Minimizing UV noise in supercritical fluid chromatography. I. Improving back pressure regulator pressure noise

Pressure fluctuations and resulting refractive index changes, induced by the back pressure regulator (BPR) can be a significant source of UV detector noise in supercritical fluid chromatography (SFC). The refractive index (RI) of pure carbon dioxide (CO(2)) changes ≈0.2%/bar at the most commonly used conditions in supercritical fluid chromatography (SFC) (40 °C and 100 bar), compared to 0.0045%/bar for water (CO(2) IS 44× worse). Changes in RI cause changes in the focal length of the detector cell which results in changes in UV intensity entering the detector. The change in RI (ΔRI/bar) of CO(2) decreases 8-fold at 200 bar, compared to 100 bar. A new back pressure regulator (BPR) design representing an order of magnitude improvement in the state of the art is shown to produce peak to peak pressure noise (PN(p-p)) as low as 0.1 bar, at 200 bar, and 20Hz, compared to older equipment that attempted to maintain PN(p-p)<1bar, at <5Hz. With this lower PN(p-p), changes in baseline UV offsets could be measured as a function of very small changes in pressure. A pressure change of ±1 bar at 100 bar, common with some older BPR's, produced a UV baseline offset >0.5 mAU. A pressure change of ±0.5 bar representing the previous state-of-the-art, resulted in a UV offset of 0.3m AU. Baseline noise <0.05 is required to validate methods for trace analysis. The new BPR, with a PN(p-p) of 0.1 bar, demonstrated UV peak to peak noise (N(p-p))<0.02 mAU with a >0.03 min (10Hz) electronic filter under some conditions. This new low noise level makes it possible to validate SFC methods for the first time.     

Carbamazepine on a carbamazepine monolayer forms unique 1D supramolecular assemblies

High-resolution STM imaging of the structures formed by carbamazepine molecules adsorbed onto a pseudo-ordered carbamazepine monolayer on Au(111) shows the formation of previously unreported 1-dimensional supramolecular assemblies.     

Photoactivated capture molecule immobilization in plasmonic nanoapertures in the ultraviolet

We demonstrate a photoactivated surface coupling scheme for achieving spatial overlap between biomolecules of interest and optical near field excitation. Using aluminium nanoapertures, we obtained increased coupling efficiency of biotinylated capture probe oligos to the photoactivated surface due to ~3× nanoaperture enhancement of UV light. We further validate DNA sensor functionality via the hybridization of Cy-5 labeled target oligos, with up to 8× fluorescence enhancement obtained from a commercial microarray scanner. This generic photoimmobilization strategy is an essential step to realizing miniaturized plasmon enhanced detection arrays by virtue of localizing capture molecules to the region of plasmonic enhancement.     

(2+1)-D propagation of spatio-temporal solitary waves including higher-order corrections

We study the propagation of bright two-dimensional spatio-temporal solitary waves using a higher-order multi-dimensional non-linear Schrödinger equation. Starting directly from Maxwell's equations, a multiple-scales derivation is presented which results in a generalized first-order vectorial evolution equation that is valid for the non-linear spatio-temporal propagation of a predominantly linearly polarized electric field with large spatial and temporal bandwidths. A reduced version of this full equation including the higher-order linear and non-linear effects of third- and fourth-order dispersion, space–time focusing, shock, stimulated Raman scattering, and ultrafast quintic index saturation, is solved numerically via a modified split-step algorithm. Material parameters corresponding to those of fused silica at λf=1.55 m are used, with the addition of a negative quintic saturation term. Without quintic saturation, the non-linear spatio-temporal wave broadens under the action of the higher-order space–time effects. In addition, in the absence of Raman scattering, the wave undergoes collapse until arrested by the remaining higher-order terms. Frequency down-shifting and spatio-temporal broadening due to Raman scattering are found to have the greatest effect on non-linear spatio-temporal wave propagation. Nevertheless, we demonstrate that quintic saturation effectively stabilizes the wave such that broadening is reduced considerably, permitting nearly stationary propagation over many confocal distances, albeit with substantial down-shift. The resulting spatio-temporal solitary waves should be useful for applications in ultrafast all-optical switching and logic, and the generalized evolution equations will provide a refined starting point for the study of spatio-temporal phenomena in other areas as well.     

Die Bestimmung von Chrom und Aluminium in Stahl und Eisen

Ohne Zusammenfassung     

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.