Fringe field quantification in an LDV probe volume by use of a magnified image

The magnified cross-section of the LDV probe volume fringe field created on a far screen (image plane) with an imaging lens is examined both analytically and experimentally. It is shown that measurements of the image plane fringe field can be used to quantitatively determine the fringe field existing within the probe volume. Because the fringe spacing in the magnified image is more accessible experimentally, both longitudinal- and lateral-coordinate variations in fringe spacing can be determined, permitting a complete mapping of the fringe field. The detailed knowledge of the fringe field thus obtained allows beam quality, alignment, and fringe uniformity to be evaluated with greater precision than is possible with other techniques.The authors would like to acknowledge C. F. Edwards and R. L. Schmitt for the loan of the beam profiler and for many helpful discussions. This work was performed at the Combustion Research Facility, Sandia National Laboratories, and was supported by the U.S. Department of Energy, Office of Industrial Technologies, Advanced Industrial Concepts Division.     

Scanning tunnelling microscopic images of the surface ordering of the liquid crystal 4-n-octyl-4'-cyanobiphenyl

Images of the surface ordering of 4-n-octyl-4'-cyanobiphenyl, a room temperature smectic liquid crystal deposited upon graphite, have been obtained by scanning tunnelling microscopy. The microscope was operated in air using the constant-current mode. Under certain tunnelling conditions it has been possible to resolve both the aliphatic and aromatic parts of the molecule, and to observe individual benzene rings. Two previously unreported conformations have been observed: an overlapping bilayer structure with spacing 3.7 nm, and a monolayer structure with spacing 2.4 nm. The latter structure may represent the first visual evidence for a surface polar ordered structure.     

Tertiary Education Faculty Planning: An Application of a Substantially New Direct Control Model

In this paper, an absorbing Markov chain representing the stocks and flows of undergraduate students in a tertiary education faculty is established.In order to assist faculty planners in achieving specific goals, a direct control model in fixed time is developed that allows a partial specification of the distribution of students within the system based on the concept of stated ratios. The attainment and maintenance of this objective, together with a given system size for each planning period, is attempted through recruitment control, as this is the most appropriate control mechanism in an educational institution. The unique specification of the distributional objective makes for considerable ease of planning.The development of a useful sensitivity analysis modus operandi, along with a new efficient solution algorithm to the direct control model, further enhances its applicability for faculty planning.     

Pre-resonance Raman intensity studies of TCNQ and TCNQ−

Pre-resonance Raman spectra have been obtained for TCNQ and LiTCNQ in acetonitrile solution using an Ar⁺—Kr⁺ laser and a tunable rhodamine 6G dye laser. Using the theory of Albrecht and Hutley, we have calculated frequency factors for the intensity variations for several symmetric vibrational modes of each molecule. The observed spectra for TCNQ and LiTCNQ with violet, blue, and green excitation give evidence for B-type resonance enhancement due to vibronic mixing between at least two violet and ultraviolet transitions. The Raman spectra for LiTCNQ with yellow, orange, and red excitation show A-type enhancement due to a single electronic excitation in the near infrared.     

Parametric excitation of an internally resonant double pendulum

Summary A system of two weakly damped, nonlinearly coupled pendulums with (uncoupled) natural frequencies of ₁ and ₂ 2 ₁ is subjected to a small, vertical oscillation of frequency 22 ₁. The resulting motion (after transients have decayed) may be either a simple (rigid-body) translation of the entire system or coupled oscillations of the pendulums superimposed on such a translation. The stability of these two types of motion is examined and their parametric domains established. There are no Hopf bifurcations, in consequence of which neither periodically modulated nor chaotic motions appear to be possible (for weak excitation). The corresponding problem for a symmetric triple pendulum is shown to be isomorphic to that for the double pendulum.

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Zusammenfassung Ein System von schwach gedämpften, nichtlinear gekoppelten Pendeln mit den (ungekoppelten) natürlichen Frequenzen ₁ und ₂2 ₁ wird vertikalen erzwungenen Schwingungen mit der Frequenz 22 ₁ unterworfen. Die entstehende Bewegung ist (nach dem Abklingen von temporären Bewegungsanteilen) entweder eine einfache Translation des (starren) Systems oder aber eine solche Translation mit überlagerten gekoppelten Schwingungen der Pendel. Die Stabilität dieser beiden Bewegungstypen wird untersucht, und ihr parametrischer Gültigkeitsbereich wird bestimmt. Es gibt keine Hopf-Bifurkationen, so daß weder periodisch modulierte noch chaotische Bewegungen möglich erscheinen (für schwache Erregungen). Das entsprechende Problem für ein symmetrisches Dreifach-Pendel ergibt sich isomorph zu dem des Doppel-Pendels.

     

Deprotonation-electrophile trapping of terminal epoxides

Organolithium-induced deprotonation of terminal epoxides in the presence of appropriate diamine ligands allows trapping with a range of electrophiles, yielding functionalised di- and tri-substituted epoxides in good yields and with control of stereochemistry at the epoxide.     

Versatile solid-phase synthesis of secondary amines from alcohols. Development of an N-Boc-(o-nitrobenzene)sulfonamide linker

The development of a versatile amine releasing linker based on the modified o-nitrobenzene sulfonamide protective group is described. This new N-Boc-o-nitrobenzenesulfonamide (Boc-ONBS) linker enables the elaboration on resin of primary and secondary amines by sequential substitution of the sulfonamide moiety using the Mitsunobu reaction. A 16-member array of secondary and Boc protected primary amines was then prepared using this linker.