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The bandwidth behavior of graded-index multimode fibers (GI-MMFs) for different launching conditions is investigated to understand and characterize the effect of differential mode delay. In order to reduce the launch-power distribution the near field of a single-mode fiber is used to produce a controlled restricted launch. The baseband response is measured by observing the broadening of a narrow input pulse (time-domain measurement). The paper verifies the degradation in bandwidth due to profile distortion by scanning the spot of the single-mode fiber with a transversal offset from the center of the test sample. In addition, the impact of the launch-power distribution tuned by different spot-size diameters is demonstrated. Measurements were taken on ‘older’ 50-μm and 62.5-μm GI-MMFs as well as on laser-performance-optimized fibers more recently developed.
A Simple and Reliable HPTLC Method for the Quantification of the Intense Sweetener Sucralose®
(2003)
This paper describes a simple and fast thin layer chromatography (TLC) method for the monitoring of the relatively new intense sweetener Sucralose® in various food matrices. The method requires little or no sample preparation to isolate or concentrate the analyte. The Sucralose® extract is separated on amino‐TLC‐plates, and the analyte is derivatized “reagent‐free” by heating the developed plate for 20 min at 190°C. Spots can be measured either in the absorption or fluorescence mode. The method allows the determination of Sucralose® at the levels of interest regarding foreseen European legislation (>50 mg/kg) with excellent repeatability (RSD = 3.4%) and recovery data (95%).
Fluorescence Enhancement of Pyrene Measured by Thin-Layer Chromatography with Diode-Array Detection
(2003)
In-situ densitometry for qualitative or quantitative purposes is a key step in thin-layer chromatography. It offers a simple way of quantifying by measuring the optical density of the separated spots directly on the plate. A new TLC scanner has been developed which is able to measure TLC plates or HPTLC plates, at different wavelengths simultaneously, without destroying the plate surface. The system enables absorbance and fluorescence measurements in one run. Fluorescence measurements are possible without filters or other adjustments.
The measurement of fluorescence from a TLC plate is a versatile means of making TLC analysis more sensitive. Fluorescence measurements with the new scanner are possible without filters or special lamps. Improvement of the signal-to-noise ratio is achieved by wavelength bundling. During plate scanning the scattered light and the fluorescence are both emitted from the surface of the TLC plate and this emitted light provides the desired spectral information from substances on the TLC plate. The measurement of fluorescence spectra and absorbance spectra directly from a TLC plate is based on differential measurement of light emerging from sample-free and sample-containing zones.
The literature recommends dipping TLC plates in viscous liquids to enhance fluorescence. Measurement of the fluorescence and absorbance spectra of pyrene spots reveals the mechanism of enhancement of plate dipping in viscous liquids—blocked contact of the fluorescent molecules with the stationary phase or other sample molecules is responsible for the enhanced fluorescence at lower concentrations.
In conclusion, dipping in TLC analysis is no miracle. It is based on similar mechanisms observable in liquids. The measured TLC spectra are also very similar to liquid spectra and this makes TLC spec-troscopy an important tool in separation analysis.
The free convection in a vertical gap is generalized to realize new analytical solutions of the Boussinesq-equations. The steady and time-dependent solutions for the temperature and velocity distribution are discussed in detail depending on the mass flux in vertical direction. The range of existence for flows with and without back flow is obtained. The transient behaviour of the solutions during the time-dependent development displays interesting physical behaviour.
The structure of the separation bubble that appears in the secondary meridional flow between two coaxially rotating spheres at low and finite Reynolds number (Re) is considered. The low Re analytical study was motivated by recognizing some errors in the analytical work on this problem by Arunachalam and Majhi (1987, Q. Jl Mech. Appl. Math., 40, 47) whilst the finite Re experimental study was motivated by the desire to observe the separation bubble in the laboratory. Though the finite Re experiments were performed in a confined apparatus, they exhibit the qualitative features of the low Re theoretical predictions for the axisymmetric separation bubble that encloses two toroidal vortices symmetrically disposed above and below the mid‐plane of sphere separation, but strong effects of confinement are apparent. The flows observed include (i) a wall‐attached bubble symmetric about the mid‐plane at low Re, (ii) symmetric free‐standing bubbles at moderate Re, and (iii) an asymmetric bubble with flow separating from one sphere and attaching to the support shaft between the spheres at sufficiently high Re.
A new formula is presented for transforming fluorescence measurements in accordance with Kubelka-Munk theory. The fluorescence signals, the absorption signals, and data from a selected reference are combined in one expression. Only diode-array techniques can measure all the required data simultaneously to linearize fluorescence data correctly. To prove the new theory HPTLC quantification of the analgesic flupirtine was performed over the mass range 300 to 5000 ng per spot. The fluorescence calibration curve was linear over the whole range. The transformation of fluorescence measurements into linear mass-dependent data extends the technique of in-situ fluorescence analysis to the high concentration range. It also extends Kubelka-Munk theory from absorption to fluorescence analysis. The results presented also emphasize the importance of Kubelka-Munk theory for in-situ measurements in scattering media, especially in planar chromatography.
Experimental and theoretical investigations of the time of equalization of the concentration of an impurity in a rectangular flow‐type chamber have been carried out. It has been shown that the process of equalization of the concentration with time is exponential in character. The characteristic equalization time has been computed using the theory of turbulent diffusion. Theoretical results describe experimental regularities with an accuracy of about 10%. The value of the coefficient of turbulent diffusion for different configurations of flows in the chamber has been obtained from a comparison of experimental and calculated results.
Lattice vibrations and electronic transitions in the rare-earth metals: Praseodymium under pressure
(2004)
Praseodymium was investigated by Raman spectroscopy under pressure. A negative pressure shift of the E2g mode is observed in the dhcp phase, which indicates that the initial structural sequence hcp→Sm−type→dhcp→fcc as a whole in the regular lanthanides is associated with a softening of this mode. The pressure response of the phonon modes, observed in the monoclinic and α-uranium phases, where 4f bonding becomes important, is characteristic for anisotropic bonding properties.
Um Simulationen schnell und kostengünstig sowie ergebnisträchtig durchzuführen, bedarf es einer sorgfältigen Vorbereitung. Der Artikel befaßt sich mit dem automatischen Ablauf einer Simulationstudie zum Materilafluß und erläutert die im Ablauf notwendigen Beiträge der Anwender. In den Einzelheiten wird über die automatische Vorgehensweise und Anwendung der Standard-Simulationsmodelle (SSM) sowie spezieller Simulationsmodule (SimDBC) berichtet. Entscheidend für eine breitere Anwendung von Simulationswerkzeugen ist die einfache Handhabung und leicht verständliche Definition der zu untersuchenden Szenarien.
In-situ densitometry for qualitative or quantitative purposes is a key step in thin-layer chromatography (TLC). It is a simple means of quantification by measurement of the optical density of the separated spots directly on the plate. A new scanner has been developed which is capable of measuring TLC or HPTLC (high-performance thin-layer chromatography) plates simultaneously at different wavelengths without damaging the plate surface. Fiber optics and special fiber interfaces are used in combination with a diode-array detector. With this new scanner sophisticated plate evaluation is now possible, which enables use of chemometric methods in HPTLC. Different regression models have been introduced which enable appropriate evaluation of all analytical questions. Fluorescent measurements are possible without filters or special lamps and signal-to-noise ratios can be improved by wavelength bundling. Because of the richly structured spectra obtained from PAH, diode-array HPTLC enables quantification of all 16 EPA PAH on one track. Although the separation is incomplete all 16 compounds can be quantified by use of suitable wavelengths. All these aspects are enable substantial improvement of in-situ quantitative densitometric analysis.
Design of next-generation cdma using orthogonal complementary codes and offset stacked spreading
(2007)
This article presents an innovative code-division multiple access system architecture that is based on orthogonal complementary spreading codes and time-frequency domain spreading. The architecture has several advantages compared to conventional CDMA systems. Specifically, it offers multiple-access-interference-free operation in AWGN channels, reduces co-channel interference significantly, and has the potential for higher capacity and spectral efficiency than conventional CDMA systems. This is accomplished by using an "offset stacked" spreading modulation technique followed by quadrature amplitude modulation, which optimizes performance in a fading environment. This new spreading modulation scheme also simplifies the rate matching algorithms relevant for multimedia services and IP-based applications.
Soot particles emitted from a light duty (LD) Volkswagen diesel engine running at different operating points (speed and torque levels) are analyzed for mean size determination using a laser‐based three Wavelength Extinction Method (3‐WEM). For this reason, collected soot samples are suspended using an appropriate sample preparation technique with optimized conditions of sonication as it revealed its effect on the soot mean particle size measured by 3‐WEM.
An online Scanning Mobility Particle Analyzer (SMPS) is also used to measure soot emission at identical engine operating points. Size values obtained from SMPS are lower than those of suspended soot samples obtained from 3‐WEM. The size discrepancies are mainly related to the required sample preparation procedure employed for 3‐WEM measurements. The engine operating points affect, differently, the size measurements obtained from SMPS and 3‐WEM.
Sedimentation Field‐Flow Fractionation (SdFFF) is used for density determination of soot samples based on size measurements of fractions collected at peak maxima of fractograms using the off‐line hyphenation with 3‐WEM. It is assumed that a size dependent separation of soot particles occurred with a uniform particle density over the whole size distribution. An average density value is used for the conversion of soot fractograms to size distributions. Discrepancies are also found with size distribution profiles obtained from SMPS for the same engine operating points, due to the sample preparation procedure employed for SdFFF measurements.
This paper presents a multicarrier code-division multiple-access (CDMA) system architecture that is based on complete complementary orthogonal spreading codes. The architecture has several advantages as compared to conventional CDMA systems. Specifically, it offers multiple-access interference-free operation in additive white Gaussian noise channels, reduces cochannel interference significantly, and has the potential of higher capacity and spectral efficiency than conventional CDMA systems. This is accomplished by using an ldquooffset stackedrdquo spreading modulation technique. To maintain good performance in the presence of fading, the offset stacked modulator is followed by a quadrature-amplitude modulation map, which is designed to optimize performance in a fading environment. This new modulation scheme also simplifies the rate-matching algorithms that are relevant for multimedia services and Internet Protocol-based applications.
The mobile devices related industries are subject to rapid change, driven by technological advances and dynamic consumer behaviour. Hence, the understanding of the mobile devices markets is an important step in the analysis phase of mobile applications development. In this paper, a brief description of the different markets is introduced followed by an analysis of the main features of the markets leaders' devices which are important in the development process of mobile web applications. Finally, approaches are proposed to deal with the mobile devices diversity.
HPTLC on amino plates, with simple heating of the plates for derivatization, has been used for quantification of glucosamine in nutritional supplements. On heating the plate glucosamine reacts to form a compound which strongly absorbs light between 305 and 330 nm, with weak fluorescence. The reaction product can be detected sensitively either by absorption of light or by fluorescence detection. The detection limit in absorption mode is approximately 25 ng per spot. In fluorescence mode a detection limit of 15 ng is achievable. A calibration plot for absorption detection is linear in the range 25 to 4000 ng glucosamine. The derivative formed from glucosamine by heating is stable for months, and the relative standard deviation is 1.64% for 600 ng glucosamine. The amounts of glucosamine found in nutritional supplements were in agreement with the label declarations.
We present an improved quantification method for urethane found in spirits. The quantification is based on a derivatization reaction using cinnamaldehyde in combination with phosphoric acid. Measurements were carried out in the wavelength range from 445 to 460 nm using a diode-TLC device. An LED was used for illumination purposes. It emits very dense light at 365 nm. The quantification range of urethane is in the lower ng range. By applying 20 µL of sprits, the urethane quantification range is from 320 µg/L to 8.1 mg urethane per litre of spirit. The range of linearity covers nearly two magnitudes. The method is cheap, fast and reliable, and is able to monitor all European legislation limits without time-consuming sample pre-treatments.
The efficiency of a chromatographic analytical method is determined by the selectivity of the chromatographic separation and the specificity of the detection method. In high-performance thin-layer chromatography (HPTLC) the separated components can be detected and quantified directly on the plate by physical and chemical methods. By coupling high-performance thin-layer chromatography with biological or biochemical inhibition tests it is possible to detect toxic substances in situ.