• Journal of Magnetics
• /
• 제9권1호
• /
• pp.1-4
• /
• 2004

Three successive phase transitions in bis-n-octhylammonium hexachlorostannate, $(n-C_8H_{17}NH_3)_2SnCl_6$, were studied by means of the ^1H nuclear magnetic resonance linewidth and spin-lattice relaxation measurements. Unlike the compounds with longer hydrocarbon chains, the order-disorder and conformational nature were found to coexist in the phase transitions.

• Archives of Metallurgy and Materials
• /
• 제65권4호
• /
• pp.1303-1306
• /
• 2020

TiNi alloys have excellent shape memory properties and corrosion resistance as well as high biocompatibility. This study investigated the effects of copper addition on the phase transitions and electrochemical corrosion behaviors of Ti₅₀Ni_50-xCu_x alloys. TiNi, Ti₅₀Ni₄₇Cu₃, Ti₅₀Ni₄₄Cu₆, and Ti₅₀Ni₄₁Cu₉ alloys were prepared using vacuum arc remelting followed by 4 h homogenization at 950℃. Differential scanning calorimetry and X-ray diffraction analyses were conducted. The corrosion behaviors of the alloys were evaluated using potentiodynamic polarization test in Hank's balanced salt solution at a temperature of 36.5 ± 1℃. The TiNi alloy showed phase transitions from the cubic B2 phase to the monoclinic B19' phase when the alloy was thermally cycled. The addition of copper to the TiNi alloy played a major role in stabilizing the orthorhombic B19 phases during the phase transitions of Ti₅₀Ni_50-xCu_x alloys. The shifts in the corrosion potential toward the positive zone and the low corrosion current density were affected by the amount of Cu added. The corrosion resistance of the TiNi alloy increased with increasing copper content.

• Journal of the Korean Data and Information Science Society
• /
• 제20권1호
• /
• pp.225-235
• /
• 2009

Lattice process models are used to explain phase transitions in statistical mechanics, a branch of physics. The Ising model, a specific form of lattice process model, was proposed by Ising in 1925. Since then, variants of the Ising model such as the Potts model and the unitary cell model have been proposed. Like the Ising model, it is believed that the more general models exhibit phase transitions on the critical surface, which is based on the mathematical equation. In statistical sense, phase transitions can be simulated through Markov Chain Monte Carlo (MCMC). We applied Swendsen-Wang algorithm, a block Gibbs algorithm, to a general lattice process models and we simulate phase transition phenomena of the unitary cell model.

• Journal of the Korean Physical Society
• /
• 제73권9호
• /
• pp.1219-1224
• /
• 2018

We investigate the evolutionary dynamics and the phase transitions of the island model which consists of subdivided populations of individuals confined to two islands. In the island model, the population is subdivided so that migration acts to determine the evolutionary dynamics along with selection and genetic drift. The individuals are assumed to be haploid and to be one of two species, X or Y. They reproduce according to their fitness values, die at random, and migrate between the islands. The evolutionary dynamics of an individual based model is formulated in terms of a master equation and is approximated by using the diffusion method as the multidimensional Fokker-Planck equation (FPE) and the coupled non-linear stochastic differential equations (SDEs) with multiplicative noise. We analyze the infinite population limit to find the phase transitions from the monomorphic state of one type to the polymorphic state to the monomorphic state of the other type as we vary the ratio of the fitness values in two islands and complete the phase diagram of our island model.

• EDISON SW 활용 경진대회 논문집
• /
• 제3회(2014년)
• /
• pp.516-520
• /
• 2014

Fractional quantum Hall Effect (FQSH) is one of most fundamental issues in condensed matter physics, and the Topological insulator becomes its prominent applications. This article reviews the general frameworks of these development and the physical properties. FQSH states and topological insulators are supposed to be topologically invariant under the minor change of geometrical shape or internal impurities. The phase transitions involved in this phenomena are known not to be explained in terms of symmetry breaking or Landau-Ginsburg theory. The new type of phase transitions related to topological invariants has acquired new name - topological phase transition. The intuitive concepts and the other area having same type of phase transitions are discussed.

• 센서학회지
• /
• 제28권6호
• /
• pp.341-344
• /
• 2019

Liquid crystal (LC) mesophase materials manifest a variety of phase transitions. The optical properties of LCs are highly dependent upon the phase and orientation of the optical axis with respect to the polarization of incoming light. Studying the LC phase transitions is significantly important for a wide range of scientific and industrial applications. In this study, we demonstrate the propagation velocity of the phase boundary between the nematic and isotropic phase of 4-Cyano-4-pentylbiphenyl (5CB) liquid crystal for different electric fields using a polarized optical microscope. The results demonstrate that the propagation velocity of the phase boundary exhibits a peak value for a specific voltage, attributed to the supercooling of the isotropic phase of the LC. The analysis of the propagation velocity for different electric fields also provides a simple optical platform to measure the thermal anisotropy and voltage dependent thermal properties of the homogeneously aligned LC.

• 대한설비공학회지:설비저널
• /
• 제17권5호
• /
• pp.590-597
• /
• 1988

Characteristics of flow regime transitions in inclined upwards gas-liquid two-phase flow have been investigated based upon a statistical analysis of instantaneous pressure drop curves through an orifice. The probability density functions of the curves indicate distinct patterns depending upon two-phase flow regime, which are very similar to those of horizontal two-phase. The dimensionless intensity of fluctuations of the pressure drops sharply change as the flow transitions such as plug-slug, pseudo slug-slug and annular-slug take place. The effects of inclination angle on the flow regime transitions have been also investigated. The results show that the method to identify the flow pattern based upon the statistical analysis of instantaneous pressure drops is suitable for inclined flow as well as horizontal flow.

• Coupled systems mechanics
• /
• 제6권1호
• /
• pp.29-40
• /
• 2017

This work employed density functional theory to investigate the structural and ferroelectric properties of the Ruddlesden-Popper (RP) phase of lead titanate, $Pb_2TiO_4$, as well as its phase transitions with epitaxial strain. A wealth of novel structural instabilities, which are absent in the host $PbTiO_3$ material, were identified in the RP phase through phonon soft-mode analysis. Our calculations showed that the ground state of $Pb_2TiO_4$ is antiferroelectric, distinct from the dominant ferroelectric phase in the corresponding host material. In addition, applied epitaxial strain was found to play a key role in the interactions among the instabilities. The induction of a sequence of antiferroelectric and antiferrodistortive (AFD) phase transitions by epitaxial strain was demonstrated, in which the ferroic instability and AFD distortion were cooperative rather than competitive, as is the case in the host $PbTiO_3$. The RP phase in conjunction with strain engineering thus represents a new approach to creating ferroic orders and modifying the interplay among structural instabilities in the same constituent materials, enabling us to tailor the functionality of perovskite oxides for novel device applications.

• 한국세라믹학회지
• /
• 제30권8호
• /
• pp.623-628
• /
• 1993

Lead monoxide has two phases at room temperature. One is a yellow orthorhombic phase, the other is a redtetragonal phase. Sometimes two phases are hybrided. The specificity of phase transitions of lead oxide is found during the milling of the batch including lead oxide. The pure orthorhombic phase of PbO can be transformed to the tetragonal phase perfectly by wet ball milling (milling liquid is distilled water) without thermal energy. However, when ethyl alcohol, isopropyl alcohol and aceton are used as milling liquid, respectively, the hybrid form of orthorhombic andtetragonal phases is obtained by wet ball milling. From the hybrid form heat-treated at $600^{\circ}C$ for 3hrs, this work results that mechanical phase transition of orthorhombic phase make a new form as distorted type orthorhombic phase of PbO.

• Journal of Magnetics
• /
• 제7권1호
• /
• pp.1-3
• /
• 2002

Piezomagnetic behaviors have been observed far above the Neel temperature in the perovskite-type layer structure compound $(C_{18}H_{37}NH_3)_2MnCl_4$undergoing structural phase transitions. Our observations were well explained by the magnetic and the structural orders coupled together via a magnetostructural coupling attributable to the Dzyaloshinsky-Moriya interaction.