grain size of ∼40nm, whereas the normal power mode gave mixed phases β and α beyond 473K, the arc-suppression mode yields larger grain sizes in the Ta thin films and the hardness decreases. These changes in the physical properties in arc-suppression mode are attributed to either the change in plasma characteristics or the energetic particle bombardment onto the substrate, or both.
Reflection rules preserving molecular flow symmetry in an arbitrarily shaped pipe
Authors: Kusumoto Yoshiro
Published: May 2007

The molecular flow symmetry through an arbitrarily shaped pipe is mathematically considered. An extension of Clausing’s method creates a new framework that unifies both the diffuse and beam reflections. Using this framework, the author shows that only the cosine law of reflection preserves the symmetry for diffuse reflections; for beam reflections, there are innumerable reflection rules preserving the symmetry, provided that the molecular flux is conserved in a collision with the pipe wall. If the molecular flux is not conserved, i.e., the pipe wall is adsorbent, only five reflection rules remain for preserving the symmetry.
Thermal stability of TiAlN∕TiAlON∕Si3N4 tandem absorbers prepared by reactive direct current magnetron sputtering
Authors: Barshilia Harish C. , Selvakumar N. , Rajam K. S.
Published: May 2007

Spectrally selective TiAlN∕TiAlON∕Si3N4 tandem absorber was deposited on copper, stainless steel, and Nimonic substrates using a reactive direct current magnetron sputtering system. The absorptance and the emittance of the tandem absorbers were characterized using solar spectrum reflectometer and emissometer. The surface morphology of the tandem absorbers was studied using atomic force microscopy. The compositions and the thicknesses of the individual component layers have been optimized in such a way to achieve high absorptance (0.958) and low emittance (0.07 at 82°C). In order to study the thermal stability of the tandem absorbers, they were subjected to heat treatment (in air and vacuum) at different temperatures and durations. The structural changes as a result of heating of the tandem absorbers were studied using micro-Raman spectroscopy. The tandem absorbers deposited on copper substrates exhibited high solar selectivity in the order of 9–10 even after heat treatment in air up to 600°C for 2h. These tandem absorbers also exhibited very high thermal stability (525°C) in air for longer durations (50h). The onset of oxidation for the tandem stack deposited on silicon substrates was 900°C, indicating a very high oxidation resistance. The results of the present study indicate the importance of TiAlN∕TiAlON∕Si3N4 tandem absorber for high temperature solar selective applications.
1.5
-
nm
-thick silicon oxide gate films grown at 150°C using modified reactive ion beam deposition with pyrolytic-gas passivation
Authors: Yamada Hiroshi
Published: May 2007

Low-temperature ultrathin silicon oxide gate film growth using modified reactive ion beam deposition (RIBD) with an in situ pyrolytic-gas passivation (PGP) method is described. RIBD uses low-energy-controlled reactive and ionized species and potentializes low-temperature film growth. By combining RIBD with PGP using N2O and NF3, 1.5-nm-thick silicon oxide gate films with high-potential barrier height energy, 3.51eV, and low-leakage current, less than about 10−5A∕cm2 at 2MV∕cm, can be obtained at a growth temperature of 150°C. From an evaluation of number densities of N, F, and O atoms near the 1.5–5.0-nm-thick RIBD-with-PGP silicon oxide films/Si(100) interfaces, it is believed that interfacial N and F atoms contribute to improve the electrical characteristics and F effectively compensates the residual inconsistent-state bonding sites after the N passivation.
Prospective Randomized Trial of Empiric Therapy with Trimethoprim-Sulfamethoxazole or Doxycycline for Outpatient Skin and Soft Tissue Infections in an Area of High Prevalence of Methicillin-Resistant
Staphylococcus aureus
Authors: Cenizal Mary Jo , Skiest Daniel , Luber Samuel , Bedimo Roger , Davis Pat , Fox Patrick , Delaney Kathleen , Hardy R. Doug
Published: May 2007

To evaluate empirical therapy with trimethoprim-sulfamethoxazole or doxycycline for outpatient skin and soft tissue infections in an area of high prevalence of methicillin-resistant
Staphylococcus aureus
, a randomized, prospective, open-label investigation was performed. The overall clinical failure rate was 9%, with all failures occurring in the trimethoprim-sulfamethoxazole group. However, there was no significant difference between the clinical failure rate of empirical trimethoprim-sulfamethoxazole therapy and that of doxycycline therapy.
Calcineurin Inhibition or Mutation Enhances Cell Wall Inhibitors against
Aspergillus fumigatus
Authors: Steinbach William J. , Cramer Robert A. , Perfect B. Zachary , Henn Christina , Nielsen Kirsten , Heitman Joseph , Perfect John R.
Published: May 2007

Calcineurin mutation or inhibition enhanced the antifungal morphological effect of cell wall inhibitors caspofungin or nikkomycin Z against
Aspergillus fumigatus
. Quantification of 1,3-β-
d
-glucan revealed decreased amounts in the calcineurin A (Δ
cnaA
) mutant. Calcineurin can be an excellent adjunct therapeutic target in combination with other cell wall inhibitors against
A. fumigatus
.
Active and Passive Immunizations with the Streptococcal Esterase Sse Protect Mice against Subcutaneous Infection with Group A Streptococci
Authors: Liu Mengyao , Zhu Hui , Zhang Jinlian , Lei Benfang
Published: May 2007

The human pathogen group AStreptococcus(GAS) produces many secreted proteins that play important roles in GAS pathogenesis, including hydrolases that degrade proteins and nucleic acids. This study targets another kind of hydrolase, carboxylic esterase, with the objectives of identifying GAS esterase and determining whether it is a protective antigen. The putative esterase gene SPy1718 was cloned, and the recombinant protein (Sse) was prepared. Sse was detected in GAS culture supernatant, and patients with streptococcal pharyngitis seroconverted to Sse, indicating that Sse was produced in vivo and in vitro. Sse hydrolyzesp-nitrophenyl butyrate, and the residue178Ser is critical for this esterase activity. There are two Sse variant complexes according to the available genome databases, consistent with the previous finding of two antigenic Sse variants. Complex I includes serotypes M1, M2, M3, M5, M6, M12, and M18, whereas M4, M28, and M49 belong to complex II. Sse variants share >98% identity in amino acid sequence within each complex but have about 37% variation between the two groups. Active immunization with M1 Sse significantly protects mice against lethal subcutaneous infection with virulent M1 and M3 strains and inhibits GAS invasion of mouse skin tissue. Passive immunization with anti-Sse antiserum also significantly protects mice against subcutaneous GAS infection, indicating that the protection is mediated by Sse-specific antibodies. The results suggest that Sse plays an important role in tissue invasion and is an antigen protective in subcutaneous infection against GAS strains of more than one serotype.