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  • 1
    Electronic Resource
    Electronic Resource
    A proposed new microstructure for gas radiation detectors: The microhole and strip plate (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2371-2376 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A new type of microstructure device for a gas radiation detector is proposed. This microstructure, the microhole and strip plate structure, merges the structures of a gas electron multiplier and a microstrip plate in one single plate. This design allows two-multiplication stages and a separation of the sensitive and the detection regions, with full optical positive feedback suppression. Simulations for gas gain and electron transparency of the microstructure are presented. Different applications are discussed. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150623
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  • 2
    Electronic Resource
    Electronic Resource
    Full-energy absorption of x-ray energies near the Xe L- and K-photoionization thresholds in xenon gas detectors: Simulation and experimental results (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 82 (1997), S. 2742-2753 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Distributions of the number of primary electrons produced per incident mono-energetic x-rays in the 1- to 41-keV energy range, which includes the xenon L- and K-absorption edges, were simulated in xenon gas detectors with the Monte Carlo technique. These simulated full-energy absorption distributions are calculated as frequency plots of the number of primary electrons produced per incident x-ray photon. The simulation includes the absorption of x-rays and the de-excitation of the residual xenon ions, followed by the development of the primary electron cloud. The discontinuities observed in the Fano factor, w-value, energy linearity and energy resolution reflect the discontinuities of the Xe photoionization cross-section at the photoabsorption edges. The simulation results are compared with experimental values measured with a gas proportional scintillation counter, and with recent data from other authors. The discontinuities in energy linearity produce an ambiguity in determining the x-ray energy in certain narrow ranges containing the edges. However, our simulation results permit a detailed analysis of observations in these regions. At the K-edge, the discontinuities in the calculated Fano factor and energy resolution were found to depend on the extent to which the K-fluorescence produced by the xenon atoms is allowed to escape. A discussion of the asymmetry of the calculated full-energy absorption peaks is made in terms of the distinction between the different decay branches initiated by photoionization of the Xe atoms, and K-fluorescence escape is found to influence strongly the skewness of the calculated distributions. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.366105
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  • 3
    Electronic Resource
    Electronic Resource
    Xenon–neon gas proportional scintillation counters: Experimental and simulation results (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 6303-6312 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: When gas proportional scintillation counters (GPSC) are used to detect very low energy x rays, the addition of the light noble gas neon to the usual xenon filling improves the collection of primary electrons that originate near the detector window. However, xenon–neon mixtures have lower electroluminescence yields than pure xenon. Increasing the scintillation electric field jeopardizes the energy resolution because of the additional fluctuations introduced by electron multiplication. In this work we investigate the effect of a limited amount of charge multiplication on the electroluminescence yield and the energy resolution R of a xenon–neon GPSC using both Monte Carlo simulation and experimental measurements. We consider xenon–neon mixtures with 5%, 10%, 20%, 30%, 40%, 50%, 70%, 90%, and 100% Xe at a total pressure of 800 Torr. Comparing the experimental and Monte Carlo data for 5.9 keV x rays, we conclude that optimum value of R is reached in a region of weak ionization with a charge gain of less than 2. By extrapolating the experimental results for R to infinite light yield we obtain the intrinsic energy resolution Rint for 5.9 keV x rays in all mixtures. From these results we can predict Fw values, where F is the relative variance in the number of primary electrons (the Fano factor) and w is the mean energy required to produce a primary electron. From a comparison between Monte Carlo and experimental electroluminescence yields, F and w values are estimated for 5.9 keV x rays in the various mixtures. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.370131
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  • 4
    Electronic Resource
    Electronic Resource
    Mechanics of Gas-Liquid Flow in Packed-Bed Contactors (1991)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Fluid Mechanics 23 (1991), S. 233-260 
    Details
    ISSN: 0066-4189
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.fl.23.010191.001313
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  • 5
    Electronic Resource
    Electronic Resource
    Variation in fish community composition along an Iberian river basin from low to high discharge: relative contributions of environmental and temporal variables (2000)
    Copenhagen : Munksgaard International Publishers
    Ecology of freshwater fish 9 (2000), S. 0 
    Details
    ISSN: 1600-0633
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract – Factors associated with the spatial and temporal variation of the lower Guadiana basin (southern Iberia) fish community were determined using data from 20 sites sampled during the summer of 1994 (dry year following a period of low discharge, total discharge from 1992 to 1994=1.45×109 m3) and again during the summer of 1996 (wet year following a period of higher discharge, total discharge from January 1995 to August 1996=6.18×109 m3). From the 17 explanatory variables initially considered six were retained for analysis by a forward selection procedure: maximum depth, altitude, channel width, substrate coarseness, SALT (a dummy variable identifying sampling locations belonging to tributaries that discharge to the brackish Guadiana) and YEAR (a dummy variable identifying the sampling year). Further, we partitioned the total variability in the Guadiana fish community into that accounted uniquely by selected environmental variables (34.9%), uniquely by sampling year (4.1%), by both sampling year and environmental variables (0.3%), and unexplained (60.7%)./〉
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1034/j.1600-0633.2000.90104.x
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  • 6
    Electronic Resource
    Electronic Resource
    Microhabitat use by Iberian nase Chondrostoma polylepis and Iberian chub Squalius carolitertii in three small streams, north-west Portugal (2004)
    Oxford, UK : Munksgaard International Publishers
    Ecology of freshwater fish 13 (2004), S. 0 
    Details
    ISSN: 1600-0633
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract –  Microhabitat use of Iberian nase Chondrostoma polylepis (Steindachner 1865) and Iberian chub Squalius carolitertii (Doadrio 1988) was studied in three small streams of the Lima basin, north-west Portugal. Measurements were made for 210 and 248 individuals, respectively, distributed in two size classes, based on fish ages, during winter, spring, summer and autumn 1998. Both species moved to shallow and slow-flowing microhabitats in summer and autumn, but this mainly reflected seasonal variation in microhabitat availability. Larger individuals of both species used deeper and lower percentage cover areas than smaller conspecifics, however significant ontogenetic differences were only found for water velocity. Different patterns of nonrandom microhabitat use were displayed by both cyprinids. Larger I. nase were in deeper and more discovered waters than those available in the habitat, whereas I. chub was over-represented in slow-flowing areas. There was no evidence of interspecific competition for microhabitat, therefore it is unlikely that spatial resource was limited during the present study.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1600-0633.2004.00054.x
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  • 7
    Electronic Resource
    Electronic Resource
    Efficacy of a nature-like bypass channel in a Portuguese lowland river (2005)
    Berlin, Germany : Blackwell Verlag GmbH
    Journal of applied ichthyology 21 (2005), S. 0 
    Details
    ISSN: 1439-0426
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Throughout Europe in the last decade there has been a steady shift away from more technical fish pass designs to more nature-like passes, such as nature-like bypass channels. Upstream fish passage in a nature-like bypass channel was investigated in a lowland river, the Lima River, for 117 days from March 2000 to May 2002. Fish passage was recorded using an automatic video recording system. Electrofishing samples within the bypass and below the weir were compared with species abundance found on the tape recordings. More than 7500 individuals of eight species passed through the bypass channel. Species composition was dominated by striped mullet (65.3%) and potamodromous species (34.3%), which used the bypass mainly at night. Of the environmental variables considered, bypass discharge explained most of the variation in the number of cyprinids, whereas water temperature was more important for diadromous species. Comparing species composition below the weir using passage recordings provided a useful tool to assess species efficacy of the bypass, although biological requirements should also be taken into account. This study proved the efficacy of the bypass for passage of almost all occurring species and life stages and also for providing suitable habitat for fish fauna, highlighting the use of these facilities for river restoration schemes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1439-0426.2005.00616.x
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  • 8
    Electronic Resource
    Electronic Resource
    Performance of fish lift recently built at the Touvedo Dam on the Lima River, Portugal (2002)
    Berlin Germany : Blackwell Verlag GmbH
    Journal of applied ichthyology 18 (2002), S. 0 
    Details
    ISSN: 1439-0426
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: From March 1998 to February 1999, upstream fish passage was continuously monitored by video tape analysis at the fish lift Touvedo Dam on the Lima River, northern Portugal. A total of 1194 individuals from seven species were transferred by the lift. Cyprinids were the dominant group collected, with Iberian nase Chondrostoma polylepis (Steindachner) (31.8%) being the most abundant species, followed by Iberian barbel Barbus bocagei (Steindachner) (21.1%), Iberian dace Leuciscus carolitertii (Doadrio) (19.2%) and Iberian red roach Rutilus arcasii (Steindachner) (7.1%). Brown trout Salmo trutta fario (L.) and European eel Anguilla anguilla (L.) accounted for 10.8%, whereas Atlantic salmon Salmo salar (L.) was rarely observed. Most cyprinid seasonal movements were observed in the spring and were associated with reproduction. The timing of the run varied and its beginning appeared to be mainly dependent on water temperature. Roach, dace and nase used the fish lift intensively from mid-April until the end of summer. Barbel use of the lift intensified in mid-May in association with warmer water. Salmonids migrated in June–July and autumn. Significant differences were not found in hourly activity, except for nase and barbel, in June and July, respectively. Fish passage was not related to river discharge. The relative effectiveness of the fish lift is discussed in relation to the various species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1439-0426.2002.00309.x
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  • 9
    Electronic Resource
    Electronic Resource
    Localised formulations for thick “sandwich” laminated and composite structures (1998)
    Springer
    Computational mechanics 22 (1998), S. 211-224 
    Details
    ISSN: 1432-0924
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A “sandwich” panel under axial compressive loading is studied over its post-buckling range. Alternative formulations were developed to cover solutions other than the deflection shape given by the classical Rayleigh-Ritz analysis. General elasticity principles are used to derive the total potential energy function in terms of the displacement field. Given a constant modal amplitude displacement field, which is introduced in the total potential energy function, the results are discussed having as background models studied earlier. Techniques for the analysis of localized solutions are presented with reference to the study of the beam on nonlinear elastic foundation. The concepts of localization are introduced by using dynamical analogy and the double scale perturbation method and applied to the sandwich panel, to derive the governing amplitude modulation equations. The resulting formulations are discussed using some examples, and by solving analytical and numerically the amplitude differential equations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004660050355
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  • 10
    Electronic Resource
    Electronic Resource
    Correlation between gender and spontaneous C-cell tumors in the thyroid gland of the Wistar rat (1999)
    Springer
    Cell & tissue research 297 (1999), S. 451-457 
    Details
    ISSN: 1432-0878
    Keywords: Key words Thyroid gland ; Calcitonin ; C-cell hyperplasia ; C-cell carcinoma ; Medullary thyroid carcinoma ; Sexual dimorphism ; Rat (Wistar)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract  In many rat strains, C-cell hyperplasia occurs in an age-dependent manner and is often associated with multifocal C-cell carcinoma. The purpose of this study was to investigate the spectrum of spontaneous, proliferative C-cell disorders by gender in Wistar rats throughout their lifespan. The incidence of C-cell hyperplasia shows a significant increase with age (P〈0.001) and is much higher in female rats than in male rats (P〈0.05). From 3 to 24 months of life, 27.5% of female rats showed a normal C-cell pattern, 55.0% showed C-cell hyperplasia, and 17.5% showed C-cell tumors; while 57.5% of male rats showed a normal C-cell pattern, 32.5% showed C-cell hyperplasia, and 10% showed C-cell tumors. Although the overall frequency of C-cell neoplasms in females was nearly double that in males, these data are not statistically significant. However, the number of C-cell tumors showed a significant increase with age (P〈0.05). Therefore, we can conclude that there were significant differences in the incidence of the total spectrum of C-cell proliferative abnormalities in the thyroid gland of Wistar rats that were both age-dependent and gender-dependent.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004410051371
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