Metamagnetic transitions and anomalous magnetoresistance in EuAg4_4As2_2 single crystal

In this paper, the magnetic and transport properties were systematically studied for EuAg$_4$As$_2$ single crystals, crystallizing in a centrosymmetric trigonal CaCu$_4$P$_2$ type structure. It was confirmed that two magnetic transitions occur at $\textit{T}$$_{N1}$ = 10 K and $\textit{T}$$_{N2}$ = 15 K, respectively. With the increasing field, the two transitions are noticeably driven to lower temperature. At low temperatures, applying a magnetic field in the $\textit{ab}$ plane induces two successive metamagnetic transitions. For both $\textit{H}$ $\parallel$ $\textit{ab}$ and $\textit{H}$ $\parallel$ $\textit{c}$, EuAg$_4$As$_2$ shows a positive, unexpected large magnetoresistance (up to 202\%) at low fields below 10 K, and a large negative magnetoresistance (up to -78\%) at high fields/intermediate temperatures. Such anomalous field dependence of magnetoresistance may have potential application in the future magnetic sensors. Finally, the magnetic phase diagrams of EuAg$_{4}$As$_{2}$ were constructed for both $\textit{H}$ $\parallel$ $\textit{ab}$ and $\textit{H}$ $\parallel$ $\textit{c}$

Gas-Purged Headspace Liquid Phase Microextraction System for Determination of Volatile and Semivolatile Analytes

In order to achieve rapid, automatic, and efficient extraction for trace chemicals from samples, a system of gas-purged headspace liquid phase microextraction (GP-HS-LPME) has been researched and developed based on the original HS-LPME technique. In this system, semiconductor condenser and heater, whose refrigerating and heating temperatures were controlled by microcontroller, were designed to cool the extraction solvent and to heat the sample, respectively. Besides, inert gas, whose gas flow rate was adjusted by mass flow controller, was continuously introduced into and discharged from the system. Under optimized parameters, extraction experiments were performed, respectively, using GP-HS-LPME system and original HS-LPME technique for enriching volatile and semivolatile target compounds from the same kind of sample of 15 PAHs standard mixture. GC-MS analysis results for the two experiments indicated that a higher enrichment factor was obtained from GP-HS-LPME. The enrichment results demonstrate that GP-HS-LPME system is potential in determination of volatile and semivolatile analytes from various kinds of samples

Effect of Carbon Particles on Aerodynamic Performance of a Radial Inflow Turbine in Closed Brayton Cycle

For the closed Brayton cycle using carbon heaters, working fluid contains some solid particles generally. These impurities will enter turbine along with gas, influence aerodynamic performance, and even make turbine work under off-design condition. Therefore, it is necessary to study the influence of particles on turbine. In this paper, a turbine using argon with carbon particles as working fluid is investigated. Particles are assumed to have no volume and are evenly divided into ten different sizes. Based on the discrete phase model (DPM), CFD method is adopted to simulate turbine flow field, and influences of carbon particle mass fraction, particle diameter and incident velocity on aerodynamic performance are analyzed. The results indicate that as particle mass fraction increases, total pressure, static pressure and Mach number decrease significantly, isentropic efficiency decreases slightly, while temperature increases. Collision and rebound of particles in flow field are more intense with a larger particle diameter, but flow field is less influenced under the same mass fraction due to decrease of particle number. Incident velocity has little effect on aerodynamic performance; however, with increase of incident velocity, diameter of particles on blade surface is larger and collision of particles is more intense especially in nozzle. These results will help understand the influence of solid particles on turbines