Simultaneous mixture analysis using a dynamic microbial sensor combined with chemometrics

A biosensor consisting of immobilized microbial cells and an oxygen electrode was used in a flow-through system as a microbial sensor flow injection analyzer (FIA). For different organic analytes, the metabolism of vital cells provides individual time-resolved responses with distinct time-dependent amplitudes. Chemometrical data analysis revealed that the individual responses are additive and depend linearly on single analyte concentrations. Based on these observations, simultaneous multicomponent analysis of organic mixtures was carried out in the FIA's time domain with analytical errors of less than 10%. For mixture analysis and monitoring in processes like enzymatic conversions, the described microbial sensor FIA ("dynamic microbial sensor") offers an alternative to expensive analytical equipment.     

Simultaneous measurements of multiple flow parameters for scramjet characterization using tunable diode-laser sensors

This paper reports the simultaneous measurements of multiple flow parameters in a scramjet facility operating at a nominal Mach number of 2.5 using a sensing system based on tunable diode-laser absorption spectroscopy (TDLAS). The TDLAS system measures velocity, temperature, and water vapor partial pressure at three different locations of the scramjet: the inlet, the combustion region near the flame stabilization cavity, and the exit of the combustor. These measurements enable the determination of the variation of the Mach number and the combustion mode in the scramjet engine, which are critical for evaluating the combustion efficiency and optimizing engine performance. The results obtained in this work clearly demonstrated the applicability of TDLAS sensors in harsh and high-speed environments. The TDLAS system, due to its unique virtues, is expected to play an important role in the development of scramjet engines.     

Particle-size and velocity measurements in flowing conditions using dynamic light scattering

The noninvasive optical technique of dynamic light scattering (DLS) is routinely used to characterize dilute and transparent submicrometer particle dispersions in laboratory environments. A variety of industrial and biological applications would, however, greatly benefit from on-line monitoring of dispersions under flowing conditions. We present a model experiment to study flowing dispersions of polystyrene latex particles of varying sizes under varying flow conditions by using a newly developed fiber-optic DLS probe. A modified correlation function proposed in an earlier study is applied to the analysis of extracting the size and velocity of laminar flowing particulate dispersions. The complementary technique of laser Doppler velocimetry is also used to measure the speed of moving particles to confirm the DLS findings.     

On-line recalibration of spectral measurements using metabolite injections and dynamic orthogonal projection

Spectrometers are enjoying increasing popularity in bioprocess monitoring due to their non-invasiveness and in situ sterilizability. Their on-line applicability and high measurement frequency create an interesting opportunity for process control and optimization tasks. However, building and maintaining a robust calibration model for the on-line estimation of key variables of interest (e.g., concentrations of selected metabolites) is time consuming and costly. One of the main drawbacks of using infrared (IR) spectrometers on-line is that IR spectra are compromised by both long-term drifts and short-term sudden shifts due to instrumental effects or process shifts that might be unseen during calibration. The effect of instrumental drifts can normally be reduced by referencing the measurements against a background solution, but this option is difficult to implement for single-beam instruments due to sterility issues. In this work, in order to maintain the robustness of calibration models for single-beam IR and to increase resistance to process and instrumental drifts, planned spikes of small amounts of analytes were injected periodically into the monitored medium. The corresponding measured difference spectra were scaled-up and used as reference measurements for updating the calibration model in real time based on dynamic orthogonal projection (DOP). Applying this technique led to a noticeable decrease in the standard error of prediction of metabolite concentrations monitored during an anaerobic fermentation of the yeast Saccharomyces cerevisiae.     

A method of increasing the accuracy of measurements of the instantaneous values of voltages using a cathode-ray oscilloscope

Translated from Izmeritel'naya Tekhnika, No. 10, pp. 49–51, October, 1992.     

Simultaneous determination of the optical constants and thickness of very thin films by using soft-x-ray reflectance measurements

A nonlinear, least-squares curve-fitting method is described that simultaneously determines the optical constants and the thickness of a very thin (? 100-?) film from reflectance versus angle of incidence (R - θ) data measured in the soft-x-ray region. The method is applied to R - θ data obtained for very thin, sputtered films of carbon (65 ? thick) and gold (94 ? thick) at photon energies of 60-900 eV. The results show that the present method is capable of accurately determining the thickness of very thin films even for transparent materials, and that the obtained optical constants are in good agreement with values reported for films with a thickness of 1000 ?.     

A.c. magnetic measurements on superconductors using two-channel dynamic analyser

A.c. magnetic measurements are powerful tools for characterizing superconducting materials. The a.c. susceptibility is the most used measurement and is commonly performed using a two-phase lock-in amplifier. This article describes a different method to carry out this measurement, employing a two-channel dynamic analyser. This instrument also allows us to measure further quantities, such as higher harmonics of the a.c. susceptibility, the so-called wide-band susceptibility and the magnetization loops. A remarkable feature of the dynamic analyser is its wide frequency range, from 244 μHz to 102 kHz, allowing simple, comprehensive and reliable characterization of superconductors.     

一种简便的超声波声时精密测量技术

本文介绍了一种用于测量超声波传播时间的新颖实时数字平均技术，它能用常规的超声脉冲回波方法直接测量给定的两个不同回波“过零电平周期”之间的时间间隔，其精度优于１．０ｎｓ（纳秒）。这一系统由简单，价廉的电子元件组成，不需要任何人工调节就可自动给出超声渡越时间，本文还给出了不同测试条件下的若干实验结果。     

Biomedical optical tomography using dynamic parameterization and bayesian conditioning on photon migration measurements

Stochastic reconstruction techniques are developed for mapping the interior optical properties of tissues from exterior frequency-domain photon migration measurements at the air-tissue interface. Parameter fields of absorption cross section, fluorescence lifetime, and quantum efficiency are accurately reconstructed from simulated noisy measurements of phase shift and amplitude modulation by use of a recursive, Bayesian, minimum-variance estimator known as the approximate extended Kalman filter. Parameter field updates are followed by data-driven zonation to improve the accuracy, stability, and computational efficiency of the method by moving the system from an underdetermined toward an overdetermined set of equations. These methods were originally developed by Eppstein and Dougherty [Water Resources Res. 32, 3321 (1996)] for applications in geohydrology. Estimates are constrained to within feasible ranges by modeling of parameters as beta-distributed random variables. No arbitrary smoothing, regularization, or interpolation is required. Results are compared with those determined by use of Newton-Raphson-based inversions. The speed and accuracy of these preliminary Bayesian reconstructions suggest the near-future application of this inversion technology to three-dimensional biomedical imaging with frequency-domain photon migration.     

Simultaneous dynamic neutron and gamma radiography

Equipment for dynamic neutron and gamma radiography has been developed at the 4.6 MW research reactor in Budapest, using thermal neutrons and gamma radiation obtained from the reactor. Radiography images are detected by scintillator screens and by low-light-level TV cameras, providing the possibility of visualizing medium-speed movements inside the investigated objects. The images are displayed on monitors and stored on video recorders. Some applications for nondestructive investigations are given.     

High-speed internal strain measurements in composite structures under dynamic load using embedded FBG sensors

Internal strain measurements in cross-ply carbon-epoxy composite plates under dynamic loads are carried out using embedded FBG sensors. The principle of the FBG interrogation is based on intensity demodulation achieved via a Fabry-Pérot filter. To account for the non-linearity of the filter, the system is calibrated and the amplitude of the strain data is validated. Strains are acquired at a rate of 100 kHz with a noise level as low as 2 με and used for modal analysis and strain monitoring in low energy impact. The experimental results under impact and modal analysis compare very well with pertinent numerical models and modal analysis obtained from laser vibrometer measurements.     

Procedure for terminology in dynamic measurements

Translated from Izmeritel'naya Tekhnika, No. 5, pp. 50–52, May, 1991.     

Wavelength-dependent measurements of optical-fiber transit time, material dispersion, and attenuation

A new, to our knowledge, method for measuring the wavelength dependence of the transit time, material dispersion, and attenuation of an optical fiber is described. We inject light from a 4-ns rise-time pulsed broadband flash lamp into fibers of various lengths and record the transmitted signals with a time-resolved spectrograph. Segments of data spanning a range of approximately 3000 A are recorded from a single flash-lamp pulse. Comparison of data acquired with short and long fibers enables the determination of the transit time and the material dispersion as functions of wavelength dependence for the entire recorded spectrum simultaneously. The wavelength-dependent attenuation is also determined from the signal intensities. The method is demonstrated with experiments using a step-index 200-mum-diameter SiO(2) fiber. The results agree with the transit time determined from the bulk glass refractive index to within ?0.035% for the visible (4000-7200-A) spectrum and 0.12% for the UV (2650-4000-A) spectrum and with the attenuation specified by the fiber manufacturer to within ?10%.