Towards tender X‐rays with Zernike phase‐contrast imaging of biological samples at 50 nm resolution

X‐ray microscopy is a commonly used method especially in material science application, where the large penetration depth of X‐rays is necessary for three‐dimensional structural studies of thick specimens with high‐Z elements. In this paper it is shown that full‐field X‐ray microscopy at 6.2 keV can be utilized for imaging of biological specimens with high resolution. A full‐field Zernike phase‐contrast microscope based on diffractive optics is used to study lipid droplet formation in hepatoma cells. It is shown that the contrast of the images is comparable with that of electron microscopy, and even better contrast at tender X‐ray energies between 2.5 keV and 4 keV is expected.     

Coherence-polarization mixing in resonance gratings

We show, using rigorous diffraction theory, that resonance gratings can be used to transfer partial spatial correlation to partial polarization even if the incident light beam is fully polarized. The phenomenon is based on the fact that either of the two orthogonal polarization components can be coupled into the leaky waveguide mode, leading to a strong phase delay, while the other one is reflected without being coupled into the grating. Numerical demonstrations are based on a Gaussian Schell-model beam and a grating analysis performed by rigorous Fourier modal method.     

Determination of bromide ion in raw and drinking waters by capillary zone electrophoresis.

A new capillary zone electrophoretic method was developed for the determination of bromide ion in raw and drinking waters. An NaCl-based low-pH buffer caused a reduction of electroosmotic flow (EOF) in the buffer zone, whereas injected water sample resulted in higher EOF in the sample zone thus pumping out the neutral water plug. Sample stacking was used for the preconcentration. The method was applicable for waters from low to intermediate ionic strengths, i.e., the concentration of chloride should preferably be less than 40 mg/l. The method had a limit of detection of 15 micrograms/l at a signal-to-noise ratio of three (S/N = 3) and a limit of quantitation of 20 micrograms/l. CZE results obtained with real samples were compared with ion chromatography--inductively coupled mass spectrometric results.     

Compact middle-wave infrared Fabry-Perot interferometer with double metallic subwavelength gratings

We demonstrate a compact middle-wave IR (MWIR) Fabry-Perot (FP) interferometer by replacing the traditional distributed Bragg reflectors consisting of thick multilayer films with two identical metallic subwavelength gratings. The transmission efficiency, resonance peak position, and finesse of the FP interferometer can be controlled by tuning the structural parameters. The performance of the MWIR FP interferometer is verified by experiment, which shows its potential application as, for example, narrowband MWIR filter for gas detection.     

On Tailoring of Nonlinear Spectral Properties of Nanocomposites Having Maxwell Garnett or Bruggeman Structure

Nonlinear spectral properties of two different types of conjugated polymers (polythiophene PT10 and polysilane PDHS) with nanoscale TiO₂ particles forming a Maxwell Garnett or a Bruggeman composite are studied. According to the present simulations, it is possible both to enhance and to tailor the magnitude and the spectral properties, respectively, of the effective degenerate third-order nonlinear susceptibility of the composite. This is done simply by tuning the volume fraction of TiO₂ inclusions and by changing the topology of the composite.     

Investigation of the quantitative properties of the quadrupole orthogonal acceleration time-of-flight mass spectrometer with electrospray ionisation using 3,4-methylenedioxymethamphetamine

This paper describes the investigation of the potential of a quadrupole orthogonal acceleration time-of-flight mass spectrometer (Q-TOF) equipped with an atmospheric pressure ionisation interface for quantitative measurements of small molecules separated by reversed phase liquid chromatography. To this end, the detection limits and linear dynamic range in particular were studied in an LC/MS/MS experiment using 3,4-methylenedioxymethamphetamine standards and 3,4-methylenedioxyethylamphetamine for internal standardisation. In a second phase, the experiment was repeated with real biological extracts (whole blood, serum, and vitreous humour). A calibration for 3,4-methylenedioxymethamphetamine and its metabolite 3,4-methylenedioxyamphetamine was prepared in each of these matrices again using 3,4-methylenedioxyethylamphetamine as internal standard. The resulting quantitative data were compared with those obtained by liquid chromatography with fluorescence detection for the same extracts. The Q-TOF results revealed excellent sensitivity and a linear dynamic range of nearly four decades (2-10 000 pg on-column, r(2) = 0.9998, 1/x weighting). Furthermore, all the calibration curves prepared in biological material were superimposable, LC/MS/MS and LC-fluorescence, and the quantitative results for actual samples compared very favourably. It was concluded that the Q-TOF achieves a linear dynamic range for quantitative LC/MS/MS work exceeding that of fluorescence detection and at much better absolute sensitivity. Copyright 1999 John Wiley & Sons, Ltd.     

Complex Analysis in Dispersion Theory

Dispersion theory of linear and nonlinear susceptibilities are considered with the aid of complex analysis.     

Modification of glass capillary gas chromatographic columns by alkylation of the glass surface with pentafluorobenzyl bromide

Summary Glass surface alkylation with pentafluorobenzyl (PFB) bromide yields glass capillary gas chromatographic columns with modified retention characteristics. Glass-alkylated OV-225 columns have been tested in the analysis of PFB fluoroacetate, and the substantial increase in retention time of this highly volatile compound was found to improve the precision of analysis. PFB-alkylated columns should prove generally useful in gas chromatographic analysis of small relative molecular mass compounds.     

Shot-noise-driven escape in hysteretic Josephson junctions

We have measured the influence of shot noise on hysteretic Josephson junctions initially in the macroscopic quantum tunneling regime. The escape threshold current into the resistive state decreases monotonically with increasing average current through the scattering conductor, which is another tunnel junction. Escape is predominantly determined by excitation due to the wideband shot noise. This process is equivalent to thermal activation (TA) over the barrier at effective temperatures up to about 4 times the critical temperature of the superconductor. The presented TA model is in excellent agreement with the experimental results.     

Suppressor current switching: a simple and effective means to reduce background noise in ion chromatography

Background noise in ion chromatography with suppressed conductivity detection was significantly reduced for the period of time when the electric current to an anion self regenerating suppressor (ASRS) running in the recycle mode was turned-off. With high capacity AS11-HC columns, it was possible to maintain current free conditions from the beginning of the run past the chloride peak, which enables routine high sensitivity analysis of early to mid eluting peaks. This suppressor current switching was utilized for the analysis of bromate in drinking water with large volume injection using on-line removal of chloride by an On-Guard Ag+-cartridge. The method detection limit (MDL) was 0.21 microg/l in fortified reagent water. Coelution of bromate with an unknown compound was observed, but it was solved by the optimization of gradient program.