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1.
This study examines the difficulties college students experience when creating and interpreting graphs in which speed is one of the variables. Nineteen students, all preservice elementary or middle school teachers, completed an upper‐level course exploring algebraic concepts. Although all of these preservice teachers had previously completed several mathematics courses, including calculus, they demonstrated widespread misconceptions about the variable speed. This study identifies four cognitive obstacles held by the students, provides excerpts of their graphical constructions and verbal interpretations, and discusses potential causes for the confusion. In particular, misconceptions arose when students interpreted the behavior and nature of speed within a graphical context, as well as in situations where they were required to construct a graph involving speed as a variable. The study concludes by offering implications for the teaching and learning of speed and its interpretation within a graphical setting. 相似文献
2.
CM Silva MF Duarte ML Mira MH Florêncio K Versluis AJ Heck 《Rapid communications in mass spectrometry : RCM》1999,13(12):1098-1103
Fast atom bombardment, combined with high-energy collision-induced tandem mass spectrometry, has been used to investigate gas-phase metal-ion interactions with captopril, enalaprilat and lisinopril, all angiotensin-converting enzyme inhibitors.Suggestions for the location of metal-binding sites are presented. For captopril, metal binding occurs most likely at both the sulphur and the nitrogen atom. For enalaprilat and lisinopril, binding preferably occurs at the amine nitrogen. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
3.
G. Evmenenko E. Theunissen H. Reynaers 《Journal of Polymer Science.Polymer Physics》2000,38(21):2851-2859
Small‐angle X‐ray scattering by means of synchrotron radiation was used to study the interaction of κ‐ and ι‐carrageenan of different molar mass in the presence of the gel‐inducing ions, K+, with the ionic surfactants cetylpyridinium chloride (CPC) and dodecylpyridinium chloride (DPC). This interaction resulted in a more or less complete shrinking of the gel and in the formation of ordered periodic structures of the surfactant in conjunction with the carrageenan molecules. The influence of the polymer concentration for a given surfactant concentration, the content of surfactant for the same concentration of the polysaccharide, the molar mass, and the linear charge density of the polymer were all investigated. Decreasing the length of the alkyl chain of the surfactant, increasing the charge density of the polymer chain, and increasing the polymer concentration for the samples explored improved the ordering in the carrageenan–surfactant complexes. The structures of the κ‐carrageenan–CPC complexes were investigated as a function of temperature during reversible heating–cooling cycles, and it was shown that the addition of the surfactant lead to a more pronounced temperature stability of polymer network. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2851–2859, 2000 相似文献
4.
In this paper the problem posed by interfaces when present in PIV measurements is addressed. Different image pre-processing,
processing and post-processing methodologies with the intention to minimize the interface effects are discussed and assessed
using Monte Carlo simulations. Image treatment prior to the correlation process is shown to be incapable of fully removing
the effects of the intensity pedestal across the object edge. The inherent assumption of periodicity in the signal causes
the FFT-based correlation technique to perform the worst when the correlation window contains a signal truncation. Instead,
an extended version of the masking technique introduced by Ronneberger et al. (Proceedings of the 9th international symposium
on applications of laser techniques to fluid mechanics, Lisbon, 1998) is able to minimize the interface-correlation, resolving only the particle displacement peak. Once the displacement vector
is obtained, the geometric center of the interrogation area is not the correct placement. Instead, the centre of mass position
allows an unbiased representation of the wall flow (Usera et al. in Proceedings of the 12th international symposium on applications
of laser techniques to fluid mechanics, Lisbon, 2004). The aforementioned concepts have been implemented in an adaptive interrogation methodology (Theunissen et al. in Meas Sci
Technol 18:275–287, 2007) where additionally non-isotropic resolution and re-orientation of the correlation windows is applied near the interface,
maximizing the wall-normal spatial resolution. The increase in resolution and robustness are demonstrated by application to
a set of experimental images of a flat-plate, subsonic, turbulent boundary layer and a hypersonic flow over a double compression
ramp. 相似文献
5.
Alberto Di Sante Raf Theunissen René A. Van den Braembussche 《Experiments in fluids》2008,44(2):179-188
A new facility to measure the time evolution of 2D velocity fields in a rotating channel is presented, and the accuracy is
discussed in detail. Measurements are made by means of a time-resolved PIV system composed of a continuous laser diode, coupled
by a fiber optics cable to a laser plane optical module, and a CMOS high-speed camera. Both the PIV system and divergent channel
are fixed on a 2.5 m rotating disk. This allows a direct measurement of the relative velocity of flows with Reynolds numbers
between 3 × 103 and 3 × 104 and Rotation numbers between 0.0 and 0.52. These values correspond to the flow conditions in small radial impellers and can
be independently adjusted by a change of the relative flow velocity and RPM. It is shown that this new facility allows high
signal-to-noise ratios, and that the direct acquisition of the data in a rotating frame drastically reduces the measurement
error. The accuracy and high spatial and temporal resolution of the measurements allow a detailed analysis of boundary layer
characteristics in stationary and rotating conditions. 相似文献
6.
There are two natural ways to extend an arbitrary map between (the carriers of) two lattices, to a map between their MacNeille
completions. In this paper we investigate which properties of lattice maps are preserved under these constructions, and for
which kind of maps the two extensions coincide.
Our perspective involves a number of topologies on lattice completions, including the Scott topologies and topologies that
are induced by the original lattice. We provide a characterization of the MacNeille completion in terms of these induced topologies.
We then turn to expansions of lattices with additional operations, and address the question of which equational properties
of such lattice expansions are preserved under various types of MacNeille completions that can be defined for these algebras.
For a number of cases, including modal algebras and residuated (ortho)lattice expansions, we provide reasonably sharp sufficient
conditions on the syntactic shape of equations that guarantee preservation. Generally, our results show that the more residuation
properties the primitive operations satisfy, the more equations are preserved.
Received August 21, 2005; accepted in final form October 17, 2006. 相似文献
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Aerts A Huybrechts W Kremer SP Kirschhock CE Theunissen E Van Isacker A Denayer JF Baron GV Thybaut JW Marin GB Jacobs PA Martens JA 《Chemical communications (Cambridge, England)》2003,(15):1888-1889
n-Alkane hydroisomerisation and hydrocracking experiments reveal that ZSM-5 materials synthesized by self-assembly of nanoslabs show different molecular shape selectivity than ZSM-5 synthesized by hydrothermal methods. 相似文献
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10.
M. L. Verheijke H. J. J. Jaspers J. M. G. Hanssen M. J. J. Theunissen 《Journal of Radioanalytical and Nuclear Chemistry》1987,113(2):397-403
The specific application of neutron activation analysis in the research on the preparation of silicon integrated circuits is discussed. The high flux irradiation facility for large silicon wafers (up to 15 cm diameter) was used, the analytical procedure, and some typical results will be described. 相似文献