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161.
Translation errors and conceptual misunderstandings made by students translating among graphical, tabular, and symbolic representations of linear functions were examined. The study situated student errors in the context of the “Translation‐Verification Model” developed specifically for the purpose of explaining student behavior during the process of translating relationships from one mathematical representation to another. Three distinct error types were identified to explain student performance. An examination of the error types revealed that specific translation errors tend to occur at different stages of the translation process. Translation errors are also related to “attribute density,” the amount of information inherently encoded in a given representation. The findings of the study have implications for teaching linear relationships—student weaknesses and strengths are identified. 相似文献
162.
We carried out molecular dynamics simulations to describe the properties of water inside a narrow graphite channel. Two stable phases were found: a low-density one made of water clusters adsorbed on the graphite sheets and a liquid one that fills the entire channel, forming several layers around a bulk-like region. We analyzed the interfacial structure, orientational order, water residence times in several regions, and hydrogen bonding of this last water phase, calculating also a quantity of electrochemical interest, the probability of electron tunneling through interfacial water. The results are in good qualitative agreement with the available experimental data. 相似文献
163.
L. Marti?ka L. Husáriková Z. Repická D. Valigura M. Valko M. Mazúr 《Applied magnetic resonance》2010,39(4):423-435
Two copper(II) ternary complex systems containing 5-chlorosalicylic acid (5-ClsalH) and different copper(II) salts with varying
3-pyridylmethanol (ron = ronicol) concentration, system I [CuSO4 (aq) +2(5-ClsalH(solv)) + xron(l)] and system II [Cu(ac)2(aq) + 2(5-ClsalH(solv)) + xron(l)], where x = 0, 2, 4, 6 and 8, were prepared and studied by electron paramagnetic resonance (EPR) spectroscopy in frozen water–methanol
solutions to observe the effects of different copper(II) salts and varying neutral ligand concentration on the formation of
resulting complexes in solution. The trend in g-values (g
|| > g
⊥ > 2.0023) indicates that the unpaired electron on the copper ion is localized in the dx2 - y2 d_{{x}^{\rm{2}} - {y}^{\rm{2}}} orbital. The detailed analysis of the second-derivative Cu(II) EPR spectra has shown well-resolved 14N superhyperfine splitting in the perpendicular part of the axially symmetric spectra. The resolution of nitrogen superhyperfine
multiplet patterns increased with increase in the ronicol concentration (ligand-to-metal ratio x). The number of superhyperfine lines was found to be constant (nonet) when x > 4 for system I and x ≥ 4 for system II. This fact indicates that for these x-values four equivalent nitrogen atoms could be coordinated to the central copper atom in the equatorial plane of both systems. 相似文献
164.
For dose delivery to patients, scanning ion beams are going to be increasingly used in the upcoming ion beam therapy facilities. Especially carbon ion beams are able to produce steep dose gradients. However, the currently used method for patient dose verification, employing ionization chamber arrays, provides a spatial resolution of 1 cm only. As continuous media, EBT films, widely used in photon therapy, are interesting candidates to be used for this purpose. The EBT film is the ancestor of the currently available EBT2 film. In our contribution two dimensional dosimetry and film response quenching in ion beams were investigated. For a real 12C patient plan a good qualitative agreement with the planned dose distribution including a high signal-to-noise ratio and a good resolution in the measured photon-equivalent dose was found. The depth-dose response of EBT films for a 12C ion beam shows response quenching, which rises towards the Bragg peak. It was quantified by the relative efficiency determined at different depths. Furthermore, the relative efficiency was measured in monoenergetic proton and carbon ion beams. All the measured efficiencies show no significant dependency on the dose up to the highest measured doses of 6 Gy. However, differences between proton and carbon ions as well as between carbon ion beams of different energies were observed. The measurements reveal, that the use of EBT films for absolute dose verification measurements requires to take the relative efficiency into account, dependent on the ion type and energy. 相似文献
165.
E. Marti E. Kaisersberger E. Moukhina 《Journal of Thermal Analysis and Calorimetry》2006,85(2):505-525
The
heat capacity or the specific heat is for any crystalline, partially amorphous
or completely amorphous substance or material a significant thermodynamic
property. The glass transition may be regarded as the melting point of amorphous
substances and materials, a transition property of an outstanding technical
importance. A crucial point is the fact that the presence of a glass transition
is an unequivocal proof of an amorphous content of a material. Furthermore,
the change of the specific heat at the glass transition temperature enables
the quantitative determination of the amorphicity on a relative or absolute
level of any substance or material. The absolute determination of the amorphicity
affords a calibration with a reference corresponding to the material under
investigation. The crystallinity for this reference substance must be known
from the preparation and or by any independent analytical method.
The
literature data for the specific heat and the glass transition of polystyrene
were collected and evaluated. Data were found for the specific heat in literature
from 10 to 470 K. The data were unified for each of the reported temperature
in a mean value and the corresponding standard deviation was determined. An
excellent conformity was found in the glassy state of polystyrene with standard
deviations lower than 0.7%. The standard deviations above the glass transition
were considerably higher. 相似文献
166.
Chromcíková M. Liška M. Martišková M. 《Journal of Thermal Analysis and Calorimetry》2004,76(1):107-113
A simple mathematical model of thermal polishing of rough glass surface as observed by light beam thermal analysis (LBTA)
is presented. The rough surface is represented by a triangular profile used for calculation of the light beam intensity attenuation
and an equivalent rectangular profile is used for the modeling of the time course of the thermal polishing. Computational
results obtained for the NBS 711 viscosity standard glass showed that the characteristic temperature, obtained from the series
of LBTA experiments after extrapolation to zero starting surface roughness, does not represent the glass transition temperature,
but it corresponds to the viscosity value of about 109 dPa.s. The validity of the proposed model was confirmed by the comparison of simultaneous LBTA and viscosity measurements
of CaO-Y2O3-Al2O3-SiO2 glasses.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
167.
On UV. irradiation in i-octane or t-butyl alcohol the α,β-unsaturated δ-hydroxy ketone 2 undergoes fragmentation to the novel 14,15-seco-steroid 3 . 相似文献
168.
Annina Steinbach Dr. Tobias Paust Dr. Manuela Pluntke Prof. Dr. Othmar Marti Prof. Dr. Dirk Volkmer 《Chemphyschem》2013,14(15):3523-3531
The site‐specific attachment of nanoparticles is of interest for biomaterials or biosensor applications. Polymer brushes can be used to regulate this adsorption, so the conditions for selective adsorption of phosphonate‐functionalized nanoparticles onto micropatterned polymer brushes with different functional groups are optimized. By choosing the strong polyelectrolytes poly(3‐sulfopropyl methacrylate), poly(sulfobetaine methacrylate), and poly[2‐(methacryloyloxy)ethyl trimethylammonium chloride], it is possible to direct the adsorption of nanoparticles to specific regions of the patterned substrates. A pH‐dependent adsorption can be achieved by using the polycarboxylate brush poly(methacrylic acid) (PMAA) as substrate coating. On PMAA brushes, the nanoparticles switch from attachment to the brush regions to attachment to the grooves of a patterned substrate on changing the pH from 3 to 7. In this manner, patterned substrates are realized that assemble nanoparticles in pattern grooves, in polymer brush areas, or substrates that resist the deposition of the nanoparticles. The nanoparticle deposition can be directed in a pH‐dependent manner on a weak polyelectrolyte, or is solely charge‐dependent on strong polyelectrolytes. These results are correlated with surface potential measurements and show that an optical trap is a versatile method to directly probe interactions between nanoparticles and polymer brushes. A model for these interactions is proposed based on the optical trap measurements. 相似文献
169.
Temperature dependent nano indentation of thin polymer films with the scanning force microscope 总被引:1,自引:0,他引:1
The scanning force microscope (SFM) was used to investigate the temperature dependent micro mechanical properties of polymethylmethacrylate (PMMA) films with a thickness of 35 nm in the range of the radius of gyration. Force-distance curves were performed in the glass transition range to create permanent nanometric indentations with maximal forces up to 4 μN. Quantitative measurements of the indentation depth during and after application of the force, hysteresis energy and slope of the loading part are carried out as function of sample temperature and applied force. The glass transition of the polymer film can be clearly identified by the change of the mechanical properties of the polymer. Surprisingly, only a small change of elasticity at the glass transition is observed. 相似文献
170.