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  • Articles  (45,898)
  • Chemistry  (45,898)
  • Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics  (45,059)
  • Computer Science  (835)
  • Geosciences  (233)
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  • Articles  (45,898)
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  • 1
    Electronic Resource
    Electronic Resource
    Analysis of otolith chemistry in Nassau grouper (Epinephelus striatus) from the Bahamas and Belize using solution-based ICP-MS (1999)
    Springer
    Coral reefs 18 (1999), S. 171-178 
    Details
    ISSN: 1432-0975
    Keywords: Key words Otolith ; Chemistry ; ICP-MS ; Stock discrimination ; Epinephelus striatus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract  We examined the utility of otolith minor and trace element chemistry, assayed with inductively coupled plasma mass spectrometry (ICP-MS), as a means of delineating population structure in the Nassau grouper (Epinephelus striatus). We characterized the elemental composition of otoliths collected in 1993 from three locations in Exuma Sound, Bahamas and from Glover Reef, Belize in 1995. A single location in Exuma Sound was sampled in 1994 to test temporal variability in otolith composition. Five elements (Ca, Zn, Sr, Ba and Pb) were routinely detected, at levels significantly above background, by solution-based ICP-MS. Results from analysis of variance of elemental data, expressed as a ratio to Ca, indicated that there were no significant differences among the Exuma locations for any element, but significant variability was found between Glover Reef and the pooled Exuma localities for Zn/Ca, Sr/Ca and Ba/Ca ratios. Significant inter-annual differences at one Exuma Sound location was restricted to Ba/Ca ratios. Discriminant function analysis correctly classified 86% and 95% of the Belize and pooled Exuma sites, respectively. Otoliths from Belize were characterized by low Zn/Ca and high Ba/Ca and Pb/Ca ratios compared to otoliths from fish collected in Exuma Sound. Although differences in Ba levels may be related to upwelling at Glover Reef, more data are needed to definitely link otolith composition with regional differences in water chemistry.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003380050176
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  • 2
    Electronic Resource
    Electronic Resource
    The importance of energetic particle precipitation on the chemical composition of the middle atmosphere (1980)
    Springer
    Pure and applied geophysics 118 (1980), S. 128-151 
    Details
    ISSN: 1420-9136
    Keywords: Galactic cosmic rays ; Solar proton events ; Particle precipitation ; Chemistry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract An assessment is made of the relative contribution of certain classes of energetic particle precipitation to the chemical composition of the middle atmosphere with emphasis placed on the production of odd nitrogen and odd hydrogen species and their subsequent role in the catalytic removal of ozone. Galactic cosmic radiation is an important source of odd nitrogen in the lower stratosphere but since the peak energy deposition occurs below the region where catalytic removal of O3 is most effective, it is questionable whether this mechanism is important in the overall terrestrial ozone budget. The precipitation of energetic solar protons can periodically produce dramatic enhancement in upper stratospheric NO. The long residence time of NO in this region of the atmosphere, where catalytic interaction with O3 is also most effective, mandates that this mechanism be included in future modelling of the global distribution of O3. Throughout the mesosphere the precipitation of energetic electrons from the outer radiation belt (60°≲Λ≲70°) can sporadically act as a major local source of odd hydrogen and odd nitrogen leading to observable O3 depletion. Future satellite studies should be directed at simultaneously measuring the precipitation flux and the concomitant atmosphere modification, and these results should be employed to develop more sophisticated models of this important coupling.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01586448
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  • 3
    Electronic Resource
    Electronic Resource
    Turbulent mixing of reactive gases in the convective boundary layer (1997)
    Springer
    Boundary layer meteorology 85 (1997), S. 197-222 
    Details
    ISSN: 1573-1472
    Keywords: Turbulence ; Chemistry ; Closure ; Convective boundary layer
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract We study the interactions of chemistry and turbulent mixing of tracersin the convective boundary layer with a second-order closure model,including higher order chemistry terms. In order to limit the number of predictive equations we prescribe the profiles for ¯w¯Θ, ¯w¯θ ¯θ and the lengthscale l. However, for model validation we treat temperature and humidity asinert tracers, and compare the results with profiles observed during theAir Mass Transformation Experiment, and with similarity expressions for thesurface layer. We find good agreement of the mean profiles, but the (co-)variances are slightly underpredicted. Furthermore, the model usesdiagnostic equations expressing third moments of concentration in terms ofsecond moments and their vertical derivatives. They are compared withlarge-eddy model results, showing good agreement and, therefore, thesimplifications are justified. The model is applied to the transport of two gases subject to one bimolecular reaction. The importance of concentration correlations on themean transformation rate is studied. For two gases diffusing in oppositedirections we find for moderate and fast chemistry a 50% and90% decreased transformation rate due to the negatively correlatedconcentrations. These values are similar to large-eddy results of Schumannand Sykes et al. For two bottom-up tracers we find that the covariance ofboth reactive species is either positive or negative, increasing or reducingthe effective transformation rate depending on the Damköhler number (the ratio of the turbulent and the chemistry timescale). A significantdirect influence of chemistry on the flux divergence is found in bothcases. According to the model the effective transport to mid-levels of theboundary layer is increased when two reactive tracers diffuse in oppositedirections, and decreased in the case of two bottom-up tracers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1000414710372
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  • 4
    Electronic Resource
    Electronic Resource
    Shower Meteoroids: Constraints From Interplanetary Dust Particles And Leonid Meteors (2000)
    Springer
    Earth, moon and planets 88 (2000), S. 35-58 
    Details
    ISSN: 1573-0794
    Keywords: Chemistry ; interplanetary dust particles (IDPs) ; Leonids ; meteor trails ; meteoroids ; meteors ; structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The cometary Leonid meteoroids represent a size range in between largest carbon-richIDPs and the smallest CI meteorites. Their dustball structure and chemistry offer anopportunity to constrain hierarchical dust accretion inferred from petrologic studies ofaggregate and cluster IDPs. The Leonid shower meteoroids of known ``comet ejection''ages provide an opportunity to study space weathering of cometary dust over periodsof up to several hundred years. The meteors and aggregate and cluster IDPs displaycontinuous thermal modification of organics and volatile element (Na, K-bearing phases), that occur as discrete minerals and amorphous solids each different response during kinetically controlled ablation. Leonid meteoroids are not excessively Na-rich. The occurrences of Leonid meteors can now be accurate predicted and combined withknowledge better models for the settling rates, collections of surviving dust becomea comet nucleus-sampling mission.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1013862627781
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  • 5
    Electronic Resource
    Electronic Resource
    Masthead (1988)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 28 (1988) 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760280701
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  • 6
    Electronic Resource
    Electronic Resource
    A boundary element simulation of compression mold filling (1988)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 28 (1988), S. 413-420 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: This paper presents the development of the boundary element equations for the compression molding process of isothermal Newtonian fluids. It shows the numerical implementation of the boundary element equations and presents a simple method of carrying out the domain integral present in the governing equations. The results and accuracy of a boundary element simulation are discussed, and the numerical results compared to experimental values.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760280703
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  • 7
    Electronic Resource
    Electronic Resource
    Fracture behavior of coated/uncoated graphite-epoxy composites (1988)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 28 (1988), S. 605-609 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The static delamination behavior of graphite/epoxy composite specimens subjected to mode I tensile opening (using UDCBUniform double cantilever beam. specimens), and pure mode II shear loading (using ENFEnd-notched flexural. specimens) were studied. The graphite epoxy composites for the study were made from commercially treated fibers, with and without an electropolymerized interlayer. The mode I fracture energy (GIC) was found to be significantly higher (more than 50 percent) for the coated fibers. However, this improvement was accompanied by a high reduction (more than 3 times) in the mode II fracture energy (GIIC). This effect is apparently related to poor adhesion between the interlayer and the epoxy resin, which may be corrected by use of a “top layer” of appropriate composition to form chemical bonds between the phases. The fracture toughness (KIC) of composites made with commercially treated fibers was also evaluated, using double side-notched specimens.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760280909
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  • 8
    Electronic Resource
    Electronic Resource
    Heat transfer effects on the processing-structure relationships of polyetheretherketone (PEEK) based composites (1988)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 28 (1988), S. 583-591 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: An analytical methodology was developed capable of describing interrelations between thermal processing and polymer structure for thermoplastic based composite laminates. Specifically, this modeling methodology was used to describe experimental results generated with a specially designed match die quench mold by processing both neat PEEK polymer and carbon fiber reinforced laminate samples at different cooling rates. The developed model accurately predicted temperature profiles for PEEK laminates of different thicknesses, under normal as well as extreme quenching conditions of 114°C/s. surface cooling rates that are possible to generate with the quench mold. In general, the modeling methodology is capable of predicting a part's thermal profile during processing in terms of the composite's microscopic intrinsic properties (fiber and matrix), composition, and lamina orientation. Furthermore, by coupling to the thermal profile description, a previously developed crystallization kinetics model for PEEK polymer and its carbon reinforced composite, a quantitative description of structural development during processing was obtained. Thus, with this analytical methodology, a skin-core crystallinity profile, where the crystallinity varies with part-thickness as a result of uneven cooling experienced during processing, was predicted both for the neat PEEK polymer and its carbon reinforced laminate forms. Finally, the developed methodology clearly established the interplay of both microscopic heat transfer and kinetics of crystallization/solidification of the matrix that must be accounted for in predicting the final structure of a carbon fiber reinforced laminate that will, in turn, govern microscopic and macroscopic performance.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760280907
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  • 9
    Electronic Resource
    Electronic Resource
    Fluid sorption characterization of PEEK matrices and composites (1988)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 28 (1988), S. 634-639 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Neat poly(ether-ether-ketone) (PEEK) and carbon fiber reinforced PEEK (APC-2) specimens were prepared using a variety of cooling rates to achieve a range of crystallinities. Amorphous specimens were exposed to a variety of fluids to determine the penetrant types which are able to strongly influence the material. This allowed the estimation of the solubility parameter and hydrogen bonding index for PEEK to be 9.5 and 3.1, respectively. Methylene chloride was used to investigate the kinetics of penetrant sorption. The data demonstrated Case II behavior, with the initial crystallinity having a pronounced effect on both the kinetic and equilibrium data. Accordingly, a model was proposed capable of describing the sorption level and penetration depth as a function of time given the sample crystallinity and sorption temperature. With Case II behavior there was no difference in the sorption kinetics of neat and fiber reinforced PEEK. Finally, the dynamic mechanical properties measured during sorption were found to be dependent on the sorption process.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760280912
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  • 10
    Electronic Resource
    Electronic Resource
    Morphology and rheological properties of polypropylene-linear low density polyethylene blends (1988)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 28 (1988), S. 670-678 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The dynamic shear viscosity and the morphology of polypropylene homopolymer and copolymer blended with linear low density polyethylene are studied. A maximum in the dynamic shear viscosity vs. blend composition is reported for the polypropylene copolymer, linear low density polyethylene system. The increasing dynamic shear viscosity is in accordance with the occurrence of a morphology of polyethylene inclusions in rubber surrounded by a polypropylene matrix. Comparing calculations of the dynamic shear viscosities - based on a shell model with interlayer - and experimental results supports this view.
    Additional Material: 17 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760281006
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