Studies of the growth, evolution, and self-aggregation of β-amyloid fibrils using tapping-mode atomic force microscopy

Amyloid peptide (Aβ) is the major protein component of plaques found in Alzheimer's disease, and the aggregation of Aβ into oligomeric and fibrillic assemblies has been shown to be an early event of the disease pathway. Visualization of the progressive evolution of nanoscale changes in the morphology of Aβ oligomeric assemblies and amyloid fibrils has been accomplished ex situ using atomic force microscopy (AFM) in ambient conditions. In this report, the size and the shape of amyloid β(1-40) fibrils, as well as the secondary organization into aggregate structures were monitored at different intervals over a period of 5 months. Characterizations with tapping-mode AFM serve to minimize the strong adhesive forces between the probe and the sample to prevent damage or displacement of fragile fibrils. The early stages of Aβ growth showed a predominance of spherical seed structures, oligomeric assemblies, and protofibrils; however the size and density of fibrils progressively increased with time. Within a few days of incubation, linear assemblies and fibrils became apparent. Over extended time scales of up to 5 months, the fibrils formed dense ensembles spanning lengths of several microns, which exhibit interesting changes due to self-organization of the fibrils into bundles or tangles. Detailed characterization of the Aβ assembly process at the nanoscale will help elucidate the role of Aβ in the pathology of Alzheimer's disease.     

Rab7 and actin cytoskeleton participate during mobilization of β1EHFNR in fibronectin-stimulated Entamoeba histolyticatrophozoites

In vitro interaction of Entamoeba histolytica trophozoites with fibronectin (FN) induces redistribution of the amoebic fibronectin receptor (β1EhFNR). Trafficking of beta1 integrins is important for cell adhesion and migration in higher eukaryotes and requires the participation of Rab proteins. In E. histolytica, the machinery involved in integrin trafficking is not completely known. EhRab7 is a 24.5-kDa protein whose alignment with other Rab7 proteins demonstrated that it shared significant homology with Rab7 proteins from other organisms, including humans. Using different types of microscopy (fluorescence and confocal microscopy), it was established that Rab7 and the actin cytoskeleton participated in the mobilization of β1EhFNR in FN-stimulated trophozoites. β1EhFNR and Rab7 co-localized only in vesicular structures at 5 min, and at longer time (1 h), both co-localized in both plasma membrane and in vesicular structures; at the same time, Rab7 co-localized with specific actin structures (phagocytic vacuoles). At 5 h the β1EhFNR, Rab7, and actin co-localized at the plasma membrane, and only β1EhFNR and Rab7 decorated vesicles of different sizes. Actin and Rab7 co-localized in a cap-like structure at one end of the cell. Fluorescence resonance energy transfer and electron microscopy confirmed the close interaction between β1EhFNR and Rab7. Moreover, the use of a lysosome-specific marker (LysoTracker) and a Golgi-specific marker (NBD C(6)-ceramide) allowed us to establish that, at some point within the endocytic route, β1EhFNR and Rab7 co-localized within a lysosome-type organelle, but not a Golgi-like organelle, which indicated that this integrin-like molecule was returned to the plasma membrane via exocytic or secretory vesicles.     

Frequency–spectrum characteristics of force in end milling with tool wear and eccentricity

The effects of chip load, tool wear, and tool eccentricity on milling force are similar; in order to distinguish them from each other, the spectral characteristics of milling force for four flute end mills was studied. With simplified milling force model, the calculation expression of instantaneous milling force under tool eccentricity was derived based on the 2D geometry of tool cutting into workpiece. Using simulation methods, the amplitude spectra of milling forces under neither wear nor eccentricity, only eccentricity, both wear and eccentricity, and the every phase spectrum of force caused only by wear of one tooth were analyzed. The analysis results showed that the basic and third harmonic amplitudes of spindle frequency were linear only with eccentric distance, the fourth harmonic amplitude was linear only with feed, the second harmonic component was in relationship only with tool wear, and harmonics with same frequency caused by wear of different teeth were in phase or out of phase. Then corresponding milling experiments were done, the relations between experimental harmonic amplitudes of force and milling parameters were analyzed, and were found being in good agreement with above simulation results. These indicate that amplitudes of these harmonics could be taken as indices in recognizing eccentricity, wear, and chip load, respectively, and their variations contain in-process information of tool wear. This study proposes a new idea of identifying tool eccentricity and wear with force itself.     

Dynamic control of reversible cell adhesion and actin cytoskeleton in the mouth of Beroë

Cell-cell adhesion in the various types of intercellular junctions of differentiated tissues is relatively stable and permanent. In migrating cells of embryos, or in wound closure, inflammatory responses and tumors of adult tissues, however, bonds between cells are made and broken and made again, i.e., cell-cell adhesions are transient and reversible. These nonjunctional contacts lack the organized structure of intercellular junctions, but may initiate their tissue-specific formation during development. Investigation of dynamic, nonjunctional cell-cell adhesions has been hampered by the asynchronous and heterogeneous distribution of these transient contacts among groups of moving cells. We recently discovered a novel system of reversible cell adhesion in a differentiated tissue that overcomes this difficulty. Here I review our current knowledge of this system, particularly its unique experimental advantages for investigating the mechanisms and control of dynamic cell adhesion.     

Molecular recognition of DNA–protein complexes: A straightforward method combining scanning force and fluorescence microscopy

Combining scanning force and fluorescent microscopy allows simultaneous identification of labeled biomolecules and analysis of their nanometer level architectural arrangement. Fluorescent polystyrene nano-spheres were used as reliable objects for alignment of optical and topographic images. This allowed the precise localization of different fluorescence particles within complex molecular assemblies whose structure was mapped in nanometer detail topography. Our experiments reveal the versatility of this method for analysis of proteins and protein–DNA complexes.     

Influence of Mg²⁺, Ni²⁺, and Cu²⁺ on DNA assembly on HOPG surfaces: atomic force microscopy study

Adsorption of circular DNA onto bare highly oriented pyrolytic graphite (HOPG) surfaces by the addition of Mg²⁺, Ni²⁺, and Cu²⁺ has been investigated by atomic force microscopy (AFM). AFM results revealed that the topography and height of DNA on HOPG surface by the addition of different metal ions are quite different. After the addition of Mg²⁺ for incubation, DNA molecules tend to form many loops on HOPG surfaces, which are derived from the crossover of intramolecular and intermolecular chains. After the addition of Ni²⁺, DNA molecules can form network on HOPG surfaces, and the density of DNA network was significantly increased with increasing DNA concentration. Consequently, dense DNA network can be obtained by using relatively low concentration of DNA and Ni²⁺. As for the addition of Cu²⁺, angular DNA loops composed of flat chains were observed. The observed flat DNA chains with an average height of 0.52 nm can be ascribed to Cu²⁺ insert into the site between bases and phosphate group of DNA inducing denaturation of DNA molecules. This study is very helpful for understanding the interactions of metal ions and DNA molecules, and for constructing various DNA structures on the carbonaceous surfaces. SCANNING 34: 68–75, 2012. © 2011 Wiley Periodicals, Inc.     

Identification and quantification of β-caryophyllene in copaiba oil using Raman spectroscopy

Copaiba oleoresin presents several compounds with known biologic activity and physiologic effects, including analgesic and insecticide properties. Among them are the terpenoids (mainly diterpenes and sesquiterpenes) with β-caryophyllene, the main representative of the terpenoids and considered to be a chemical marker. This study employed Raman spectroscopy and principal component analysis (PCA) techniques to identify and quantify the β-caryophyllene marker in copaiba oil samples purchased from popular markets in Brazil. A dispersive Raman spectrometer (830?nm, 250?mW, 2?cm^?1 spectral resolution) was used. Results showed the identification of the main Raman peaks from the β-caryophyllene in copaiba oil samples (main peaks at 507, 771, 1442, 1638, and 1673?cm^?1). The loading vector 2 (PC2) extracted the spectral information from β-caryophyllene in the samples and the eigenvalue 2 (score 2) allowed the estimation of the concentration of this marker in commercial samples, with the concentrations from 15 to 34%. Raman spectroscopy combined with PCA may be considered to be a potential analytical tool for the quality control of Copaifera oil samples by quantifying β-caryophyllene using its unique spectral information.     

Optimization of thrust force, torque, and tool wear in drilling of coir fiber-reinforced composites using Nelder–Mead and genetic algorithm methods

Machining of composite materials is an important and current topic in modern researches on manufacturing processes. Determination of optimal cutting parameters is one of the most important elements in the machinability study of composites. Optimization has significant practical importance particularly for operating the machineries. In order to increase the accuracy of drill holes, the tool must be in good condition always as much as possible. To achieve good condition of tool, the optimization of machining parameters like drill bit diameter, spindle speed, and feed rate are mandatory. The objective of this paper is to study the effect of these process parameters on thrust force, torque, and tool wear in drilling of coir fiber-reinforced composites. The optimal settings of the parameters were determined through experiments planned, conducted, and analyzed using the Box–Behnken design, Nelder–Mead, and genetic algorithm methods. This paper also aimed to increase the cutting condition of tool, i.e., minimization of tool wear by applying the optimized input parameters using Nelder–Mead and genetic algorithm techniques.     

Analysis of surface roughness and cutting force when turning AISI 1045 steel with grooved tools through Scott–Knott method

The chip breaker presents an important role in chip control on turning operation, as well as a significant influence on cutting force, surface integrity, wear, and tool life. In this experimental study, the grooved chip breaker, feed rate, and cutting velocity influence on cutting force and surface roughness of turning process of AISI 1045 steel were investigated through a complete factorial design and the Scott–Knott method. The multiple comparison method of Scott–Knott was used to identify which combination of the factor levels was specifically different when a source of variation was statistically significant in ANOVA. This multiple comparison method was essential to choose an optimal combination between cutting conditions and chip breaker type assuring the lowest cutting force and surface roughness levels without ambiguity. The methodology proposed was effective at achieving process improvement.     

Investigations of flank wear, cutting force, and surface roughness in the machining of Al-6061�CTiB2 in situ metal matrix composites produced by flux-assisted synthesis

This paper presents the results of an experimental investigation on the machinability of in situ Al-6061?CTiB₂ metal matrix composite (MMC) prepared by flux-assisted synthesis. These composites were characterized by scanning electron microscopy, X-ray diffraction, and micro-hardness analysis. The influence of reinforcement ratio of 0, 3, 6, and 9?wt.% of TiB₂ on machinability was examined. The effect of machinability parameters such as cutting speed, feed rate, and depth of cut on flank wear, cutting force and surface roughness were analyzed during turning operations. From the test results, we observe that higher TiB₂ reinforcement ratio produces higher tool wear, surface roughness and minimizes the cutting forces. When machining the in situ MMC with high speed causes rapid tool wear due to generation of high temperature in the machining interface. The rate of flank wear, cutting force, and surface roughness are high when machining with a higher depth of cut. An increase in feed rate increases the flank wear, cutting force and surface roughness.     

Experimental investigation and analysis of thrust force in drilling cast hybrid metal matrix (Al–15%SiC–4%graphite) composites

Composite materials are used in different engineering applications and are continuously displacing conventional materials due to their excellent properties. This paper discusses the influence of drilling parameter on thrust force in drilling Al 6061/15%SiC 4%Gr metal matrix composites. The composite materials are fabricated by stir casting method. The experiments are conducted on computer numeric control vertical machining centre using titanium nitride coated solid carbide twist drills of 4 mm, 8 mm and 12 mm diameter under dry conditions. A response surface analysis is carried out. The effect of drilling parameters on thrust force is studied and presented. The results indicated that feed rate is the main parameter which influences the thrust force in drilling of hybrid metal matrix composites.     

Structure and Mechanical Properties of Al–Mg Alloy Workpieces in Multilayer Surfacing with Interlayer Deformation

Russian Engineering Research - Al–Mg alloy samples are produced by multilayer surfacing according to various strategies, with and without interlayer deformation. The samples undergo tensile...     

Determination of Thiophanate-Methyl and Carbendazim in Rapeseed by Solid–Phase Extraction and Ultra–High Performance Chromatography with Photodiode Array Detection

A rapid and reliable ultra-high performance liquid chromatography method using a photodiode array detector with QuEChERS (quick, easy, cheap, effective, rugged, and safe) sample preparation was developed to determine thiophanate-methyl and carbendazim in rapeseed. Samples were extracted with acetonitrile and partitioned with a mixture of NaCl and anhydrous MgSO₄. The cleanup step was performed using dispersive solid-phase extraction with anhydrous MgSO₄ and primary secondary amine. This step was repeated to improve the results. The limits of detection and quantification of thiophanate-methyl and carbendazim in rapeseed were 15 and 50 μg kg^?1, respectively. The recoveries of thiophanate-methyl and carbendazim were from 77.44–100.9%, with relative standard deviations between 2.20% and 6.62%. The method was employed to determine thiophanate-methyl and carbendazim in rapeseed. This study has established a novel method and a safety evaluation system for the analytes in rapeseed.     

Subsurface damage pattern and formation mechanism of monocrystalline β-Ga2O3 in grinding process

Monocrystalline beta-phase gallium oxide (β-Ga₂O₃) is a promising ultrawide bandgap semiconductor material. However, the deformation mechanism in ultraprecision machining has not yet been revealed. The aim of this study is to investigate the damage pattern and formation mechanism of monocrystalline β-Ga₂O₃ in different grinding processes. Transmission electron microscopy was used to observe the subsurface damage in rough, fine, and ultrafine grinding processes. Nanocrystals and stacking faults existed in all three processes, dislocations and twins were observed in the rough and fine grinding processes, cracks were also observed in the rough grinding process, and amorphous phase were only present in the ultrafine grinding process. The subsurface damage thickness of the samples decreased with the reduction in the grit radius and the grit depth of cut. Subsurface damage models for grinding process were established on the basis of the grinding principle, revealing the mechanism of the mechanical effect of grits on the damage pattern. The formation of nanocrystals and amorphous phase was related to the grinding conditions and material characteristics. It is important to investigate the ultraprecision grinding process of monocrystalline β-Ga₂O₃. The results in this work are supposed to provide guidance for the damage control of monocrystalline β-Ga₂O₃ grinding process.     

A study on the variation of the performance and the cost of power generation in a combined heat and power plant with the change of the user facility’s return temperature

Journal of Mechanical Science and Technology - A combined heat and power (CHP) system generates electricity from thermal energy and generates heat by utilizing the remaining thermal energy. The...     

Experimental and numerical studies on metrological characteristics of swirlmeters with different swirler helix angles in a gas–solid two-phase flow

Swirlmeters are widely used to measure natural gas because of their simple structure, absence of internal moving parts and high measurement accuracy. However, fine particles in natural gas can affect swirlmeters’ metering accuracy. Hence, this study evaluated the metrological characteristics of swirlmeters measuring gas–solid two-phase flow with fine particles and different swirler helix angles. Experiments and simulations for swirlmeters with different solid–gas mass ratios and helix angles were performed. The results demonstrated that the swirlmeter meter factors decreased and pressure losses increased as the solid–gas mass ratio increased. With different solid–gas mass ratios, the most effective sensor detection position was at the throat outlet a half radius from the centre of the runner. The swirler with a smaller helix angle could significantly increase the meter factor, while the swirler with a larger helix angle could significantly decrease pressure losses. The swirlmeter internal flow losses were mainly derived from the swirler.     

Measurement of electromagnetic radiation with respect to the hours and days of a week at 100kHz–3GHz frequency band in a turkish dwelling

In this paper, the electromagnetic (EM) radiation to which we are exposed in our life is aimed to be observed during a week. The measurements are carried out in a randomly selected apartment during 24 h a day at 4 s sampling period for all days of a week. Due to the result of the study, we can see whether any radiation above specified limits occurs during a day and week or not and also we can determine how an ordinary instantaneous measurement represents the usual radiation level in related area. Measurement results showed that EM radiation levels in 100 kHz–3 GHz frequency band were considerably below specified limit values. There is statistically no difference between measured values in Monday and Saturday with respect to days. However, it is observed that the measured values in other days except for Monday and Saturday are statistically considerably different.