High-throughput, non-destructive determination of oil content in intact seeds by continuous wave-free precession NMR

A new method, based on continuous wave-free precession nuclear magnetic resonance, is proposed as a high-throughput technique for measuring the oil content of intact seeds. The method has the potential to analyze more than 20 000 intact seeds per hour and is shown to be applicable even to mixtures of seeds of different species with similar fatty acid composition.     

On the limits of the application of the n.m.r. pulsed-field gradient technique for self-diffusion measurements in zeolites

The main limitations for an application of the n.m.r. pulsed-field gradient technique to self-diffusion studies in zeolites are reviewed. It is shown that small amounts of highly mobile molecules adsorbed on the outer surface or within intracrystalline cracks will, in general, lead to an enhanced damping of the n.m.r. signal that may be interpreted erroneously as a high overall mobility of the adsorbed molecules if the two-phase character of the signal is not taken into consideration. As an example, for benzene adsorbed on ZSM-5-type zeolites, the n.m.r. pulsed-field gradient technique is shown to provide only an upper limit of the intracrystalline diffusivity of the order of 10⁻¹⁰ m² s⁻¹. This value does not conflict with the previously reported uptake diffusivities of the order of 10⁻¹³ m² s⁻¹.     

Comparison between defects and micro-notches in multiaxial fatigue – The size effect and the gradient effect

This paper attempts to improve the understanding of the multiaxial high cycle fatigue response of micro sized stress concentrations or notches of different geometries. The investigation is composed of an experimental part and a numerical part. In the former, three types of micro-notches or “artificial defects” are compared: spherical, elliptical and circumferential. All types have the same basic dimensions, the difference being the 3D geometry. The notches were machined on the surface of smooth cylindrical specimens made of mild steel. The fatigue limits under reversed tension (push–pull) and reversed torsional loading conditions for different micro-notch sizes have been experimentally determined. In the numerical part, finite elements simulations using a cyclic elasto-plastic material behaviour law show that the mechanical state ahead of the different stress concentrations change drastically with the loading mode and the geometry of the artificial defect. From a fatigue point of view, it is shown that a stress gradient correction is required for all the loading, size and geometry configurations. Once the gradient correction is made and a proper multiaxial criterion is used, it appears that the size effect due to increasing the loaded surface area at the notch tip for the different geometries is negligible compared to the gradient effect.     

In situ analysis of three-dimensional electrolyte convection evolving during the electrodeposition of copper in magnetic gradient fields

A novel three-dimensional particle tracking velocimetry technique was used to examine the flow during electrodeposition of Cu. For the first time electrode-normal, circumferential, and radial velocities were spatially resolved during deposition in superimposed low and high magnetic gradient fields. In this way the complex interaction of magnetic field gradient force and Lorentz force induced convective effects could be measured and analyzed. Magnetic field gradient force induced electrolyte flow was detected only in high gradient magnetic fields, and it was found to be directed toward regions of gradient maxima. Since this electrode-normal flow causes enhanced transport of Cu(2+) ions from the bulk electrolyte to those regions of the working electrode where maxima of magnetic gradients are present, a structured deposit is formed during diffusion-limited electrodeposition. Lorentz force driven convection was observed during deposition in the low and the high magnetic gradient experiments. The overall fluid motion and the convection near the working electrode were determined experimentally and discussed with regard to the acting magnetic forces and numerical simulations.     

In situ derivatization/solid-phase microextraction for the determination of haloacetic acids in water

An in situ derivatization solid-phase microextraction method has been developed for the determination of haloacetic acids (HAAs) in water. The analytical procedure involves derivatization of HAAs to their methyl esters with dimethyl sulfate, headspace sampling using solid-phase microextraction (SPME), and gas chromatography-ion trap mass spectrometry (GC/ITMS) determination. Parameters affecting both derivatization efficiency and head-space SPME procedure, such as the selection of the SPME coating, derivatization-extraction time and temperature, and ionic strength, were optimized. The commercially available Carboxen-poly(dimethylsiloxane) (CAR-PDMS) fiber appears to be the most suitable for the determination of HAAs. Moreover, the formation of HAA methyl esters was dramatically improved (up to 90-fold) by the addition of tetrabutylammonium hydrogen sulfate (4.7 micromol) to the sample as ion-pairing agent in the derivatization step. The precision of the in situ derivatization/HS-SPME/GC/ITMS method evaluated using an internal standard gave relative standard deviations (RSDs) between 6.3 and 11.4%. The method was linear over 2 orders of magnitude, and detection limits were compound-dependent, but ranged from 10 to 450 ng/L. The method was compared with the EPA method 552.2 for the analysis of HAAs in various water samples, and good agreement was obtained. Consequently, in situ derivatization/HS-SPME/GC/ITMS is proposed for the analysis of HAAs in water.     

In situ trace analysis of oil in water with mid-infrared fiberoptic chemical sensors

The determination of trace amounts of oil in water facilitates the forensic analysis on the presence and origin of oil in the aqueous environment. To this end, the present study focuses on direct sensing schemes for quantifying trace amounts of oil in water using mid-infrared (MIR) evanescent field absorption spectroscopy via fiberoptic chemical sensors. MIR transparent silver halide fibers were utilized as optical transducer for interrogating oil-in-water emulsions via the evanescent field emanating from the waveguide surface, and penetrating the surrounding aqueous environment by a couple of micrometers. Unmodified fibers and fibers surface-modified with grafted epoxidized polybutadiene layers enabled the direct detection of crude oil in a deionized water matrix at the ppm level to ppb concentration level, respectively. Thus, direct chemical sensing of crude oil IR signatures without any sample preparation as low as 46 ppb was achieved with a response time of a few seconds.     

In situ observation and measurement of the SAW thin-film acoustoelectric effect

The thin-film acoustoelectric effect in SAW devices describes the interaction of electrical energy between a SAW in a piezoelectric medium and a thin film in the wave's propagation path. The real-time observation of the thin-film acoustoelectric interaction is useful in the design and characterization of SAW sensors (i.e., temperature, humidity, viscosity, voltage, current, Hall effects, etc.). An in situ test fixture was designed to be mechanically, thermally, and electrically stable. Data acquisition software and an electron beam evaporation system were configured for real-time thin-film characterization during film growth. Data have been observed for more than 20 SAW devices and over a wide range of frequencies (i.e., 62 MHz to 1 GHz). The results suggest that the use of the in situ procedure yielded good agreement between theoretical predictions and the measured data, which demonstrates a method for the characterization of a SAW H(2)-gas sensor in real-time.     

A study of size effects and length scales in fracture and fatigue of metals by second gradient modelling*

As the dimensions of structures are scaled down to the micro‐ and nano‐domains, the mechanical behaviour becomes size dependent and thus, we cannot expect the classical elasticity solutions to hold. In particular, recent experimental investigations of fatigue strength of metals show pronounced strengthening due to the influences of small geometrical dimensions. Based on second gradient elasticity framework as particularized on beams, closed form solutions to idealized problems of elastic cantilever bending, elastic three‐point bending and elasto‐plastic torsion have been found, showing considerable stiffening, toughening and hardening, respectively, compared to the classical theory predictions. In these models, the intrinsic material length scale was taken to be constant. Furthermore, we describe a gradient solid with a characteristic length which is not a fixed material parameter but depends on the amount of plastic effective strain amplitude, as obtained from cyclic strain hardening. A respective evolution law is suggested and discussed.     

Use of pulsed gradient spin-echo NMR as a tool in MALDI method development for polymer molecular weight determination

This study shows how mass spectrometry and pulsed gradient spin-echo (PGSE) nuclear magnetic resonance can be advantageously combined to achieve more reliable molecular weight information for polymers. Specifically, PGSE was shown to be a convenient tool for a rapid evaluation of Mw values to be further used as guidelines in matrix-assisted laser desorption/ionization (MALDI) sample preparation. PGSE calibration curves, established under given experimental conditions, were shown to be particularly robust, as they could be applied satisfactorily on different commonly available NMR instruments and different time frames. PGSE results were shown to compare well with size exclusion chromatography data used as a reference to validate this alternative technique. Moreover, because PGSE is relatively fast, it can be used interactively with MALDI analysis to check and understand mass spectrum profiles. This approach was first tested on poly(methyl methacrylate) (PMMA) standards and then successfully applied to determine the molecular weight of two unknown samples, a PMMA and a poly(ethylene glycol) monomethacrylate polymer.     

FE-investigations of a deterministic and statistical size effect in granular bodies within a micro-polar hypoplasticity

The paper deals with numerical investigations of a deterministic and statistical size effect in granular bodies during shearing of an infinite layer under plane strain conditions and free dilatancy. For a simulation of the mechanical behavior of a cohesionless granular material during a monotonous deformation path, a micro-polar hypoplastic constitutive was used which takes into account particle rotations, curvatures, non-symmetric stresses, couple stresses and the mean grain diameter as a characteristic length. The proposed model captures the essential mechanical features of granular bodies in a wide range of densities and pressures with a single set of constants. To describe a deterministic size effect, the calculations were carried out with an uniform distribution of the initial void ratio for four different heights of the granular layer: 5, 50, 500 and 2,000 mm. To investigate a statistical size effect, the distribution of the initial void ratio in infinite granular layers was assumed to be spatially correlated. As only primary stochastic calculations were performed, single examples of different random fields of the initial void ratio were generated. For this purpose a conditional rejection method was used.     

In situ determination of the remotely sensed reflectance and the absorption coefficient: closure and inversion

We tested closure between in situ radiometric and absorption coefficient measurements by using a nearly backscattering-independent remote-sensing reflectance model that employs the remote-sensing reflectance at three wavelengths. We show that only a small error is introduced into the closure model when the proper functional relationships of f/Q and the backscattering is taken to be a constant when using the sea-viewing wide field-of-view sensor wavelengths 443, 490, and 555 nm. A method of inverting the model to obtain the absorption coefficient by use of simple linear spectral relationships of the absorption coefficient is provided. The results of the model show that the independent measurements of reflectance and absorption obtain closure with a high degree of accuracy.     

Investigation of the size effect on optical properties of polycrystalline Ge deposition by pulse laser deposition

The size effect of optical properties of the polycrystalline Ge/Si films prepared by pulse laser deposition (PLD) is investigated by photoluminescence (PL) and photocurrent (PC) spectra. The size of Ge nanocrystals is precisely controlled by the pulsed deposition time and then observed by the atomic force microscopy (AFM). The average size of Ge nanocrystals is about 2, 5 and 25 nm for 1, 2 and 3 min deposited sample, respectively. The size effect on optical properties of Ge nanocrystals has been analyzed by photoluminescence (PL) and photocurrent (PC) spectra. The PL peaks shift from 0.799 eV for 1 min to 0.762 eV for 3 mins; at the same time, the photocurrent peaks of the films sharply changes from 0.781 eV to 0.749 eV, the shifts of PL and PC are contributed to the quantum size effect of Ge nanocrystals.     

In situ fastening graphene sheets into a polyurethane sponge for the highly efficient continuous cleanup of oil spills

Oil sorbents are an attractive option for oil-spill cleanup as they may be used for collection and complete removal of oil without adversely affecting the environment.However,traditional oil sorbents exhibit low oil/water separation efficiency and/or low oil-sorpfion capacity.In this study,an ultra-high performance graphene/polyurethane (PU) sponge has been successfully obtained by in situ polymerization in the presence of graphene dispersed in N-methylpyrrolidone (NMP).During polymerization,the NMP/graphene dispersion not only serves as a weak amine catalyst for the formation of the sponge,but promotes fixation of the graphene sheets in the framework of the PU sponge owing to the strong dipole interaction between NMP and graphene.The as-prepared graphene/PU sponge was used as an absorbing material for the continuous removal of oil from oil-spill water.The graphene/PU sponge can continuously and rapidly remove oils from immiscible oil/water mixtures in corrosive solutions,including strong acids and bases,hot water,and ice water,with an excellent separation efficiency of above 99.99％.In addition,the as-prepared graphene/PU sponge was effective in separating surfactant-stabilized emulsions with a high separation efficiency of ＞99.91％.     

Photoelastic determination of mode i stress intensity factor in tensile strips—effect of crack length

This paper reports an experimental investigation carried out, using the photoelastic technique, to determine the Mode I stress intensity factor in case of cracks of varying $\text{a}\text{w}$ ratio in single edge-notch specimens. The photoelastic information was analysed using the several methods proposed by earlier workers. The experimental results are compared with the analytical expressions.     

In situ characterization of humidity effect on the fatigue damage evolution of a cast aluminium alloy

In this paper, the feedback signal of ultrasonic fatigue system was used to deduce the accumulated fatigue damage in situ using the ultrasonic nonlinearity parameter. It was observed that, compared with the decrease in resonant frequency, the ultrasonic nonlinearity parameter shows a greater sensitivity to fatigue damage evolution (i.e. crack initiation and propagation). Ultrasonic nonlinearity parameters obtained from tests conducted under various environmental humidity levels were monitored and analysed. Through changes in the ultrasonic nonlinearity parameter, it was concluded that both of the fatigue crack initiation life and crack propagation life were reduced by increasing the humidity levels.