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91.
Richard D. Foust Jr. Brandon Cruickshank Michael Stringer Julie Olander 《The Chemical Educator》1999,4(3):108-111
Four semesters of student evaluations of an environmental chemistry class have been analyzed for differences that can be attributed to Web-based enhancements. The enhancements included Web-based lecture notes, reading and problem assignments, bookmark files, and videotaped lectures. We developed these materials as part of a larger project to provide university-level technical courses over the Internet. Student perceptions of the course improved significantly (α = 0.10) after adding Web-based enhancements. Student’s opinion of the instructor improved, but the change is not significant at the 90% confidence level. The student responses to “Was the course challenging?” “Was my interest stimulated?” and “Was the instructor concerned?” were unchanged in the two groups of students. Drop rates were unchanged between the two student groups. The grade-average was nearly identical for the two student groups (82.9% vs. 83.5%), but the grade-distribution changed significantly. The percentage of A’s decreased slightly when Web-based enhancements were added, but the number of B’s increased from 22% to 40%. The percentage of C’s, D’s and F’s decreased for the students with access to Web-based enhancements. These results indicate that Web-based materials helped weaker students improve their performance and, therefore, their opinion of the class and of the instructor was more favorable. 相似文献
92.
A variety of ab initio methods have been used to calculate the X (2)Pi and A (2)Sigma(+) state spectroscopic parameters of the GeCX (X=F,Cl,Br) free radicals. The theoretical methods and basis sets were tested on GeCH, for which extensive experimental data are available, and found to give predictions sufficiently reliable to guide experimental searches for spectra. In all cases, the linear Ge=C-X species was found to be the global minimum on the potential energy surface, with the bent X-Ge=C ((2)A(')) isomer as a local minimum much higher (62-36 kcal/mol) in energy. In both the ground and excited states, the GeC moiety is very similar to that of GeCH, with a double bond in the lower state and a triple bond in the excited state, indicating that halogenation does not radically perturb the energetics or structure of germanium methylidyne. Ground state GeCX radicals have suitable rotational constants for microwave studies, although they suffer from only modest dipole moments. Matrix infrared experiments are most likely to detect the nu(1) fundamentals in the 1450-1100 cm(-1) region or the nu(3) fundamentals at the transition between the mid- and far-infrared regions. We have used the ab initio values for the Renner-Teller parameter, the average bending frequency, and the spin-orbit coupling constant to calculate the ground state energy levels, which will be helpful in the interpretation of A-X single vibronic level emission spectra, if they can be observed. The electronic absorption spectra of the (2)Pi(32) spin component of the 0(0) (0) bands of all three radicals have been calculated assuming typical jet-expansion conditions and should be useful in future laser-induced fluorescence, resonance enhanced multiphoton ionization, or cavity ringdown searches for the electronic band systems. 相似文献
93.
We demonstrate the possibility of serially guiding and sorting nanometer-sized particles without the use of any external control. The working principle is based on an equilibrium between scattering and binding forces, the latter depending on the properties of the particles. A configuration is proposed that utilizes this property and is shown to efficiently sort small particles as function of their size. 相似文献
94.
Hall DR Ngan CH Zerbe BS Kozakov D Vajda S 《Journal of chemical information and modeling》2012,52(1):199-209
Fragment-based drug design (FBDD) starts with finding fragment-sized compounds that are highly ligand efficient and can serve as a core moiety for developing high-affinity leads. Although the core-bound structure of a protein facilitates the construction of leads, effective design is far from straightforward. We show that protein mapping, a computational method developed to find binding hot spots and implemented as the FTMap server, provides information that complements the fragment screening results and can drive the evolution of core fragments into larger leads with a minimal loss or, in some cases, even a gain in ligand efficiency. The method places small molecular probes, the size of organic solvents, on a dense grid around the protein and identifies the hot spots as consensus clusters formed by clusters of several probes. The hot spots are ranked based on the number of probe clusters, which predicts the binding propensity of the subsites and hence their importance for drug design. Accordingly, with a single exception the main hot spot identified by FTMap binds the core compound found by fragment screening. The most useful information is provided by the neighboring secondary hot spots, indicating the regions where the core can be extended to increase its affinity. To quantify this information, we calculate the density of probes from mapping, which describes the binding propensity at each point, and show that the change in the correlation between a ligand position and the probe density upon extending or repositioning the core moiety predicts the expected change in ligand efficiency. 相似文献
95.
96.
A series of sodium borosilicate glasses containing cesium, molybdenum, and chromium was prepared to investigate the partitioning of chromium amongst the glass and phase-separated crystalline molybdates. The precipitates were examined by (133)Cs, (23)Na, and (95)Mo MAS NMR, revealing a phase assemblage consisting of Na(2)MoO(4), Na(2)MoO(4)·2H(2)O, Cs(2)MoO(4), Cs(2)CrO(4), CsNaMoO(4)·2H(2)O, and Cs(3)Na(MoO(4))(2). (133)Cs MAS NMR indicates random substitution of Cr into the Mo sites of Cs(3)Na(MoO(4))(2) and provides a quantitative assessment of Cr incorporation. The sample compositions were verified by various analytical techniques and highlight the centrality of NMR in the identification and quantification of heterogeneous crystalline composites, including sensitivity to cationic substitution. The observation and facile interconversion of hydrated phases invites careful consideration of these materials for nuclear waste disposal. 相似文献
97.
PD McCrary PA Beasley SP Kelley S Schneider JA Boatz TW Hawkins JP Perez BW McMahon M Pfiel SF Son SL Anderson RD Rogers 《Physical chemistry chemical physics : PCCP》2012,14(38):13194-13198
The passivation and stability of suspensions of titanium nanoparticles in azolium azolate ionic liquids can be tuned by introducing metal specific binding sites in the azolate anion. 相似文献
98.
A sensitive LC/MS/MS assay for determining zidovudine (ZDV) and lamivudine (3TC) in human plasma was validated to support antiretroviral pharmacology research programs. After addition of stable labeled isotopic zidovudine (ZDV‐IS) and lamivudine (3TC‐IS) as internal standard, a solid‐phase extraction was performed with an Oasis HLB 1 cm3 cartridge, with recoveries of 92.3% for ZDV and 93.9% for 3TC. A Phenomonex Synergi Hydro‐RP (2.0 × 150 mm) reversed‐phase analytical column was utilized for chromatographic separation. The mobile phase consisted of an aqueous solution of 15% acetonitrile and 0.1% acetic acid. Detection was accomplished by ESI/MS/MS in the positive ion mode, monitoring 268/127, 271/130, 230/112 and 233/115 transitions, for ZDV, ZDV‐IS, 3TC and 3TC‐IS, respectively. The method was linear from 1 to 3000 ng/mL with a minimum quantifiable limit of 1 ng/mL when 100 μL of plasma was analyzed. Validation results demonstrated high accuracy (≤8.3% deviation) and high precision (≤10% CV) for the quality control samples. The method was also shown to be specific and reproducible. The value of the high sensitivity was demonstrated by quantitation of approximately 100 existing samples that had ZDV below the limit of quantitation using a previously validated, less sensitive HPLC‐UV method utilized in the laboratory. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
99.
Zachary Nuño Brandon Hessler Bryan Heiberg Ralph Damato Terry Dunlap Young-Seok Shon Yohannes Abate 《Journal of nanoparticle research》2012,14(3):766
Spectroscopic near-field imaging of single silica-shell/Au-core and pure silica nanoparticles deposited on a silicon substrate
is performed in the infrared wavelength range (λ = 9–11 μm) using scattering-type scanning near-field optical microscopy (s-SNOM).
By tuning the wavelength of the incident light, we have acquired information on the spectral phonon–polariton resonant near-field
interactions of the silica-shell/Au-core and pure silica nanoparticles with the probing tip. We made use of the enhanced near-field
coupling between the high index Au-core and the probing tip to achieve spectral near-field contrast of the thin silica coating
(thickness < 10 nm). Our results show that spectroscopic imaging of thin coating layers and complex core–shell nanoparticles
can be directly performed by s-SNOM. 相似文献
100.
BM Kobilka AV Dubrovskiy MD Ewan AL Tomlinson RC Larock S Chaudhary M Jeffries-El 《Chemical communications (Cambridge, England)》2012,48(71):8919-8921
3,7-Diiodo-2,6-di(thiophen-2-yl)benzo[1,2-b:4,5-b']difurans are efficiently prepared by an iodine-promoted double cyclization. This new heterocyclic core is readily modified by the attachment of alkyl chains for improved solubility. The use of these compounds for the synthesis of new conjugated polymers is also reported. 相似文献