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  • 1
    Electronic Resource
    Electronic Resource
    Determination of wurtzite GaN lattice polarity based on surface reconstruction (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 72 (1998), S. 2114-2116 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We identify two categories of reconstructions occurring on wurtzite GaN surfaces, the first associated with the N face, (0001¯), and the second associated with the Ga face, (0001). Not only do these two categories of reconstructions have completely different symmetries, but they also have different temperature dependence. It is thus demonstrated that surface reconstructions can be used to identify lattice polarity. Confirmation of the polarity assignment is provided by polarity-selective wet chemical etching of these surfaces. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.121293
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  • 2
    Electronic Resource
    Electronic Resource
    Iron solubility in highly boron-doped silicon (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 1424-1426 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have directly measured the solubility of iron in high and low boron-doped silicon using instrumental neutron activation analysis. Iron solubilities were measured at 800, 900, 1000, and 1100 °C in silicon doped with either 1.5×1019 or 6.5×1014 boron atoms/cm3. We have measured a greater iron solubility in high boron-doped silicon as compared to low boron-doped silicon, however, the degree of enhancement is lower than anticipated at temperatures 〉800 °C. The decreased enhancement is explained by a shift in the iron donor energy level towards the valence band at elevated temperatures. Based on this data, we have calculated the position of the iron donor level in the silicon band gap at elevated temperatures. We incorporate the iron energy level shift in calculations of iron solubility in silicon over a wide range of temperatures and boron-doping levels, providing a means to accurately predict iron segregation between high and low boron-doped silicon. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.121964
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  • 3
    Electronic Resource
    Electronic Resource
    Bulk and surface characterization of a dewetting thin film polymer bilayer (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 3775-3777 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have monitored the progression of the dewetting of a partially brominated polystyrene (PBrS) thin film on top of a polystyrene (PS) thin film with scanning transmission x-ray microscopy (STXM) as well as photoemission electron microscopy (PEEM). We mapped the projected thickness of each constituent polymer species and the total thickness of the film with STXM, while we determined the surface composition with PEEM. Our data show that the PBrS top layer becomes encapsulated during the later stages of dewetting and that atomic force microscopy topographs cannot be utilized to determine the contact angle between PBrS and PS. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.122891
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  • 4
    Electronic Resource
    Electronic Resource
    Laparoscopic colposuspension (1998)
    Oxford, UK : Blackwell Publishing Ltd
    BJOG 105 (1998), S. 0 
    Details
    ISSN: 1471-0528
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-0528.1998.tb10119.x
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  • 5
    Electronic Resource
    Electronic Resource
    Variations in the amino acid composition of xylem sap of Betula pendula Roth. trees due to remobilization of stored N in the spring (1998)
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 21 (1998), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Seasonal patterns of N translocation in the xylem sap of Betula pendula were studied, to determine whether specific amino acids were recovered in spring as a consequence of N remobilization. Seedlings were grown in sand culture and provided with 15NH415NO3 (at 2·2 atom percent excess) for one growing season. The following winter dormant trees were transplanted into fresh sand and given N at natural abundance thereafter. Destructive harvests were taken during bud burst and leaf growth to determine the pattern of 15N remobilization and N uptake, along with isolation of xylem sap for analysis of their amino acid profiles and 15N enrichment by GC-MS. 15N remobilization occurred immediately following bud burst, while N derived from root uptake did not appear in the leaves until 12 d after bud burst. During N remobilization there was a 10-fold increase in the concentration of N in the xylem sap, due predominantly to increases in citrulline and glutamine. The 15N enrichment of these two amino acids demonstrated the increase in their concentration in the xylem sap following bud burst was due to N remobilization. These results are discussed in relation to measuring N remobilization and storage capacity of trees in the field.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3040.1998.00313.x
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  • 6
    Electronic Resource
    Electronic Resource
    Rapid data collection and assessment of the biology of Acanthurus nigrofuscus at Woleai Atoll, Micronesia (1998)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 52 (1998), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Traditional community fishing methods commonly employed in the tropical Pacific were used to generate information on the fishery biology of Acanthurus nigrofuscus at Woleai Atoll, Micronesia, over a short time period. A simple depletion model was used to estimate the biomass of A. nigrofuscus at four back reef lagoon sites at Woleai, using two different fishing methods; spear fishing and drive-in-net fishing. The mean biomass and density of A. nigrofuscus on the lagoon reefs was 8000 g ha −1 and 183 fish ha −1 respectively, with a total estimated standing stock for the lagoon of 91 500 fish or a biomass of 4·0 t. The size frequencies of fish caught by spear fishing were biased towards larger sized individuals, while those from drive-in-net fishing were thought to be more representative of the true population size frequencies. Variation in the density and biomass of A. nigrofuscus at the four reef sites was thought to be due to the length of time between episodes of community fishing at each reef site. The sex ratio (male: female) of A. nigrofuscus was significantly different from unity (1: 0·47) and males grew larger than females. Sexually mature fish were present in all size classes above the minimum capture length and spawning activity was greatest during the period of the full moon.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1095-8649.1998.tb00806.x
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  • 7
    Electronic Resource
    Electronic Resource
    An electrostrictive drive for fine pitch control in double-crystal monochromators (1998)
    Chester : International Union of Crystallography (IUCr)
    Journal of synchrotron radiation 5 (1998), S. 829-831 
    Details
    ISSN: 1600-5775
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Precise control of the pitch angle of the crystals in a double-crystal monochromator is essential to preserve their accurate alignment while the instrument is scanned. Computer-controlled piezoceramic electrostrictive actuators have recently been installed to the top crystal in two monochromators at the Daresbury SRS to facilitate this. This complements the coarser control provided by the existing stepper motor to give an accurate positioning of the crystal alignment over the full rocking-curve width of the crystals. To maintain accurate alignment during a scan, a number of servo feedback options have been devised. In this paper an analysis of the performance of these drives is presented and their utility in a variety of different experimental techniques is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0909049597014714
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  • 8
    Electronic Resource
    Electronic Resource
    Ptolemy, Alhazen, and Kepler and the Problem of Optical Images (1998)
    Cambridge : Cambridge University Press
    Arabic sciences and philosophy 8 (1998), S. 9-44 
    Details
    ISSN: 0957-4239
    Source: Cambridge Journals Digital Archives
    Topics: Natural Sciences in General
    Notes: “Although up to now the [visual] image has been [understood as] a construct of reason,” Kepler observes in the fifth chapter of his Ad Vitellionem Paralipomena (1604), “henceforth the [visible] representations of objects should be considered as paintings [picturae] that are actual[ly projected] on paper or some other screen.” While not intended as a historical generalization (“up to now” having surely been meant within the narrow context of the treatise itself), this claim nonetheless reflects historical reality. Virtually all visual theorists before Kepler did, in fact, conceive of optical images as subjective, not objective constructs – or, to put it in modern terms, as virtual rather than real entities. By current lights, of course, the distinction between virtual and real images is both obvious and common-place: whereas the latter can be physically projected upon a screen, the former cannot.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1017/S0957423900002423
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  • 9
    Electronic Resource
    Electronic Resource
    Microbial factors and gingival crevicular fluid aspartate aminotransferase levels (1998)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of clinical periodontology 25 (1998), S. 0 
    Details
    ISSN: 1600-051X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract. The aim of this cross-sectional study was to investigate the clinical application of chairside tests for gingival crevicular fluid (GCF) aspartale amino-transferase (AST) levels and plaque BANA hydrolysis activity with the presence of the periodontal pathogens Porphyromonas gingivalis and Actinohacillus action-mycetemcomitans. The study comprised 100 periodontitis sites (pocket depths≥4 mm. GI = 3) from 10 patients with chronic adult periodontitis and 100 control sites (pocket depths 〈4 mm. GI〈3) from 10 periodontally healthy patients comprising 55 healthy sites (pocket depths 〈4 mm. GI=0) and 45 gingivitis sites (pocket depths 〈4 mm, GI=1 or 2). The values for both BANA hydrolysis and AST levels were significantly higher in samples from periodontitis compared with gingivitis and healthy sites (p〈0.001), A. actinomycetemcomitans was identified in 45% and P. gingivalis in 17% of periodontitis sites but neither pathogen was recovered from control sites and there was no significant correlation with (he clinical parameters measured. There was no significant relationship between the presence of P. gingivalis and/or A. actinmycetemcomitans with BANA hydrolysis or AST levels. A significant correlation (p=0.0017) was observed between BANA hydrolysis and pocket depth and between AST hydrolysis and the GI (p=0.01). This study failed to demonstrate a positive association between chairside analysis of GCF metabolites for AST levels and/or BANA hydrolysis with P. gingivalis and A. actinomycetemcomitans. However, the GCF metabolites had a significant correlation with periodontally diseased sites in patients with chronic adult periodontitis and may help confirm clinical observations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1600-051X.1998.tb02450.x
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  • 10
    Electronic Resource
    Electronic Resource
    Harmonic Radar as a Means of Tracking the Pheromone-Finding and Pheromone-Following Flight of Male Moths (1998)
    Springer
    Journal of insect behavior 11 (1998), S. 287-296 
    Details
    ISSN: 1572-8889
    Keywords: radar tracking ; harmonic radar ; foraging flight ; Lepidoptera ; Agrotis segetum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1021004209198
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