The total synthesis of (±)-naphthyridinomycin. I. Preparation of a key tricyclic lactam intermediate.

A synthetic strategy for the preparation of the quinone antibiotic naphthyridinomycin is outlined. An efficient synthesis of key tricyclic intermediate 6 is described.     

Radio-frequency μSR experiments at the ISIS pulsed muon facility

This paper explores the use of pulsed radio-frequency (RF) techniques to remove the frequency limitations imposed on conventional transverse muon spin rotation (μSR) experiments at a pulsed muon source by the finite muon pulse width. The implementation of the 90° pulse technique is demonstrated by observing the free precession signal of diamagnetic muons implanted in polythene, the change in signal amplitude as a function of RF pulse length is plotted and the precise condition for a 90° pulse determined. The technique is evaluated by comparing measurements made using conventional spin rotation experiments to those employing pulsed RF methods. The potential for applying standard NMR multiple-pulse methods to the μSR experiment is considered and the use of two-pulse RF sequences (90° _x ?τ?90° _x and 90° _x ?τ?180° _x ) to form a muon spin echo demonstrated.     

Pressure dependence of the electric field gradient and knight shift tensors of single crystal gallium

Nuclear pure quadrupole resonance has been observed in single crystal gallium as a function of hydrostatic pressure up to 7 kbar at temperatures of 77, 198 and 273 K. The resonance frequency v_Q increases linearly with pressure and the slope ($\text{δv}{}_{\mathrm{O}}\text{δP}$)_T is 13.7, 15.5 and 16.3 Hz/bar at 77, 198 and 273 K respectively. The asymmetry parameter decreases nonlinearly with pressure. Using compressibility and thermal expansion data, the volume dependence of the major principle component of the electric field gradient was deduced. The principal components K_x, K_y and K_z of the Knight shift tensor have been measured as a function of pressure to 6 kbar at 77 K. The isotropic and anisotropic components of the Knight shift were deduced as a function of pressure, and K_iso is found to vary with volume as V^{4.95 ± 0.80}.     

A simple model to describe the kinetics of the coagulation of casein (milk) and fibrin (blood)

Summary It is shown that, on the assumption that the accelerating (growth) and decelerating (decay) phases of coagulation are most simply described by exponential equations, whereas the direct combination of these equations leads to a power equation, the introduction of a power which falls linearly with time, leads to the coagulation equation which has already been found to hold extremely well for both blood and milk. The three equations, in differentiated form, form part of a series in which the negative power of time increases by unity for each successive term. But it is stressed that this treatment postulates the simplest possible conditions and that, like all basic equations, the coagulation equation will doubtless require modification for some systems.

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Zusammenfassung Es wird gezeigt, daß unter der Annahme, daß die Beschleunigungs-(Wachstums-) und Verzögerungs-(Zerfalls-)Phasen der Koagulation sich sehr leicht durch Exponentialgleichungen beschreiben lassen, wobei die direkte Kombination dieser Gleichungen zu einer Kraftbeziehung führen, die Einführung einer linear mit der Zeit abnehmenden Kraft zu einer Koagulationsgleichung führt, von der bereits jetzt bekannt ist, daß sie sehr gut sowohl auf Blut als auch auf Milch anwendbar ist. Die 3 Gleichungen stellen in der differenzierten Form den Teil einer Reihe dar, bei der die negative Potenz der Zeit für jeden folgenden Term um eine Größenordnung ansteigt. Es wird betont, daß dieser Weg die einfachst möglichen Bedingungen erfordert und daß die Koagulationsgleichung, ähnlich wie alle Grundgleichungen, zweifellos eine Modifikation für einige Systeme erfordert.

     

Sound propagation over curved boundary surfaces

A model for the determination of the variation of intensity of sound, due to a point source on a convex boundary surface, propagating over the surface is described. It is found that attenuation rates depend upon the surface compliant properties and are much higher for a pressure release surface than for a rigid one. The possibility of a surface giving still higher attenuation rates is explored. However, preliminary indications are that such a surface would have to be active.