DETERMINATION OF PICOMOLE CONCENTRATIONS OF ALUMINUM (III) IN HUMAN SALIVA AND URINE BY A LUMINOL-CARBOXYMETHYL CHITOSAN CHEMILUMINESCENCE SYSTEM

A luminol–carboxymethyl chitosan (CMCS) system was established using flow injection chemiluminescence (CL) based on the enhancing effect of CMCS on the luminol–dissolved oxygen reaction. The CL intensity was linear with the CMCS concentration ranging from 0.01–30.0 µM. Al(III) was shown to quench the CL of the luminol–CMCS reaction, and the decrease of CL intensity was linear with the logarithm of Al(III) concentration over the range from 10–1000 pM with a detection limit of 3.5 pM (3σ). At a flow rate of 2.0 mL min^?1, the analysis was performed within 30 s. The proposed CL method was successfully applied to the determination of picomole levels Al(III) in human saliva and urine after oral intake of two aluminum hydroxide tablets, with recoveries from 90.6–108.7% and relative standard deviations <3% (n = 5). The results indicated that the excreted Al(III) in saliva and urine reached its maximum values at 3 hr and 2 hr, and the total excretive ratio were 1.24 × 10^?3% and 3.45% in 6 hr and 12 hr, respectively. The elimination rate constant k and the half–life time t _1/2 in human saliva and urine were 0.3747 hr^?1, 1.8495 hr, 0.7132 hr^?1, and 0.9717 hr, respectively. The possible CL mechanism of the luminol–CMCS–Al(III) reaction is discussed.     

STUDY ON THE INCLUSION INTERACTION BETWEEN SULFOBUTYLETHER-β-CYCLODEXTRIN AND CLOZAPINE BY FLOW INJECTION CHEMILUMINESCENCE

The inclusion interaction of sulfobutylether-β-cyclodextrin with clozapine was studied using flow injection chemiluminescence and molecular docking. By use of a homemade flow injection chemiluminescence model of lg[(I ₀?I _s)/I _s] = lgK + nlg[C _clozapine], the formation constant K, the stoichiometric ratio n, and thermodynamic parameters between sulfobutylether-β-cyclodextrin and clozapine were obtained. Results showed that the inclusion forming process of sulfobutylether-β-cyclodextrin/clozapine with a stoichiometric ratio of 1:1 was spontaneous through hydrophobic interaction. The molecular docking results showed that clozapine entered into the cavity of sulfobutylether-β-cyclodextrin with one hydrogen bond. Based on the good linear relationship of quenching of chemiluminescence intensity versus the logarithm of concentration between 0.07 and 50.0 ng mL^?1, a flow injection chemiluminescence method for clozapine was established for the first time with a detection limit of 0.02 ng mL^?1 (3σ). The proposed method was successfully applied for the determination of clozapine in spiked human urine and serum samples, with recoveries from 92.1–108.2% and relative standard deviations less than 2.7%.     

Mechanical and tribological properties of Cr–Nb double-glow plasma coatings deposited on Ti–Al alloy

Double-glow plasma (DGP) coatings are recommended for metallic components to mitigate the damage induced by complex working conditions in previous studies. In this paper, Nb-rich (Cr–Nb₄) and Cr-rich (Cr₄–Nb) -alloyed layers were formed onto the Ti–Al substrate via a DGP process to enhance its wear resistance. Scratch and Nano-indentation tests were used to evaluate the mechanical properties of the coatings. The tribological behaviour of the coatings were investigated using a pin-on-disc tribometer by rubbing against the GCr15 ball. Results from surface analysis techniques showed that the coatings mainly comprised Cr, Nb and Cr₂–Nb phases, and were well bonded to the substrate. The hardness of the Cr–Nb₄ coating was 11.61GPa and the Cr₄–Nb coating was 9.66 GPa which all higher than that of the uncoated Ti–Al which was 5.65 GPa. However, the critical load of the Cr₄–Nb coating ~21.64 was higher than that of the Cr–Nb₄ coating ~17.6. And the specific wear rate of Cr–Nb₄ coating, Cr₄–Nb coating and uncoated Ti–Al were 3.54 × 10^?4, 0.01 × 10^?4 and 1.53 × 10^?4mm³ N^?1 m^?1_, respectively. The low-wear mechanism of the coatings is discussed in detail in this paper.     

Characterization of the interaction between bovine serum albumin and doxycycline by chemiluminescence and molecular docking

The interaction of bovine serum albumin with doxycycline was investigated using chemiluminescence and molecular docking. Doxycycline at concentrations from 1.0 to 2.5 × 10³ pmol · L^?1 quenched the chemiluminescence from the luminol–bovine serum albumin system. The data were analyzed using a chemiluminescence mathematic model for protein–ligand interaction, log[(I₀ – I)/I] = logK + nlog[D]. The binding constant of bovine serum albumin with doxycycline was 3.36 × 10⁵ L · mol^?1 at 298 K with one binding site. The binding constant, enthalpy change, entropy change, and binding free energy change showed that the bonding of doxycycline to bovine serum albumin was spontaneous and enthalpy driven via hydrogen bonding and van der Waals forces. Further molecular docking analysis substantiated that doxycycline was well positioned in the pocket at the subdomain IIA (site I) of bovine serum albumin with a binding constant of 3.31 × 10⁵ L · mol^?1. Doxycycline served as both a hydrogen acceptor and donor and mainly interacted with the Arg217 residue through four hydrogen bonds with an average length of 2.55 Å. The chemiluminescence mechanism of doxycycline on luminol–bovine serum albumin system was evaluated, showing that a ternary complex of luminol–bovine serum albumin–doxycycline was formed with luminol and doxycycline at sites III and I of bovine serum albumin.     

Contact resistance and saturation effects in the scanning tunnelling microscope: the resistance quantum unit

We present a theoretical analysis of the contact resistance in the Scanning Tunnelling Microscope. Under the assumption of a single contact atom on the tip's apex, we find that the resistance saturates at close contact, its value being h/2e². Our analysis of the recent experimental results of Gimzewski & Möller (1987), shows that the mechanical instability pradicted by Pethica & Sutton (1988), appears for a distance 1·5 Å larger than the close contact distance between the tip and the sample.     

Effect of counterface balls on the friction layer of Ni3Al matrix composites with 1.5 wt% graphene nanoplatelets

Research on the friction layer is needed to minimize friction- and wear-related mechanical failures in moving mechanical assemblies. Dry sliding tribological tests of Ni₃Al matrix composites (NMCs) with 1.5 wt% graphene nanoplatelets (GNPs) sliding against different counterface balls are undertaken at the condition of 10 N–0.234 m s^?1 in this study. When sliding against GCr15 steel, a uniform and thick friction layer is formed, resulting in a lower friction coefficient (0.29–0.31) and wear rate (2.0–3.1 × 10^?5 mm³ N^?1 m^?1). While sliding against Al₂O₃ and Si₃N₄, the formation and stability of the friction layers are restricted in the severe wear regime, and the NMCs exhibit higher friction coefficients and wear rates. Therefore, various counterface balls have a great effect on the stability and thickness of the friction layer, thus affecting the tribology performance of NMCs. The result also shows that GNPs exhibit enrichment and self-organized microstructures in the friction layer. In addition, the friction layer is also found to be divided into two layers, protecting the subsurface from further damage and reducing shear.     

Pulse current auxiliary TLP diffusion bonding of SiCp/2024Al composite sheet using mixed Al–Cu–Ti powder interlayer

Pulse current auxiliary transient liquid-phase (TLP) diffusion bonding of SiCp/2024Al composite sheet was investigated at 580 °C using mixed Al–Cu–Ti powder interlayer. The optimal process parameters were applied as follows: pulse current density of 1.15?×?10² A/mm², pressure of 0.5 MPa, vacuum of 1.3 ×?10^?3 Pa, and bonding time from 15 to 60 min. The bonding quality is evaluated by microstructure characterization and mechanical properties of the joints. The mechanism of pulse current auxiliary TLP diffusion bonding process is analyzed. The results indicated that the dense joints without cavity consisted of the Al-based solid solution, pure Ti, Al₂Cu, and TiAl₃ intermetallic phase. Microhardness of joints was obviously higher than Cu diffusion zone and substrate materials zone. The shear strength of the joints monotonically increased with bonding time. The maximum value exceeded 154.1 MPa in bonding time of 60 min. Pulse current generated Joule heat, high-temperature spark plasma, and electromigration, which guarantee the feasibility of bonding process and high-quality joint.     

Preparation of STM tips for in-situ characterization of electrode surfaces

The total current between the tip and the sample in a scanning tunnelling microscopy study of a solid/liquid interface can be dominated by Faradaic charge transfer currents. In such a situation, feedback control of the tunnelling gap, and imaging, is precluded. In this contribution we describe the preparation of glass and polymer coated STM tips that possess < 100 Ų of exposed metal. These tips effectively discriminate against Faradaic current and enable STM imaging in the presence of reversible electroactive solution species at appreciable tip/sample biases.     

Determination of propyl gallate in edible oil by high-performance liquid chromatography with chemiluminescence detection

A novel and convenient method based on high-performance liquid chromatography coupled with chemiluminescence (HPLC) for the determination of propyl gallate in edible oil is reported. The detection was based on the inhibition of chemiluminescence between luminol and hydrogen peroxide in alkaline solution. The analysis was performed using a C₁₈ column with isocratic 60:40 methanol/water. Under the optimum conditions, the concentration of propyl gallate was linear from 9?×?10^?6?mol?L^?1 to 1?×?10^?4?mol?L^?1 with a detection limit of 2?×?10^?7?mol?L^?1. The method is simple, sensitive, and inexpensive and was used for the determination of propyl gallate in edible oil.     

Optimized design for time-of-flight total neutron scattering instrumentation using Monte Carlo simulations with application for the characterization of disordered macromolecules

Abstract

A time-of-flight neutron total scattering instrument for the China Spallation Neutron Source (CSNS) was designed. The instrument is designed for disordered macromolecular systems with characteristic lengths below 10?nm. The coupled hydrogen moderator of CSNS was selected to ensure the favorable statistics at the smallest scattering vector of 0.01?Å^?1. The optics and geometry of the instrument were optimized to cover a wide range of scattering vectors from 0.01 to 70?Å^?1. The performance of the instrument was examined using a series of Monte Carlo simulations, which demonstrate that the flux on the sample, the resolution, and the range of the scattering vectors are comparable to those of other advanced neutron total instruments. Finally, a virtual experiment was performed with silica powder. The resulting scattering pattern is consistent with both the numeric calculation and the estimated resolution of the instrument. The designed total scattering instrument at CSNS allows the simultaneous observation of both atomic and nanometer scale structures, having the potential to become a powerful tool for studying the structure of disordered materials in the fields of polymers, biology, and condensed matter physics.     

Electron beam damage of behenic acid films

The rate of fading of electron diffraction patterns of behenic acid monolayer crystals as well as multilayer crystals was measured at 100 kV at room temperature to investigate the dependence of beam damage on specimen thickness. The diffracted intensities for monolayers and double layers decreased nearly exponentially with electron exposure; however, the intensities for multilayers were unchanged during initial electron exposures, often increased temporarily and then decreased with electron exposure. The critical dose, D_e, defined as the dose at which the diffracted intensity falls to 1/e of its initial value, was 1.0 electrons/Ų for the monolayers, 1.8 electrons/Ų for the double layers and more for multilayers. These results lead to the conclusion that D_e for behenic acid increases nearly linearly with specimen thickness in the range of about 25–100 Å for dose rate of 0.1–2 electrons/Ų min.     

Effect of the Synergetic Action on Tribological Characteristics of Ni-Based Composites Containing Multiple-Lubricants

Ni-based self-lubricating composites with multiple-lubricants addition were prepared by a powder metallurgy technique, and the effect of multiple-lubricants on tribological properties was investigated from room temperature to 700?°C. The synergetic effects of graphite, MoS₂, and metallic silver lubricants on the tribological characteristics of composites were analyzed. XRD analysis showed that new Cr _x S _y and Mo₂C phase were formed in the composites containing graphite, MoS₂ and metallic Ag lubricants during the sintering process. The average friction coefficients (0.69?C0.22) and wear rates (11.90?C0.09?×?10^?5?mm³?N^?1?m^?1) were obtained when rubbing against Inconel 718 alloy from room temperature to 700?°C due to synergetic lubricating action of multiple-lubricants. A smooth lubricating was gradually generated on the worn surface, and the improving of tribological properties was attributed to the formation of lubricious glaze film on the worn surface and their partially transferred to the counterface. The graphite played the main role of lubrication at room temperature, while molybdate phase and graphite were responsible for low friction coefficients and wear rates at mid/high temperatures. The synergetic lubricating effect of molybdate (produced in the rubbing process at high temperatures) iron oxide (transfer from disk material to the pin) and remaining graphite multiple-lubricants play an important lubricating role during friction tests at a wide temperature range.     

A HYDROGEN PEROXIDE SENSOR BASED ON PRUSSIAN BLUE AND DNA-MODIFIED ELECTRODE

The polyvinylpyrrolidone (PVP) protected Prussian blue (PB) nanoparticles were prepared for use as a sensor for the catalytic reduction of hydrogen peroxide. The nanoparticles were used to modify a gold electrode, which was applied to detect hydrogen peroxide. Impedance spectra and differential pulse voltammetry were applied to detect the performance of the novel electrode and its response to H₂O₂ and Ramos cell smash fluid. Under the optimized experimental conditions, hydrogen peroxide was detected in a linear range of 6.25 × 10^?7 to 1.0 × 10^?5 mol · L^?1, and the detection limit was 7.12 × 10^?8 mol · L^?1 according to 3σ rule. Under the same conditions, hydrogen peroxide was determined in Ramos cell smash fluid with a linear range from 400–80000 mol mL^?1, with a detection limit of 114 mL^?1 according to 3σ rule. The modified electrode with Prussian blue nanoparticles displayed high sensitivity, good reproducibility, and long-term stability to hydrogen peroxide.     

Tribological Properties of Adaptive Ni-Based Composites with Addition of Lubricious Ag2MoO4 at Elevated Temperatures

The Ni-based self-lubricating composites with addition of 10 and 20?wt% Ag₂MoO₄ were fabricated by powder metallurgy technique, and the effect of Ag₂MoO₄ on tribological properties was investigated from room temperature to 700?°C. The tribo-chemical reaction films formed on rubbing surface and their effects on the tribological properties of composites at different temperatures were addressed according to the surface characterization by SEM and Micro-Raman. The results show that the Ag₂MoO₄ decomposed into Ag and Mo during the high-temperature fabrication process. The friction coefficient and wear rate of the composites decrease with the increasing of temperature and Ag₂MoO₄ contents and the composites with addition of 20?wt% Ag₂MoO₄ exhibits the lowest friction coefficient (0.26) and wear rate (1.02?×?10^?5?mm³?N^?1?m^?1) at 700?°C. The composition of the tribo-layers on the worn surfaces of the composites is varied at different temperatures. It is proposed that the improving of tribological properties of the composites at high temperatures are attributed to the synergistic lubricating effect of silver molybdate (reproduced in the rubbing process at high temperatures) and Fe oxide (transfer from disk material to the pin) formed on the worn surface.     

DETERMINATION OF TRACE CADMIUM BY FLOW INJECTION ON-LINE MICROCOLUMN PRECONCENTRATION COUPLED WITH FLAME ATOMIC ABSORPTION SPECTROMETRY USING HUMAN HAIR AS A SORBENT

A novel method using a cone-shaped pipette tip packed with human hair as an adsorption material has been developed for the on-line flow injection preconcentration of trace Cd(II) ions based on its complex formation with the ammonium pyrrolidine dithiocarbamate (APDC) prior to flame atomic absorption spectrometric (FAAS) determination. Cd-PDC complex sorbed on the human hair was eluted by 4.0 mol L^?1 HNO₃. The enhancement factor is 19, and the detection limit (3σ) is 0.77 μg L^?1. The proposed method was successfully applied to the determination of trace cadmium in drinking water, beverage samples, and the certified reference materials.     

Dislocations in nanostructured two‐phase Fe30Ni20Mn20Al30

In a previous study, the dislocations in Fe₃₀Ni₂₀Mn₂₅Al₂₅ (at. %), which consist of 50 nm wide alternating b.c.c. and B2 phases, were shown to have a/2<111> Burgers vectors after room temperature deformation. The dislocations were found to glide in pairs on both {110} and {112} slip planes and were relatively widely separated in the b.c.c. phase, where the dislocations were uncoupled, and closely spaced in the B2 phase, where the dislocations were connected by an anti‐phase boundary. In this article, we analyze the dislocations in the two ～5 nm‐wide B2 phases in a related two‐phase alloy Fe₃₀Ni₂₀Mn₂₀Al₃₀, with compositions Fe‐23Ni‐21Mn‐24Al and Fe‐39Ni‐12Mn‐34Al, compressed to ～3% strain at a strain rate 5 × 10^?4 s^?1 at 873 K (the lowest temperature at which substantial plastic flow was observed). It is shown that slip occursby the glide of a<100> dislocations. A review of the literature suggests that the differences in the observed slip vector between these B2 phases could be due to the differences in composition, differences in deformation temperature, or possibly both. Microsc. Res. Tech. 76:263–267, 2013. © 2013 Wiley Periodicals, Inc.     

Friction Characteristics in Vacuum of Single and Polycrystalline Aluminum Oxide in Contact with Themselves and with Various Metals

Friction experiments were conducted in vacuum with outgassed surfaces. Experiments were made with single and polycrystalline Al₂O₃, sliding on themselves and in contact with metals at a sliding velocity of 0.013 cm per second, at loads to 1500 gm, temperatures to 575 C and ambient pressures to 10^?10 mm Hg. These studies were made with a hemispherical or spherical rider sliding on the flat of a rotating disk. The results of the investigation indicate that (a) the friction characteristics of sapphire sliding on sapphire is highly anisotropic, (b) with metals sliding on sapphire, fracture in sapphire occurs while with polycrystalline Al₂O₃ shear occurs in the metal, and (c) hexagonal metals exhibited lower friction co-efficients than cubic metals in contact with polycrystalline Al₂O₃.     

Radiation damage to lyophilized mineral solutions during electron probe analysis: quantitative study of chlorine loss as a function of beam current-density and sample mass-thickness

The quantitative effects of beam current-density and sample mass-thickness on the loss of chlorine which occurs from lyophilized solutes of micro-droplets of mineral salt solutions irradiated in an electron probe analyser were studied. Results are reported for chlorine loss from lyophilized deposits with mass-thickness varying between 5 and 50 mg mm^?2 for NaCl salts and 5 and 80 mg mm^?2 for KCl salts. Electron accelerating voltage was kept constant at 15 kV. The range of beam current-density (I/S, current/sample surface area) was from 0.1 to 1.5 A mm^?2. Samples were irradiated for 1200 s. The results show that under some conditions there is a period of stable chlorine signal before chlorine loss occurs. This is observed between 0.1 and 1 A mm^?2, for a period which can last several hundred seconds depending on beam current-density and sample mass-thickness. For each value of I/S, however, no stable chlorine signal can be observed for samples whose mass-thickness exceeds a value negatively correlated with I/S. The curves of decrease of characteristic chlorine X-ray signal (expressed as per cent of count rate in the initial counting interval) versus irradiation time can be fitted by the sum of two exponentials with half lives T₁ and T₂. In NaCl, T₁ and T₂ values are highly correlated with I/S but not with mass-thickness. In KCl, T₁ is correlated only with mass-thickness and T₂ only with I/S. Mixing plasma with mineral solutions prevents chlorine loss.     

Re(de)construction-induced friction signatures of polished polycrystalline diamond films in vacuum and hydrogen

Pin-on-flat SEM tribometry was performed with polished, mostly C(100)-textured and acid-cleaned polycrystalline CVD diamond films heated to 950°C then cooled to room temperature. Testing in~1.33×10^-3 Pa = 1× 10^-5 Torr vacuum was followed by similar experimentation in 13 to 40 Pa (0.1to 0.3 Torr) partial pressures of 99.999%-pure H₂. In vacuum, all tests showed the characteristic step function-with-trough coefficient of friction (COF) signatures previously hypothesized as footprints of wear- and thermal desorption-induced generation, re(de)construction and passivation of the danglingσ bonds on the interacting surfaces. In hydrogen, all wear tracks exhibited stepfunction-like COF curves caused by adsorbate de(re)sorption on heating and cooling. A distinct re(de)construction COF trough obtained at the highest temperatures could be duplicated during repeated sliding in the same track on a large number (but not all) of the wear paths. The repeatable, incremental reduction in COF at the onset of heating and its substantial reduction on final cooling are attributed to tribocatalytically enhanced dissociative chemisorption of molecular hydrogen. The wear rates of the polished diamondon the pin tip, as controlled by the progressively reduced unit stresses caused by the enlargement of the wear scar, are between3.9×10^-16 and 2.6×10^-16m³/(N m) in P_{H 2}, in good agreement with previous data. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effect of Ag and Ti3SiC2 on Tribological Properties of TiAl Matrix Self-lubricating Composites at Room and Increased Temperatures

Dry sliding tribological properties of TiAl matrix self-lubricating composites (TMSC) containing Ag, Ti₃SiC₂, Ag and Ti₃SiC₂ were investigated from 25 to 800 °C under ball-on-disk test conditions against Si₃N₄ counterface under the same conditions of 10 N-0.234 m/s. The results indicated that the tribological properties were strongly dependent on the lubricant additives. TMSC with the addition of Ag and Ti₃SiC₂ (TAT) exhibited the lower friction coefficients (0.32–0.43) and less wear rates (1.23–4.13 × 10^?4 mm³ N^?1m^?1) in the wide temperature range of 25–800 °C. The excellent tribological properties of TAT over the wide temperature range were attributed to the synergetic effect of Ag and Ti₃SiC₂ lubricants, silver diffusion forming a rich-silver smooth tribo-film on the frictional surface of TAT at low and moderate temperatures from 25 to 400 °C, while Ti₃SiC₂ oxidation reaction forming rich-oxide tribo-film on the worn surface of TAT at higher temperatures of 600 and 800 °C.