Variations In System Properties Research Articles

Study of system properties in reversed-phase liquid chromatography for binary and ternary solvent mobile phase compositions using the solvation parameter model

System maps for the individual system constant of the solvation parameter model and five binary solvent containing 20–70% (v/v) acetonitrile, acetone, methanol, 2-propanol, and tetrahydrofuran on a single octadecylsiloxane-bonded silica column (Luna C18) are used to provide insight into the variation of system properties with mobile phase composition and solvent type. Selectivity differences are dominated by variation in solute size and hydrogen-bond basicity with solvent-dependent variation in dipole-type and hydrogen-bond acid interactions. Interactions involving lone pair electrons are important only in the case of the alcohols and to a lesser extent tetrahydrofuran. Selectivity differences are also dependent on solvent strength. To expand the selectivity space four ternary solvent systems (acetonitrile-methanol-water, acetonitrile-2-propanol-water, methanol-tetrahydrofuran-water, and tetrahydrofuran-2-propanol-water) 1:1:2% (v/v) containing 50% (v/v) total organic solvent are compared with the binary solvent systems at the same organic solvent composition. There is no simple model that links the system properties of the ternary solvents to the binary solvent systems, but it is demonstrated that the ternary solvent systems expand the selectivity space available for reversed-phase separations. The solvation properties of the bulk organic solvents provide insufficient information to predict selectivity in RPLC because of the dominant contribution of water and effects related to the selective solvation of the stationary phase and possible changes in the solvent-dependent microstructure of the mobile phase.

Three‐Dimensional Distribution of Groundwater Residence Time Metrics in the Glaciated United States Using Metamodels Trained on General Numerical Simulation Models

AbstractResidence time distribution (RTD) is a critically important characteristic of groundwater flow systems; however, it cannot be measured directly. RTD can be inferred from tracer data with analytical models (few parameters) or with numerical models (many parameters). The second approach permits more variation in system properties but is used less frequently than the first because large‐scale numerical models can be resource intensive. Using a novel automated approach, a set of 115 inexpensive general simulation models (GSMs) was used to create RTD metrics (fraction of young groundwater, defined as <65 years old; mean travel time of young fraction; median travel time of old fraction; and mean path length). GSMs captured the general trends in measured tritium concentrations in 431 wells. Boosted Regression Tree metamodels were trained to predict these RTD metrics using available wall‐to‐wall hydrogeographic digital sets as explanatory features. The metamodels produced a three‐dimensional distribution of predictions throughout the glacial system that generally matched with the numerical model RTD metrics. In addition to the expected importance of aquifer thickness and recharge rate in predicting RTD metrics, two new data sets, Multi‐Order Hydrologic Position (MOHP) and hydrogeologic terrane were important predictors. These variables by themselves produced metamodels with Nash‐Sutcliffe efficiency close to the full metamodel. Metamodel predictions showed that the volume of young groundwater stored in the glaciated United States is about 6,000 km3, or about 0.5% of globally stored young groundwater.

Stochastic bending characteristics of finite element modeled Nano-composite plates

This study reported, the effect of random variation in system properties on bending response of single wall carbon nanotube reinforced composite (SWCNTRC) plates subjected to transverse uniform loading is examined. System parameters such as the SWCNT armchair, material properties, plate thickness and volume fraction of SWCNT are modelled as basic random variables. The basic formulation is based on higher order shear deformation theory to model the system behavior of the SWCNTRC composite plate. A C0 finite element method in conjunction with the first order perturbation technique procedure developed earlier by the authors for the plate subjected to lateral loading is employed to obtain the mean and variance of the transverse deflection of the plate. The performance of the stochastic SWCNTRC composite model is demonstrated through a comparison of mean transverse central deflection with those results available in the literature and standard deviation of the deflection with an independent First Order perturbation Technique (FOPT), Second Order perturbation Technique (SOPT) and Monte Carlo simulation.

Physics of railroad degradation: The role of a varying dynamic stiffness and transition radiation processes

Variations in dynamic stiffness along railway tracks are at the basis of long-term degradation problems under train operation. For a spatially invariant and straight track, the dynamic response to constant axle loading at a constant velocity is stationary in a convective reference system. This is no longer true if geometrical and/or constitutive track properties are non-uniform over the length. Such discontinuities appear on many scales; the sleeper bay is an example with a periodical character, whereas examples with an incidental character are level crossings, bridges, tunnels, abutments, culverts but also switch panels and ballast and foundation stiffness variations. Also track irregularities may be considered as a non-uniformity. Any longitudinal variation in system properties causes a transient disturbance in the convective, stationary response field. A local and often strong amplification of the stress and strain field in the structure is the result. In terms of mechanical energy: the energy state varies continuously in a convective reference system due to transition radiation. Depending on its intensity it is accompanied by dissipation of mechanical energy. For repeating axle and train loading, such process is cyclic and a long-term degradation mechanism is established. For the running train, the inherent time- and position-dependent energy loss function could be described as ‘dynamic drag’, in analogy to the well-known ‘viscous drag’. The present paper exposes in more detail the physical backgrounds of track degradation, with a focus on soft soils, where transition problems concentrate. Some propositions are made, on a conceptual level, for modelling and an improved design of track transitions with a reduced maintenance need.

Effect of random system properties on bending response of thermo-mechanically loaded laminated composite plates

In this paper, effect of random variation in system properties on bending response of geometrically linear laminated composite plates subjected to transverse uniform lateral pressure and thermal loading is examined. System parameters such as the lamina material properties, expansion of thermal coefficients, lamina plate thickness and lateral load are modeled as basic random variables. The basic formulation is based on higher order shear deformation theory to model the system behavior of the composite plate. A C 0 finite element method in conjunction with the first order perturbation technique procedure developed earlier by authors for the plate subjected to lateral loading is employed to obtain the second order response statistics (mean and variance) of the transverse deflection of the plate. Typical numerical results for the second order statistics of the transverse central deflection of geometrically linear composite plates with temperature independent and dependent material properties subjected to uniform temperature and combination of uniform and linearly varying temperature distribution are obtained for various combinations of geometric parameters, uniform lateral pressures, staking sequences and boundary conditions. The performance of the stochastic laminated composite model is demonstrated through comparison of mean transverse central deflection with those results available in literature and standard deviation of the deflection with an independent Monte Carlo simulation.

Application of stochastic simulation in the optimisation process of hydroelectric generators

In this paper, stochastic optimisation and risk estimation techniques are applied to the problem of hydroelectric generator design. Optimisation results from deterministic simulations can involve considerable risks due to unavoidable variations in system properties as well as environmental conditions. Therefore, stochastic simulation is used to include the effects of parameter scatter and noise effects in the computer models. This allows the evaluation of the scatter in performance and thus an assessment of reliability and quality of the simulated system.

4859826 Simultaneously cutting and welding sheet metal using laser energy : Albert J Hess assigned to Laser Applications Inc

1.1.|The circadian rhythm of rectal temperature and the sleep-wake cycle can persist independently of each other and of zeitgebers, and seem to be controlled by separate oscillators.2.2.|‘Masking’ of temperature by sleep or zeitgeber signals is to be distinguished from entrainment mechanisms.3.3.|Heat production and conductance coact in generating the temperature rhythm.4.4.|Circadian variations in system properties, as observed, e.g. in threshold, need to be confirmed in the absence of a sleep-wake (light-dark) cycle.