A comprehensive study of the performance of a heat pipe by using of various nanofluids

In this paper, a two-dimensional numerical model is developed to simulate the performance of a heat pipe using various nanofluids. The effect of different nanofluids (prepared using alumina, copper oxide, and silver nanoparticles) at different concentrations and particle diameters on the performance of heat pipe is also studied by through finite volume method. The obtained results show that using a nanofluid instead of water leads to the increased thermal efficiency and reduction in heat at wall of the heat pipe. Also, the temperature difference between the evaporator and the condenser is a function of input power; this means that by an increase in the input capacity, the temperature difference between the evaporator and the condenser increases. It was observed that the use of nanofluid reduces the axial-flow pressure of the fluid inside the wick. As a result, the transmission of fluid flow inside the wick from the condenser to the evaporator is easily done with the cost of using a nanofluid. Moreover, with an increase in thermal capacity, fluid pressure drop becomes maximum and thus temperature difference between the evaporator and the condenser increases.     

Determination of indium and nitrogen contents of InGaAsN quantum wells by HRXRD study supported by BAC calculation of the measured energy gap

Determination of indium and nitrogen content in InGaAsN quantum wells (QWs) is often based on the analysis of high-resolution X-ray diffraction (HRXRD) measurements. The comparison of diffraction curves of two similar samples, with and without nitrogen, together with an assumption of constant indium incorporation efficiency during the growth of layers with and without nitrogen, may lead to a large deviation in the determined In and N content. The HRXRD curve simulations supported by bandgap determination and calculations seem to be a solution of this problem. Comparison of the results achieved from simulated HRXRD curves with the calculations of all QWs transitions measured by contactless electro-reflectance (CER) can lead to reduction of deviations in composition determination of InGaAsN quantum wells. The proposed algorithm was applied for investigation of InGaAsN QWs grown by atmospheric pressure metalorganic vapor phase epitaxy (APMOVPE).     

Comparison of experimental data and semi-empirical calculation for an incompressible turbulent boundary layer with pressure gradient

A comparison is made of the velocity profiles obtained by semiempirical methods of calculation and those from universal empirical relations. A method of simplifying the semiempirical calculation is proposed.     

A semi-empirical model for coating flat glass by dipping into metal-organic solutions

A sol-gel process was used to produce coloured coatings of composition SiO₂ ·R _m O _n , whereR = chromium, manganese, iron, cobalt and copper. Microscope slide glasses were dipped into the solutions and extracted vertically at different speeds. Viscosity, density and surface tension were measured for each solution. Capillary numbers and dimensionless thicknesses were then calculated. The results showed that capillary numbers did not depend on the dimensionless thicknesses. A flow rate constant for each solution was observed. A simple formula was used to calculate the heat treated coating thicknesses from the liquid coating thicknesses. Finally, a method based on a semi-empirical approach was successfully applied to predict adequately the thickness obtained as a function of the properties of the solutions and the withdrawal speed.     

Comparison of two O(N) methods for total-energy semi-empirical tight-binding calculation

We compare two O(N) methods, to calculate the total energy of a system, based on a local evaluation of the density matrix (DM) via the Lanczos-Haydock recursion scheme. We have recently introduced the first method, in which an approximated DM is directly computed from the local tridiagonalized hamiltonian (LTH). In the second method, the DM is obtained from the diagonalized LTH without any further approximation. The use of the first method is restricted to temperatures higher than 1000 K, but there is no limitation for the second one. The methods are compared when applied to a grain boundary in silicon and germanium.     

Structure of point defects in B2 Fe-Al alloys: An atomistic study by semi-empirical simulation

We present the first results of a simulation study of point-defect properties in B2 ordered Fe-Al alloys (34% < x_Al < 52%). After examining the T = 0 K energetics of simple defects, we turn to complexes and discuss the usual hypothesis of independent elementary defects. Almost all complex defects involving an Al vacancy and an Al antisite atom in nearest neighbour position are shown to be unstable, confirming that Al vacancies are rare in these alloys. Small deviations from stoichiometry induce a change in the nature of defects: whereas on the Al-rich side, isolated Al antisite atoms dominate, Fe antisite atoms have a strong trend towards clustering on the Fe-rich side, leading to the formation of local DO₃ order.     

On the conformational disorder of PHTP:oligothiophene inclusion compounds: A semi-empirical and ab initio study

A study at the semi-empirical and ab initio level of models of the supramolecular architecture of perhydrotriphenylene and terthiophene (PHTP:T3) inclusion compound shows that the observed conformational disorder in this kind of molecular systems is subject to some constraints, the most important is that there exists an important degree of order inside the nanochannels preventing free rotational orientation of the T3 guest molecules as well as free distribution in the axial direction of the channels. For trigonal channels, T3 guests distort in two (planar and non-planar) configurations, depending on size factors of the nanochannels and small changes from the trigonal to orthorhombic symmetry favour the planar configuration of the guest molecule.     

A hydration study of various calcium sulfoaluminate cements

The present work studies the hydration process and microstructural features of five calcium sulfoaluminate (CSA) cements and a ternary mixture including also ordinary Portland cement (OPC). The pastes were studied with simultaneous differential thermal-thermogravimetric (DTA-TG) analysis, mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM), and expansion/shrinkage tests. The DTA-TG analysis confirmed the role of the hydration reactions involving the main CSA clinker constituent, tetracalcium trialuminate sulfate, which produced (i) ettringite when combined with lime and calcium sulfate, (ii) ettringite and aluminum hydroxide in the presence of calcium sulfate alone, and (iii) monosulfate and aluminum hydroxide in the absence of both lime and calcium sulfate. The MIP and SEM were able to discriminate between expansive (ternary mixture and CSA cement containing 50% gypsum) and non-expansive cements. Expansive cement pastes had (i) a nearly unimodal pore size distribution shifted toward higher radii and (ii) ettringite crystals smaller in size during the first day of curing. In a SEM image of a hardened paste of the CSA cement containing 50% gypsum, a stellate ettringite cluster was observed.     

A semi-empirical model of the aerodynamics of manoeuvring insect flight

Blade element modelling provides a quick analytical method for estimating the aerodynamic forces produced during insect flight, but such models have yet to be tested rigorously using kinematic data recorded from free-flying insects. This is largely because of the paucity of detailed free-flight kinematic data, but also because analytical limitations in existing blade element models mean that they cannot incorporate the complex three-dimensional movements of the wings and body that occur during insect flight. Here, we present a blade element model with empirically fitted aerodynamic force coefficients that incorporates the full three-dimensional wing kinematics of manoeuvring Eristalis hoverflies, including torsional deformation of their wings. The two free parameters were fitted to a large free-flight dataset comprising N = 26 541 wingbeats, and the fitted model captured approximately 80% of the variation in the stroke-averaged forces in the sagittal plane. We tested the robustness of the model by subsampling the data, and found little variation in the parameter estimates across subsamples comprising 10% of the flight sequences. The simplicity and generality of the model that we present is such that it can be readily applied to kinematic datasets from other insects, and also used for the study of insect flight dynamics.     

Mechanical characteristics of optical coatings prepared by various techniques: a comparative study

Good performance of optical coatings depends on the appropriate combination of optical and mechanical properties. Therefore, successful applications require good understanding of the relationship between optical microstructural and mechanical characteristics and film stability. In addition, there is a lack of standard mechanical tests that allow one to compare film properties measured in different laboratories. We give an overview of the methodology of mechanical measurements suitable for optical coatings; this includes depth-sensing indentation, scratch resistance, friction, abrasion and wear testing, and stress and adhesion evaluation. We used the techniques mentioned above in the same laboratory to systematically compare the mechanical behavior of frequently used high- and low-index materials, namely, TiO2, Ta2O5, and SiO2, prepared by different complementary techniques. They include ion-beam-assisted deposition by electron-beam evaporation, magnetron sputtering, dual-ion-beam sputtering, plasma-enhanced chemical-vapor deposition, and filtered cathodic arc deposition. The mechanical properties are correlated with the film microstructure that is inherently related to energetic conditions during film growth.     

Experimental study of quantum simulation for quantum chemistry with a nuclear magnetic resonance simulator

Quantum computers have been proved to be able to mimic quantum systems efficiently in polynomial time. Quantum chemistry problems, such as static molecular energy calculations and dynamical chemical reaction simulations, become very intractable on classical computers with scaling up of the system. Therefore, quantum simulation is a feasible and effective approach to tackle quantum chemistry problems. Proof-of-principle experiments have been implemented on the calculation of the hydrogen molecular energies and one-dimensional chemical isomerization reaction dynamics using nuclear magnetic resonance systems. We conclude that quantum simulation will surpass classical computers for quantum chemistry in the near future.     

电炉真空系统的设计与计算(一)

为了满足目前一些读者的需要,我们较系统地介绍了前苏联这方面的有关资料.内容有电炉真空系统计算的理论基础与计算方法及有关数据,最后给出真空感应炉、真空电阻炉、真空电弧炉和电子轰击炉真空系统的计算实例.这些数据和方法,对开发、研制各种真空电炉时,计算真空系统有一定的参考价值.     

电炉真空系统的设计与计算(二)

为了满足目前一些读者的需要,我们较系统地介绍了前苏联这方面的有关资料(文中保留原使用单位Torr,1 Torr=133 Pa).内容有电炉真空系统计算的理论基础与计算方法及有关数据,最后给出真空感应炉、真空电阻炉、真空电弧炉和电子轰击炉真空系统的计算实例.这些数据和方法,对开发、研制各种真空电炉时,计算真空系统有一定的参考价值.     

Calculated optical transitions in a silicon quantum wire modulated by a quantum dot

The photoluminescence lifetimes of Si quantum wires and dots have been previously calculated within a continuum model that takes into account the anisotropy of silicon band structure. Here, we present our calculations on the optical transitions in Si quantum wires modulated by a quantum dot. The geometrical parameters of the buldged wire are appropriate for porous Si and the ground state is localized. The photoluminescence lifetimes are calculated and compared with those of straight wires and dots. The magnitude of the lifetime is sensitive to the structural parameters of the nanostructures. Lifetimes varying from nanoseconds to milliseconds have been obtained. The results of the calculations provide insight to the optical properties of Si nanostructures.     

Calculated optical transitions in a silicon quantum wire modulated by a quantum dot

The photoluminescence lifetimes of Si quantum wires and dots have been previously calculated within a continuum model that takes into account the anisotropy of silicon band structure. Here, we present our calculations on the optical transitions in Si quantum wires modulated by a quantum dot. The geometrical parameters of the buldged wire are appropriate for porous Si and the ground state is localized. The photoluminescence lifetimes are calculated and compared with those of straight wires and dots. The magnitude of the lifetime is sensitive to the structural parameters of the nanostructures. Lifetimes varying from nanoseconds to milliseconds have been obtained. The results of the calculations provide insight to the optical properties of Si nanostructures.     

A semi-empirical unified model of strain fatigue life for insulation plastics

The paper focuses on modeling the strain fatigue lives of three commonly used cable insulation polymers, namely (1) polyvinyl chloride, (2) crosslinked polyethylene, and (3) polyphenylene ether under selected strain and temperature ranges. On the basis of results obtained from their fatigue tests, Coffin–Manson model, mean/maximum strain fatigue model, and a set of new semi-empirical equations were applied to establish the relationship between fatigue lives and strains. The unified strain model, herein we name it the Wei–Wong model, is developed to predict the fatigue lives of three polymers studied and their prediction capability was examined using our experimental data. It was found that the proposed Wei–Wong model can provide a better life prediction compared to the experimental data and other methods in the literature at selected temperatures, namely −40, 25, and 65 °C.     

Different shape of GaAs quantum structures under various growth conditions

We report the influences of growth parameters on the characteristics of GaAs quantum rings (QRs) and quantum dots (QDs) formed on AlGaAs/GaAs by the droplet epitaxy (DE) method. After forming Ga droplets on the AlGaAs/GaAs surface, varying amounts of arsenic (As) flux were introduced to fabricate the GaAs quantum structures. By decreasing the As flux from 8 × 10^− 5 to 3 × 10^− 5 Torr, the shape of the GaAs quantum structures was changed from QDs to elongated QRs. With further decreasing As flux, the shape of the elongated QRs became symmetric. The formation characteristics of the GaAs QRs from the QDs with the amount of As flux were discussed in terms of migration behaviors of the gallium (Ga) atoms on the GaAs(001)-c(4 × 4) surface. The effects of the amount of Ga supply and the growth temperature for the deposition of Ga droplets on the formation of the GaAs quantum structures were also considered.     

A quantum loop in magnetic field and a quantum interference rectifier

The electron transport in a curvilinear quantum wire exposed to a magnetic field was studied. A possible design of the quantum interference rectifier is suggested.     

A coupled quantum/continuum mechanics study of graphene fracture

A new technique is presented to study fracture in nanomaterials by coupling quantum mechanics (QM) and continuum mechanics (CM). A key new feature of this method is that broken bonds are identified by a sharp decrease in electron density at the bond midpoint in the QM model. As fracture occurs, the crack tip position and crack path are updated from the broken bonds in the QM model. At each step in the simulation, the QM model is centered on the crack tip to adaptively follow the path. This adaptivity makes it possible to trace paths with complicated geometries. The method is applied to study the propagation of cracks in graphene which are initially perpendicular to zigzag and armchair edges. The simulations demonstrate that the growth of zigzag cracks is self-similar whereas armchair cracks advance in an irregular manner. The critical stress intensity factors for graphene were found to be 4.21 MPa\({\sqrt {\rm m}}\) for zigzag cracks and 3.71 MPa\({\sqrt{\rm m}}\) for armchair cracks, which is about 10% of that for steel.