Phase Transitions Induced by Top-Priority of Randomization

We study the characteristics of phase transition to take the top-priority of randomization in the rules of NaSch model (i.e.noise-first model) into account via computing the relaxation time and the order parameter.The scaling exponents of the relaxation time and the scaling relation of order parameter,respectively,axe obtained.     

Phase Transitions of Single Semistiff Polymer Chains

We study numerically a lattice model of semiflexible homopolymers with nearest neighbor (nn) attraction and energetic preference for straight joints between bonded monomers. For this we use a new Monte Carlo algorithm, the “prunedenriched Rosenbluth Method” (PERM). It is very efficient both for relatively open configurations at high temperatures and for compact and frozen-in low-T states. This allows us to study in detail the phase diagram as a function of nn attractionε and stiffnessx. It shows aθ-collapse line with a transition from open coils (smallε) to molten compact globules (largeε) and a freezing transition toward a state with orientational global order (large stiffnessx). Qualitatively this is similar to a recently studied mean-field theory [S. Doniach, T. Garel, and H. Orland (1996),J. Chem. Phys. 105(4), 1601], but there are important differences in details. In contrast to the mean-field theory and to naive expectations, theθ-temperatureincreases with stiffnessx. The freezing temperature increases even faster, and reaches theθ-line at a finite value ofx. For even stiffer chains, the freezing transition takes place directly, without the formation of an intermediate globular state. Although being in conflict with mean-field theory, the latter had been conjectured already by Doniachet al. on the basis of heuristic arguments and of low-statistics Monte Carlo simulations. Finally, we discuss the relevance of the present model as a very crude model for protein folding.     

Autowaves of Localized Deformation Induced by Phase Transformation

Physics of the Solid State - An approach and a model of the birth and development of deformation bands and their fronts under plastic deformation due to phase transformation are proposed. A solid...     

Photochromism and Photo-Induced Phase Transitions in the Conjugated Polymer Polydiacetylenes

A model for describing photochromism and photo-induced phase transition in polydiacetylenes (PDAs) is presented, the lattice deformational energies under photo-excitation are calculated numerically. The mechanism for photo-induced structure phase transition is discussed in detail. It is considered that the excitonic diffusion and relaxation are responsiblefor photochromism and photo-induced structure phase change in PDAs. Based on this model, the experimental results have been explained correctly.     

The Complex Nature of Thermal Phase Transitions in Albumin Solutions

Technical Physics - Dielectric and optical methods were used to reveal the complex nature of globule–coil–coil associate phase transitions in solutions of human serum albumin. The...     

An Integrodifferential Model for Phase Transitions: Stationary Solutions in Higher Space Dimensions

We study the existence and stability of stationary solutions of an integrodifferential model for phase transitions, which is a gradient flow for a free energy functional with general nonlocal integrals penalizing spatial nonuniformity. As such, this model is a nonlocal extension of the Allen–Cahn equation, which incorporates long-range interactions. We find that the set of stationary solutions for this model is much larger than that of the Allen–Cahn equation.     

二元共混聚合物的热诱导周期性相分离

采用 Cahn-Hilliard-Cook 理论模拟了二元共混聚合物体系的诱导周期性相分离.模拟结果显示,共混体系呈现二尺度相分离结构中,小尺度相区周期性的产生并消失,而大尺度相区逐渐增长.通过结因子的演化,讨论了二尺度相分离结构的形成机理,并且考察了相互用参数的震荡幅度与体系特征尺度的关系.     

Thermal Phase Transitions of IOTA Carrageenan in CaCl2 Solutions: A Fluorescence Study

The fluorescence technique was employed to study thermal phase transitions of iota (ι-) carrageenan (IC) in CaCl₂ solution. IC gels underwent coil to double helix (c-h) and double helix to dimer (h-d) transitions upon cooling. Upon heating IC gels presented dimer to double helix (d-h) and double helix to coil (h-c) transitions, showing hysteresis types of transition paths. Scattered light, I_sc and fluorescence intensity, I, were monitored against temperature to determine phase transitions. Transition temperatures were determined from the derivative of the transition paths. The critical gel fraction exponent, β, was measured and found to be in accord with the classic Flory–Stockmayer model.     

Dynamics of Spiral Waves Induced by Periodic Mechanical Deformation with Phase Difference

The dynamics of spiral waves under the influences of periodic mechanical deformation are studied. Here, the mechanical deformation propagating along the medium with phase differences are considered. It is found that weak mechanical deformation may lead to resonant drift of spiral waves. The drift direction and velocity can be changed by the wave length of the deformation. Strong mechanical deformation may result in breakup of spiral waves. The characteristics of breakup are discussed. The critical amplitudes are determined by two factors, i.e. the wave length and frequency of the periodic mechanical deformation. When the wave length of mechanical deformation is comparable to the spiral wave, simulation shows that the critical amplitude is substantially increased. As the frequency of the mechanical deformation is around 1.5 times of the spiral wave, the critical amplitudes are minimal.     

Capillary-Induced Phase Separation in Ultrathin Jets of Rigid-Chain Polymer Solutions

JETP Letters - In the present paper, we study the terminal stage of the capillary thinning of a polymer solution jet formed with rod-like molecules. On long scales exceeding the rod length a...     

Phase Transitions in the Early Universe with Negatively Induced Supergravity Cosmological Constant

We consider that the observable cosmological constant is the sum of the vacuum （Avac） and the induced term （Aind - 3m^2/4） with m being the ultra-llght masses （≈ Hubble parameter） implemented in the theory from supergravities arguments and non-minimal coupling. In the absence of a scalar buildup of matter fields, we study its effects on spontaneous symmetry breaking with a Higgs potential and show how the presence of the ultra-light masses yields some important consequences for the early universe and new constraints on the Higgs and electroweak gauge bosons masses.     

A Simple,Scalable Process for the Production of Porous Polymer Microspheres by Ink‐Jetting Combined with Thermally Induced Phase Separation

Porous microspheres capable of delivering high payloads of biomolecules with suitable biodegradability and biocompatibility would be valuable in delivery systems to aid tissue regeneration. This study describes a facile, scalable technique to produce biodegradable porous microspheres by combining continuous ink‐jetting through a piezoelectric nozzle with thermally induced phase separation (TIPS). A selection of biomaterials is investigated to suit delivery in tissue engineering, the synthetic polyesters poly(lactic‐co‐glycolic acid) (PLGA), and poly caprolactone (PCL) and a natural polymer, gelatin. The parameters governing the microsphere production are determined experimentally and compared to theoretical predictions derived from the fluid mechanics and heat transfer during the ink‐jetting process. The microspheres produced have open interconnected pores with mean particle diameters of 80–200 μm and no significant skin region. The physical properties, such as the mean particle diameter, pore size, and surface area could be controlled by varying production parameters including the ink‐jetting pressure, nozzle height, and the size and oscillation frequency of the nozzle. The technique is demonstrated to successfully encapsulate a model hydrophobic molecule during microsphere production with uniform distribution. Porous PLGA microspheres are also used to achieve much higher adsorption capacities of a short peptide than non‐porous microspheres of the same material.     

高压诱致的反式联苯乙烯酮结构相变与化学反应

 利用金刚石对顶砧（DAC）高压装置在室温下对反式联苯乙烯酮（Trans, Trans-Dibenzylideneacetone）分子晶体进行了高压拉曼谱、荧光光谱和能量色散X射线衍射（EDXRD）研究。结果表明,在压力为1.0~1.3 GPa时,反式联苯乙烯酮发生了晶体—晶体的结构相变,同时开始伴随有压力诱导的化学反应,反应完成的压力为6.5 GPa。高压X射线研究表明,这次相变有新的共价键产生,可能的化学变化过程是,C＝C双键打开再与相邻的分子结合生成新的共价键。在压力大约为11 GPa时,反式联苯乙烯酮分子晶体再次发生了晶体的结构相变。新产生的物质在卸压后依然保持稳定。     

Structural Properties and Phase Behavior of Crosslinked Networks in Polymer Solutions

Structural properties and phase behavior of crosslinked networks embedded in polymer solutions are theoretically investigated. The partial structure factor of the network is calculated using a matrix formulation of the random phase approximation and the forward scattering limit is correlated with the phase behavior. Swelling and deswelling processes are analyzed in terms of the polymer concentration, the mismatch of solvent quality with respect to polymer and network, the polymers incompatibility and their characteristic sizes. Most studies reported so far in the literature have focussed on the swelling of crosslinked networks and gels in pure solvents but the correlation of the structural properties with the phase behavior in the presence of high molecular weight polymers in solution has not been given sufficient attention. The present work is intended to fill this gap in view of the current efforts to develop novel drug encapsulating and targeted delivery devices.     

Gravity as a Source of Phase Transitions

After going through several distinguished examples, we argue that gravity is definitely a source of phase transitions of quite different nature: usual scalar effective potential ones, chiral symmetry transitions and even transitions involving the chromomagnetic vacuum. In such context, we emphasize the fact that curvature-induced phase transitions of those kinds—where an interplay between general relativity and elementary particle physics occurs—can be used in the construction of new models of the inflationary universe.     

Gamma-Ray Transitions Induced in Nuclear Spin Isomers by X-Rays

Because of the high density of energy storage and the large cross section for its release, nuclear spin isomers have attracted considerable recent interest. The triggering of induced gamma emission from them has encouraged efforts to develop intense sources of short-wavelength radiation. One of the more interesting examples is the 16⁺ 4-qp isomer of ¹⁷⁸Hf which stores 2.445 MeV for a half-life of 31 years meaning that as a material, such isomeric ¹⁷⁸Hf would store 1.3 GJ/g. Recently, a sample containing 6.3×10¹⁴ nuclei of the isomer of ¹⁷⁸Hf was irradiated with X-ray pulses derived from a device operated at 15 mA to produce bremsstrahlung radiation with end point energies set to values between 60 and 90 keV. Emission of gamma radiation from the sample was increased by 1–2% above the quiescent value of spontaneous emission. Such an accelerated decay of the ¹⁷⁸Hf isomer is consistent with an integrated cross section of 2.2×10⁻²² cm² keV if the resonant absorption of the X-rays takes place below 20 keV as indicated by the use of selective absorbing filters in the irradiating beam. The work reported here describes the current experimental focus and results recently obtained with the use of coincident detection of emitted gamma photons by several detectors. This revised version was published online in July 2006 with corrections to the Cover Date.     

Transitions in a Logistic Growth Model Induced by Noise Coupling and Noise Color

With unified colored noise approximation, the logistic growth model is used to analyze cancer cell population when colored noise is included. It is found that both the coupling between noise terms and the noise color can induce continuous first-order-like and re-entrance-like phase transitions in the system. The coupling and the noise color can also increase tumor cell growth for small number of cell mass and repress tumor cell growth for large number of cell mass. It is shown that the approximate analytic expressions are consistent with the numerical simulations.     

Transitions in a Logistic Growth Model Induced by Noise Coupling and Noise Color

With unified colored noise approximation, the logistic growth model is used to analyze cancer cell population when colored noise is included. It is found that both the coupling between noise terms and the noise color can induce continuous first-order-like and re-entrance-like phase transitions in the system. The coupling and the noise color can also increase tumor cell growth for small number of cell mass and repress tumor cell growth for large number of cell mass. It is shown that the approximate analytic expressions are consistent with the numerical simulations.