Effect of β3‐Amino Acids on the Performance of the Peptidic Catalyst H‐dPro‐Pro‐Glu‐NH2

The effect of β³‐amino acids on the conformation and catalytic performance of the peptidic catalyst H‐d Pro‐Pro‐Glu‐NH₂ was investigated. Analogues of the peptidic catalyst bearing instead of the α‐amino acids the respective β³‐amino acids were prepared and their reactivity and stereoselectivity was investigated in conjugate addition reactions of aldehydes to nitroolefins. Additional computational studies provided insights into the preferred conformations of the peptidic catalysts. The results show that conformational flexibility at the N‐terminus has a severe effect on the stereoselectivity but is tolerated at the C‐terminus.     

On the dispersion spectrum

A measure for the denseness of sequences (an) mod 1, irrational, is the dispersion constantD() introduced byH. Niederreiter. In this paper the smallest accumulation point ₁ of the set of theD() is determined and all those are explicitely given for whichD () < ₁ holds.     

High temperature thermogravimetry of chlorides and sulphates : A study of the application to soils

Quantitative volatilization of NaCl and KCI occurs between 900 and 1200°. CaCl₂ and MgCl₂ are converted to the oxides at lower temperatures. CaSO₄, Na₂SO₄ and K₂SO₄ require the admixture of quartz to catalyse their decomposition with a total loss of SO₃ between 1150 and 1335°. MgSO₄ does not require quartz for its decomposition. The catalytic effects of Al₂O₃ and Fe₂O₃ on sulphate decomposition were also examined. The findings were applied to the analysis of saline soils. The thermogravimetric determination of chlorides in soils is subject to several interferences, but the conditions are more favourable for sulphates.     

Ein Beitrag zur gaschromatographischen Eichung und Auswertung

Zusammenfassung In der vorliegenden Arbeit wurde eine Programmgruppe zur Eichung und Auswertung chromatographischer Serienanalysen erstellt. Die Arbeitsweise und die Genauigkeit der damit erzielten Ergebnisse wurden an Hand von Beleganalysen aus drei heterogenen physikalisch-chemischen Systemen mit chlorierten Kohlenwasserstoffen eingehend dargestellt. Die Erkenntnisse der mathematischen Statistik, die für die Genauigkeit und Richtigkeit der erhaltenen Analysenwerte sehr wichtig sind, wurden verwertet und ihre ausschlaggebende Rolle an einem eigenen Beispiel (Tabelle 4) gezeigt.

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A report to gas chromatographic calibration and standardization

Summary For series of tests in analyzing of mixtures (e. g. chlorinated hydrocarbons with water and other components) programmes on gas chromatographic standardization and calibration are obtained. These programmes ought to guarantee a treatment of experimental data with the greatest possible speed and accuracy.

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Die Programme wurden auf der UNIVAC-494-Rechenanlage des Grazer Forschungszentrums erstellt.     

SERRS and visible extinction spectroscopy of copper chlorophyllin on silver colloids as a function of pH

A study of sodium copper chlorophyllin adsorbed on silver colloids (CuChl/Ag) is conducted using surface-enhanced resonance Raman scattering (SERRS) and visible extinction spectroscopy to examine how the system changes as a function of pH. Initially at basic pH, SERRS signal is not detected even though CuChl is adsorbed onto the silver surface and deprotonated. Upon decreasing the solution pH slightly, colloidal aggregation is induced, evidenced by the broadening of the visible extinction spectra. The larger aggregates possess a surface plasmon that is in resonance with the laser excitation frequency (633-nm) and SERRS signal is detected. As the acid protonates CuChl, the overall negatively-charged surface approaches neutrality which induces more aggregation. Complete protonation of CuChl by pH 4.6 results in colloidal precipitation. However, when aggregation is halted about pH 5, adding NaOH(aq) to the system maintains the extent of aggregation and an intense SERRS signal is detected at basic pH.     

Spin-dependence and glueball mixing with θ(1640) in ordinary meson spectroscopy

It is shown from a fairly general point of view that meson spectroscopy implies that the spin-spin and tensor forces are due to very short-ranged interactions. The (Q₁, Q₂) ? (Q_A, Q_B) mixing of axial vector $\text{I =}\text{1}\text{2}$ mesons implies the presence of a substantial repulsive Thomas term as well as an attractive short-ranged spin-orbit force of comparable magnitude. This analysis makes no reference to detailed potentials or wave functions. Inverted multiplets are predicted as a consequence of the large repulsive Thomas term. The spin-dependent potentials can be interpreted as effective exchanges dominated by short-ranged vector exchange and a confining potential transforming as a Lorentz scalar, although small amounts of other exchanges are also possible. A model-dependent analysis of the gluon annihilation contribution to the mass matrix and two-body decays of the I = 0 2⁺⁺ mesons indicates significant gluon mixing in these states. The presence of a $\text{non-q}\text{q}$ state (glueball?) which mixes with f'(1514) and another I = 0 2⁺⁺ state is required by the mixing model. The possibility that this additional state is θ(1640) is considered. The mass of such a state satisfies f'(1514)<M(G₀)<θ(1640). The model predicts $\text{0.01 < Λ(θ → ηη)/Λ(θ →}\text{K}\text{K}\text{)<0.18}$, with the actual widths sensitive to the details of singlet-octet mixing in the η wave function.     

Multiphoton endoscopy

Despite widespread use of multiphoton fluorescence microscopy, development of endoscopes for nonlinear optical imaging has been stymied by the degradation of ultrashort excitation pulses that occurs within optical fiber as a result of the combined effects of group-velocity dispersion and self-phase modulation. We introduce microendoscopes (350-1000 microm in diameter) based on gradient-index microlenses that effectively eliminate self-phase modulation within the endoscope. Laser-scanning multiphoton fluorescence endoscopy exhibits micrometer-scale resolution. We used multiphoton endoscopes to image fluorescently labeled neurons and dendrites.     

Fast-scanning two-photon fluorescence imaging based on a microelectromechanical systems two- dimensional scanning mirror

Towards overcoming the size limitations of conventional two-photon fluorescence microscopy, we introduce two-photon imaging based on microelectromechanical systems (MEMS) scanners. Single crystalline silicon scanning mirrors that are 0.75 mm x 0.75 mm in size and driven in two dimensions by microfabricated vertical comb electrostatic actuators can provide optical deflection angles through a range of approximately16 degrees . Using such scanners we demonstrated two-photon microscopy and microendoscopy with fast-axis acquisition rates up to 3.52 kHz.     

Supersymmetric skyrmions in four dimensions

Possible topological solitons (skyrmions) of four-dimensional supersymmetric nonlinear σ-models are investigated. The requirements of supersymmetry limit our study to the CP¹ model. A stable soliton seems possible, but in the absence of a demonstrated lower-bound for the mass, the stability of the soliton is unproved. The semi-classical spectrum of the CP¹ skyrmion, as well as its supersymmetric extension, is studied.