Influence of nanowire density on the shape and optical properties of ternary InGaAs nanowires

We have synthesized ternary InGaAs nanowires on (111)B GaAs surfaces by metal-organic chemical vapor deposition. Au colloidal nanoparticles were employed to catalyze nanowire growth. We observed the strong influence of nanowire density on nanowire height, tapering, and base shape specific to the nanowires with high In composition. This dependency was attributed to the large difference of diffusion length on (111)B surfaces between In and Ga reaction species, with In being the more mobile species. Energy dispersive X-ray spectroscopy analysis together with high-resolution electron microscopy study of individual InGaAs nanowires shows large In/Ga compositional variation along the nanowire supporting the present diffusion model. Photoluminescence spectra exhibit a red shift with decreasing nanowire density due to the higher degree of In incorporation in more sparsely distributed InGaAs nanowires.     

Effect of aggregate shape on the mechanical properties of a simple concrete

The influence of aggregate shape on the fracture energy, tensile strength and elasticity modulus in concrete is considered. For this purpose, eight simple cement-based composites were designed, manufactured and tested, with two purposes: to provide experimental data that can throw some light on this involved problem and help in the design of future cement-based composites, and supply information that can be used as a benchmark for checking numerical models of concrete failure, as this simple composite is amenable to being modelled quite easily. Thirty-six notched beams were tested and values of the fracture energy and elasticity modulus were recorded. The tensile strength was measured from indirect standard tensile tests. Comparison with available experimental data is also included and discussed. Fracture was modelled using a cohesive crack with a bilinear softening function; data of the softening function inferred from the experimental measurements are also provided and discussed.     

Influence of mineralogical composition on the properties of lightweight aggregate

When sintering artificial lightweight aggregate, rapid cooling will generate micro-cracks. The paper investigates the effect of MgO contents on the physical, chemical and microstructural properties of artificial lightweight aggregate prepared under natural cooling in the furnace (SC) and rapid cooling outside the furnace (RC). Results indicate that cordierite (2MgO?2Al₂O₃?5SiO₂) starts forming in lightweight aggregate when MgO content reaches 2%, accompanied by a reduction in mullite. Cordierite has a better thermal-shock resistance and its presence minimizes the potential for micro-crack formation, thus decreasing water absorption under rapid cooling conditions for the 2% MgO system.     

Influence of type of aggregate and surface roughness on the interface fracture properties

An experimental investigation of interface fracture in high strength concrete is reported. An attempt has been made to study the influence of strength of mortar, type of aggregate and its roughness on interface fracture properties. The parameters include load-CMOD variations, tensile strength, and fracture energy of the interface. Stiffness, compliance and ductility factors of the composite specimens have been evaluated in Mode-I loading. The fracture energy increases as the roughness of the aggregate surface increases. The stiffness of the composite specimen increases as the roughness of the aggregate surface increases. The ductility factor (i.e. the fracture energy per unit of peak load) decreases as the surface area of the interface increases in sandwiched composite specimens in Mode-I failure, whereas it increases with the interface area in composite specimens with mortar cast against rough concrete aggregates. The interface exhibits brittle behavior with catastrophic failure indicating the application of LEFM to the interface.

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Résumé L'article présente une recherche expérimentale sur la rupture de l'interface du béton à haute résistance. Cet article tente d'étudier l'influence de la résistance du mortier, du type de granulat et de sa rugosité sur les propriétés de la rupture d'interface. Les paramètres incluent les variations charge-CMOD, la résistance à la traction, l'énergie de rupture de l'interface. Les facteurs de raideur, de conformité et de ductilité des échantillons en matériaux composites ont été évalués au moyen du type de chargement Mode I. L'énergie de rupture augmente à mesure que la rugosité de la surface du granulat augmente. La raideur du matériau composite augmente à mesure que la rugosité de la surface du granulat augmente. Le facteur de ductilité, à savoir l'énergie de rupture par unité de charge maximale, baisse lorsque la surface de l'interface augmente dans des échantillons composites moisés en rupture en Mode I, tandis qu'il augmente avec la zone d'interface des échantillons en matériaux composites avec le mortier projeté contre le béton à gros granulats. L'interface démontre un comportement fragile, témoin d'une rupture catastrophique indiquant l'application de LEFM à l'interface.

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Influence of field recycled coarse aggregate on properties of concrete

This paper investigates the influence of different amounts of recycled coarse aggregates obtained from a demolished RCC culvert 15 years old on the properties of recycled aggregate concrete (RAC). A new term called “coarse aggregate replacement ratio (CRR)” is introduced and is defined as the ratio of weight of recycled coarse aggregate to the total weight of coarse aggregate in a concrete mix. To analyze the behaviour of concrete in both the fresh and hardened state, a coarse aggregate replacement ratio of 0, 0.25, 0.50 and 1.0 are adopted in the concrete mixes. The properties namely compressive and indirect tensile strengths, modulus of elasticity, water absorption, volume of voids, density of hardened concrete and depth of chloride penetration are studied. From the experimental results it is observed that the concrete cured in air after 7 days of wet curing shows better strength than concrete cured completely under water for 28 days for all coarse aggregate replacement ratios. The volume of voids and water absorption of recycled aggregate concrete are 2.61 and 1.82% higher than those of normal concrete due to the high absorption capacity of old mortar adhered to recycled aggregates. The relationships among compressive strength, tensile strengths and modulus of elasticity are developed and verified with the models reported in the literature for both normal and recycled aggregate concrete. In addition, the non-destructive testing parameters such as rebound number and UPV (Ultrasonic pulse velocity) are reported. The study demonstrates the potential use of field recycled coarse aggregates (RCA) in concrete.     

Rheological properties of the whole blood of rheumatological patients

Using the method of nonstationary rheometry, the changes occurring in the rheological properties of the blood of rheumatological patients in plasmapheresis in the range of rates of shear of 1–10 sec⁻¹ at a temperature of 37°C were studied. These studies were paralleled by measurements of the hematocrit index to correct the viscosity of the blood. A statistically reliable mathematical dependence of the change in the rheological properties of blood in plasmapheresis has been constructed. The role of the rheological factor of blood as a possible additional diagnostic parameter in plasmapheresis has been evaluated. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 73, No. 4, pp. 792–796, July–August, 2000.     

Influence of the aggregate quality on the physical properties of natural feebly-hydraulic lime mortars

This paper examines the influence of the shape, average size and calcite content of the aggregate on strength, porosity, water absorption, density and capillary suction of natural feebly-hydraulic lime (NHL 2) mortars. Four types of aggregate were analysed in order to determine calcite content, particle shape and average particle size. Four different mortar mixes were then designed and produced using each of the aggregate types and NHL 2 as a binder. The mixing and curing as well as the aggregate:binder proportions were kept constant in order to attribute variation of mortar properties to the quality of the aggregate. The results suggest that an increase in the aggregate’s calcite content lowers the flexural and compressive strength of the mortar. This study also determined that sharp aggregate as well as aggregate with a small average particle size tends to increase the mechanical strength and bulk density of a mortar simultaneously reducing porosity, water absorption and capillary suction. Furthermore, this paper concludes that aggregates containing particles of a wide size range will also increase the mechanical strength and bulk density of the hardened mortar diminishing porosity, water absorption and capillary suction.      

Influence of anions on the formation and properties of chitosan-DNA nanoparticles

Chitosan-DNA nanoparticles were prepared by using different anions (such as chloride, sulfate, citrate, and tripolyphosphate) as mediation agents. The research suggested that the formation and morphological characteristics of chitosan-DNA nanoparticles largely depended on concentration, molecular size, charge number, and chemical structure of anions, as well as chitosan/DNA ratio. The observation by atom force microscopy showed that chitosan-DNA nanoparticles mediated by four anions (in their appropriate range of concentration) had a spherical shape, narrow size distribution, and good monodispersivity. Especially, nanoparticles mediated by sulfate and TPP had a size distribution of 40-50 nm. Additionally, the nanoparticles presented high encapsulation efficiency and good protection of DNA from DNasel digestion. The zeta-potential of nanoparticles could be adjusted moderately by adding different anions and controlling their concentrations, and DNA encapsulation efficiency was not influenced, which would reduce nonspecific interactions with the cell membrane and nanoparticle toxicity. Smaller size and lower zeta-potential will be beneficial for improving gene therapy. In addition, the anion mediation method has potential for the preparation of cationic polymer nanoparticles as drug or gene vectors.     

Influence of annealing on the optical properties of amorphous germanium films

The influence of annealing on the optical, electrical and structural properties of thin amorphous Ge films deposited under well-defined conditions has been investigated. The results below the onset of recrystallization are interpreted as due to a progressive elimination of defects and an evolution of the films towards an “ideal” amorphous state. Various mechanisms are discussed in relation with various structural models.     

Influence of ZrO2 particles on the optical properties of pc-LEDs

Experimental and modeling progress and results aiming to increase the color uniformity of hemisphere-type pcW-LEDs are proposed. By adding micrometric zirconia particles, the light scattering is enhanced, that induces a decrease of phosphor necessary to obtain a specific CCT. The optical model is able to determine the optical properties (CCT, angular CCT distribution, chromaticity and packaging efficiency) in a hemisphere LED for various amount of YAG-phosphor and ZrO₂-zirconia particles. Based on previous process, the work is in the first step to fit the effective radius and refractive index that will be implemented in the optical model. In the second step, the optical model is compared with the experimental measurement to determine the absorption coefficient and conversion efficiency of a package of silicone resin containing phosphor and zirconia. Finally, the model, confirmed by selected experimental results, allows determining the optical properties of any king of package that lead to a CCT emission ranging from 4500 K to 6500 K. The analysis of these data is interpreted by comparing, for a specific CCT, the phosphor loss, the packaging efficiency and the angular distribution of CCT. The results show that if the effort is targeted on one of the previous parameters, there is always a counterpart on the other ones. Increasing the color uniformity will induce to decrease the packaging efficiency.     

颗粒整形对再生粗骨料性能的影响

为了有效提高再生粗骨料的性能,必须对再生骨料进行机械强化处理.首次提出了利用高速(线速度≥80m/s)运动的再生骨料之间的反复相互冲击与摩擦作用,有效地打掉较为突出的棱角和除去颗粒表面附着的砂浆和水泥石的一种新技术.研究表明:颗粒整形使再生骨料的颗粒堆积密度平均提高了9.3%、表观密度从2.56g/cm3提高到2.59g/cm3、空隙率从53.3%降至48.5%、吸水率从4.7%降至2.9%、压碎指标值从15.8%降至9.4%,而且堆积密度、密实密度和针片状骨料含量等指标均优于天然碎石骨料,完全能够满足配制普通混凝土的要求.     

Ultrasonic attenuation and backscatter from flowing whole blood are dependent on shear rate and hematocrit between 10 and 50 MHz

Ultrasonic backscatter has recently been used extensively to investigate erythrocyte aggregation, which is an inherent hematological phenomenon in the blood circulation system. The size of rouleaux can be estimated by measuring certain parameters of signals backscattered from flowing blood. However, most measurements of backscatter from blood use a constant value for the attenuation coefficient to compensate for the loss of ultrasound energy. This correction may be inaccurate because the attenuation varies with the blood properties, which prompted us to explore the effects of hemodynamic properties on ultrasonic attenuation and backscatter to better understand the blood rheological behaviors. Experiments were performed on porcine whole blood in a Couette flow apparatus. Ultrasonic attenuation and the backscattering coefficient of blood were measured at various frequencies (from 10 to 50 MHz), hematocrits (from 0 to 60%), and shear rates (from 0.1 to 200 s?1). The results indicated that the attenuation and backscattering coefficients of blood are highly variable, depending in a complex manner on shear rate, hematocrit, and the measurement ultrasound frequency. The attenuation of blood decreased rapidly with increasing shear rates, eventually reaching a steady state asymptotically, and increased linearly with the hematocrit from 10 to 50 MHz at various shear rates, and also with the ultrasound frequency. The effect of erythrocyte aggregation means that the change in ultrasonic attenuation in blood with shear rate may be attributed to the absorption mechanism, which is enhanced by the increased blood viscosity at lower shear rates. Compensating the measured backscattering coefficients of blood for the shear-rate-dependent attenuation coefficient increased the accuracy of erythrocyte aggregation assessments. Together, the experimental results suggest that the shear-rate-dependent attenuation coefficient should be considered in future developments of ultrasonic technologies for characterizing blood rheology when the ultrasound frequency is higher than 20 MHz.     

Influence of texture on optical and electrical properties of diamond films

The optical and electrical properties of variously textured diamond films have been investigated in this paper. SEM and Raman spectrum indicated that the films produced were of high quality with either (0 0 1) or (1 1 1) orientation. A four-layer model was used to fit the measured spectroscopic ellipsometry data. The results indicated that the properties of (0 0 1)-oriented diamond films were superior to those of (1 1 1)-oriented one. The refractive index and extinction coefficient of (0 0 1)-oriented diamond film in the infrared region of 2500-12500 nm was measured as 2.391 and of the order of 10⁻⁵, respectively and that for (1 1 1)-oriented one was 2.375 and of the order of 10⁻⁴, respectively. The dark current of the (0 0 1)-oriented diamond film was measured as 33.7 nA for an applied electric field of 100 kV cm⁻¹, its resistivity being about 2.33×10¹⁰ Ω cm. Current passing through the (0 0 1)-oriented diamond film during testing did not change significantly.     

Relationship between aggregate and sediment bed properties: Influence of inter-particle adhesion

The influence of the magnitude of inter-particle attraction and adhesion, aggregate size and aggregate structure on the shear and compressive rheological behaviour of flocculated suspensions has been studied. Ninety nanometer diameter silica particles have been flocculated with poly diallyldimethylammonium chloride based cationic polymers of molecular weight approximately 100–300 kDa and 10–100% cationic charge. The amount of charge on the polymer influences the adsorption conformation of the polymer which influences the dominant mechanism for inter-particle attraction. Low charge density results in primarily bridging flocculation while high charge density results in primarily charge patch attraction. Although the bridging adhesion is generally lower in magnitude than for the charge patch, the bridging flocculation typically produces large aggregates while the charge patch mechanism results in smaller aggregates due to the influence of shear during aggregation. The optimum dose for aggregation (supernatant clarity) of each type of polymer corresponds well with the polymer concentration which produces the maximum adhesive force measured with AFM. The influence of aggregate size on the compressive and shear yield stresses is weak, but the compressive and shear yield stresses increase linearly with increasing adhesion force.     

Influence of nitrogen on the optical and mechanical properties of diamond-like carbon films

Optical and mechanical properties of diamond-like carbon films grown by chemical vapor deposition were investigated as a function of the nitrogen content in the gas mixture. The nonmonotonic variation of the optical band gap and the microhardness of the films are interpreted using a model which allows for the influence of nitrogen on their structure. It is shown that nitrogen-containing diamond-like carbon films hold out promise as protective and antireflection coatings for silicon solar cells. Pis’ma Zh. Tekh. Fiz. 24, 87–92 (May 26, 1998)     

Influence of thermoviscoelastic properties and loading conditions on the recovery performance of shape memory polymers

This work investigated the influence of material properties and loading conditions on the recovery performance of amorphous shape memory polymers using a recently developed thermoviscoelastic model. The model incorporated the time-dependent mechanisms of stress and structural relaxation and viscoplastic flow to describe the glass transition of the material from a soft viscoelastic rubber to a hard viscoplastic glass. The model captured many important features of the unconstrained strain recovery response and of the stress hysteresis observed in the constrained recovery response. A parameter study was developed that varied the model and loading parameters one-by-one to compare their effects on the start and end temperatures and recovery rate of the unconstrained recovery response and on the stress hysteresis of the constrained recovery response. The loading parameters included the cooling rate, the annealing time, and the high and low temperatures of the programming stage and the heating rate of the recovery stage. The results confirmed experimental observations that viscoelasticity is the underlying mechanism of the unconstrained recovery response. In contrast, the constrained recovery response was influenced by the interaction of many different mechanisms, including thermal expansion and structural and stress relaxation. For the loading parameters, the cooling rate of the programming stage and the heating rate of the recovery stage had the largest influence on both the constrained and unconstrained recovery response.     

Influence of self-oxide formation regimes on the properties of oxide-p-InSe heterojunctions

Oxide-p-InSe heterojunctions were formed by thermal oxidation of a p-InSe crystal substrate in various temperature-time regimes. Measurements of the current-voltage characteristics confirmed that these were of good optical quality. The optimum technological conditions for fabricating these junctions were determined. Pis’ma Zh. Tekh. Fiz. 25, 34–36 (July 12, 1999)