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Atomic-Scale Simulation of Tribological and Related Phenomena
Published in Bharat Bhushan, Handbook of Micro/Nano Tribology, 2020
Judith A. Harrison, Steven J. Stuart, Donald W. Brenner
Simulations of adsorbed monolayers of rare gas atoms are also found in the literature. These studies typically make comparisons with quartz crystal microbalance (QCM) experiments. Early QCM experiments by Krim and co-workers (Watts et al., 1990; Krim et al., 1991) examined the friction between adsorbed gas atoms (Ar, Kr, Xe) and a (111)-oriented noble metal substrate (Au or Ag). Krypton adsorbed on Au first as islands of liquid. These islands grew in size until the gas atoms were adsorbed as an entire monolayer. (This monolayer existed as a disordered, two-dimensional liquid at low doses.) For Kr, as more atoms were adsorbed, the liquid became denser and eventually underwent a phase change into a crystalline state that was incommensurate with the Au substrate. Krim and co-workers observed that both the solid and liquid Kr monolayers exhibited a viscous force law, meaning that no threshold force was needed to initiate the sliding and the friction was proportional to the relative velocity. This behavior is more commonly associated with the macroscopic friction of liquids. In addition, Krim and co-workers determined that the solid monolayers slid more easily than the liquid monolayers. That is, the frictional force on the solid monolayer was less than the force on the liquid monolayer and the force on the liquid monolayer was approximately three orders of magnitude weaker than that between Kr layers in a bulk fluid.
HPLC-Hyphenation
Published in Grinberg Nelu, Rodriguez Sonia, Ewing’s Analytical Instrumentation Handbook, Fourth Edition, 2019
R.A. Shalliker, M. J. Gray, D. Kocic, S. Pravadali-Cekic
EI, CI, and electron capture [43] spectra can be produced with this interface. Although the interface provides excellent results in the analysis of polyaromatic hydrocarbons and flavonoids, it does have some problems. Poor linearity with regard to variation in different concentrations of p-phenylenediamine [38] has been observed. However, this has been partially solved by the addition of mobile phase additives (ammonium acetate/oxalate). Also, a non-linear response has been observed for p-phenylenediamine in the presence of co-eluting compounds [38]. Peak area response also may decrease with a decrease in the volatility of the mobile phase [39]. This indicates that the interface may perform poorly during gradient elution chromatography. Therefore, the strength of PB and MA GIC LC-MS lies in isocratic normal phase separations [44]. Non-linear responses due to co-eluting substances are easily resolved through the recent developments of two-dimensional liquid chromatography [44]. With this in mind, particle beam instruments are still used in conjunction with two-dimensional liquid chromatography in the analysis of vitamin D [44] (using CI and ammonia as the reagent gas). An advantage of this interface (even though it is no longer commercially available) is that spectral information can be applied to current mass-market spectral libraries for structural elucidation.
Liquid Crystal Thermography on the Rotating Surfaces of Turbomachinery Systems
Published in Chunill Hah, Turbomachinery Fluid Dynamics and Heat Transfer, 2017
The current experiments described in this paper have been performed by generating a completely axisymmetric flow and heat transfer situation on the rotating disk surface. Because of the infrared measurement system’s finite time response (80 milliseconds), the measurement has been time averaged over six rotations of the disk at 0.135 m radius, at 5000 rpm. Time averaged character of infrared measurements is not an influencing factor as long as the flow and heat transfer parameters do not vary in circumferential direction. Rotating disk problems may have variations in axisymmetric direction in applications other than perfect free disk problems. For example, the existence of a bolt head or a step may cause a strong temperature distribution in both the radial and the circumferential directions. When thermal nonuniformities in the circumferential direction and radial direction are introduced, freezing the liquid crystal image by using a stroboscope light can be extremely beneficial. A stationary visual image of the liquid crystal coated surface can provide an accurate two-dimensional liquid crystal view of a highly three-dimensional thermal field on a rotating surface.
Emerging contaminants in the atmosphere: Analysis, occurrence and future challenges
Published in Critical Reviews in Environmental Science and Technology, 2019
Pedro José Barroso, Juan Luis Santos, Julia Martín, Irene Aparicio, Esteban Alonso
Regarding sample treatment procedures, many studies reported different techniques of extraction, purification and analysis for different families of EC in air, although few of them were developed for multiresidue analysis. Future methodologies should extend the spectrum of compounds that can be determined. Soxhlet and USE are still the most used techniques when dealing with EC in the air matrix. Although these techniques are now automatized, they are still long, time consuming and require large volumes of solvents. Future efforts should focus towards environmental friendliness, low cost, miniaturization, automation and simplicity. New developments such as in vivo-SPME and microdialysis have been identified as successful techniques for in situ determination of EC in crops and therefore extensible to leave matrices. Furthermore, additional research is clearly needed to fill the existing gap of a multiresidual analytical methodology for the determination of EC and their intermediate degradation products as well as enantiomeric compounds. Transformation products and chiral compounds will gain more environmental concern in the next future and to our knowledge no information have been find at this respect in the atmospheric compartment. To this end, the recourse to high resolution MS platforms (quadrupole time of flight (QqTOF), quadrupole-linear ion trap (QqLIT) and Orbitrap) has been increasing significantly, as well as the previous separation of such compounds by using chiral chromatography, hydrophilic interaction chromatography (HILIC) or two-dimensional liquid chromatography (LCxLC) systems.
Lattice Boltzmann Simulation of Falling Film Flow under Low Reynolds Number
Published in Heat Transfer Engineering, 2018
In this case, a rectangle computational domain with a grid size of 160 × 60 (NX × NY) was chosen. A two-dimensional liquid droplet with a radius of 25 was initially generated at the center of a plate. The periodic boundaries were implemented at the left and right sides and bounce back scheme was taken for the upper and lower boundary. In this case, the fluid density ratio (the heavier over the lighter, ρ*) was taken as 100. The different contact angles θeq = 30°, 60°, 90°, 120° and 150° were simulated by choosing different wetting potential ω. The equilibrium contact angles were measured by the geometric formula of droplet height and the length of contact line. Figure 4 shows the comparison between the measured contact angles and analytical ones. It can be observed that the angles obtained by the model agree well with the analytical ones. Furthermore, the droplet recovering process on the plate with contact angle θeq = 30° is shown in Figure 5, in which the color represents the density while the red part and blue part are corresponding to the liquid droplet and the gas, respectively. The droplet automatically achieved equilibrium state from initial state after a short period, which indicates that the proposed model is appropriate to treat the contact angle issue.
Mesomorphic structure peculiarities of two mix-substituted phthalocyanines of the A3B type
Published in Liquid Crystals, 2018
Antonina I. Smirnova, Nadezhda V. Usol’tseva, Benoît Heinrich, Bertrand Donnio
History of phthalocyanine and its derivatives as dyes and pigments dates back to the 1930s [5], but their ability to form two-dimensional liquid crystalline state was found relatively recently. The first examples of thermotropic mesomorphism were reported in 1982 and 1983 for copper and metal-free phthalocyanines, respectively [6,7]. Following these pioneering contributions, the number of liquid crystalline phthalocyanines and corresponding metalloderivatives increased drastically [2,8]. The overwhelming majority consisted essentially of symmetrically homo-substituted compounds, although a few unsymmetrical (mix-substituted, hetero-substituted) compounds have also been reported [9,10]. Most of the recent studies on mesomorphic Pc derivatives are now primarily focused on devices and applications, in particular as prospective sensitisers for dye-sensitised solar cells [2,4,11,12]. These previous studies bring to the fore that Pc could be made mesomorphic just by connecting peripheral chains (mostly alkyl chains) to the macrocycle, but not always (e.g. bulky phenyl groups [13,14]): columnar mesophases then naturally emerged through the intrinsic propensity of Pc rings to stack face-to-face and through the repelling of so-formed columns at lattice nodes by the molten periphery [9]. The cross section of the columns is either cylindrical or ellipsoidal, depending on the out-of-plane tilt angle of the Pc discoid-shaped; most columnar arrangements therefore possess a hexagonal symmetry with one column per lattice (Colh, Z = 1) or a rectangular symmetry (Colr, Z = 2) [8]. These observations hold for derivatives with chains connected at either ‘peripheral’ or ‘radial’ positions (2,3,9,10,16,17,23,24 and 1,4,8,11,15,18,22,25 substitution patterns, respectively), though for the latter geometry, the alkoxy derivatives are devoid of mesomorphic properties [9].