Search

This paper deals with the attempt to develop and study the performance of ground granulated blast furnace slag (GGBS) and sugarcane bagasse ash (SCBA) based sustainable geopolymer concrete. NaOH (8M, 10M, and 12M) and Na2SiO3 were used as alkaline activators with a ratio of 2.5. SCBA mainly acted as amorphous silica and has been utilized as a substitute material for GGBS. The effect of SCBA contents (0%, 5%, 10%, 15% & 20% by the mass of binder) in terms of fresh, hardened, microstructural, and correlation properties of geopolymer concrete developed have been evaluated. Different tests such as the slump cone test, compression test, split tensile test, flexure test, and ultrasonic pulse velocity test were conducted. Scanning electron microscopy, Energy dispersive analysis, and X-ray diffraction analysis were investigated for understanding the microstructural properties. The research findings have shown that with an increase in molarity from 8M to 12M there is an increase in the strength properties of geopolymer concrete. The results in this current study show that 28 days compressive strength was found to increase by 4–15% when the NaOH molarity was increased from 8M to 10M and 8–21% when the NaOH molarity was increased from 8M to 12M. The geopolymer concrete developed with 20% SCBA and 80% GGBS with 8M NaOH solution and SS/SH ratio of 2.5 can be used for a target strength of 30–35 MPa. Scanning electron microscope images show a packed and dense matrix, which clearly outlines the reason behind the attainment of higher strength in higher molarity of GGBS-SCBA based geopolymer concrete samples and the presence of CASH gel confirmed this in the geopolymer matrix. Furthermore, there is a strong correlation between the experimental findings and the model equations proposed. These presented models will be useful in improving the strength of geopolymer concrete incorporating agricultural and industrial wastes.

There is considerable evidence that mineral dust has an important impact on alpine ecosystems, but the relationship remains unclear in some instances. In an attempt to fill this knowledge gap, we investigated 1) the mineralogical composition of dust components at Hochtor (Hohe Tauern, Austria), 2) its effects on soil formation and biological soil crusts (BSCs), and 3) the effect of mineral dust on plant growth in this interdisciplinary study. Mineral particles such as silicates, carbonates, oxides, volcanic quartz phenocrysts, opaque ore minerals, and spheres, such as microtektites, micrometeorites and fly ash aggregates, were detected using a scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectrometer (SEM-EDX). Rare micrometeorites are of extra-terrestrial origin (cosmic dust) and the decorated spheres are aggregates of fly ashes from anthropogenic origin. In terms of size, fine particles (100 µm) characterize the dust composition, originating mainly from adjacent rock outcrops, while the transport from the North African desert appears to be less important and diluted by local sources. The research was carried out as part of the pan-European biodiversity project “Soil Crust International” (SCIN). The results suggest that mineral dust aids in the rapid formation of BSCs in highly disturbed treated plots, and thus, both fine sand and available phosphorus are statistically proven to be determinants of the rapid growth of biocrusts. The number of plant individuals also increases between 2016 and 2020, however at a relatively moderate rate due to permanent mechanical erosion and debris flow within the treatment plots. Silica dust is believed to be a contributing factor to the widespread distribution of silicate plants in limestone habitats, such as Primula minima and Cerastium uniflorum, two “acidophilic” species that have been tested more closely. Finally, it is deduced that 1) aeolian dust plays a role in the continuous process of soil and crust formation, and 2) it works as a growth regulator in complex biological communities such as BSCs and vascular plant communities by creating new habitats and increasing biodiversity.

In this study, the effects of the electrohydrodynamic (EHD) drying method with needle and wire, the hot air method and a combination of the EHD-hot air methods on the drying kinetics, color, rehydration ratio and scanning electron microscope images of apricot samples were investigated. In addition, the experimental drying data were modeled using ten different mathematical thin layer drying models. It was determined that the rehydration ratio values of the samples dried with the combination of EHD and hot air were generally higher than the rehydration ratios of the samples dried with hot air or EHD only. Samples from all the drying methods were compared with fresh samples; the color parameters were affected, and scanning electron microscopy images revealed the different physical changes in the microstructure of the products. As a result, it is determined that EHD technology can be used as an alternative drying method suitable for apricot samples. [ABSTRACT FROM AUTHOR]

We have discovered what appear to be micrometeorites imbedded in seven late Pleistocene Alaskan mammoth tusks and a Siberian bison skull. The micrometeorites apparently shattered on impact leaving 2 to 5 mm hemispherical debris patterns surrounded by carbonized rings. Multiple impacts are observed on only one side of the tusks and skull consistent with the micrometeorites having come from a single direction. The impact sites are strongly magnetic indicating significant iron content. We analyzed several imbedded micrometeorite fragments from both tusks and skull with laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and X-ray fluorescence (XRF). These analyses confirm the high iron content and indicate compositions highly enriched in nickel and depleted in titanium, unlike any natural terrestrial sources. In addition, electron microprobe (EMP) analyses of a Fe-Ni sulfide grain (tusk 2) show it contains between 3 and 20 weight percent Ni. Prompt gamma-ray activation analysis (PGAA) of a particle extracted from the bison skull indicates ~;;0.4 mg of iron, in agreement with a micrometeorite ~;;1 mm in diameter. In addition, scanning electron microscope (SEM) images and XRF analyses of the skull show possible entry channels containing Fe-rich material. The majority of tusks (5/7) have a calibrated weighted mean 14C age of 32.9 +- 1.8 ka BP, which coincides with the onset of significant declines

The U.S. Government has been conducting actinide material processing experiments with the goal of identifying processing signatures of nuclear forensic value. Valuable signatures have the ability to credibly predict the source characteristics of material. In the search for potential signatures, a large amount of effort is invested in gathering detailed scanning electron microscope (SEM) images of processed material with a subsequent analysis of particle measurements using image analysis software, such as Morphological Analysis of Materials (MAMA). Based on many measured particles, the software calculates many distributional characteristics of particles, including the perimeter, vector area, etc. Often, each distribution is summarized as a mean and standard deviation for use in the prediction of source characteristics. However, distributional measurements contain a wealth of information such as distributional shape and skewness, which can provide meaningful information in discriminating source characteristics. To this end, methods using the entire distribution of measurements are being developed. Leveraging statistical functional regression approaches for entire distributions improves the prediction of source characteristics over the traditional approach of using simple summaries. The methodology is demonstrated with data from a bench-scale uranium study. [ABSTRACT FROM AUTHOR]

The paper deals with new experiments and corresponding numerical simulations to study the effect of stress state on damage and fracture behavior of ductile metals. Different branches of ductile damage criteria are considered corresponding to various mechanisms depending on stress intensity, stress triaxiality and the Lode parameter. New experiments with two-dimensionally loaded specimens have been developed covering a wide range of stress triaxialities and Lode parameters in the tension, shear and compression domains. Scanning electron microscope (SEM) analyses of the fracture surfaces show various failure modes corresponding to different stress states detected by numerical simulations of the experiments. [ABSTRACT FROM AUTHOR]

In the telenanomanipulation system based on scanning electron microscope( SEM) , aiming at the problem it is difficult to obtain multi-view images from scanning electron microscope and the lack of three-dimensional information in single view images, and in order to study how quickly achieve the precise three-dimensional positioning of manipulation tool in single-view SEM image, sub-pixel edge detection algorithm based on the gradient direction of Gauss curve fitting is used to achieve precise positioning of the horizontal coordinate information, and image similarity degree is used to obtain manipulation tools information of vertical coordinate information. The experimental data obtained from the single-view SEM images show that the horizontal coordinate information has achieved sub-pixel level of accuracy, and the vertical coordinate information can be precise positioning in a small range of target. [ABSTRACT FROM AUTHOR]

Multi-walled carbon nanotubes (MWCNTs) coated intensity modulated fiber optic sensor for the detection of ethanol and methanol vapors at room temperature is reported. Pure, 30 and 60 min iso-butyl methyl ketone (IBMK) treated MWCNT were coated on cladding removed polymethyl methacrylate fiber by the dip coating technique. The pure and IBMK treated MWCNT coated fibers were used as sensors. Response of the sensors was studied by measuring the change in output light intensity for different methanol and ethanol vapor concentrations in the range of 0-500 ppm. The 60 min IBMK treated MWCNT coated sensor showed 2 and 3.4 fold increase in the sensitivity for methanol and ethanol vapors at 640 and 630 nm wavelengths light, respectively, compared with the pristine MWCNT coated sensor. Fourier transform infrared spectroscopy confirmed the attachment of C=O functional group in IBMK treated MWCNT. Thermogravimetry results reveal the functionalized nanotubes decomposed at 475 °C after the elimination of attached functional groups. The pristine nanotubes start to decompose at 540 °C. The randomly oriented nanotubes layer of average thickness 1.5 μm on the cladding modified fiber is observed from scanning electron microscope images. [ABSTRACT FROM PUBLISHER]

We present a fabrication technique for discrete, released carbon-nanotube-based nanomechanical force sensors. The fabrication technique uses prepatterned coordinate markers to align the device design to predeposited single-walled carbon nanotubes (SWNTs): Atomic force microscope (AFM) images are recorded to determine spatial orientation and location of each discrete nanotube to be integrated in a nanoscaled force sensor. Electron beam lithography is subsequently used to pattern the metallic electrodes for the nanoscale structures. Diluted hydrofluoric acid etching followed by critical point drying completes the nanosized device fabrication. We use discrete, highly purified, and chemically stable carbon nanotubes as active elements. We show AFM and scanning electron microscope images of the successfully realized SWNTs embedded nanoelectromechanical systems (NEMS). Finally, we present electromechanical measurements of the suspended SWNT NEMS structures [ABSTRACT FROM PUBLISHER]

In this paper, the mechanical degradation of a commercial gas diffusion layer subjected to repeated freeze–thaw thermal cycles is studied. In a fuel cell, the mechanical assembly state directly affects the performance of polymer electrolyte membrane fuel cells. Particularly, the gas diffusion layer repeatedly withstands the complex heat and humidity environmental conditions in which the temperature and humidity are always greatly changed. Studying the three-dimensional mechanical degradation of gas diffusion layers due to orthotropic properties is very useful in extending the lifetime and durability of fuel cells. To investigate this, we first established the standard freeze–thaw thermal cycle and studied the gas diffusion layer's mechanical degradation performance with up to 400 repeated freeze–thaw thermal cycles. Furthermore, different types of failure in the gas diffusion layer caused by the repeated thermal aging treatment were observed using a scanning electron microscope, to explain the change in the mechanical deterioration. As a result, the different thermal failure plays different roles in the explanation of the gas diffusion layer's mechanical degradation under different thermal cycles. In particular, the thermal failure that resulted from the first 100 thermal cycles has the greatest effect on the compressive and tensile performance, compared to the shear behavior. [ABSTRACT FROM AUTHOR]

Reverse‐bias operations for a light‐emitting diode can quickly screen the weakness of the device. Electromigration around the electrode on the lateral and vertical directions can be observed by optical microscope images, scanning electron microscope images and energy dispersive spectroscopy. The failure process caused by the electromigration can be revealed by the changes of forward‐bias and reverse‐bias electroluminescence images and the emergence of the reverse‐bias EL may be attributed to the diffusion of gold. Furthermore, the increase of the leakage current may supress the forward‐bias band to band recombination current especially near the metal contact. [ABSTRACT FROM AUTHOR]