Polarizable coarse‐grained models for molecular dynamics simulation of liquid cyclohexane

Force field parameters for polarizable coarse‐grained (CG) supra‐atomic models of liquid cyclohexane are proposed. Two different bead sizes were investigated, one representing two fine‐grained (FG) CH₂r united atoms of the cyclohexane ring, and one representing three FG CH₂r united atoms. Electronic polarizability is represented by a massless charge‐on‐spring particle connected to each CG bead. The model parameters were calibrated against the experimental density and heat of vaporization of liquid cyclohexane, and the free energy of cyclohexane hydration. Both models show good agreement with thermodynamic properties of cyclohexane, yet overestimate the self‐diffusion. The dielectric properties of the polarizable models agree very well with experiment. © 2015 Wiley Periodicals, Inc.     

Dielectric study on pure and KOH-doped tetrahydrofuran clathrate hydrates

Complex dielectric permittivities of pure and KOH-doped (x = 1.8 x 10^–4) tetrahydrofuran clathrate hydrates were measured in the temperature range 20–260 K and in the frequency range 20 Hz-1 MHz. The relaxation time of the water reorientational motion was found to decrease drastically as a result of the doping; e.g., the relaxation time of the doped sample was 10^–9 times shorter than that of the pure sample at 70 K. The activation enthalpy of the motion was reduced to 7.4 kJ mol^–1. On cooling the crystal, the value of decreased suddenly at the 62 K phase transition to the ₂ value of the pure sample and at the same time disappeared. No dispersion effect due to the guest reorientation was observed below the transition. These data indicate that both the host and guest molecules become ordered or, at least, change their mobility drastically. In the pure sample, a relaxation phenomenon of ₀₂ was found around the glass transition region. The relaxation times agreed well with those derived from the enthalpy of relaxation in a calorimetric study.Dedicated to Dr D. W. Davidson in honor of his great contributions to the sciences of inclusion phenomena.     

On the definition of the excess permittivity of a fluid mixture. II

In a previous work, an ideal fluid mixture is assumed to be a homogeneous linear and isotropic system that verifies the following conditions: (I) no interaction between molecules, (II) point-like molecules and (III) under fixed temperature and pressure conditions the number of molecules per unit volume is the same for both the individual components and the mixture. It was shown that for such ideal mixture the permittivity is the sum of the individual permittivities weighted with the mole fractions of the components.In this work it is shown that independently of the latter assumption the permittivity of the system can be expressed as the sum of the individual permittivities weighted with the volume fractions of the components.     

A New Chiral Quinoxaline Derivative with Ferroelectric Property

Reaction of 1,2‐di(thiophen‐2‐yl)ethane‐1,2‐dione and (1R,2R)‐(−)‐diaminocyclohexane afforded a homochiral quinoxaline derivative (4aR,8aR)‐2,3‐di(thiophen‐2‐yl)‐decahydroquinoxaline ( 1 ). Fluorescent analysis exhibits an intense blue emission band at 386 nm. Crystallographic analysis showed that it belongs to chiral space group P2₁ with ferroelectric behavior, and a typical ferroelectric feature of electric hysteresis loop was obtained. The dielectric constant of compound 1 was measured at room temperature.     

Frequency dispersive complex permittivity and permeability of ferromagnetic metallic granular composite at microwave frequencies

We experimentally studied the frequency dependent complex permittivity ε and permeability μ of composite composed of carbonyl iron powder (CIP) and epoxy resin in the frequency range 1-18 GHz. We found that the intrinsic ε and μ of CIP extracted from the measured ε and μ of composites follow the classical Maxwell equations and the Landau-Lifshitz-Gilbert (LLG) equation, respectively. The dependences of ε and μ of composites on the volume fraction of CIP (vf_CIP) were investigated using the two-exponent phenomenological percolation equation (TEPPE). We found that the TEPPE can fit the experimental results very well. Comparing the results of percolation parameters derived by experimental data at different frequencies, we show that the TEPPE is frequency independent for the composites at microwave frequencies. The results also show that the ε and μ spectrums of composites with definite vf_CIP can be correctly calculated by combining the TEPPE with the theoretical models of intrinsic ε and μ.     

La3+掺杂Ca1-xLaxCu3Ti4O12陶瓷的制备及性能研究

采用固相反应法制备了La3+掺杂的CaCu3Ti4O12(CCTO)陶瓷,研究了La3+掺杂量对Ca1-xLaxCu3Ti4O12(x=0;,1;,3;,5;,7;)陶瓷物相结构、微观形貌和介电性能影响,对La3+掺杂影响CCTO陶瓷介电性能的机理进行了分析.结果表明:x为3;时,开始出现杂相;x高于5;时,陶瓷晶粒开始细化;La3+掺杂可以显著提高CaCu3Ti4O12陶瓷的介电常数,同时介电损耗在高频段也相应降低,从而有助于CCTO陶瓷的综合介电性能的提升.     

Open Resonator System for Automatic and Precise Dielectric Measurement at Millimeter Wavelengths

As low loss dielectric materials, ZnS, MgF₂, MgAl₂O₄ and quartz ceramic have a very important application at millimeter frequencies. However, there is little information about their dielectric properties in the millimeter wavelength band. To obtain their dielectric properties, an automatic open resonator measurement system at Ka-band is designed and constructed. The importance on the precision determination of cavity length over a broad band and the checking of a measurement system are emphasized and their solutions are put forward in this paper for the first time so far as we know. The solutions of above problems ensure the credibility and high accuracy of our measurement system. The certified measurement system after a series of checking is used to measure the above materials. Lots of measurement results show that the standard deviation of measurement error is less than 0.154% in permittivity and 20.42% in loss tangent. Meanwhile, some experimental summaries on the open resonator technique are provided. Software that controls the measurement system is developed and it improves the testing efficiency greatly.     

Robustness of Interdependent Networks with Weak Dependency Based on Bond Percolation

Real-world systems interact with one another via dependency connectivities. Dependency connectivities make systems less robust because failures may spread iteratively among systems via dependency links. Most previous studies have assumed that two nodes connected by a dependency link are strongly dependent on each other; that is, if one node fails, its dependent partner would also immediately fail. However, in many real scenarios, nodes from different networks may be weakly dependent, and links may fail instead of nodes. How interdependent networks with weak dependency react to link failures remains unknown. In this paper, we build a model of fully interdependent networks with weak dependency and define a parameter α in order to describe the node-coupling strength. If a node fails, its dependent partner has a probability of failing of 1−α. Then, we develop an analytical tool for analyzing the robustness of interdependent networks with weak dependency under link failures, with which we can accurately predict the system robustness when 1−p fractions of links are randomly removed. We find that as the node coupling strength increases, interdependent networks show a discontinuous phase transition when α<αc and a continuous phase transition when α>αc. Compared to site percolation with nodes being attacked, the crossover points αc are larger in the bond percolation with links being attacked. This finding can give us some suggestions for designing and protecting systems in which link failures can happen.     

Field-induced phase transitions in chiral smectic liquid crystals studied by the constant current method

In ferroelectric liquid crystals, phase transitions can be induced by an electric field. The current constant method allows these transition to be quickly localized and thus the(E, T) phase diagram of the studied product can be obtained.In this work, we make a slight modification to the measurement principles based on this method. This modification allows the characteristic parameters of ferroelectric liquid crystal to be quantitatively measured. The use of a current square signal highlights a phenomenon of ferroelectric hysteresis with remnant polarization at null field, which points out an effect of memory in this compound.