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991.
Jeffrey E. Barrett Julie Sarama Douglas H. Clements Craig Cullen Jenni McCool Chepina Witkowski-Rumsey 《Mathematical Thinking and Learning》2013,15(1):28-54
We examined children's development of strategic and conceptual knowledge for linear measurement. We conducted teaching experiments with eight students in grades 2 and 3, based on our hypothetical learning trajectory for length to check its coherence and to strengthen the domain-specific model for learning and teaching. We checked the hierarchical structure of the trajectory by generating formative instructional task loops with each student and examining the consistency between our predictions and students' ways of reasoning. We found that attending to intervals as countable units was not an adequate instructional support for progress into the Consistent Length Measurer level; rather, students must integrate spaces, hash marks, and number labels on rulers all at once. The findings have implications for teaching measure-related topics, delineating a typical developmental transition from inconsistent to consistent counting strategies for length measuring. We present the revised trajectory and recommend steps to extend and validate the trajectory. 相似文献
992.
Julie Latreille Khaled Ezzedine Anissa Elfakir Laurence Ambroisine Sophie Gardinier Pilar Galan Serge Hercberg Florian Gruber Jonathan Rees Erwin Tschachler Christiane Guinot 《Photochemistry and photobiology》2009,85(6):1451-1458
The melanocortin-1 receptor ( MC1R ) gene is known to play a major role in skin and hair pigmentation and to be highly polymorphic in Caucasians. This study was performed to investigate the relationships between MC1R gene polymorphisms and skin color in a large sample of French middle-aged Caucasian women. The codons 60 to 265 and the codon 294 of the MC1R gene were sequenced in 488 women. The skin color was measured on the inner side of the forearm using a spectrophotometric instrument. Fifteen variants were identified: Arg151Cys, Arg160Trp, Arg142His, Asp294His, Ile155Thr, Asp84Glu, Val60Leu, Val92Met, Arg163Gln, Ser83Pro, Thr95Met, Pro256Ser, Val265Ile, Ala166Ala and Gln233Gln. Women carrying Arg151Cys, Asp294His, Arg160Trp and Asp84Glu variants had a significantly higher reflectance in the red region, which indicates a lower level of functional melanin. This association was the most pronounced for women carrying Asp84Glu. In contrast, no significant difference was observed for other variants. Moreover, associations between MC1R polymorphisms and the risks of experiencing sunburn and of having freckles were found independently of skin color. Our findings support the hypothesis that MC1R polymorphisms do not necessarily alter the skin color but should sensitize the skin to UV-induced DNA damage. 相似文献
993.
A biosensor based on the ionic liquid, 1-n-butyl-3-methylimidazolium hexafluorophosphate containing dispersed iridium nanoparticles (Ir-BMI.PF6) and polyphenol oxidase was constructed. This enzyme was obtained from the sugar apple (Annona squamosa), immobilized in chitosan ionically crosslinked with oxalate. The biosensor was used for determination of chlorogenic acid by square wave voltammetry. The polyphenol oxidase catalyzes the oxidation of chlorogenic acid to the corresponding o-quinone, which is electrochemically reduced back to this substance at +0.25 V vs. Ag/AgCl. Under optimized operational conditions the chlorogenic acid concentration was linear in the range of 3.48 × 10−6 to 4.95 × 10−5 mol L−1 with a detection limit of 9.15 × 10−7 mol L−1. The biosensor was applied in the determination of chlorogenic acid in organic and decaffeinated coffee and the results compared with those obtained using the capillary electrophoresis method. The recovery study for chlorogenic acid in these samples gave values of 93.2-105.7%. 相似文献
994.
Julie R. Peller Stephen P. Mezyk William J. Cooper 《Research on Chemical Intermediates》2009,35(1):21-34
The oxidative reactions of bisphenol A (BPA) with radiolytically generated hydroxyl radicals were studied in both deionized
water and tertiary treated wastewaters. In deionized water, bisphenol A reacts with the hydroxyl radical by addition to the
aromatic ring, k = 6.9 × 109 (±0.2) M−1 s−1, to eventually form the prominent, long-lived, hydroxylated intermediate product. In contrast, in tertiary treated water
solutions, although the initial hydroxyl radical addition reaction occurs, the hydroxylation is averted, and a different mechanistic
pathway ensues. The removal constant for the hydroxyl radical reaction with BPA is 0.45 ± 0.04 μmol/kGy, corresponding to
an overall degradation efficiency of 76%. 相似文献
995.
Thomas M. Gøgsig Anders T. Lindhardt Dr. Mouloud Dekhane Dr. Julie Grouleff Troels Skrydstrup Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(24):5950-5955
Easy and direct : Regioselective Mizoroki–Heck‐coupling reactions using heteroaromatic tosylates as electrophiles were achieved, thus providing direct and easy access to highly functionalized α‐heteroarylvinyl amides and ethers.
996.
The purpose of this study was to compare teacher efficacy beliefs of secondary Biology I teachers whose students' mean scores on the statewide End‐of‐Instruction (EOI) Biology I test met or exceeded the state academic proficiency level (Proficient Group) to teacher efficacy beliefs of secondary Biology I teachers whose students' mean scores on the EOI Biology I test fell below the state academic proficiency level (Non‐proficient Group). The mean difference on the Personal Science Teaching Efficacy (PSTE) subscale scores between the two groups was not statistically significant. This indicates that personal science teaching efficacy was not statistically related to how a teacher s students scored on the EOI Biology I test. The mean difference on the Science Teaching Outcome Expectancy (STOE) subscale scores demonstrated a statistically significant difference between the science teaching outcome expectancy of the Non‐proficient Group and Proficient Group teachers. Proficient Group teachers had significantly higher STOE scores than teachers Non‐proficient Group teachers. This finding suggests that End‐of‐Instruction Biology I test scores were related to the expectations that a teacher held for his/her students to learn biology regardless of student home environment, availability of classroom materials, or student motivation. 相似文献
997.
Steve L. Taylor Julie A. Nordlee Lynn M. Niemann Debra M. Lambrecht 《Analytical and bioanalytical chemistry》2009,395(1):83-92
The enzyme-linked immunosorbent assay (ELISA) offers many advantages for the detection of potentially hazardous allergenic
food residues that might become adventitious components of other foods during the course of food production and processing.
ELISAs detect proteins, and food allergens are proteins. ELISAs are sufficiently sensitive and specific for detection of food
allergen residues. ELISAs can also be produced in formats that are compatible with the industrial food processing environment.
However, ELISAs also have disadvantages that should be carefully evaluated and widely recognized. Various food-processing
operations can have profound effects on the detectability of allergenic food residues. ELISAs detect intact proteins but protein
hydrolysates evade detection in some ELISA formats. The residual proteins present in some ingredients derived from commonly
allergenic sources may also not be easily detected with ELISAs because of the nature of the protein residues remaining, e.g.
lipophilic. Processing operations can dramatically lower the solubility of proteins. In some food formulations, heat processing,
in particular, induces chemical modifications that can affect antibody binding to epitopes in the ELISA. The use of naturally
incurred standards where allergenic food residues are incorporated into various representative food matrices and then processed
in a manner similar to “real-world” food processing can reveal some of the limitations of allergen ELISAs. Methods for the
preparation of naturally incurred standards in chocolate, cookie, muffin, ice cream, pasta, frankfurter, and cream of potato
soup are provided as examples. 相似文献
998.
Lavisse S Peronneau P Rouffiac V Paci A Vigouroux J Opolon P Roche A Lassau N 《Ultrasonics》2008,48(1):26-34
The biocompatible trisacryl particles (TMP) are made of a cross-linked acrylic copolymer. Their inherent acoustic properties, studied for a contrast agent application, have been previously demonstrated in a in vitro Couette device. To measure their acoustic behaviour under circulating blood conditions, the TMP backscatter enhancement was further evaluated on a home-made flow phantom at different TMP doses (0.12-15.6 mg/ml) suspended in aqueous and blood media, and in nude mice (aorta and B16 grafted melanoma). Integrated backscatter (IB) was measured by spectral analysis of the Doppler signals recorded from an ultrasound system (Aplio®) combined with a 12-MHz probe. Doppler phantom experiments revealed a maximal IB of 17 ± 0.88 dB and 7.5 ± 0.7 dB in aqueous and blood media, respectively. IB measured on mice aorta, in pulsed Doppler mode, confirmed a constant maximal value of 7.29 ± 1.72 dB over the first minutes after injection of a 7.8 mg/ml TMP suspension. Following the injection, a 60% enhancement of intratumoral vascularization detection was observed in power Doppler mode. A preliminary histological study revealed inert presence of some TMP in lungs 8 and 16 days after injection.Doppler phantom experiments on whole blood allowed to anticipate the in vivo acoustic behaviour. Both protocols demonstrated TMP effectiveness in significantly increasing Doppler signal intensity and intratumoral vascularization detection. However, it was also shown that blood conditions seemed to shadow the TMP contrast effect, as compared to in vitro observations. These results encourage further investigations on the specific TMP targeting and on their bio-distribution in the different tissues. 相似文献
999.
Marcel Graf Emmanuel Dupont Hui Luo Soufien Haffouz Zbig R. Wasilewski Anthony J. Spring Thorpe Dayan Ban H.C. Liu 《Infrared Physics & Technology》2009,52(6):289-293
We report on recent measurements on GaAs/AlGaAs THz quantum well infrared photodetectors (QWIPs), investigating linewidth broadening as function of doping level. Structures with 3% and 2% Al content in the barrier were grown using molecular beam epitaxy (MBE) and metal-organic chemical vapor deposition (MOCVD), respectively. Linewidth widening with increasing doping of the GaAs quantum well could be observed in the detection spectra. The observed shift of peak detection wavelength for different well dopings fits with values obtained from wavefunction calculations, taking into account many-particle effects, namely exchange and correlation energies and the effect of depolarization on the absorption. In addition, activation energies extracted from dark current measurements as function of device temperature are also in agreement with the calculations. 相似文献
1000.
Sally Bloodworth Gabriela Sitinova Shamim Alom Sara Vidal George R. Bacanu Stuart J. Elliott Mark E. Light Julie M. Herniman G. John Langley Malcolm H. Levitt Richard J. Whitby 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(15):5092-5097
The endohedral fullerene CH4@C60, in which each C60 fullerene cage encapsulates a single methane molecule, has been synthesized for the first time. Methane is the first organic molecule, as well as the largest, to have been encapsulated in C60 to date. The key orifice contraction step, a photochemical desulfinylation of an open fullerene, was completed, even though it is inhibited by the endohedral molecule. The crystal structure of the nickel(II) octaethylporphyrin/ benzene solvate shows no significant distortion of the carbon cage, relative to the C60 analogue, and shows the methane hydrogens as a shell of electron density around the central carbon, indicative of the quantum nature of the methane. The 1H spin‐lattice relaxation times (T1) for endohedral methane are similar to those observed in the gas phase, indicating that methane is freely rotating inside the C60 cage. The synthesis of CH4@C60 opens a route to endofullerenes incorporating large guest molecules and atoms. 相似文献