Measurement sensitivity improvement in tapping-mode atomic force microscopy through bi-harmonic drive signal

This article presents a novel method to improve the measurement sensitivity and reduce impact forces in tapping-mode atomic force microscopy by reshaping the tip trajectory. A tapping drive signal composed of two harmonics is used to generate an oscillating trajectory with a broader valley compared to the typical sinusoidal trajectory. The wide broad valley reduces the velocity of the tip in the vicinity of the sample and allots a greater portion of each period in the vicinity of the sample. Numerical simulations show that this results in decreased impact force and increased sensitivity of the cantilever oscillation to changes in tip-sample offset. Experimental results demonstrate an increase in image sharpness and decrease in tip wear using the bi-harmonic driving signal.     

COBRA-STAR, a five frame point-projection x-ray imaging system for 1 MA scale wire-array Z pinches

A new imaging system for 1 MA scale wire-array Z-pinch experiments that produces up to five high-resolution x-ray images per experimental pulse has been developed. Calibrated areal density measurements of the Z-pinch plasma can be obtained from each pulse. The system substitutes five molybdenum (Mo) X pinches for the normal copper return-current conductors to provide point sources of x-rays for point-projection radiography. Each backlighting X pinch consists of four Mo wires, the x-ray burst timing of which was controlled by varying the wire diameter (mass) from 10.2 to 30 microm in the five X pinches. Typical images have a 16x8 mm2 field of view at the wire array and a magnification of about 6.5:1 on the x-ray-sensitive film. Titanium (Ti) filters in front of the films transmit continuum radiation in the spectral range of 3-5 keV. Inclusion on the Ti of a step wedge having known thickness increments of the same material as the wires enables the calibrated areal density measurements to be made of the exploding wire plasmas. Here, we used tungsten (W) step wedges with step thicknesses ranging from 0.015 to 1.1 microm to obtain accurate (+/-10%) areal density measurements of W plasmas from the spatial profile of film exposure. When imaging arrays that produce intense radiation pulses, a plastic monofilament "quencher" is placed on axis to avoid film saturation. Images have subnanosecond temporal resolution and about 7 microm spatial resolution.     

Subtleties in ADF imaging and spatially resolved EELS: A case study of low-angle twist boundaries in SrTiO3

A screw dislocation network at the low-angle SrTiO3/Nb:SrTiO3 twist grain boundary has been analyzed by annular dark field (ADF) imaging and spatially resolved electron energy loss spectroscopy (EELS) in a scanning transmission electron microscope (STEM). The cores of one set of dislocations running parallel to the beam direction appear dark in the ADF STEM images. EELS on the dislocation core reveals a reduced Sr/Ti ratio compared to the bulk suggesting Sr-deficient cores. The second set of dislocations, orthogonal to the latter, is imaged by its strain field using low-angle annular dark field (LAADF) imaging. Multislice image simulations suggest channeling of the electron probe on the atomic columns for small tilts, theta < 1 degree, where the Sr columns act as beam guides. Only for larger tilts is the channeling effect strongly reduced and the fringe contrast approaches the value predicted by a purely incoherent imaging model. Ti-L(2,3) EELS across the dislocation core shows an asymmetry between the EELS and the ADF signal which cannot be explained by the geometry or beam broadening. This asymmetry might be explained by an effective nonlocal potential representing inelastic scattering in EELS.     

Spectroscopic study of carbaryl sorption on smectite from aqueous suspension

Sorption of carbaryl (1-naphthyl-N-methyl-carbamate) from aqueous suspension to smectite was studied using Fourier transform infrared (FTIR), high-performance liquid chromatography (HPLC) (for batch sorption), and quantum chemical methods. The amount of carbaryl sorbed was strongly dependent on the surface-charge density of the smectite with more sorption occurring on the two "low" surface-charge density smectites (SHCa-1 and SWy-2) compared to that of the high surface-charge SAz-1 smectite. In addition, the amount of carbaryl sorbed was strongly dependent on the nature of the exchangeable cation and followed the order of Ba approximately Cs approximately Ca > Mg approximately K > Na approximately Li for SWy-2. A similartrend was found for hectorite (SHCa-1) of Cs > Ba > Ca > K approximately Mg > Na approximately Li. Using the shift of the carbonyl stretching band as an indicator of the strength of interaction between carbaryl and the exchangeable cation, the observed order was Mg > Ca > Ba approximately K > Na > Cs. The position of the carbonyl stretching band shifted to lower wavenumbers with increasing ionic potential of the exchangeable cation. Density functional theory predicted a cation-induced lengthening of the C=O bond, resulting from the carbonyl group interacting directly with the exchangeable cation in support of the spectroscopic observations. Further evidence was provided by a concomitant shift in the opposite direction by several vibrational bands in the 1355-1375 cm(-1) region assigned to stretching bands of the carbamate N-Ccarbonyl and Oether-Ccarbonyl bonds. These data indicate that carbaryl sorption is due, in part, to site-specific interactions between the carbamate functional group and exchangeable cations, as evidenced by the FTIR data. However, these data suggest that hydrophobic interactions also contribute to the overall amount of carbaryl sorbed. For example, the FTIR data indicated thatthe weakest interaction occurred when Cs+ was the exchangeable cation. In contrast, the highest amount of carbaryl sorption was observed on Cs-exchanged smectite. Of all the cations studied, Cs has the lowest enthalpy of hydration. It is suggested that this low hydration energy provides the carbaryl with greater access to the hydrophobic regions of the siloxane surface.     

Microbiological quality of sausages containing chickpea flour (Cicer arietinum)

English-type fresh skinless pork sausages in which 30% of the protein was replaced by unheated chickpea flour or by chickpea flour heated at 80°C for 1 h were evaluated microbiologically. During storage at 0°C, but not 22°C, incorporation of unheated chickpea flour lowered the microbiological quality of the sausages, but incorporation of chickpea flour previously heated at 80°C for 1 h led to no less of microbiological quality.     

Interferometer-based structured-illumination microscopy utilizing complementary phase relationship through constructive and destructive image detection by two cameras

In an interferometer-based fluorescence microscope, a beam splitter is often used to combine two emission wavefronts interferometrically. There are two perpendicular paths along which the interference fringes can propagate and normally only one is used for imaging. However, the other path also contains useful information. Here we introduced a second camera to our interferometer-based three-dimensional structured-illumination microscope (I(5)S) to capture the fringes along the normally unused path, which are out of phase by π relative to the fringes along the other path. Based on this complementary phase relationship and the well-defined phase interrelationships among the I(5)S data components, we can deduce and then computationally eliminate the path length errors within the interferometer loop using the simultaneously recorded fringes along the two imaging paths. This self-correction capability can greatly relax the requirement for eliminating the path length differences before and maintaining that status during each imaging session, which are practically challenging tasks. Experimental data is shown to support the theory.     

Toxicity of benzotriazole and benzotriazole derivatives to three aquatic species

Benzotriazole and its derivatives comprise an important class of corrosion inhibitors, typically used as trace additives in industrial chemical mixtures such as coolants, deicers, surface coatings, cutting fluids, and hydraulic fluids. Recent studies have shown that benzotriazole derivatives are a major component of aircraft deicing fluids (ADFs) responsible for toxicity to bacteria (Microtox). Our current research compared the toxicity of benzotriazole (BT), two methylbenzotriazole (MeBT) isomers, and butylbenzotriazole (BBT). Acute toxicity assays were used to model the response of three common test organisms: Microtox bacteria (Vibrio fischeri), fathead minnow (Pimephales promelas) and water flea (Ceriodaphnia dubia). The response of all the three organisms varied over two orders of magnitude among all compounds. Vibrio fischeri was more sensitive than either C. dubia or P. promelas to all the test materials, while C. dubia was less sensitive than P. promelas. The response of test organisms to unmethylated benzotriazole and 4-methylbenzotriazole was similar, whereas 5-methylbenzotriazole was more toxic than either of these two compounds. BBT was the most toxic benzotriazole derivative tested, inducing acute toxicity at a concentration of < or = 3.3 mg/l to all organisms.     

交流同步起动发电机在变频起动中机械特性的分析与计算

立足于铁道部正在研制的第一台交流传动内燃调车机车,在已设计的同步起动发电机参数的基础上,结合变频起动装置的工作原理,分析并计算该起动发电机在起动过程中的机械特性。     

A swept frequency multiplication technique for air-coupled ultrasonic NDE

A new technique has been investigated for improving the signals that can be obtained in air-coupled nondestruction evaluation (NDE). This relies on the wide bandwidth available from polymer-filmed capacitive transducers. The technique relies on a swept-frequency "chirp" signal, which is transmitted from a transducer in air. The new technique differs from existing time-domain correlation techniques, such as pulse compression, in that a single multiplication process is performed in the time domain to give a difference frequency signal. This then can be isolated easily in the frequency domain. It will be demonstrated that this new swept frequency multiplication (SFM) approach gives the potential for rapid air-coupled imaging.     

Oligonucleotide loading determines cellular uptake of DNA-modified gold nanoparticles

The cellular internalization of oligonucleotide-modified nanoparticles is investigated. Uptake is dependent on the density of the oligonucleotide loading on the surface of the particles, where higher densities lead to greater uptake. Densely functionalized nanoparticles adsorb a large number of proteins on the nanoparticle surface. Nanoparticle uptake is greatest where a large number of proteins are associated with the particle.