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Hydrophobic deep eutectic solvents as “green” extraction media for polycyclic aromatic hydrocarbons in aqueous samples
No full textThe paper presents novel nonionic and hydrophobic deep eutectic solvents which were synthesized from natural compounds, i.e., thymol, ±camphor, decanoic and 10-undecylenic acids. Fundamental physicochemical properties of the synthesized deep eutectic solvents were determined, followed by their application as extractants in ultrasound-assisted dispersive liquid-liquid microextraction to isolate and enrich polycyclic aromatic hydrocarbons from aqueous samples characterized by a complex matrix. The final determination was carried out by gas chromatography-mass spectrometry. The most important extraction parameters were optimized and the procedure was validated. The developed procedure is characterized by low limits of detection and quantitation, equal to 0.0039-0.0098 μg/L and 0.012-0.029 μg/L, respectively, good precision (RSD \u3c6.09%), analyte recovery ranging from 73.5 to 126.2%, and a wide linear range. The procedure was applied to analysis of industrial effluents from the production of bitumens before and after treatment by advanced oxidation processes. A total of 16 PAHs at concentrations ranging from 0.12 to 46.2 μg/L were identified and determined
Microfluidic device and method using double anodic bonding
Get PDFA microfluidic device for use with a microfluidic delivery system, such as an organic vapor jet printing device, includes a glass layer that is directly bonded to a microfabricated die and a metal plate via a double anodic bond. The double anodic bond is formed by forming a first anodic bond at an interface of the microfabricated die and the glass layer, and forming a second anodic bond at an interface of the metal plate and the glass layer, where the second anodic bond is formed using a voltage that is lower than the voltage used to form the first anodic bond. The second anodic bond is formed with the polarity of the voltage reversed with respect to the glass layer and the formation of the first anodic bond. The metal plate includes attachment features that allow removal of the microfluidic device from a fixture
A Stochastic Model for Automated Teller Machines Subject to Catastrophic Failures and Repairs
No full textIn this paper we develop a queueing model useful in service industries dealing with automatic teller machines (ATMs) that are commonly used by people all over the world. We assume that these service systems are subject to failures due to catastrophic events such as power outage, mechanical or electrical problems. Arrivals of customers are modeled using a Markovian arrival process and the service times are assumed to be of phase type. Individual customer cash requirements are modeled using a probabilistic rule and the machine has a finite capacity for holding the cash. Assuming the failure times, repair times, and cash replenishment times to be exponential, we analyze the model using matrixanalytic methods, and present two illustrative examples to bring out the salient features. Some well known queueing-inventory models are shown to be special cases and in some of these cases we derive explicit expressions for the steady-state probability vectors. The model studied is generic in that it can be applied in the context of queueing-inventory situations
Multiple-Phase-Shift Control for a Dual Active Bridge to Secure Zero-Voltage Switching and Enhance Light-Load Performance
No full textAn ac/dc + dual active bridge (DAB) circuit was found as one solution for the high-efficiency and high-power-density electric vehicle charger. One control option is to let the ac/dc part only convert the grid voltage to a double-line-frequency folded sine wave and let the DAB stage handle both the power factor (PF) and power delivery. While conventional single-phase-shift tends to lose zero-voltage switching (ZVS) at light load and the variable-switching-frequency dual-phase-shift (DPS) sacrifices the light-load performance, this letter proposes a multiple-phase-shift control, which allows for a fixed-switching-frequency triple-phase-shift (TPS) control at the light load to enhance the grid power quality. At medium- and heavy-load conditions, a phase-shift jump from TPS to DPS is performed to reduce the circulating current and improve efficiency. The proposed control strategy secures ZVS, realizes unity PF accurately and minimizes the control complexity. Experimental results on a SiC-based 7.2-kW charger validated its effectiveness and the smooth transition between the heavy load and light load
Extracting Natural Frequencies of Layered Beams Using a Continuous Variation Model and Modal Analysis
No full textThis study involves the determination of the bending natural frequencies of beams composed by stacked cells of different materials. The focus is on cases with two cells. The analytical model is based on Euler-Bernoulli theory with the variations from one cell to another modeled via logistic functions. This approach leads to a single differential equation with variable coefficients, which is solved numerically using MAPLE®‘s differential equation solvers. A forced motion method is used. Forcing frequencies are changed until large motions and sign changes are observed, leading to the resonant frequencies. Of interest is the validation of the analytically obtained frequencies via experimental results. Here, an experiment is set in which a simple two-cell beam is analyzed, via modal analysis, in order to verify the analytically calculated frequencies. The beam is excited using an impact hammer and the response is recorded using accelerometers. Mode shapes are also obtained via digital image correlation. The beam, including distinct materials, is composed of one cell made of steel and another made of aluminum. The joining method is discussed and results for fixed-free beams are obtained
Synergistic Effects of Enviromental Exposures on Ploymer Matrix with or without Metallic Coating Protection
No full textEpoxy and vinyl ester resins are widely being used in fiber-reinforced polymer matrix composites due to their superior physical and mechanical properties; however, they suffer significant degradation during prolonged environmental exposure that is affecting their extended use. The current study shows that the synergistic exposure to ultraviolet radiation, high temperature, and moisture has detrimental effects on the microstructure, strength, ductility, and toughness of both resins with more pronounced effects on the epoxy. The environmental damage in the microstructure of epoxy appeared primarily in the form of surface cavities and blisters while for the vinyl ester emerged mainly as microcracking events. Correlation between degradation of microstructure and loss in the flexural properties of epoxy and vinyl ester was also presented. Furthermore, the protective effect of copper metallic thin films on the epoxy substrate was characterized, revealing that the copper coating can be an effective barrier in preventing environmental degradation of epoxy based composites
Measurements of Ultrasound Backscatter Coefficient
No full textQuantitative ultrasound imaging can produce images based on underlying physical properties of tissue. Of the various parameters that are available for imaging, the backscatter coefficient (BSC) has been of particular interest as it relates to tissue microsctructure and may indicate the presence or progression of various conditions. Despite being a basic physical parameter of tissue, measurements of BSC remain difficult in practice. Interlaboratory comparisons have yielded results that vary by up to two orders of magnitude for identical samples of tissue-mimicking materials. This investigation seeks to characterize two possible reasons for such discrepancies: nonlinear propagation and errors arising from data reduction. BSC was measured for a tissue-mimicking material consisting of glass microspheres embedded in agar gel. Data were collected over a range of peak acoustic pressures and using a variety of data reduction and analysis schemes. Results indicate that data reduction methods yield comparable results and that BSC can depend dramatically on input pressure, with difference of an order of magnitude for results collected at pressures ranging from 0.15 to 1.5 MPa in water
