Combined use of gas chromatography and selected ion flow tube mass spectrometry for absolute trace gas quantification

The value of the gas chromatography (GC) and selected ion flow tube mass spectrometry (SIFT-MS) combination for the analysis of trace gases is demonstrated by the quantification of acetone in air samples using the three precursor ions available to SIFT-MS, viz. H3O+, NO+ and O2+, and by the separation of the isomers 1-propanol and 2-propanol, and their analysis using H3O+ precursor ions. It is shown that the GC/SIFT-MS combination allows for accurate trace gas quantification obviating the regular, time-consuming calibrations that are usually required for the more commonly used detectors of GC systems, and the positive identification of isomers in mixtures that is often challenging using SIFT-MS alone. Thus, the GC/SIFT-MS combination paves the way to more confident analyses of complex mixtures such as exhaled breath.     

First efficient and general copper-catalyzed [2,3]-rearrangement of tetrahydropyridinium ylids

The factors affecting the copper-catalyzed rearrangement of ammonium ylids derived from tetrahydropyridines and diazoesters have been examined,and the first examples of high-yielding metal-catalyzed [2,3]-sigmatropic rearrangements of a wide range of such ylids are reported. The nature of the alpha-substituent in the diazo component of the reaction has a dramatic effect upon the yields of the reaction, with electron-withdrawing substituents enhancing the yield of the reaction. [reaction: see text]     

Utility of neodymium diiodide as a reductant in ketone coupling reactions

[reaction: see text] The viability of NdI(2) as a one-electron reducing agent in organic synthesis has been examined by studying coupling reactions between alkyl chlorides and ketones and aldehydes.     

Model dependence of single-energy fits to pion photoproduction data

Model dependence of multipole analysis has been explored through energy-dependent and single-energy fits to pion photoproduction data. The MAID energy-dependent solution has been used as input for an event generator producing realistic pseudo data. These were fitted using the SAID parametrization approach to determine single-energy and energy-dependent solutions over a range of lab photon energies from 200 to 1200MeV. The resulting solutions were found to be consistent with the input amplitudes from MAID. Fits with a χ-squared per datum of unity or less were generally achieved. We discuss energy regions where consistent results are expected, and explore the sensitivity of fits to the number of included single- and double-polarization observables. The influence of Watson’s theorem is examined in detail.     

Implementing Problem-Based Learning in Science Classrooms

Many new curricular and instructional models must be developed or adapted as the nation moves towards educational reform in science classrooms. This article describes how problem-based learning, an innovative curricular and instructional model developed in medical graduate school programs, has been adapted for use in elementary and high school settings. Included in the integration of problem-based learning and science are components of all problem-based episodes including initiating learning with an ill-structured problem, using the problem to structure the learning agenda, and teacher as metacognitive coach, with important goals of a reformed science curriculum such as learning based on concepts of significance, student-designed experiments, and development of scientific reasoning skills.     

Development of a new experimental setup for studying collisions of keV-electrons with thick and thin targets

Development of a new lectron-recoil ion/photon coincidence setup for investigating some of the electron induced collision processes, such as electron bremsstrahlung, electron backscattering, innershell excitation and multiple ionization of target atoms/molecules in bombardment of electrons having energies from 2.0 keV to 30.0 keV with solid and gaseous targets is described. The new features include the use of a compact multipurpose scattering chamber, a time-of-flight spectrometer for detection of multiply charged target ions, a 45°-parallel plate electrostatic analyzer for measuring energy and angle of the ejected electrons, a room temperature high resolution Si-PIN photo diode X-ray detector for counting the collisionally induced photons, a coincidence data acquisition system consisting of a 200 MHz Pentium based 8K-multichannel analyzer and a standard network of a fast/slow coincidence electronics. In particular, the details of design, fabrication and assembly of indigenous components employed in the setup are presented. Selected experiments planned with the setup are mentioned and briefly discussed. A report on performance, optimization, efficiency, time resolution etc. of the time-of-flight (TOF) spectrometer and that of the 45°-parallel plate electrostatic analyzer (PPEA) is presented. Test spectra of electron-recoil ion coincidences, energy distribution of ejected electrons and characteristic plus non-characteristic X-ray spectrum are illustrated to exhibit the satisfactory performance of the developed setup.     

Partial-wave analysis and baryon spectroscopy<Superscript>⋆</Superscript>

We continue to update our PWA of fundamental reactions as new data become available. Of primary interest to the N^* program are πN elastic scattering and the photo- and electroproduction of pions. Other photo-reactions are more model dependent, but may reveal resonances coupling weakly to πN final states. We also mention recent results from nucleon-nucleon elastic scattering, which have a less well-known connection to experimental programs proposing to extract N ^* properties from complete experiments.