Whiteboard math movies

In this article, we discuss whiteboard math movies (a.k.a. mathcasts)and their applications to mathematics education. A whiteboardmath (wbm) movie is a screen recording of writing plus voiceand/or text explaining a mathematical concept or solving a problem.The movie is then produced to Flash movie format and distributedvia CD or Internet. The wbm movies are the ultimate in asynchronouslearning—providing a simple and inexpensive means of interactionat the teacher–student, teacher–teacher, student–teacherand student–student level. With wbm movies both the creatorand the viewer get to see and hear the mathematical thinkingstep-by-step. They get the process and not just the result andthey can have it when and as many times as they want. We talkabout how Tim Fahlberg came up with this idea over 8 years agoand describe the developments in technology—that are atleast partially the result of our team's work—that nowmake wbm movie making a cost-efficient, effective and even afun way of truly learning mathematics.     

Determination of neomycin in animal tissues by liquid chromatography

Tissue samples are digested under hot alkaline conditions after initial conditioning at room temperature with phosphate-buffered saline. The cooled digest is deproteinated with concentrated perchloric acid. After centrifugation and pH adjustment, the clear supernatant is applied to an ion-exchange cartridge, and after the cartridge is washed, the neomycin is eluted with dilute perchloric acid. This eluate is derivatized with 9-fluorenylmethyl chloroformate prior to liquid chromatography using a wide-pore spherical silica C4 column and fluorescence detection. Recovery and repeatability are calculated from tissue extract standard calibration curves produced from the same assay. Recoveries ranged from 80 to 120% for fortifications of 0.25-1.00 mg/kg for muscle tissue and from 80 to 100% for fortifications of 0.50-10.0 mg/kg for kidney tissue. Limits of quantitation were 0.25 and 0.50 mg/kg, respectively, for muscle and kidney tissues. Limits of detection were 0.125 and 0.20 mg/kg, respectively, for muscle and kidney tissues.     

Exciton Coupling in Redox-Active Salen based Self-Assembled Metallacycles

The incorporation of a redox-active nickel salen complex into supramolecular structures was explored via coordination-driven self-assembly with homobimetallic ruthenium complexes (bridged by oxalato or 5,8-dihydroxy-1,4-naphthoquinato ligands). The self-assembly resulted in the formation of a discrete rectangle using the oxalato complex and either a rectangle or a catenane employing the larger naphthoquinonato complex. The formation of the interlocked self-assembly was determined to be solvent and concentration dependent. The electronic structure and stability of the oxidized metallacycles was probed using electrochemical experiments, UV-Vis-NIR absorption, EPR spectroscopy and DFT calculations, confirming ligand radical formation. Exciton coupling of the intense near-infrared (NIR) ligand radical intervalence charge transfer (IVCT) bands provided further confirmation of the geometric and electronic structures in solution.     

Determination of eight synthetic pyrethroids in bovine fat by gas chromatography with electron capture detection

Synthetic pyrethroids are among the most widely used classes of insecticides, and their uses are varied, including plant protection, animal dips, and as a treatment for human clothing and bedding in very hot climates. Veterinary applications include ear tags, pour-on formulations, sprays, and dips. Persistent residues have been reported in livestock, and routine monitoring programs in other countries have found detectable residues of various pyrethroids in fat. A method has been developed using solid-phase extraction that reduces the quantities of solvents used, the time required, and the amount of glassware used compared to an earlier method on which it was based. The scope of analytes tested included the 5 compounds cited in the earlier method (flucythrinate, permethrin, cypermethrin, fenvalerate, and deltamethrin) and, in addition, cyfluthrin, lambda-cyhalothrin, and fluvalinate. Sample extracts were analyzed by gas chromatography with electron capture detection using selected chromatographic peaks characteristic of each compound. Limits of quantification for the compounds were from 25-50 microg/kg, with a linear response for all compounds to 200 microg/kg. Recoveries ranged from 80 to 123%.     

An analytical method to screen for six thyreostatic drug residues in the thyroid gland and muscle tissues of food producing animals by liquid chromatography with ultraviolet absorption detection and liquid chromatography/mass spectrometry

A method was developed and validated to screen for residues of the thyreostatic drugs, tapazole (TAP), mercaptobenzimidazole (MBI), thiouracil (TU), methylthiouracil (MTU), propylthiouracil (PrTU), and phenylthiouracil (PhTU) in bovine, equine, ovine, and porcine thyroid and muscle tissues at concentrations > or = 5 ng/g using 2-methoxy-mercaptobenzimidazole (MeMBI) and dimethylthiouracil (DMTU) as internal standards. In this method, the drugs were solvent extracted from thyroid and muscle tissue and cleaned up on an amino-propyl solid-phase extraction (SPE) cartridge. The unretained fraction containing TAP and MBI and the internal standard, MeMBI, was collected as Fraction 1. The retained fraction containing TU, MTU, PrTU, PhTU, and the internal standard, DMTU, was eluted with 3% acetic acid-isopropanol as Fraction 2. Fraction 1 was further cleaned up on an alumina B SPE cartridge and analyzed by gradient elution on a C18 high-performance liquid chromatography (HPLC) column with ultraviolet detection at wavelengths of 255 and 300 nm. Fraction 2 was taken to dryness, derivatized with 4-chloro-7-nitrobenzo-2-furazan at pH 8, and analyzed by gradient elution on a C18 LC column with mass spectrometry (MS) detection. Any "presumptive positive" test results were submitted for further analysis by LC/MS/MS. The validated method was applied to the analysis of over 300 thyroid tissue samples.     

Asymmetric total synthesis of (-)-panacene and correction of its relative configuration

[reaction: see text] The first synthesis of (-)-panacene has been accomplished in concise, highly stereoselective fashion from commercially available 2-methoxy-6-methylbenzoic acid (15 steps, 8.3% overall yield). The synthesis unambiguously establishes the correct relative and absolute configuration of panacene, and demonstrates the serviceability of Pd(II)-mediated tandem intramolecular alkoxycarbonylation-lactonization for the expedient assembly of its tricyclic core, and the dual role of asymmetric alkynylation as an initial source of chirality and as a powerful tool for manipulating diastereoselectivity.     

Quantitative thin-layer chromatography of pesticides.

Thus, it may be seen that quantitative TLC for pesticide residue analysis is still in an exploratory stage. Most work to date has been in method development with few actual field applications. At its best, quantitative TLC offers a viable alternative to gas chromatography or high speed liquid chromatography in terms of flexibility, cost, convenience and sensitivity. The availability of good instrumentation and sensitive methods of analysis for many compounds should lead to a wider acceptance and application of these techniques.