Experimental Results Of Changes Research Articles

Tuning the Johari-Goldstein β-Relaxation and Its Separation from α-Relaxation of Poly(n-alkyl methacrylate)s by Small Molecule-bridged Hydrogen Bonds

Introducing small molecule-bridged hydrogen bonds (HBs) between polymer chains has been reported to effectively reduce the inter-chain cooperativity despite of strengthening the intermolecular interaction. Here, a systematic investigation on tuning the Johari–Goldstein β (βJG) relaxation by adding various low-molecular-weight phenols in poly(n-alkyl methacrylate)s is carried out to further clarify the anomalous dynamics. Given these small molecules capable of coupling the motion with pendent groups of host polymers due to forming at least two HBs per molecule, poly(n-alkyl methacrylate) mixtures exhibit rich dynamic changes in the βJG-properties and α, βJG separations. An increased loading of phenols with a small size and strong inter-HB strength (Δυi) clearly benefits for significant retardation and suppression of the βJG-relaxation, narrows the α, βJG separation and converges the βJG-peak with the α-peak, which demonstrates the alleviation of inter-chain topological constraints. However, small molecules with a relatively big size and weak Δυi are found to amplify the magnitude of the α, βJG separation of poly(butyl methacrylate), even though experimental results of changes in α-dispersion and dynamic fragility confirm a reduction of the coupling factor n in all of these hybrids. The counterintuitive phenomenon suggests that the crossover time tc in the Coupling Model is no longer a universal quantity if the inter-chain of polymers is strengthened by HBs. These compelling findings shed vital insights into the HB-induced anomalous dynamics, and provide essential guidance for tailoring the βJG behavior and designing glassy polymeric materials.

On the features of production, design and reliability assessment of enclosing composite structures with effective thermal insulation

The article gives priority results on the production, design and assessment of the reliability of composite structures made of materials with energy-saving thermal insulation, physical heterogeneity of the parameters and the adhesion strength of the thermal insulation to the metal finishes. Addresses experimental results of changes in bulk mass, tensile and compressive strength, elastic properties in tension and compression along the thickness of the products perpendicular (⊥) and parallel to (ǁ) the product plane. Establishes the parameters of adhesion to the upper and lower finishes and their probability distributions according to Gauss, Gram-Charles, Pearson, Weibull and the log-normal law. This allows to set the standard values of thermal insulation. The article is aimed at the maximum use in buildings of sandwich panels of full factory production.

Changes in Dielectric and Mechanical Properties of Spheroplastic Containing Metallized Glass Microspheres under Compressive Deformation

The article presents experimental results of changes in the dielectric and mechanical characteristics of spheroplastics based on an organosilicon elastomer and metallized glass microspheres caused by static and shock compression. Two regions of the frequency dispersion of the dielectric constant are established that are associated with the metal coating of microspheres. It was found that both the low- and high-frequency dispersions of the complex dielectric constant decrease sharply at a relative compressive strain of no less than 70%. Possible causes of the detected change in the complex permittivity are discussed.

A research of microstresses and phase composition in alloys T30К4, T5К10 using diffraction of thermal neutrons

Samples T30К4, T5К10 are examined using diffraction of thermal neutrons in temperatures interval 20-600°C on reactor ИБР-2М (ОИЯИ). Temperature dependencies of a parameter of a hurdle of inner stresses of 3-rd type were calculated using Ritveld method taking into account diffraction specter. Experimental results of changes of crystal hurdles (TiW)C and WC are presented.

First-Principles Study of the Charge Distributions in Water Confined between Dissimilar Surfaces and Implications in Regard to Contact Electrification

The role of humidity in contact electrification is complex and multifaceted. With the aim of elucidating this role, we carry out first-principles molecular dynamics simulations of water confined between dissimilar surfaces. We address water confined between the (0001) surfaces of quartz and sapphire, as these surfaces have simple structures that allow for rigorous simulation while also being amenable to experimental investigation. The water takes on a layered structure, with the molecules somewhat oriented by the electric fields that arise in the system. The simulations find that the quartz charges negatively with respect to the sapphire, which concurs with previous experimental results. Yet interestingly we find that the water phase obtains a significant positive charge; we believe that this effect can have consequences in the contact electrification process, and also elucidate several experimental results for changes in electrostatic charge due to changes in relative humidity or pressure.

Recovery time of soil carbon pools of conversional Chinese fir plantations from broadleaved forests in subtropical regions, China

The conversion from natural forest to plantation has been widely applied, with consequences on ecosystem carbon pool. The experimental results of changes of soil carbon stocks after forest conversion are often contradictory. Moreover, the recovery time of soil carbon stocks after forest conversion varies among different sites. To examine the changes of soil carbon stocks following the forest conversions in the long-term and to estimate the recovery time, we selected 116 subtropical forests, including 29 pair-wise replicates for evergreen broadleaved forests (EBF, 40–100-year-old), young Chinese fir plantations (Cunninghamia lanceolata) (YCP, 4–8-year-old), middle-aged Chinese fir plantations (MACP, 13–20-year-old), and mature Chinese fir plantations (MCP, 23–32-year-old), and estimated soil carbon stocks. Soil carbon stocks of YCP and MACP decreased in average 12.5 and 28.7Mgha−1 compared with EBF, and showed no variation between MCP and EBF. Soil carbon stocks were positively correlated to soil total nitrogen stocks and C:N ratio. Our results showed that the forest conversions didn't cause a variation of soil carbon stocks in the long-term, although there was a short-term decline after conversion. The recovery time of soil carbon stock is 27years. These results indicate that the conversion from evergreen broadleaved forests to Chinese fir plantations in subtropical region of China causes soil carbon release in early stage, but has no effect on soil carbon stocks in the long-term. Prolonging the rotation period (>27years) would offset the adverse effects of the forest conversion on soil carbon stocks, and be critical in alleviating global climate change.

Raman spectroscopy for the control of soil contamination by copper ions

The experimental results of changes in the plant optical characteristics depending on the concentration of copper ions in the soil were presented by a method of Raman spectroscopy. Raman spectral features of plant tissue growing under the influence of copper ions in the soil that excess the MPC were obtained. The basic changes were registered at Raman bands 1325 cm-1, 1527 cm-1 and 1547 cm-1 that responsible for the stretching vibrations of chlorophyll a and b, carotene and chlorophyll a. The optical coefficient based on the dependence of the copper ion concentration from the optical parameters of plants was introduced. When the concentration of copper ions in the soil of 3 MPC observed increase optical coefficient values on the first day of experiments.

Change of Percolation Threshold in Carbon Powder-Filled Polystyrene Matrix Composites

This paper investigates the change of the percolation threshold in the carbon powder-filled polystyrene matrix composites based on the experimental results of changes in the resistivity and relative permittivity of the carbon powder filling, the electric field dependence of the current, and the critical exponent of conductivity. In this research, the percolation behavior, the critical exponent of resistivity, and electrical conduction mechanism of the carbon powder-filled polystyrene matrix composites are discussed based on a study of the overall change in the resistivity. It was found that the formation of infinite clusters is interrupted by a tunneling gap in the volume fraction of the carbon powder filling, where the change in the resistivity is extremely large. In addition, it was found that the critical exponent of conductivity for the universal law of conductivity is satisfied if the percolation threshold is estimated at the volume fraction of carbon powder where non-ohmic current behavior becomes ohmic. It was considered that the mechanism for changing the gaps between the carbon powder aggregates into ohmic contacts is identical to that of the connecting conducting phases above the percolation threshold in a random resister network system. The electric field dependence is discussed with a tunneling mechanism. It is concluded that the percolation threshold should be defined at this volume fraction (the second transition of resistivity for the carbon powder-filled polystyrene matrix composites) of carbon powder.

Removal of 2,4-Dichloro phenoxy acetic acid pesticide by solvent sublation: Experimental and theoretical studies

The removal of the pesticide 2, 4 D from water using solvent sublation process was investigated in this paper. A lab scale unit was set up and various experimental runs were carried out to study the efficiency of the removal process. The experimental findings show that the method is very effective (>90% removal) in removing traces (ppb level) of the pesticide which is not easily removable by simple air stripping. In addition a mathematical model was developed to describe the experimental findings. Some parameters of the model were measured or calculated while others such as the aqueous mass transfer coefficient and the solute partition coefficient were adjusted to fit the experimental data. The calibration of the model was carried out using the experimental results of change in gas flow rate (the easiest parameter to vary). A numerical sensitivity analysis was carried out using the calibrated model to study the effect of various parameters such as the bubble radius, aqueous phase drag-up by air, column radius and ratio of organic to aqueous volume phases.

Effect of head covers on directivity pattern of human head

In this paper are presented the experimental results of changes in directivity patterns of artificial head with three different types of head covers. The mathematical model of human head approximated by radially vibrating spherical cap set in a sphere is discussed. For the purpose of this research, the physical model of a human speaker head is constructed, and the far‐field detailed directivity patterns of the model with and without head covers is measured. Hair as porous absorber, cap and straw hat, as sound barriers, are discussed, and their influence on sound wave propagation is considered. Measured detailed directivity pattern changes affected by head covers in far field are calculated in step of ten degrees for spherical coordinates (polar angle and azimuth) and presented in form of two‐ and three‐dimensional polar plots.

Gas concentration and temperature in acoustically excited Delft turbulent jet flames

This paper shows the experimental results for changes in the flame structure when acoustic fields are applied in natural gas Delft turbulent diffusion flames. The acoustic field (pulsating combustion) generates zones of intense mixture of reactants in the flame region, promoting a more complete combustion and, consequently, lower pollutant emissions, increase in convective heat transfer rates, and lower fuel consumption. The results show that the presence of the acoustic field changes drastically the flame structure, mainly in the burner natural frequencies. However, for higher acoustic amplitudes, or acoustic pressures, a hydrogen pilot flame is necessary in order to keep the main flame anchored. In the flame regions where the acoustic field is more intense, premixed flame characteristics were observed. Besides, the pulsating regime modifies the axial and radial combustion structure, which could be verified by the radial distribution of concentrations of O 2, CO, CO 2, and NO x , and by the temperature profile. The experiments also presented the reduction of flame length with the increase of acoustic amplitude.

Model of local temperature changes in brain upon functional activation.

Experimental results for changes in brain temperature during functional activation show large variations. It is, therefore, desirable to develop a careful numerical model for such changes. Here, a three-dimensional model of temperature in the human head using the bioheat equation, which includes effects of metabolism, perfusion, and thermal conduction, is employed to examine potential temperature changes due to functional activation in brain. It is found that, depending on location in brain and corresponding baseline temperature relative to blood temperature, temperature may increase or decrease on activation and concomitant increases in perfusion and rate of metabolism. Changes in perfusion are generally seen to have a greater effect on temperature than are changes in metabolism, and hence active brain is predicted to approach blood temperature from its initial temperature. All calculated changes in temperature for reasonable physiological parameters have magnitudes <0.12 degrees C and are well within the range reported in recent experimental studies involving human subjects.

Correlation between grain boundary faceting–defaceting transition and change of grain boundary properties with temperature

The temperature dependence of grain boundary (GB) properties (e.g., grain boundary tension, migration rate and sliding rate) shows abrupt changes at certain temperatures, and such changes are accepted as evidence of a grain boundary phase transition. It has been suggested that such changes in the temperature dependence are interpreted as being related to a phase transition called the special–general grain boundary transition. However, they have not been well explained by the special–general grain boundary transition model. In this paper, this transition model and the experimental results of changes of grain boundary properties are briefly introduced, and the application of the model to the temperature dependence of grain properties is critically reviewed. A correlation between grain boundary faceting–defaceting transition and the changes in the temperature dependence of grain boundary properties are proposed.

Change of Inelastic Electron Tunneling Spectra of Organic Ultrathin Films by Voltage Pulses and Application to High-Density Recording Systems

Electron tunneling spectroscopy is important from both characterization and potential application viewpoints because it provides valuable information about the structure, orientation, and interactions of molecules in organic thin films. In particular, inelastic electron tunneling spectroscopy (IETS) using a scanning electron tunneling microscope reveals spatial and spectral information and is attractive as a high-density storage system. We describe the basic experimental results of changes in IETS patterns of organic monolayers induced by the voltage pulse, and the potential for application to high-density recording systems.

Activities of Water and Nitric Acid in Simulated Reprocessing Waste Solutions

Simulations were carried out for thermodynamic activities of water and nitric acid in simulated reprocessing solutions under a high level liquid waste (HLLW) evaporation condition. A prediction method based on a “Hydration Model” was developed to evaluate the activity coefficients of nitric acid and water in nitric acid solutions containing fission products. Suitability of the “Hydration Model” was confirmed; the changes in activity coefficient were well explained. Models predictions agreed well with the reported experimental results for changes of nitric acid concentration in the HLLW solution during the evaporation concentration process. The calculated activities of water and nitric acid were constant during the concentration process, except for the initial transient stage. Therefore nitric acid concentration changes should not have significant effects on chemical reactions, such as precipitation or volatilization, in the solution during HLLW concentration.

Particles in Thickening: Mathematical Model

A mathematical model to describe the changes in the particle size distribution immediately below the solid/liquid interface in gravity thickening was formulated and tested against experimental results. The distribution is predicted to change by coagulation and differential sedimentation. Modifications to the collision efficiency functions for Brownian motion, fluid shear, and differential sedimentation were necessary to account for the high concentrations in thickening. The model correctly predicted the observed trends for both the coagulation and differential sedimentation aspects of the experimental results for changes with time, solids concentration, particle stability, and the subsidence velocity of the interface. The model is limited by the fact that the subsidence velocity cannot be predicted and by the simplified approach to the hydrodynamics of differential sedimentation which is incorporated. The substantial agreement between the model and experimental results indicates that the conceptual approach of the model is well-founded. The lack of agreement in some cases also has led to further insight into the mechanisms of particle transport in a concentrated heterodisperse suspension.

Center-region geometry of the Berkeley 88-inch cyclotron

In order to determine the proper position of the dee edge, ion source, puller, and beam-defining clipper with respect to the magnet center, measurements of the structure of the electric field in the surroundings of the ion source were made with a half-scale model in an electrolytic tank. The acceleration process during the first three revolutions was studied for different geometries and starting phases, by a graphical approximation method for orbit plotting. A more detailed study was then made to determine initial conditions—such as orbit-center distribution, energy spread, axial focusing, and energy bunching—as functions of the center geometry and starting phase. By increasing the particle path length during the first half revolution approximately 20 deg—achieved by azimuthal displacement of the source—good results were obtained. The ion-start location was finally determined so as to bring the beam close to an equilibrium orbit at 10 in. radius. This was done with an orbit code, modified to take account of the increased transit time through the acceleration gap of smaller radii. Some experimental results of changes in the cyclotron beam quality, caused by changes in the ion-starting conditions, are presented.