Nucleation of single-walled carbon nanotubes

The nucleation pathway for single-wall carbon nanotubes on a metal surface is demonstrated by a series of total energy calculations using density functional theory. Incorporation of pentagons at an early stage of nucleation is energetically favorable as they reduce the number of dangling bonds and facilitate curvature of the structure and bonding to the metal. In the presence of the metal surface, nucleation of a closed cap or a capped single-wall carbon nanotube is overwhelmingly favored compared to any structure with dangling bonds or to a fullerene.     

Plane quartics with Jacobians isomorphic to a hyperelliptic Jacobian

We show how for every integer one can explicitly construct distinct plane quartics and one hyperelliptic curve over all of whose Jacobians are isomorphic to one another as abelian varieties without polarization. When we say that the curves can be constructed ``explicitly', we mean that the coefficients of the defining equations of the curves are simple rational expressions in algebraic numbers in whose minimal polynomials over can be given exactly and whose decimal approximations can be given to as many places as is necessary to distinguish them from their conjugates. We also prove a simply-stated theorem that allows one to decide whether or not two plane quartics over , each with a pair of commuting involutions, are isomorphic to one another.

     

Analysis of flow-structure coupling in a mechanical model of the vocal folds and the subglottal system

An analysis is made of the nonlinear interactions between flow in the subglottal vocal tract and glottis, sound waves in the subglottal system and a mechanical model of the vocal folds. The mean flow through the system is produced by a nominally steady contraction of the lungs, and mechanical experiments frequently involve a ‘lung cavity’ coupled to an experimental subglottal tube of arbitrary or ill-defined effective length L, on the basis that the actual value of L has little or no influence on excitation of the vocal folds. A simple, self-exciting single-mass mathematical model of the vocal folds is used to investigate the sound generated within the subglottal domain and the unsteady volume flux from the glottis for experiments where it is required to suppress feedback of sound from the supraglottal vocal tract. In experiments where the assumed absorption of sound within the sponge-like interior of the lungs is small, the influence of changes in L can be very significant: when the subglottal tube behaves as an open-ended resonator (when L is as large as half the acoustic wavelength) there is predicted to be a mild increase in volume flux magnitude and a small change in waveform. However, the strong appearance of second harmonics of the acoustic field is predicted at intermediate lengths, when L is roughly one quarter of the acoustic wavelength. In cases of large lung damping, however, only modest changes in the volume flux are predicted to occur with variations in L.     

Evaluation of the potential of Raman microspectroscopy for prediction of chemotherapeutic response to cisplatin in lung adenocarcinoma

The study of the interaction of anticancer drugs with mammalian cells in vitro is important to elucidate the mechanisms of action of the drug on its biological targets. In this context, Raman spectroscopy is a potential candidate for high throughput, non-invasive analysis. To explore this potential, the interaction of cis-diamminedichloroplatinum(II) (cisplatin) with a human lung adenocarcinoma cell line (A549) was investigated using Raman microspectroscopy. The results were correlated with parallel measurements from the MTT cytotoxicity assay, which yielded an IC(50) value of 1.2 ± 0.2 μM. To further confirm the spectral results, Raman spectra were also acquired from DNA extracted from A549 cells exposed to cisplatin and from unexposed controls. Partial least squares (PLS) multivariate regression and PLS Jackknifing were employed to highlight spectral regions which varied in a statistically significant manner with exposure to cisplatin and with the resultant changes in cellular physiology measured by the MTT assay. The results demonstrate the potential of the cellular Raman spectrum to non-invasively elucidate spectral changes that have their origin either in the biochemical interaction of external agents with the cell or its physiological response, allowing the prediction of the cellular response and the identification of the origin of the chemotherapeutic response at a molecular level in the cell.     

Ueber Instrumente zur Messung hoher Temperaturen

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A rapid method for estimating iodine-125 in water samples using X-ray fluorescence for yield correction

Large sample volumes are needed when monitoring low levels of¹²⁵I in fresh water systems. Small anion exchange resin columns concentrate the radioactivity and also act as counting sources in thin NaI(T1) well scintillation detectors. Isotope identity is confirmed by decay counting or Ge spectroscopy. Recovery corrections are made by comparing the X-ray fluorescence of stable iodide carrier added initially with that retained on the counting column. The benefits from this simple, quick and accurate procedure could be adapted to other radiochemical estimations which rely on carrier recovery.     

Binary-phase spatial filter for real-time swept-source optical coherence microscopy

We report a novel scheme to optimize the focusing condition for real-time, swept-source optical coherence microscopy. The axial and lateral behaviors of four-zone binary-phase spatial filters are presented numerically. A nearly constant axial intensity distribution along an extended depth of focus of 1.5 mm and a lateral resolution of 5 microm are experimentally verified. The A-line scan rate is up to 16 kHz, yielding a frame rate of 25 Hz and 640 lines per image.