Contributions Of Different Mechanisms Research Articles

Analysis of the Two-Phase Heat Transfer Coefficient of Propane in a Small Channel

This study investigates the contributions of different mechanisms of heat transfer in two phase flow boiling heat transfer coefficient for propane (natural refrigerant) in a small channel. The effects of heat flux and mass flux towards maximizing the heat transfer is studied by comparing experimental data from 7.6mm diameter horizontal channel and outcomes from optimization using multi-objective genetic algorithm (MOGA). The latter is utilized as a tool for a fast prediction of the heat transfer coefficient, investigating the conditions for optimized mass flux, heat flux and vapor quality that can simultaneously generate maximized heat transfer due to nucleate boiling as well as forced convection. A swift prediction of the performance of “new” refrigerants can save time and money in our efforts towards a greener environment. Two correlations are investigated to predict the heat transfer coefficient. In the low vapor quality region, the optimized outcomes based on established correlations follow the trend of the experimental data. The optimized predicted heat transfer coefficient due to nucleate boiling contribution decreases with increasing quality while that due to forced convection increases. Discrepancies still exist between correlations since they include/exclude terms that are believed to be contributing factors in the overall heat transfer coefficient. The capability of MOGA exhibited here contributes towards a faster prediction of the heat transfer pattern and trend which is useful in the investigations of the performance of future “new” refrigerants as well as newly developed correlations under different flow and experimental conditions.

The many facets of tunneling magnetoresistance in $$\hbox {Sr}_2\hbox {FeMoO}_6$$ Sr 2 FeMoO 6

The nature and shape of the magnetoresistance versus magnetic field responses of polycrystalline $$\hbox {Sr}_2\hbox {FeMoO}_6$$ has been a matter of intense debate. Other than the conventional intergranular tunneling magnetoresistance with nonmagnetic grain boundaries as tunnel barriers, intragranular contributions due to the presence of magnetic anti-phase boundaries as barriers and magnetically frustrated grain surface barriers giving rise to spin-valve-type magnetoresistance also turn out to be important. We find that each of these descriptions are partially true, while it is the physical state of the sample resulting from different sample synthesis and treatment conditions that defines the relative contributions of different mechanisms. It is also shown that a purely conventional intergranular TMR response can be realized only when small grain, well ordered pellets are annealed at or above 1500 $$^{\circ }\hbox {C}$$ . Low temperature annealing of already highly ordered samples lead to formation of $$\hbox {SrMoO}_4$$ patches which further modify the magnetoresistance of this material. The dissolution of this phase takes place only after annealing above 1100 $$^{\circ }\hbox {C}$$ which leads to the enhancement in the moment and ordering of the sample.

Contributions of microbial activity and ash deposition to post-fire nitrogen availability in a pine savanna

Abstract. Many ecosystems experience drastic changes to soil nutrient availability associated with fire, but the magnitude and duration of these changes are highly variable among vegetation and fire types. In pyrogenic pine savannas across the southeastern United States, pulses of soil inorganic nitrogen (N) occur in tandem with ecosystem-scale nutrient losses from prescribed burns. Despite the importance of this management tool for restoring and maintaining fire-dependent plant communities, the contributions of different mechanisms underlying fire-associated changes to soil N availability remain unclear. Pulses of N availability following fire have been hypothesized to occur through (1) changes to microbial cycling rates and (2) direct ash deposition. Here, we document fire-associated changes to N availability across the growing season in a longleaf pine savanna in North Carolina. To differentiate between possible mechanisms driving soil N pulses, we measured net microbial cycling rates and changes to soil δ15N before and after a burn. Our findings refute both proposed mechanisms: we found no evidence for changes in microbial activity, and limited evidence that ash deposition could account for the increase in ammonium availability to more than 5–25 times background levels. Consequently, we propose a third mechanism to explain post-fire patterns of soil N availability, namely that (3) changes to plant sink strength may contribute to ephemeral increases in soil N availability, and encourage future studies to explicitly test this mechanism.

Formation of 3He in the reactions of stopped pion absorption

The results of the measurements of spectra and yields of helium isotope 3He formed in the stopped pion absorption by nuclei are presented. The contributions of different mechanisms of the helium formation in these reactions on medium and heavy nuclei were determined. The proposed phenomenological model reproduces the 3He spectra at energies >30 MeV satisfactorily.

Double Charmonia Production at LHCb

In this note next-to-leading order corrections to double charmonium production at LHCb are considered. It is shown that real gluon emission leads to significant change of the cross sections of considered processes. For example, forbidden at leading order production of C-odd state XcJ/Ψ is possible at NLO. Distributions over various kinematical variables are analyzed and the question of separating contributions of different mechanisms (direct J/ΨJ/Ψ production, radiative feed-down from XcJ/Ψ, double parton scattering) is considered.

Hydrate plugging mechanisms of oil-dominated, water- dominated and partially dispersed system

It is the hydrate plugging mechanisms of multiphase flow that are the key to implement hydrate risk management, which have always been the focus of flow assurance industry. This paper reviews the experiments and principle analysis conducted by many researchers, and summarizes types of experimental equipment and methods, and then concludes different mechanisms for hydrate plugging in oil-dominated system, water-dominated system and partially dispersed system, while giving out some suggestions for further researches. Because of the lack of field data and the difficulty of conducting field plugging experiments, at present, designing experimental apparatus is the common solution around the world, such as autoclave and flowloop, to undertake simulation study, with the purpose to investigate plugging mechanisms. Stirring and rocking are two main methods for autoclaves to simulate pipe flow, which results in the flow characters of autoclaves is different from the real pipe flow. So flowloops are superior to autoclaves in simulating pipe flow, while some visual autoclaves (sapphire cell and so on) are better than flowloops in direct visual observation. In micro level, FBRM and PVM could provide particle distribution and behavior information. MMF apparatus could measure cohesive force between particles and adhesive force between particles and pipe walls. These micro level apparatus would help to estimate the tensile strength and the size of aggregates, which are meaningful to predict rheological properties of the fluid and the pressure drop of the pipeline. More efforts should be done on the combination of micro measurement and macro measurement, and finding a better way for autoclaves to simulate pipe flow more accurately and a better way for flowloops to improve visual observation. Plugging mechanism will be different when it comes to different multiphase systems. For oil-dominated system, which has been researched for the longest time and has the most mature theoretical system, agglomeration, adhesion to pipe walls and bedding are the governing factors of plugging. When oil-dominated system is treated by AAs, under risk management, agglomeration will be weaken significantly. Then the plugging mechanism of this condition would be controlled by bedding and adhesion to pipe walls. More works should be done on the theoretical modeling of adhesion to pipe walls and bedding for oil dominated system, and confirm the contribution of different mechanism to the pressure drop. For water-dominated system, research of which is prospective, bedding of hydrate particles or hydrate network is the determining reason for plugging. Since the hydrate growth rate of water-dominated system is relatively low, this system has the lowest plugging tendency. The molding of hydrate growth for water-dominated system would be the next step work. Research on partially dispersed system is carried out with the increasing water cut in the offshore oil fields, which is now in the experiment exploration period. Plugging of this system is resulted from film growth of the free water and agglomeration in the bulk phase, which resulting in the most severe plugging tendency. The quantification of the free water for partially dispersed system is fundamental for the continuing study. Moreover, it is significant to take the impact of flow patterns on the plugging mechanisms into consideration.

Separating climate change signals into thermodynamic, lapse-rate and circulation effects: theory and application to the European summer climate

Climate models robustly project a strong overall summer warming across Europe showing a characteristic north-south gradient with enhanced warming and drying in southern Europe. However, the processes that are responsible for this pattern are not fully understood. We here employ an extended surrogate or pseudo-warming approach to disentangle the contribution of different mechanisms to this response pattern. The basic idea of the surrogate technique is to use a regional climate model and apply a large-scale warming to the lateral boundary conditions of a present-day reference simulation, while maintaining the relative humidity (and thus implicitly increasing the specific moisture content). In comparison to previous studies, our approach includes two important extensions: first, different vertical warming profiles are applied in order to separate the effects of a mean warming from lapse-rate effects. Second, a twin-design is used, in which the climate change signals are not only added to present-day conditions, but also subtracted from a scenario experiment. We demonstrate that these extensions provide an elegant way to separate the full climate change signal into contributions from large-scale thermodynamic (TD), lapse-rate (LR), and circulation and other remaining effects (CO). The latter in particular include changes in land-ocean contrast and spatial variations of the SST warming patterns. We find that the TD effect yields a large-scale warming across Europe with no distinct latitudinal gradient. The LR effect, which is quantified for the first time in our study, leads to a stronger warming and some drying in southern Europe. It explains about 50 % of the warming amplification over the Iberian Peninsula, thus demonstrating the important role of lapse-rate changes. The effect is linked to an extending Hadley circulation. The CO effect as inherited from the driving GCM is shown to further amplify the north-south temperature change gradient. In terms of mean summer precipitation the TD effect leads to a significant overall increase in precipitation all across Europe, which is compensated and regionally reversed by the LR and CO effects in particular in southern Europe.

Rail strengthening in prolonged operation

In rail operation (with traffic corresponding to passed tonnage of gross loads of 500 and 1000 million t), the surface layer of the steel is significantly strengthened. Electron-microscope data permit quantitative analysis of the contribution of different mechanisms to rail strengthening in prolonged operation, at different distances from the contact surface. The strengthening is multifactorial: it involves substructural strengthening associated with nanofragment formation; dispersional strengthening by carbide particles; the formation of atmospheres at dislocations; and polar stress due to interphase and intraphase boundaries. The significant increase in the surface strength of rail steel after prolonged operation (passed tonnage of gross loads of 1000 million t) is due to the presence of long-range internal stress fields and to the fragmentation of material with the formation of nanostructure.

CrossHub: a tool for multi-way analysis of The Cancer Genome Atlas (TCGA) in the context of gene expression regulation mechanisms.

The contribution of different mechanisms to the regulation of gene expression varies for different tissues and tumors. Complementation of predicted mRNA–miRNA and gene–transcription factor (TF) relationships with the results of expression correlation analyses derived for specific tumor types outlines the interactions with functional impact in the current biomaterial. We developed CrossHub software, which enables two-way identification of most possible TF–gene interactions: on the basis of ENCODE ChIP-Seq binding evidence or Jaspar prediction and co-expression according to the data of The Cancer Genome Atlas (TCGA) project, the largest cancer omics resource. Similarly, CrossHub identifies mRNA–miRNA pairs with predicted or validated binding sites (TargetScan, mirSVR, PicTar, DIANA microT, miRTarBase) and strong negative expression correlations. We observed partial consistency between ChIP-Seq or miRNA target predictions and gene–TF/miRNA co-expression, demonstrating a link between these indicators. Additionally, CrossHub expression-methylation correlation analysis can be used to identify hypermethylated CpG sites or regions with the greatest potential impact on gene expression. Thus, CrossHub is capable of outlining molecular portraits of a specific gene and determining the three most common sources of expression regulation: promoter/enhancer methylation, miRNA interference and TF-mediated activation or repression. CrossHub generates formatted Excel workbooks with the detailed results. CrossHub is freely available at https://sourceforge.net/projects/crosshub/.

Nonradiative recombination of excitons in semimagnetic quantum dots

The mechanisms of the nonradiative recombination of excitons in neutral and charged quantum dots based on II–VI semimagnetic semiconductors are investigated. It is shown that, along with the dipole–dipole and direct-exchange mechanisms, there is one more mechanism referred to as the indirect-exchange mechanism and related to sp–d mixing. The selection rules for nonradiative recombination by exchange mechanisms are subsequently derived. The dependence of the efficiency of all recombination mechanisms on the quantum-dot size is studied. The experimentally observed growth in the intracenter photoluminescence intensity with decreasing size of dots and nanocrystals is accounted for. Methods for experimental determination of the contributions of different mechanisms to nonradiative recombination are discussed.

Living up to expectations: Estimating direct and indirect rebound effects for UK households

This study estimates the combined direct and indirect rebound effects from various types of energy efficiency improvement by UK households. In contrast to most studies of this topic, we base our estimates on cross-price elasticities and therefore capture both the income and substitution effects of energy efficiency improvements. Our approach involves estimating a household demand model to obtain price and expenditure elasticities of different goods and services, utilising a multiregional input–output model to estimate the GHG emission intensities of those goods and services, combining the two to estimate direct and indirect rebound effects, and decomposing those effects to reveal the relative contribution of different mechanisms and commodities. We estimate that the total rebound effects are 41% for measures that improve the efficiency of domestic gas use, 48% for electricity use and 78% for vehicle fuel use. The primary source of this rebound is increased consumption of the cheaper energy service (i.e. direct rebound) and this is primarily driven by substitution effects. Our results suggest that the neglect of substitution effects may have led prior research to underestimate the total rebound effect. However, we provide a number of caveats to this conclusion, as well as indicating priorities for future research.

A modeling approach to scattering and reverberation in shallow water

A physics-based modeling approach is described that allows prediction of reverberation in complex shallow water environments. An integral expression is presented for the backscatter intensity with a factorized integrand comprised of two kernels, the two-way propagator and the scattering kernel. The propagator is defined by Green’s function, describes the local intensity, and can be calculated using available models, such as PE, normal modes, or ray approximations. An expression for the scattering kernel is obtained using a unified approach to volume and roughness scattering [Ivakin, JASA Feb. 1998], and represents a sum of volume and roughness scattering coefficients. They are specified for sea-water column and rough heterogeneous seabed with continuous spatial fluctuations of compressibility and density, and/or discrete randomly distributed targets, such as bubbles, fish, shells, and others. Results of numerical simulations for shallow water reverberation time/range series, based on a PE propagation model, are presented, and potential contributions of different mechanisms of scattering are compared and discussed. The approach is applied to consider reverberation in a complex shelly sand/mud environment, such as one at the Target and Reverberation Experiment 2013 (TREX), and results in model/data comparisons based on analysis of TREX acoustic scattering data and environmental ground truth measurements. [Work supported by ONR-OA.]

Expression of different mechanisms of resistance to insects in groundnut under field conditions

Host plant resistance is an important component of pest management, and information on contribution of different mechanisms of resistance is important for developing cultivars with resistance to the target pests. Therfore, we studied the contribution of different components of resistance in five groundnut genotypes to three insect species occurring in India under field conditions. Plant damage by the larvae of Helicoverpa armigera, Spodoptera litura, and leafhoppers (Empoasca kerri) was evaluated visually on a 1 – 9 damage rating (DR) scale (1 being 80 % leaf damage). Further, the activities of various plant defensive enzymes [peroxidase (POD), polyphenol oxidase (PPO), phenylalanine ammonia lyase (PAL), superoxide dismutase (SOD), ascorbate peroxidase (APX), lipoxygenase (LOX) and catalase (CAT)], and the amounts of total phenols, condensed tannins, hydrogen peroxide (H2O2), malondialdehyde (MDA) and proteins were also recorded. The genotypes ICGV 86699, ICGV 86031, ICG 2271 and ICG 1697 suffered lower leaf damage by H. armigera and S. litura (DR 2.6 – 3.2) and E. kerri (DR 2.0 - 3.2) as compared to JL 24 (DR 7.2 and 6.0, respectively). ICGV 86699, ICGV 86031, ICG 2271 and ICG 1697 exhibited greater enzymatic activity, and had more amounts of phenols, condensed tannins, hydrogen peroxide and proteins than the susceptible check, JL 24. There was a positive association between leaf damage and the activity of the defensive enzymes, and the amounts of phenols, condensed tannins and H2O2. These results suggested that the plant defensive enzymes such as POD, PPO, LOX, PAL, SOD, APX and CAT were involved in genotypic resistance to insects, and the resistant genotypes accumulated phenols, condensed tannins, and H2O2 to impart resistance to insects. This information will be useful for developing groundnut genotypes with resistance to insects for sustainable crop production.

Elucidation of structure-to-property relationships of piezoresistive polymer-carbon nanotube nanocomposites

Polymeric nanocomposites (PNC) filled with carbon nanotubes (CNTs) possess superior multifunctionality, including electrical, thermal, and mechanical properties, making them an emerging family of advanced and multifunctional materials. In recent years, flexible polymer/CNT nanocomposites are increasingly being considered as promising alternatives to conventional smart materials. Their piezoresistive behaviours have led to many potential applications in strain sensing. Despite extensive experimental and theoretical research, the underlying mechanisms for polymer/CNT nanocomposites' piezoresistive behaviours have yet been elucidated. This paper reports comprehensive investigations on the mechanisms and the structure-to-property relationships of these piezoresistive nanocomposites. Quantitative analyses revealed that piezoresistivity of polymer/CNT nanocomposites is predominantly governed by the three mechanisms related to the strain-induced morphological evolution of the CNT network embedded in the polymer matrix. Furthermore, both CNT content and CNT alignment are key structural parameters that affect the contribution of different mechanisms on PNCs' piezoresistivity and the sensitivity of flexible PNCs as strain sensors. For PNC filled with high content of randomly dispersed CNTs, the piezoresistivity was predominantly caused by the breakage of a complex conductive network into two or more simpler conductive paths. For PNC filled with low content of highly aligned CNTs, the piezoresistivity was mainly contributed by the complete disruption of originally interconnected CNTs in electrically conductive pathways.

Fragmentation of crystals upon deformation twinning and dynamic recrystallization

The mechanism of the formation of a fragmented structure has been studied using the EBSD analysis on the example of the microstructure of the zone of the welding joint obtained by explosive welding of copper sheets. The process of the structure formation included, besides the formation of boundaries of deformation origin, also deformation twinning and dynamic recrystallization. A method of a computer analysis of the distribution of interfragment misorientations, which makes it possible to determine the partial contributions of different mechanisms of fragmentation and to estimate the parameters of the distribution, is suggested. Based on the analysis performed, it is recommended to select metals inclined to deformation twinning to obtain ultrafine-grained materials.

Angular distributions of the alpha particle production in the 7Li+144Sm system at near-barrier energies

We have studied the production of alpha particles in reactions induced by 7Li projectiles on a 144Sm target at bombarding energies of 18, 24 and 30 MeV over the 15°-140° angular range. The purpose of the investigation has been to determine the contribution of different mechanisms in reactions that involve weakly bound projectiles. We have included in our analysis several processes that can either directly or sequentially lead to the emission of alpha particles: complete fusion, direct transfer of 3H, capture breakup (incomplete fusion, sequential complete fusion) and non-capture breakup. In order to distinguish alpha particles stemming from these processes it is necessary to determine the mass and charge of the reaction products and to obtain precise measurements of their energies and scattering angles over relatively wide ranges of these variables. We have done this using a detection system consisting of an ionization chamber plus three position sensitive detectors. We present results of these measurements and a preliminary interpretation based on kinematical considerations and comparisons with predictions from a statistical model.

Analysis of Strouhal number based equivalence of pitching and plunging airfoils and wake deflection

Numerical simulations have been used to analyze the equivalence of pitching and plunging motions found in a flapping NACA0012 airfoil. Two-dimensional incompressible Navier–Stokes equations are solved at Reynolds number of 103 over a range of Strouhal numbers. A novel criterion based on the Strouhal number is proposed which provides equivalence of pitching and plunging motions using the length scale traversed by the trailing edge in each case. Aerodynamic coefficients are found to match well for both the kinematics in temporal as well as spectral domains. Detailed analysis provides contribution of different mechanisms, such as vortex shedding, added mass, interaction of leading and trailing edge vortices, in the overall aerodynamic forces produced by a pitching or plunging airfoil. Wake deflection is observed for a plunging airfoil at high Strouhal numbers resulting in a bias in the lift coefficient. Further investigation reveals the dominance of second harmonic of the fundamental frequency in the lift spectrum emphasizing the role of quadratic nonlinearity in the observed phenomenon.

Ultrasound-assisted homogeneous photocatalytic degradation of Reactive Blue 4 in aqueous solution

The catalytic degradation of Reactive Blue 4 (RB4) by an emerging ultrasound-assisted photo-Fenton process with artificial ultraviolet light was investigated. The photocatalytic degradation efficiency was determined by the decrease in Total Organic Carbon (TOC) content. The influences of pH and initial concentrations of Fe(II) and H2O2 on the RB4 solution mineralization were studied. Under the optimal conditions, TOC removal increased up to 94% in 60min, and this system permitted the use of a low ferrous concentration of only 5mgL−1. The RB4-mineralization process in the sono-photo-Fenton system can be described by a mechanism involving mineralization by direct photolysis, ultrasonically generated oxidative species, direct oxidation reaction with H2O2, radical reaction (mainly HO•) and thermal pyrolysis inside the bubble. The radical reaction in the bulk solution or in the vicinity of the bubble was found to be the main mineralization pathway. The contribution of different mechanisms to overall mineralization was the following: radical reaction (93.60%), direct reaction with H2O2 (2.56%), photolysis (1.92%) and reaction by ultrasonically generated oxidative species (1.92%). The influence of the Fe catalyst on the radical reaction was evaluated by conducting the reaction in the presence and absence of the scavenging agent potassium iodide (KI). The toxicity profile of sono-photo-Fenton process was also evaluated.

Contributions of I(F) and Sarcoplasmic Reticulum Ca2+ in the Control of Spontaneous Cardiac Beating Rate in Mouse and Guinea-Pig

Spontaneous beating rate was studied in mouse isolated atrial preparations and in guinea-pig single myocytes isolated from the sinus node (SAN) region of the heart. In atrial preparations, the I(f) blockers ZD7288 (1 μM) and ivabradine (3 μM) both reduced spontaneous beating rate by more than 200 bpm, and the change in beating rate caused by the combination of ivabradine and ZD7288 was not significantly different from the changes caused by either drug alone. Application of cyclopiazonic acid (CPA, to inhibit SERCA) also reduced beating rate by about 150 bpm. ZD7288 alone, ivabradine and the combination of ZD7288 and ivabradine all depressed the log(concentration)-effect curves for the effect of isoproterenol on rate by similar amounts. CPA alone caused a greater depression of isoproterenol log(concentration)-effect curves than was the case with the I(f) blockers. The combination of I(f) blockers and CPA caused a profound further depression of the effects of isoproterenol on spontaneous rate so that the log(concentration)-effect curve was almost flat. The effects I(f) blockers and CPA were also investigated in guinea-pig isolated SAN myocytes loaded with the Ca2+ probe, fluo-5F, and were broadly comparable to those observed in intact spontaneously beating atria. The observations are consistent with roles for both I(f) and SR Ca2+ in the control of spontaneous beating rate. The balance between the contributions of different mechanisms to the control of spontaneous rate varies with conditions, particularly in their influence on the increase in rate caused by isoproterenol. The presence and function of Ca2+-stimulated adenylyl cyclases is likely to be an important factor with the potential to link the contributions of these interacting processes.

Volume scattering and reverberation in shallow water: A simplified modeling approach

A simplified physics-based approach is described that allows significantly faster yet reasonably accurate estimations of volume reverberation in complex shallow water environments. An integral expression is presented for scattering intensity with a factorized integrand comprised of two kernels, the double propagator and local volume scattering coefficient. The propagator describes the local intensity and can be calculated using available models, such as PE, normal modes, or ray approximations. The scattering kernel can be specified using available volume scattering models for continuous or discrete heterogeneity of sea-water column and seabed caused by spatial fluctuations of compressibility and density, or randomly distributed discrete targets, such as bubbles, fish, shells, and others. The approach is more general than and can be used for verification of existing reverberation models. For instance, calculation of bottom reverberation is not based on using the equivalent surface scattering strength (although considers it as a particular case). Numerical examples for shallow water reverberation time series, based on a PE propagation model, are presented to estimate potential contributions of different mechanisms of scattering. The estimations provide a comparison of relative contributions of scatterers with the same scattering strengths but located at different depths in water column or in the sediment. [Work supported by the US Office of Naval Research.]