Salt-Responsive Phenol Formaldehyde Resin: Changes of Interface Energy on the Aggregation Process.

Phenol formaldehyde resins (PFRs) as a colloidal oil displacement agent were commonly used to plug pores in crude oil reservoirs for enhanced oil recovery (EOR). The aggregation-dispersion and charging behavior of PFR may affect the rheology and plugging performance of the suspension. To understand the aggregation-dispersion and charge of PFR, turbidity, dynamic light scattering, and electrophoretic light scattering experiments were carried out at pH = 10 with different concentrations of salt solutions (NaCl, MgCl2, CaCl2, NaCl/MgCl2, and NaCl/CaCl2). The aggregation rate and ζ-potential were measured, and the critical coagulation concentration (CCC) and critical coagulation ionic strength (CCIS) were further obtained. Based on the triple-layer surface complexation (TL) model, the adsorption ability of cations and the surface characteristics of the PFR particles were studied, and these differences were explained by interface energy. Thus, Derjaguin-Landau and Verwey-Overbeek (DLVO) theory modified by interface energy was applied to explain the aggregation behavior of PFR particles in different types of ion systems. We concluded that, in the presence of multiple ions, DLVO theory modified by interface energy has good applicability to the aggregation-dispersion of PFR particles.

Twin-tube terahertz fiber for a polarization filter.

A simple polymer twin-tube terahertz (THz) fiber that can be used as a polarization filter is proposed and investigated using the finite element method in this paper. The twin-tube THz fiber consists of two closely spaced identical tubes located symmetrically inside the protecting jacket. The simulation results show that the y-polarization fundamental mode (YPFM) can be well confined between the two tube walls near the fiber center, while the x-polarization fundamental mode (XPFM) has a huge confinement loss due to the coupling with the tube mode. For the fundamental mode (FM), a polarization extinction ratio (PER) of 30 dB can be realized after a 1.3 cm length of the fiber, and the insertion loss of the YPFM is less than 0.5 dB at 1 THz. In addition, higher order modes (HOMs) can be effectively suppressed by further increasing the fiber length. Simulation results indicate that all HOMs have powers being 30 dB lower than that of the supported YPFM after a 7.44 cm length of the fiber, and the insertion loss of the YPFM is less than 2.7 dB at 1 THz. Furthermore, the effects of fiber structure parameters on the loss properties are investigated, proving that the proposed fiber has a good fabrication tolerance. Owing to the simple structure, the proposed fiber polarization filter is easy to be fabricated and low-cost, which makes it a potential application in commercial THz systems.

Attitudes Toward Psychiatry Among Medical Students With a Psychiatric Major at Chongqing Medical University.

OBJECTIVES: To understand the attitudes of medical students with a psychiatry major toward psychiatry at Chongqing medical university in China and to find out factors influencing students' career choice. METHODS: The present study used an online web survey tool to assess the attitudes toward psychiatry amongst 422 students majoring in psychiatry at Chongqing medical university in China using sociodemographic and Attitudes Toward Psychiatry-30 items (ATP-30) scales. Descriptive statistics and logistic regression analysis were used to examine associated factors. RESULTS: Three hundred and sixty-nine students (87%) answered the questionnaire. Nearly 54.5% of participants had overall positive attitudes to psychiatry and 80.8% thought psychiatrist could be a career choice. Of the students, 5.1% showed that they did not want to be a psychiatrist while the remaining 14.1% were undecided. The first and fifth year students showed less desire to be a psychiatrist (74.3 and 69.8%, respectively); the highest percentage recorded is of the third year (90.6%). Female participants, in contact with patients suffering from mental illness, were willing to study psychiatry as a master degree and see good prospects were positive factors in choosing psychiatry as a career. CONCLUSIONS: Students generally have good expectations toward psychiatry, but different opinions are also held and the field is still faced with various challenges in order to provide more psychiatrists.