In situ monitoring of friction surfaces and their sequence pattern analysis

Friction occurs between solid surfaces, and even sometimes on lubricated surfaces. To understand tribological subjects, it is important to know the changes that occur in friction surfaces. In this study, a laser strobe technique is applied to a friction surface observation. The recorded surface images were analysed using pattern-matching methods and their correlations are discussed. A test using pin-on-plate methods with carbon steels was performed using a reciprocating motion speed of 10 Hz for 4.9 N. A pulsed laser light (Nd:YAG SHG=532 nm, 5 ns per pulse) was irradiated onto the friction surface. It was induced using an optical microscope that was located just to the side of the pin. The laser pulse was synchronized with the plate motion, which was a trigger of the laser pulse. The surface image was stored for every cycle. These sequences were calculated and their correlations were analysed as a function of the surface pattern and the friction track size and shape. Analysis revealed that some groups were distinguishable as parameters of the damage size and shape.     

Miniature triaxial metastable ionization detector for gas chromatographic trace analysis of extraterrestrial volatiles

Gas chromatography has found highly successful application in NASA's flight programs. Gas chromatographs have been flown to both Mars and Venus where detailed compositional measurements were made. These instruments were quite small and relatively sensitive when compared to commercially available instruments; however, they do not appear adequate for future missions currently being planned. The earlier flight GC's had incorporated thermistor bead thermal conductivity cells as the detector. This detector requires very precise temperature control and only provides about 1 ppm sensitivity. Temperature stabilization causes the detector to be quite heavy, i.e., about 200 g. Greater sensitivity will be required for measurements of trace components in extraterrestrial environments. Review of other detector types revealed the metastable ionization detector as a likely candidate because of its superior thermal stability and high sensitivity. The metastable detector, first described by Lovelock as an argon ionization detector, has been studied and somewhat modified by others. The commercial design by Hartmann and Dimick was used for comparison purposes in our work. In the past, three features of the metastable detector are prominent: it has part-per-billion sensitivity, contamination must be carefully controlled, and anomalous response is common. Since it is an ionization detector, however, temperature instabilities do not cause the major perturbations experienced by the thermal conductivity detectors. This paper describes a miniature metastable ionization detector featuring an unconventional electrode configuration, whose performance characteristics parallel those of traditional design, while its weight is quite small. The prototype has been used in our laboratories routinely for 2 years, and the concept will be incorporated into a flight GC for use in the Space Shuttle.     

Effective sampling trajectory optimisation for sensitivity analysis of biological systems

Sensitivity analysis has been widely applied to study the biological systems, including metabolic networks, signalling pathways, and genetic circuits. The Morris method is a kind of screening sensitivity analysis approach, which can fast identify a few key factors from numerous biological parameters and inputs. The parameter or input space is randomly sampled to produce a very limited number of trajectories for the calculation of elementary effects. It is clear that the sampled trajectories are not enough to cover the whole uncertain space, which eventually causes unstable sensitivity measures. This paper presents a novel trajectory optimisation algorithm for the Morris‐based sensitivity calculation to ensure a good scan throughout the whole uncertain space. The paper demonstrates that this presented method gets more consistent sensitivity results through a benchmark example. The application to a previously published ordinary differential equation model of a cellular signalling network is presented. In detail, the parameter sensitivity analysis verifies the good agreement with data of the literatures.Inspec keywords: genetics, differential equations, sensitivity analysis, biology, sampling methods, optimisationOther keywords: biological systems, metabolic networks, genetic circuits, Morris‐based sensitivity calculation, ordinary differential equation, sampling trajectory optimisation, sensitivity analysis, parameter sensitivity analysis, cellular signalling network     

Microwave acid digestion and preconcentration neutron activation analysis of biological and diet samples for iodine

A simple preconcentration neutron activation analysis (PNAA) method has been developed for the determination of low levels of iodine in biological and nutritional materials. The method involves dissolution of the samples by microwave digestion in the presence of acids in closed Teflon bombs and preconcentration of total iodine, after reduction to iodide with hydrazine sulfate, by coprecipitation with bismuth sulfide. The effects of different factors such as acidity, time for complete precipitation, and concentrations of bismuth, sulfide, and diverse ions on the quantitative recovery of iodide have been studied. The absolute detection limit of the PNAA method is 5 ng of iodine. Precision of measurement, expressed in terms of relative standard deviation, is about 5% at 100 ppb and 10% at 20 ppb levels of iodine. The PNAA method has been applied to several biological reference materials and total diet samples.     

In situ sequencing of peptides from biological tissues and single cells using MALDI-PSD/CID analysis

The ability to directly sequence peptides from biological cells using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) with postsource decay (PSD) and collision-induced dissociation (CID) fragment ion mass analysis is explored. Three different sample preparation methods are described for sequencing peptides in tissue samples and in single neurons from the invertebrate model Aplysia californica. To characterize peptides from the atrial gland, MALDI-PSD/CID is applied directly to a tissue blot covered with the matrix alpha-cyano-4-hydroxycinnamic acid (CHCA). The resulting fragment ions combined with database searching confirm the structure of several novel peptides encoded by egg-laying hormone genes. Moreover, MS profiling of a single unidentified neuron detects peptides with molecular weights of myomodulins C and E; this assignment is confirmed using MALDI-PSD with the matrix 2,5-dihydroxybenzoic acid (DHB). DHB does not always provide adequate fragmentation for PSD experiments; therefore, a unique dual-matrix sampling method, employing both DHB and CHCA, is developed to directly sequence a decapeptide from a single cerebral ganglion B cell. Mass accuracy of fragment ions from cellular samples is typical for the instrument employed and is not deleteriously affected by the morphology and complexity of the samples.     

Flow-through sampling for electrophoresis-based microchips and their applications for protein analysis

This work presents a model behind the operation of a flow-through sampling chip and its application for immunoseparation, as well as its integration with a wash/elution bed for protein purification, concentration, and detection. This device used hydrodynamic pressure to drive the sample flow, and a gating voltage was applied to the electrophoretic channel on the microchip to control the sample loading for the separation and to inhibit sample leakage. The deduced model indicates that the critical gating voltage (VC) that is defined as the minimum gating voltage applied to the microchip for sampling is a function of the pump flow rate, the configuration of the microchannel on the chip, and the electroosmosis of the buffer solution. It was found that the theoretical V(C) values calculated from the measured electroosmotic mobilities and flow split ratios were comparable to those experimentally obtained from two microchips with different sampling channel sizes. This had an error percentage ranging from 1 to 20%. Because the hydrodynamic flow is insensitive to electrophoretic mobility, this electrophoresis-based microchip device was free of injection bias due to different ionic strength and electrophoretic mobility in the sample. Additionally, the usefulness of this device was demonstrated for the study of affinity interactions. Mixtures of Cy5-labeled bovine serum albumin (Cy5-BSA) and anti-BSA in various proportions were introduced into the microchip via a syringe pump, and the immunocomplex was electrophoretically separated from the free Cy5-BSA on the microchip. Based on the relative intensity of the free and complex BSA, the binding constant of BSA and anti-BSA was estimated as 3.3 x 10(7) M(-1). Furthermore, a C18 microcartridge (20 microL) was connected to the hydrodynamic inlet of the microchip. Using this device, the wash/elution step can be integrated on-line with the electrophoretic separation and detection on the microchip. Results show that the calibration curve of Cy5-BSA obtained from this integrated device has an R2 value greater than 0.99 and a minimum of quantitation at approximately 10 ng. This direct sampling method is another means of subfractionation, resulting in a relatively greater concentration factor than the average concentration of the whole fraction. Moreover, the electrical field-free bed ensures that the protein interaction will not be affected by the electric field during the wash/elution step.     

In situ surface monitoring system for synchrotron mirrors under high heat load

A portable electro-optical system capable of real-time measurements of surface slope distortions down to 0.5 murad is described; the system is limited primarily by its short-term stability. The system employs an angle measurement technique that, in combination with the least-squares signal extraction method, reduces system fluctuations. In addition, a multireflection technique is used to enhance the detectable resolution. Although designed for use with mirrors for synchrotron radiation sources, this system has the flexibility to be applied to other optical components. The prototype system has been tested on a sample mirror piece, and preliminary results are presented. A brief discussion about the extension of this metrology unit to adaptive optics is also given.     

A new sampling strategy for SVM-based response surface for structural reliability analysis

To evaluate failure probability of structures in the most general case is computationally demanding. The cost can be reduced by using the Response Surface Methodology, which builds a surrogate model of the target limit state function. In this paper authors consider a specific type of response surface, based on the Support Vector Method (SVM). Using the SVM the reliability problem is treated as a classification approach and extensive numerical experimentation has shown that each type of limit state can be adequately represented; however it could require a high number of sampling points. This work demonstrates that, by using a novel sampling strategy based on sampling directions, it is possible to obtain a good approximation of the limit state without high computational complexity. A second-order polynomial SVM model has been adopted, so the need of determining free parameters has been avoided. However, if needed, higher-order polynomial or Gaussian kernel can be adopted to approximate any kind of limit state. Some representative numerical examples show the accuracy and effectiveness of the presented procedure.     

In situ laser surface coating of TiC metal-matrix composite layer

Surface alloys are of great interest for improving the mechanical and/or chemical properties of the near-surface region on metallic materials. A new method, in situ laser surface coating of metal-matrix composite, is described, by which to produce a surface composite layer. Using this process, -Ni-TiC _x composite surface layers were achieved on mild steel; they exhibited increased hardness, and in situ formed TiC_x particles, 0.5–0.8 m in size, were homogeneously distributed in the top half of the matrix layer.     

In situ calibration for wide-angle, three-dimensional stereoscopic image analysis

Accurate measurement of three-dimensional object coordinates from stereoscopic images is an essential element in various applications that require three-dimensional position information. Conventionally, optical ray tracing has been the measurement method of choice. However, it requires accurate knowledge of geometrical and optical parameters, such as the image distance, camera locations relative to the object field, and size, shape, and refractive index of intervening elements, such as apparatus windows. On the other hand, all these parameters need not be known if an optical transformation method based on an in situ calibration experiment is used. Furthermore, the use of in situ calibration not only increases the effective accuracy of the measured three-dimensional object coordinates but also reduces significantly the computational time compared with conventional optical ray tracing. The computational efficiency of the technique used is essential, especially when the application requires multiple determinations of a large number of three-dimensional coordinates, such as is the case with three-dimensional particle-tracking velocimetry. The basic concept and formulation of an optical transformation method based on an in situ calibration experiment is introduced. The technique is first demonstrated with synthetic data, then case studies with actual in situ calibration data are discussed.     

In situ surface-enhanced Raman scattering analysis of biofilm

Biofilms represent the predominant form of microbial life on Earth. They are aggregates of microorganisms embedded in a matrix formed by extracellular polymeric substances (EPS). Detailed information about chemical composition and structure of the EPS matrix is relevant e.g. for the optimization of biocides, of antifouling strategies and for biological wastewater treatment. Raman microscopy (RM) is a capable tool that can provide detailed chemical information about biofilm constituents with spatial resolution of optical microscope. However, the sensitivity of RM is limited. Surface-enhanced Raman scattering (SERS), which enables investigations of biomolecules at very low concentration levels, allows overcoming this drawback. To our knowledge, this paper is the first report on reproducible SERS spectra from different constituents of a multispecies biofilm. We believe that the reproducibility is partly owed to the in situ measurement of the biofilm, while up to now SERS measurements of microbiological samples by RM were carried out after sample drying. We employed colloidal silver nanoparticles for in situ SERS measurements by RM. The achieved enhancement factor of up to 2 orders of magnitude illustrates a high potential of SERS for ultrasensitive chemical analysis of biofilms, including the detection of different components and the determination of their relative abundance in the complex biofilm matrix.     

Instrumental methods for investigating physical fields of biological objects

We give an analysis of the state-of-the-art and trends in development of instrumental methods for detection and amplification of the physical fields of biological objects in different wavelength ranges. Translated from Izmeritel'naya Tekhnika, No. 7, pp. 62–67, July, 1997.     

In situ synthesis of graphene/cobalt nanocomposites and their magnetic properties

Graphene, which possesses unique nanostructure and excellent properties, is considered as a low cost alternative to carbon nanotubes in nanocomposites. In this study, we present a simple in situ approach for the deposition of cobalt (Co) nanoparticles onto surfaces of graphene sheets by hydrazine hydrate reduction. The as-synthesized composites were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, Raman spectroscopy, transmission electron microscopy (TEM) and thermogravimetry and differential scanning calorimetry. It was shown that the as-formed Co nanoparticles were densely and homogeneously deposited on the surfaces of the graphene sheets and as a result, the restacking of the as-reduced graphene sheets was effectively inhibited. Magnetic studies reveal that the graphene/Co nanocomposite displays ferromagnetic behavior with saturation magnetizations of 53.4 emu g⁻¹, remanent magnetization of 6.0 emu g⁻¹ and coercivity of 226 Oe at room temperature, which make it promising for practical applications in future nanotechnology.     

In situ and multisubstrate detection of elastase enzymatic activity external to microdialysis sampling probes using LC-ESI-MS

Extracellular proteases play significant roles in mammalian development and disease. Enzymatic activity external to a microdialysis sampling probe can be determined by infusing judicious choices of substrates followed by collecting and measuring the products. Porcine pancreatic elastase was used as a model enzyme with two substrates possessing different cleavage sites, N-methoxysuccinyl-Ala-Ala-Pro-Val-7-amino-4-methylcoumarin (FL-substrate) and N-succinyl-Ala-Ala-Ala-p-nitroanilide (UV-substrate). These substrates were infused through the microdialysis sampling probe to a solution containing elastase. The resulting four products and the remaining two substrates were collected into the dialysate and were subsequently analyzed off-line using liquid chromatography-mass spectrometry (LC-MS) with electrospray ionization (ESI). All analytes were identified using extracted ion chromatograms of m/z 628 (FL-substrate), m/z 452 (UV-substrate), m/z 471 (N-methoxysuccinyl-Ala-Ala-Pro-Val, FL-NTP), m/z 332 (N-succinyl-Ala-Ala-Ala, UV-NTP), m/z 176 (7-amino-4-methylcoumarin, AMC), and m/z 139 (p-nitroaniline, pNA). FL-NTP and FL-substrate exhibited 10-fold higher ion production as compared to AMC with equimolar standards. Microdialysis sampling combined with LC-ESI-MS detection allowed for in situ determination of the enzymatic activity of a protease external to the microdialysis probe when using different peptide-based substrates.     

In situ sampling uncovers the dynamics of particle genesis and growth in an aerosol tube reactor

Making metal and ceramic powders using aerosol synthesis from vapour precursors, either in a flame or hot-wall tube reactor, is the basis for producing many thousands of tons of powder on an annual basis. To properly study this system, we have designed and built a model reactor with sampling points at evenly spaced axial positions. This allows us to take snapshots of the aerosol population at many points within the reactor. Nucleation followed by a surface reaction produces a solid phase extremely rapidly, within 0.01 s under typical conditions. This is followed by a transient state where nucleation, surface reaction and coagulation all interact to produce a strongly bimodal size distribution. After nucleation is extinguished, the size distribution approaches the self-preserving limit as predicted for a coagulation-dominated process. The final structure is determined by the dominant sintering mechanism, which can be estimated from theory. The knowledge of this mechanism offers the possibility of selecting reactor conditions to produce powders with optimized properties.     

In situ sampling uncovers the dynamics of particle genesis and growth in an aerosol tube reactor

Making metal and ceramic powders using aerosol synthesis from vapour precursors, either in a flame or hot-wall tube reactor, is the basis for producing many thousands of tons of powder on an annual basis. To properly study this system, we have designed and built a model reactor with sampling points at evenly spaced axial positions. This allows us to take snapshots of the aerosol population at many points within the reactor. Nucleation followed by a surface reaction produces a solid phase extremely rapidly, within 0.01 s under typical conditions. This is followed by a transient state where nucleation, surface reaction and coagulation all interact to produce a strongly bimodal size distribution. After nucleation is extinguished, the size distribution approaches the self-preserving limit as predicted for a coagulation-dominated process. The final structure is determined by the dominant sintering mechanism, which can be estimated from theory. The knowledge of this mechanism offers the possibility of selecting reactor conditions to produce powders with optimized properties. An erratum to this article can be found at     

Simultaneous optimization of the microextraction of coffee volatiles using response surface methodology and principal component analysis

It is well known that no single experimental condition can be found under which the extraction of all the volatile compounds in a gas chromatographic analysis of roasted coffee beans by headspace-solid phase microextraction (HS-SPME) is maximized. This is due to the large number of peaks recorded. In this work, the scores vector of the first principal component obtained from PCA on chromatographic peak areas was used as the response to find the optimal conditions for simultaneous optimization of coffee volatiles extraction via response surface methodology (RSM). This strategy consists in compressing several highly correlated peak areas into a single response variable for a central composite design (CCD). RSM was used to identify an optimal factor combination that reflects a compromise between the partially conflicting behavior of the volatiles groups. This simultaneous optimization approach was compared with the desirability function method. The versatility of the PCA-RSM methodology allows it to be used in other chromatographic applications, resulting in an interpretable procedure to solve new analytical problems.     

In situ generation of surface plasmon polaritons using a near-infrared laser diode

We demonstrate a semiconductor laser-based approach which enables plasmonic active devices in the telecom wavelength range. We show that optimized laser structures based on tensile-strained InGaAlAs quantum wells-coupled to integrated metallic patternings-enable surface plasmon generation in an electrically driven compact device. Experimental evidence of surface plasmon generation is obtained with the slit-doublet experiment in the near-field, using near-field scanning optical microscopy measurements.