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Solids with dimpled potential-energy surfaces are ubiquitous in nature and, typically, exhibit structural (elastic or phonon) instabilities. Dimpled potentials are not harmonic; thus, the conventional quasiharmonic approximation at finite temperatures fails to describe anharmonic vibrations in such solids. At sufficiently high temperatures, their crystal structure is stabilized by entropy; in this phase, a diffraction pattern of a periodic crystal is combined with vibrational properties of a phonon glass. As temperature is lowered, the solid undergoes a symmetry-breaking transition and transforms into a lower-symmetry phase with lower lattice entropy. Here, we identify specific features in the potential-energy surface that lead to such polymorphic behavior; we establish reliable estimates for the relative energies and temperatures associated with the anharmonic vibrations and the solid–solid symmetry-breaking phase transitions. We show that computational phonon methods can be applied to address anharmonic vibrations in a polymorphic solid at fixed temperature. To illustrate the ubiquity of this class of materials, we present a range of examples (elemental metals, a shape-memory alloy, and a layered charge-density-wave system); we show that our theoretical predictions compare well with known experimental data.

In this document, a numerical study of the natural convection of steady-state laminar heat transfer in a horizontal ring between a heated hexagonal inner cylinder and a cold hexagonal outer cylinder. A Cu - water nanofluid traverses this annular space. The system of equations governing the problem was solved numerically by the fluent calculation code based on the finite volume method. Based on the Boussinesq approximation. The interior and exterior sides from the two cylinders are maintained at a fixed temperature. We investigated the impacts of various thermal Rayleigh numbers (103≤ Rat ≤2.5x105), and the volume fraction from the nanoparticles (0≤ Ø ≤0.12) on fluid flow and heat transfer performance. It is found that in high thermal Rayleigh numbers, a thin thermal boundary layer is illustrated at the flow that heavily strikes the ceiling and lower from the outer cylinder. In addition, the local and mean Nusselt number from a nanofluid are enhanced by enhancing the volume fraction of the nanoparticles.The results are shown within the figure of isocurrents, isotherms, and mean and local Nusselt numbers. Detailed results of the numerical has been compared with literature ones, and it gives a reliable agreement.

Abstract Based on the semiclassical Holstein model, the dynamics of a quantum particle in one-dimensional molecular chain with a trapping site is modeled. Numerical simulation is used to investigate the dynamics of a polaron in a chain with small random Langevin-like perturbations which imitate the thermostat. Parameter values are chosen such that the polaron energy at the trapping site is much greater than the energy of temperature fluctuations. Results of modeling demonstrate that temperature decay of a polaron depends on the chain length even at very low temperatures.

Предложен метод оценки площади A, приходящейся на молекулу монослоя ПАВ, вначале перехода от жидко-растянутой к жидко-конденсированной фазе на основе двух теоретических моделей. Термодинамическая модель поведения дифильных монослоев с учетом неидеальности энтропии смешения позволяет оценить величину энергий Гиббса кластеризации ПАВ на основе П-А-изотерм, полученных при различных температурах. С другой стороны квантово-химический подход также дает возможность рассчитать данный термодинамический параметр и оценить структурные особенности получаемых монослоев. Величины энергий Гиббса кластеризации малых ассоциатов ПАВ и геометрических параметров элементарных ячеек монослоев были рассчитаны ранее с помощью квантово-химического полуэмпирического метода РМ3 для восьми классов дифильных соединений: насыщенные и этоксилированные спирты, насыщенные и цис-моноеновые карбоновые кислоты, α -гидрокси- и α -аминокислоты, N -ацилпроизводные аланина и диалкилзамещенные меламина. Эти параметры были использованы в термодинамической модели с учетом неидеальности энтропии смешения для расчета величин A. Оцененные значения A адекватно отражают экспериментальную температурную зависимость для рассматриваемого фазового перехода: с ростом температуры площадь, приходящаяся на молекулу ПАВ фиксированной длины цепи, уменьшается, и, наоборот, с ростом длины цепи ПАВ при фиксированной температуре величина A увеличивается. Это позволяет использовать предложенный подход в прогностических целях. A method is proposed to estimate the area per molecule of a surfactant monolayer A at the transition onset of the liquid-expanded to a liquid-condensed phase based on two theoretical models. A thermodynamic model with account for nonideality of the mixing entropy makes it possible to estimate the Gibbs energy of surfactant clusterization using the П-A isotherms obtained at different temperatures. On the other hand, the quantum-chemical approach also makes it possible to calculate this thermodynamic parameter and assess the structural features of the obtained monolayers. The values of the Gibbs clusterization energies of small surfactant associates and the geometric parameters of the monolayer unit cells were previously calculated using the quantum-chemical semiempirical method PM3 for eight classes of amphiphilic compounds: saturated and ethoxylated alcohols, saturated and cis-monoenic carboxylic acids, α-hydroxylic and α-amino acids, N -acyl-substituted alanines and dialkyl-substituted melamine. These parameters are used in the thermodynamic model with account for nonideality of the mixing entropy to calculate A. The estimated values Aadequately reflect the experimental temperature dependence for the considered phase transition: with an increase in temperature the area per surfactant molecule of a fixed chain length decreases, and vice versa, with an increase in the surfactant chain length at a fixed temperature, the value A increases. This makes it possible to use the proposed approach for prognostic purposes.

During this first paper, numerical research from the natural convection of steady-state laminar heat transfer into a horizontal ring within a heated internal elliptical surface and a cold external square surface is presented. A Cu - water nanofluid, traverses this annular space. For different thermal Rayleigh numbers varying from 103 to 2.5x105 and different volume fractions from the nanoparticles. The arrangement from equations directing the problem was resolved numerically with the Fluent computational language founded on the finite volume approach. Based approaching the Boussinesq approach. The interior and exterior surfaces from the two cylinders are maintained at a fixed temperature. We investigated the impacts of various thermal Rayleigh numbers, the volume fraction from the nanoparticles, and the effect of the eccentricity of the internal cylinder on the natural convection. The results are shown within the figure of isocurrents, isotherms, and mean and local Nusselt numbers. The objective of this investigation is to examine the impact of different parameters on the heat transfer flow.

The epitaxial lift-off (ELO) process based on selectively etching a thin sacrificial AlAs layer from GaAs substrate was performed using high-concentrated aqueous hydrofluoric (HF) etchant. However, because of using the wet etching method, the traditional ELO process has many drawbacks and limitations. Supercritical fluids (SCFs) naturally have the characteristics of low viscosity, high diffusivity, and zero surface tension. Therefore, the development of a gas-phase-like dry etching method based on mixing HF into CO2 and operating the mixture of HF/CO2 in SCFs condition as etchant is hereby proposed to overcome those bottlenecks existing in traditional wet ELO processes. However, there are no available experimental results for etching AlAs layers by HF in SCFs yet. Therefore, a HF-compatible corrosion-resistant high-pressure system was designed and built up to perform the idea. The capabilities of etching sample in supercritical CO2 (scCO2) had been systemically investigated under various pressures (2000–3000 psi) and temperatures (40–60[Formula: see text]C). Besides, the etching performances separately conducted by using aqueous-HF and anhydrous HF/Pyridine as the source etchant and mixing with scCO2 at a fixed temperature, pressure and etching time were also examined and compared under different equivalent HF concentrations. An evaluation of using acetone as the co-solvent mixed with HF/scCO2 mixture for enhancing the etch rate in different volume ratio of HF/co-solvent was further investigated and discussed. With this system, we demonstrate releasing a size of [Formula: see text] (width × length) and 3 [Formula: see text]m-thick free-standing GaAs sheet from a 150 nm AlAs sacrificial layer by the etching sample in HF/scCO2 mixture. The released GaAs sheet was also successfully transferred to a flexible PET substrate by using a PDMS stamp and an adhesive layer of NOA61.

In this work, R1234yf is tested in an air-conditioning system as a proposed alternative to R134a. The system is tested at 30, 35, 40, 45 and 50[Formula: see text]Hz evaporator fan frequency to cool the air entering into the evaporator section at a fixed temperature of 35∘C. The system is charged with 600, 700, 800, 1000 and 1200[Formula: see text]g of each refrigerant. The charge mass of 800 grams gives the best performance for both refrigerants. Also, R1234yf has higher COP, exergetic efficiency, second law efficiency, and lower compressor power consumption. Both refrigerants operate at a moderate range of compressor discharge temperature of 85∘C.

<p>A single fault process model was created to test the sensitivity of each TOUGH2 rock parameter on the convection flow rate and fluid enthalpy within a simulated fault. With a fixed temperature base the single fault process model found a negative correlation with the fault permeability and convection fluid enthalpy and a positive liner increases in mass flow with fault area.  Next a large scale Supercritical TOUGH2 model was built to simulate the entire Rotokawa geothermal system incorporating findings of the fault process model. The single porosity model 20 x 10 x 6km with 20 layers and 57,600 grid blocks. Unlike previous models of the Rotokawa reservoir and larger scale TVZ numerical models a fixed temperature base with a no flow boundary was used to represent the brittle ductile transition. The model permeability below the currently explored reservoir was bounded by 3-D magnetologic data. Lower resistivity zones were given higher bulk permeability in the model.  The model resulted in a comparable temperature and pressure match to the Rotokawa natural state conditions. Convection of supercritical fluid reached depths shallower than -4500mRL but only occurred in zones with a bulk vertical permeability less than 2 mD. Further modelling work with a supercritical wellbore coupled reservoir model will be need to evaluate the potential deliverability of a super critical well from the Rotokawa geothermal system.</p>

<p>A single fault process model was created to test the sensitivity of each TOUGH2 rock parameter on the convection flow rate and fluid enthalpy within a simulated fault. With a fixed temperature base the single fault process model found a negative correlation with the fault permeability and convection fluid enthalpy and a positive liner increases in mass flow with fault area.  Next a large scale Supercritical TOUGH2 model was built to simulate the entire Rotokawa geothermal system incorporating findings of the fault process model. The single porosity model 20 x 10 x 6km with 20 layers and 57,600 grid blocks. Unlike previous models of the Rotokawa reservoir and larger scale TVZ numerical models a fixed temperature base with a no flow boundary was used to represent the brittle ductile transition. The model permeability below the currently explored reservoir was bounded by 3-D magnetologic data. Lower resistivity zones were given higher bulk permeability in the model.  The model resulted in a comparable temperature and pressure match to the Rotokawa natural state conditions. Convection of supercritical fluid reached depths shallower than -4500mRL but only occurred in zones with a bulk vertical permeability less than 2 mD. Further modelling work with a supercritical wellbore coupled reservoir model will be need to evaluate the potential deliverability of a super critical well from the Rotokawa geothermal system.</p>