The use of mass spectrometry to study amyloid-β peptides

Amyloid-β peptide (Aβ) varies in size from 39 to 43 amino acids and arises from sequential β- and γ-secretase processing of the amyloid precursor protein. Whereas the non-pathological role for Aβ is yet to be established, there is no disputing that Aβ is now widely regarded as central to the development of Alzheimer's disease (AD). The so named "amyloid cascade hypothesis" states that disease progression is the result of an increased Aβ burden in affected areas of the brain. To elucidate the Aβ role in AD, many analytical approaches have been proposed as suitable tools to investigate not only the total Aβ load but also many other issues that are considered crucial for AD, such as: (i) the aggregation state in which Aβ is present; (ii) its interaction with other species or metals; (iii) its ability to induce oxidative stress; and (iv) its degradative pathways. This review provides an insight into the use of mass spectrometry (MS) in the field of Aβ investigation aimed to assess its role in AD. In particular, the different MS-based approaches applied in vitro and in vivo that can provide detailed information on the above-mentioned issues are reviewed. Moreover, the advantages offered by the MS methods over all the other techniques are highlighted, together with the recent developments and uses of combined analytical approaches to detect and characterize Aβ.     

The role of mass spectrometry to study the Oklo-Bangombé natural reactors

The discovery of the existence of chain reactions at the Oklo natural reactors in Gabon, Central Africa in 1972 was a triumph for the accuracy of mass spectrometric measurements, in that a 0.5% anomaly in the (235)U/(238)U ratio of certain U ore samples indicated a depletion in (235)U. Mass spectrometric techniques thereafter played a dominant role in determining the nuclear parameters of the reactor zones themselves, and in deciphering the geochemical characteristics of various elements in the U-rich ore and in the surrounding rock strata. The variations in the isotopic composition of a large number of elements, caused by a combination of nuclear fission, neutron capture and radioactive decay, provide a powerful tool for investigating this unique geological environment. Mass spectrometry can be used to measure the present-day elemental and isotopic abundances of numerous elements, so as to decipher the past history of the reactors and examine the retentivity/mobility of these elements. Many of the fission products have a radioactive decay history that have been used to date the age and duration of the reactor zones, and to provide insight into their nuclear and geochemical behavior as a function of time. The Oklo fission reactors and their near neighbor at Bangombé, some 30 km to the south-east of Oklo, are unique in that not only did they become critical some 2 x 10(9) years ago, but also the deposits have been preserved over this period of geological time. The long-term geochemical behavior of actinides and fission products have been extensively studied by a variety of mass spectrometric techniques over the past 30 years to provide us with significant information on the mobility/retentivity of this material in a natural geological repository. The Oklo-Bangombé natural reactors are therefore geological analogs that can be evaluated in terms of possible radioactive waste containment sites. As more reactor zones were discovered, it was realized that they could be classified into two groups according to their burial depth in the Oklo mine-site. Reactor Zones 10, 13, and 16 were buried more deeply, and were therefore less weathered than the other zones. The less-weathered zones are of great importance in mobility/retentivity studies and therefore to the question of radioactive waste containment. Isotopic studies of these natural reactors are also of value in physics to examine possible variations in fundamental constants over the past 2 billion years.     

Automated ultratrace determination of musty odiferous compounds from environmental waters by online purge and trap (P&T) gas chromatography–mass spectrometry (GC–MS)

Abstract

Odoriferous compounds are troublesome in natural waters in many parts of the world. The simultaneous determination of these complex compounds due to their low sample concentration and odor thresholds has been difficult. A simple, sensitive and automated technique for the determination of eight odoriferous compounds from aqueous samples was developed using online purge and trap (P&T) coupled to gas chromatography with mass spectrometry. P&T was selected to extract and purify the water samples. Several parameters that affect the extraction and concentration performance were investigated, including the trap sorbent, ionic strength, purge time, sample temperature and desorption time. Under the optimal conditions, the adsorption capacity for the Tenax TA sorbent to 2-isopropyl-3-methoxypyrazine, 4-chloroanisole, 2-isobutyl-3-methoxypyrazine, 2-methylisoborneol, 2-tert-butylphenol, 2,4-dichloroanisole, 2,4,6-trichloroanisole and geosmin reached an equilibration when sample volume was 25?ml at a concentration of 150.0?μg/l. The method provided good linearity in the range from 1.0 to1000?ng/l and the limits of detection were from 0.1 to 0.3?ng/l, which are below the odor thresholds for most of these compounds. The proposed method was applied to the determination of eight odoriferous compounds in surface and tap waters with recoveries from 74.7% to 112.8% and relative standard deviations from 2.6% to 10.8%. This method may be widely employed for monitoring odoriferous compounds in water samples.     

Note: Laser-induced acoustic desorption∕synchrotron vacuum ultraviolet photoionization mass spectrometry for analysis of fragile compounds and heavy oils

In this work, we coupled synchrotron vacuum ultraviolet photoionization (SVUV PI) method with the laser-induced acoustic desorption (LIAD) technique for mass spectrometric analysis. The LIAD technique is a "soft" desorption method, which could avoid the degradation of analytes during desorption process. Meanwhile, SVUV PI is an efficient "soft" ionization source. The new combination of the "soft" desorption technique and "soft" photoionization method is well suitable to reduce the difficulty for interpreting the mass spectra of the fragile compounds and heavy oils.     

Geographic analysis of the cultivation region of Ai pian derived from Blumea balsamifera through the determination of volatiles in the medicinal product and blood of treated mice by gas chromatography – mass spectrometry (GC-MS)

Abstract

Ai pian, derived from Blumea balsamifera (L.) DC. has various medicinal effects and a complex composition. The goal of this study was to analyze the chemical composition of Ai pian by using samples from different regions to explore differences between the chemical composition and its blood composition from treated mice to clarify whether its efficacy is related to synergism of multiple components to provide references for rational quality control. Gas chromatography – mass spectrometry (GC-MS) was used to determine and compare chemical compositions of blank and Ai pian containing serum of mice after 30?min of oral administration of Ai pian of seven batches from Zhenfeng, Wangmo and Luodian Counties; Guizhou Province; and Tian’e County; and Guangxi Province. Sixteen to twenty-two compounds of Ai pian were identified, with fourteen common compounds including L-borneol, L-camphor, borneol acetate, L-linalool, α-gurjunene, and 3-t-butyl-1, 2-dimethoxybenzene. Four to seven compounds were identified as blood components of Ai pian, and L-borneol, L-camphor, and borneol acetate were common prototypes with relative compositions from 13.720 to 36.509%, 2.336 to 5.219%, and 0.401 to 1.188%, respectively. Methyl oleate was a common metabolic component with a relative concentration of 0.021 to 0.446%. The chemical composition and blood components of Ai pian were complex, and its efficacy was related to synergism between several components including L-borneol, L-camphor, and borneol acetate. Therefore, detecting multiple index components of Ai pian is essential for quality control.     

Comparative study of the tribological behavior of self-lubricating W–S–C and Mo–Se–C sputtered coatings

Transition metal dichalcogenides (TMD) have been one of the best alternatives as low friction coatings for tribological applications, particularly in dry and vacuum environments. However, besides their deficient behavior in humid containing atmospheres, their extensive application has also been restricted due to their low load-bearing capacity. In order to overcome these problems, recently the alloying with C has been tried with the expectation of simultaneously improving the coatings hardness and reaching sliding contacting phases more convenient for achieving low friction in humid environments.The practical application of this concept was extensively studied with the W–S–C system, with the C addition being achieved either by reactive or co-sputtering processes. The best tribological results were obtained by co-sputtering from a C target embedded with an increasing number of WS₂ pellets. Excellent results were reached from the more than one order of magnitude increase in the coatings hardness up to friction coefficients which are close to those of the references of self-lubricating coatings: TMD for dry or vacuum atmospheres or C-based coatings for terrestrial sliding conditions.Following the good results achieved with W–S–C system, other TMDs systems have been envisaged to be studied. The main focus was placed on the Mo–Se–C system.In this paper, the general comparison between W–S–C and Mo–Se–C coatings is presented. The main effort is pointed on the tribological behavior of both systems when tested by pin-on-disk against steel counterpart balls under different testing conditions: applied normal loads, temperatures and relative humidity of the atmospheres. Both coatings were deposited by co-sputtering from a C target with a varying number of TMD pellets which could lead to C contents in the films in the range from 30  up to 70 at.%. A Ti interlayer was interposed between the films and the substrates for improving the adhesion.Typically, W–S–C films are harder than Mo–Se–C films. From the tribological point of view, W–S–C films are more thermally stable than Mo–Se–C films although the friction coefficients of these last ones are lower when tested in humid containing atmospheres.     

Mechanical and tribological properties of sputtered Mo–Se–C coatings

Transition metal dichalcogenides belong to the more developed class of materials for solid lubrication. However, the main limitation of these materials is the detrimental effect of air humidity causing an increase in the friction. In previous works, molybdenum diselenide has been shown to be a promising coating retaining low friction even in very humid environment. In this study, Mo–Se–C films were deposited by sputtering from a C target with pellets of MoSe₂. Besides the evaluation of the chemical composition, the structure, the morphology, the hardness and the cohesion/adhesion, special attention was paid to the tribological characterization.The C content varied from 29 to 68 at.% which led to a progressive increase of the Se/Mo ratio. As a typical trend, the hardness increases with increasing C content. The coatings were tested at room temperature with different air humidity levels and at temperatures up to 500 °C on a pin-on-disc tribometer. The friction coefficient of Mo–Se–C coatings increased with air humidity from ～0.04 to ～0.12, while it was as low as 0.02 at temperature range 100–250 °C. The coatings were very sensitive to the elevated temperature being worn out at 300 °C due to adhesion problems at coating–titanium interface.     

EDM of hybrid Al–SiCp–B4Cp and Al–SiCp–Glassp MMCs

Hybrid metal matrix composites are a class of material system, with two or more discrete particulate reinforcement. Notwithstanding their superior properties, their widespread application is constrained by the difficulty in machining them. Non-conventional processes such as electrical discharge machining can be applied to machine such composites. This work reports on the application of EDM to machine cast aluminum–silicon carbide–boron carbide and cast aluminum–silicon carbide–glass hybrid metal matrix composites and how the metal removal rate and surface finish vary in response to the various EDM parameters     

Deformation and stress of a composite–metal assembly

Compliant structures, e.g. automobile body panel and airplane wing box are widely used. A compliant structure consists of one or more flexible parts, and these parts share the mating features among them. Because of process-induced deformation and part-to-part variations, external forces are applied during the assembly process and the parts are deformed. As a result, the final assembly is pre-stressed and its geometrical shape may deviate from the designed shape. Therefore, the assembly variation and residual stress need to be analysed in order to evaluate the structure performance. In this study, a new approach based on response surface methodology is developed. A number of organised virtual experiments are conducted with the aid of finite element analysis and regression models are fitted to the resulting data. These regression models relate part variations to assembly variation and residual stress. Monte Carlo simulation can be conveniently done using these simple regression models. The effectiveness of this method was illustrated using a composite–metal assembly. It is shown that the method presented in this paper provides a practical and reliable solution to the analysis of compliant structures.     

Comparison between rubber–ice and sand–ice friction and the effect of loose snow contamination

The application of sand particles is a common method to improve the friction of aircraft tires on snow or ice covered runways. Hence, an understanding of the prevailing rubber–ice and sand–ice friction mechanisms is of practical interest. Rubber–ice and sand–ice friction measurements were made with a British Pendulum Tester at temperatures between ?22 and 0 °C and the effect of loose snow contamination on top of the ice was investigated. The results (the response of the instrument) were expressed in a sliding length averaged friction coefficient μ_BP. Close to the melting point the friction of rubber on ice was low and increased with decreasing ice temperature. Below ?5 °C, reasonably high friction levels (0.2<μ_BP<0.5) were obtained between rubber and ice, but the friction level dropped drastically by the presence of a very thin layer of snow. The sand–ice friction level was less dependent on ice temperature and clearly not as much affected by the presence of snow, compared to rubber–ice friction. The micromechanisms involved in rubber–ice and sand–ice frictions were investigated by the application of etching and replicating technique (ERT) developed for the examinations of the dynamics of dislocations in ice during deformation.     

Effect of Plasma Nitriding Environment and Time on Plain Fatigue and Fretting Fatigue Behavior of Ti–6Al–4V

Plasma nitriding was performed on Ti–6Al–4V fatigue test samples at 520°C in two environments (nitrogen and nitrogen–hydrogen mixture in a ratio of 3:1) for two time periods (4 and 18 h). Plain fatigue and fretting fatigue tests were conducted on unnitrided and plasma nitrided samples. Plasma nitriding degraded lives under both plain fatigue and fretting fatigue loadings. The samples nitrided in nitrogen exhibited superior lives compared with the samples nitrided in the nitrogen–hydrogen mixture, possibly due to the relatively higher hardness (and presumably lower toughness) of the nitrided layer of the samples nitrided in the nitrogen–hydrogen mixture environment. For those samples nitrided in the nitrogen–hydrogen mixture, those nitrided for 18 h exhibited superior lives compared with those nitrided for 4 h. This trend was observed for samples nitrided in nitrogen gas at lower stress levels only; the converse was true at higher stress levels of 550 MPa and 700 MPa under plain fatigue loading. However, under fretting fatigue loading, the plasma nitriding time did not influence the lives significantly.     

Relations of counterface materials with stability of tribo-oxide layer and wear behavior of Ti–6.5Al–3.5Mo–1.5Zr–0.3Si alloy

Dry sliding wear tests of Ti–6.5Al–3.5Mo–1.5Zr–0.3Si alloy (TC11 alloy) sliding against AISI 52100 and AISI M2 steels were performed under the load of 50–250 N at 25–600 °C. For two kinds of counterface materials, the titanium alloy presented totally different wear behaviours as the function of temperature. The appreciable variations of the titanium alloy sliding against different counterface materials were attributed the fact that a hard counterface caused unstable existence of tribo-layers by its microcutting action, thus resulting in the increase of wear rate. It is suggested that the hard counterface must be avoided as the counterface for the titanium alloy/steel sliding system.     

Tribological Properties of Twin Electron-Beam Evaporated Cr–N and Al–Cr–N Coatings Under Laboratory Sliding and Drill Experiments

The tribological behavior of substoichiometric Cr–N and Al–Cr–N coatings prepared by twin electron-beam evaporation at 450 °C was studied. Al–Cr–N coatings with Al to Cr ratios in the range of 1–8 (and nitrogen concentrations of ~45 at.%) were synthesized and compared to Cr–N reference samples. The focus of this work is on Al–Cr–N (Al ≥ 30 at.%) coatings with the aim of (a) replacing Cr with Al due to environmental concerns and (b) achieving improved mechanical properties, and tribological performance. The composition, structure, mechanical and tribological properties of the coatings were determined using X-ray photoelectron spectroscopy, X-ray diffraction, and scanning electron microscopy in combination with nanoindentation measurements, laboratory controlled ball-on-disk sliding experiments, and wet and dry drilling experiments. It was found that all Al–Cr–N coatings exhibit higher hardness values compared to Cr–N coatings. Al–Cr–N coatings with Al contents and Al/Cr ratios of ≤38 at.% and ≤1.7, respectively, showed better performance than the rest of the coatings during both drilling and laboratory tribological experiments.     

Role of Third Bodies in Friction and Wear of Cold-Sprayed Ti and Ti–TiC Composite Coatings

Titanium (Ti) and Ti-based alloy wear performance is often poor unless coating or lubricants are used. An alternative is to use hard phase reinforcement. Cold spray is a relatively new method to deposit composite coatings, where here we report the deposition of a Ti–TiC coating and its sliding wear behavior. Mixtures of mechanically blended Ti–TiC with various TiC content were injected into a de Laval nozzle and sprayed onto substrates. Two composite coatings and a pure Ti coating are reported here, where the as-sprayed compositions of the composites were 13.8 and 33.4 vol% TiC. Reciprocating dry sliding wear was performed using a custom-built in situ tribometer. All tests were conducted with a sliding speed of 3 mm/s and at a normal load of 0.5 N. Using a transparent sapphire hemisphere of 6.25 mm as counterface, dynamic behavior of third bodies was directly observed. It was found that adhesive transfer of Ti was the primary wear mechanism for the Ti coating, with oxidative and abrasive wear also occurring for longer sliding cycles. The superior wear resistance of the composite coatings compared to Ti was related to dual function of TiC particles, where they reinforced the Ti matrix and facilitated the formation of a stable and protective tribofilms. The tribofilms contained carbonaceous material that provided easier shear and lower friction. The formation of these tribofilms was highly dependent on the TiC particles, which contained excess carbon compared to the equilibrium composition. Higher TiC content was more effective in quickly developing and sustaining the tribofilms.     

Lubrication of aluminium–silicon surfaces with ZDDP and detergents

Abstract

A review of the lubrication of aluminium–silicon (Al-Si) substrates by zinc dialkyldithiophosphate (ZDDP) and detergent engine oil additives is presented. Greater attention has been paid to understand the interactions of ZDDP, rather than detergents, with the aforementioned non-ferrous substrates. Zinc dialkyldithiophosphate generates tribofilms on both aluminium and silicon regions of aluminium–silicon alloys. However, film formation is believed to occur on silicon grains within the alloy, and those layers observed on aluminium regions are material transfer or the product of ZDDP thermal decomposition. There were many similarities in terms of film thickness, reduced elastic modulus, tribochemistry and topography of ZDDP derived tribofilms on both ferrous and Al–Si substrates. Calcium carbonate based films were observed on silicon grains when the aluminium alloys were lubricated with overbased calcium sulphonate, the tribochemistry and topography of which were similar to layers formed on ferrous substrates. When lubricated with either fully formulated oil or lubricants containing both detergent and ZDDP, the subsequently generated films were of varying chemistry, but often contained zinc or calcium phosphate compounds. The antiwear characteristics of ZDDP and calcium sulphonate tribofilms on ferrous and aluminium–silicon substrates are discussed, with the mechanical and film thickness data for such layers presented.     

Development of High-Speed On–Off Valves and Their Applications

With the widespread application of the computer and microelectronic technology in the industry, digitization becomes the inevitable developing trend of the hydraulic technology. Digitization of the hydraulic components is critical in the digital hydraulic technology. High-speed on-off valves(HSVs) which convert a train of input pulses into the fast and accurate switching between the on and off states belong to widely used basic digital hydraulic elements.In some ways, the characteristics of the ...     

Dielectric and Optical Properties of Strontium–Barium Niobate Films in the Range of 0.2–1.3 THz

The knowledge of optical and dielectric properties of ferroelectric films, in particular, strontium–barium niobate films, in the terahertz spectral range is needed to use these films as a basis of active elements and structures for detection and control of terahertz radiation. The properties of strontium–barium niobate films with x = 0.5 grown on oriented sapphire substrates with a deposited electrode are studied by the method of terahertz time-domain spectroscopy in the spectral range of 0.2–1.3 THz. It is found that strontium–barium niobate films can be used to develop devices for detection and control of terahertz radiation.     

Parameter optimization and mechanism of laser–arc hybrid welding of dissimilar Al alloy and stainless steel

Laser–cold metal transfer arc hybrid welding of 6061 Al alloy and AISI304 stainless steel (304SS) was carried out. Bead morphologies and intermetallic compound (IMC) layer characterizations of the joints were studied in detail. The optimal parameter range for accepted bead appearances (OPRBA) without surface and interface defects was obtained, and the growth mechanism of the IMC layer was summarized. The results showed that the nonuniformity in the thickness and shape along the fusion zone/304SS interface from the top surface to the bottom increases with increasing heat input and is more sensitive to laser power because the interface temperature is dominated by a high-temperature laser keyhole throughout the molten pool. As the welding parameters are within the OPRBA and the heat input is within the range of 80–110 J/mm, the joints are stronger than 130 MPa and the corresponding IMC layer thickness is at the range of 3–6.5 μm. The kinetic analysis showed that a controlling interface temperature no more than 1,120 °C may limit the growth of the IMC layer.     

Microstructural and abrasive characteristics of high carbon Fe–Cr–C hardfacing alloy

A series of high carbon Fe–Cr–C hardfacing alloys were produced by gas tungsten arc welding (GTAW). Chromium and graphite alloy fillers were used to deposit hardfacing alloys on ASTM A36 steel substrates. Depending on the four different graphite additions in these alloy fillers, this research produced hypereutectic microstructures of Fe–Cr phase and (Cr,Fe)₇C₃ carbides on hard-facing alloys. The microstructural results indicated that primary (Cr,Fe)₇C₃ carbides and eutectic colonies of [Cr–Fe+(Cr,Fe)₇C₃] existed in hardfacing alloys. With increasing the C contents of the hardfacing alloys, the fraction of primary (Cr,Fe)₇C₃ carbides increased and their size decreased. The hardness of hardfacing alloys increased with fraction of primary (Cr.Fe)₇C₃ carbides. Regarding the abrasive characteristics, the wear resistance of hardfacing alloys were related to the fraction of primary (Cr,Fe)₇C₃ carbides. The wear mechanism was also dominated by the fraction of primary (Cr,Fe)₇C₃ carbides. Fewer primary carbides resulted in continuous scratches worn on the surface of hardfacing alloy. In addition, the formation of craters resulted from the fracture of carbides. However, the scratches became discontinuous with increasing fraction of the carbides. More primary carbides can effectively prevent the eutectic colonies from the damage of abrasive particles.     

Experimental and theoretical analysis of friction stir welding of Al–Cu joints

This paper presents a study of friction stir welding of aluminium and copper using experimental work and theoretical modelling. The 5083-H116 aluminium alloy and pure copper were successfully friction-stir-welded by offsetting the pin to the aluminium side and controlling the FSW parameters. A theoretical analysis is presented along with key findings. The process temperatures are predicted analytically using the inverse heat transfer method and correlated with experimental measurements. The temperature distribution in the immediate surroundings of the weld zone is investigated together with the microstructures and mechanical properties of the joint. This was supported by a finite element analysis using COMSOL Multiphysics. In this study, two rotational speeds were used and a range of offsets was applied to the pin. The microstructure analysis of the joints was undertaken. This revealed some particles of Cu inclusion in the nugget zone. The energy dispersive spectroscopy showed a higher diffusion rate of aluminium towards the interface while copper maintained a straight base line.