Role Of Compositional Changes Research Articles

Effect of glass frit composition on reliability of silver paste metallization in crystalline silicon solar cells

Glass frit used in conductive silver (Ag) pastes has a significant impact not only on the electrical performance but also on the long-term reliability of metallized electrodes in crystalline silicon (c-Si) solar cells. Here, we investigated the role of compositional changes on the metallization process of silver pastes by adjusting the SiO2, ZnO, Li2O, or Bi2O3 in lead borate glass melts, and performed damp heat (DH) tests in an acidic damp heat environment. It was found that the addition of Bi2O3 resulted in a decrease in conversion efficiency (Eta) of only 6.44% after the cell was treated with dilute acetic acid. Under scanning electron microscopy (SEM), it was observed that the cell with this glass frit had minimal changes in the microstructure of its silver-silicon contacts and silver electrodes. This finding helps to improve the performance and stability of solar cells in harsh environments.

Role of compositional changes on thermal, magnetic, and mechanical properties of Fe-P-C-based amorphous alloys

This work aimed to tune the comprehensive properties of Fe-P-C-based amorphous system through investigating the role of microalloying process on the crystallization behavior, glass forming ability (GFA), soft magnetic features, and mechanical properties. Considering minor addition of elements into the system, it was found that the simultaneous microalloying of Ni and Co leads to the highest GFA, which was due to the optimization of compositional heterogeneity and creation of near-eutectic composition. Moreover, the FeCoNiCuPC amorphous alloy exhibited the best anelastic/viscoplastic behavior under the nanoindentation test, which was owing to the intensified structural fluctuations in the system. However, the improved plasticity by the extra Cu addition comes at the expense of magnetic properties, so that the saturation magnetization of this alloying system is significantly decreased compared to the FeCoPC amorphous alloy with the highest soft magnetic properties. In total, the results indicated that a combination of added elemental constitutes, i.e., Fe69Co5Ni5Cu1P13C7 composition, provides an optimized state for the comprehensive properties in the alloying system.

Spatial distribution and determinants of the change in pre-lacteal feeding practice over time in Ethiopia: A spatial and multivariate decomposition analysis.

Pre-lacteal feeding persists in low and middle-income countries as deep-rooted nutritional malpractice. It imposes significant negative consequences on neonatal health, including increased risk of illness and mortality. Different studies revealed that pre-lacteal feeding practice is decreased over time. Even though different studies are done on the prevalence and determinants of pre-lacteal feeding practice, up to our knowledge, the spatial distribution and the determinants of the change in pre-lacteal feeding practice over time are not researched. To assess the spatial distribution and determinants of the change in pre-lacteal feeding practice over time in Ethiopia. We used the Ethiopian demographic and health surveys (EDHSs) data. For this study, a total weighted sample of 14672 (5789 from EDHS 2005, 4510 from EDHS 2011, and 4373 from EDHS 2016) reproductive-age women who gave birth within two years preceding the respective surveys and whoever breastfeed were used. The logit-based multivariate decomposition analysis was used to identify factors that contributed to the decrease in pre-lacteal feeding practice over the last 10 years (from 2005 to 2016). Using the 2016 EDHS data, we also conducted a spatial analysis by using ArcGIS version 10.3 and SaTScan version 9.6 software to explore the spatial distribution and hotspot clusters of pre-lacteal feeding practice. Pre-lacteal feeding practice was decreased from 29% [95% Confidence interval (CI): 27.63-29.96%] in 2005 to 8% [95% CI: 7.72-8.83%] in 2016 with annual rate of reduction of 7.2%. The overall decomposition analysis showed that about 20.31% of the overall decrease in pre-lacteal feeding practice over the last 10 years was attributable to the difference in composition of women (endowment) across the surveys, while, the remaining 79.39% of the overall decrease was explained by the difference in the effect of characteristics (coefficient) across the surveys. In the endowment component, the difference in composition of residence, perception of distance from the health facility, maternal educational level, wealth status, occupation, ANC visit, place of delivery, the timing of breastfeeding initiation, and wanted last-child/pregnancy were found to be significant contributing factors for the decrease in pre-lacteal feeding practice. After controlling for the role of compositional changes, the difference in the effect of distance from the health facility, wealth status, occupation, antenatal care (ANC) visit, and wanted last-child/pregnancy across the surveys were significantly contributed to the observed decrease in pre-lacteal feeding practice. Regarding the spatial distribution, pre-lacteal feeding practice was non-random in Ethiopia in which the primary and secondary clusters' of pre-lacteal feeding identified in Somalia and the Afar region respectively. Pre-lacteal feeding practice has shown a significant decline over the 10-year period. Program interventions considering women with poor maternal health service utilization such as ANC visits, women with poor socioeconomic status, women with an unintended pregnancy, and women from remote areas especially at border areas such as Somali and Afar could decrease pre-lacteal feeding practice in Ethiopia.

Surface oxidation mechanism of a refractory high-entropy alloy

High-entropy alloys (HEAs) synthesized using refractory elements are being strongly considered as candidates for high temperature structural applications. The role of compositional changes of HEA surfaces due to oxidation is crucial to sustain the material properties, but a detailed description of the thermodynamic mechanism driving the adsorption of oxygen on such complex surfaces is absent. We examine and explain the reaction process of oxygen on a representative refractory HEA surface using first principles and atomistic thermodynamic models. The HEA surface is highly reactive to oxygen yielding a full monolayer coverage at temperatures between 300 and 1500 K. The preferential adsorption of oxygen to specific sites of the HEA surface is attributed to the electronic configuration of the bonding shells of the constituent surface atoms. On further oxygen addition, the oxygen atoms diffuse into the bulk regions of the alloy. Manipulation of temperature and oxygen pressure reveals that it is difficult to rid the alloy surface of oxygen even at extremely low pressures of 10−9 bar at 2000 K.

Evaluating taxonomic homogenization of freshwater fish assemblages in Chile

Pervasive introductions of non-native taxa are behind processes of homogenization of various types affecting the global flora and fauna. Chile’s freshwater ecosystems encompass a diverse and highly endemic fish fauna that might be sensitive to the introduction of non-native species, an ongoing process that started two centuries ago, but has to date received little attention. Using historical (native) and present-day (native and non-native) presence-absence data sets of compositional similarity, our goal was twofold: (1) evaluate patterns of taxonomic homogenization at various spatial scales and (2) identify clusters of widely versus narrowly distributed species to assess their relative role in compositional changes. We expect that non-native species with wide distributions might have a larger influence in taxonomic homogenization than those with narrow distributions. Chile’s fish assemblages have become increasingly homogenized during the last two centuries when evaluating changes in compositional similarity among 201 watersheds (65.3 % of total comparisons showed homogenization) distributed among six defined biotic units. Taxonomic differentiation was significantly more prevalent than taxonomic homogenization within biotic units. Among biotic units, comparisons between historical and current compositional similarity were all significantly different. We identified one cluster of non-native fishes that were distributed across the entire five or six biotic units. This cluster included Brown Trout (Salmo trutta) and Rainbow Trout (Oncorhynchus mykiss) as the two most representative species. A second cluster we identified included fishes such that on average spanned only one or two biotic units. We provide first evidence for an ongoing and large-scale process of taxonomic homogenization among Chile’s watersheds occurring at various scales. Our findings provide taxonomic and biogeographic baseline information for management plans and courses of action for conservation of native fishes, many of which are endemic. We also discuss management guidelines of non-native fishes in Chile. Baseline information of both native and non-native fish taxa might be applicable to other isolated regions elsewhere.

FIP BIAS EVOLUTION IN A DECAYING ACTIVE REGION

Solar coronal plasma composition is typically characterized by first ionization potential (FIP) bias. Using spectra obtained by Hinode's EUV Imaging Spectrometer (EIS) instrument, we present a series of large-scale, spatially resolved composition maps of active region (AR) 11389. The composition maps show how FIP bias evolves within the decaying AR from 2012 January 4-6. Globally, FIP bias decreases throughout the AR. We analyzed areas of significant plasma composition changes within the decaying AR and found that small-scale evolution in the photospheric magnetic field is closely linked to the FIP bias evolution observed in the corona. During the AR's decay phase, small bipoles emerging within supergranular cells reconnect with the pre-existing AR field, creating a pathway along which photospheric and coronal plasmas can mix. The mixing time scales are shorter than those of plasma enrichment processes. Eruptive activity also results in shifting the FIP bias closer to photospheric in the affected areas. Finally, the FIP bias still remains dominantly coronal only in a part of the AR's high-flux density core. We conclude that in the decay phase of an AR's lifetime, the FIP bias is becoming increasingly modulated by episodes of small-scale flux emergence, i.e. decreasing the AR's overall FIP bias. Our results show that magnetic field evolution plays an important role in compositional changes during AR development, revealing a more complex relationship than expected from previous well-known Skylab results showing that FIP bias increases almost linearly with age in young ARs (Widing $\&$ Feldman, 2001, ApJ, 555, 426).

Experimental investigation of the S and S-isotope distribution between H2O–S ± Cl fluids and basaltic melts during decompression

Decompression experiments (from 400 to 70MPa) were conducted to investigate sulfur (S) distribution and S-isotope fractionation between basaltic melts and coexisting fluids. Volatile-bearing [~3 to ~7wt.% water (H2O), ~300 to ~1200ppmS, 0 to ~3600ppm chlorine (Cl)] basaltic glasses were used as starting materials. The MgO content in the melt was either ~1wt.% (Mg-poor basalt) or ~10wt.% (alkali basalt) to investigate the possible role of compositional changes in basaltic systems on fluid-melt distribution of S and S-isotopes. The experiments were performed in internally heated pressure vessels (IHPV) at 1050°C to 1250°C, variable oxygen fugacities (fO2; ranging from log(fO2/bar)~QFM to ~QFM+4; QFM=quartz–fayalite–magnetite buffer) and at a constant decompression rate (r) of 0.1MPa/s. The annealing time (tA) at final pressure (p) and temperature (T) after decompression was varied from 0 to 5.5h to study the fluid–melt equilibration process.Sulfur and H2O contents in the melt decreased significantly during decompression, while the Cl contents remained almost constant. No changes in H2O and Cl content were observed with tA, while S concentrations decreased slightly with tA <2h; i.e., near-equilibrium fluid–melt conditions were reached within ~2h after decompression, even in experiments performed at the lowest T of 1050°C. Thus, fluid–melt partitioning coefficients of S (DSfl/m) were determined from experiments with tA ≥2h.The MgO (~1 to ~10wt.%), H2O (~3 to ~7wt.%) and Cl contents (<0.4wt.%) in the melt have no significant effect on DSfl/m. Consistent with previous studies we found that DSfl/m decreased strongly with increasing fO2; e.g., at ~1200°C DSfl/m≈180 at QFM+1 and DSfl/m≈40 at QFM+4. A positive correlation was observed between DSfl/m and T in the range of 1150 to 1250°C at both oxidizing (QFM+4; DSfl/m=52±27 to 76±30) and intermediate (QFM+1.5; DSfl/m=94±20 to 209±80) redox conditions. Data compiled at 1050°C and relatively reducing conditions (~QFM; DSfl/m=58±18) indicate that the trends may be extrapolated to lower T, at least for intermediate to reducing conditions (~QFM+1.5 to ~QFM).The S-isotope composition in glasses of selected samples was measured by secondary ion mass spectrometry (SIMS). Gas–melt isotopic fractionation factors (αfl–m) were calculated via mass balance. At 1200°C an average αfl–m of 0.9981±0.0015 was determined for oxidizing conditions (~QFM+4), while an average αfl–m of 1.0025±0.0010 was found for fairly reducing conditions (~QFM+1). Furthermore, at lower T (1050°C) an average αfl–m of 1.0037±0.0009 was determined for reducing conditions (~QFM). The data showed that equilibrium fractionation effects during closed-system degassing of basaltic melts at T relevant for magmatic systems (1050 to 1250°C) can induce a S-isotope fluid–melt fractionation of about +4‰ in relatively reduced systems and of about −2‰ in relatively oxidized systems.The reported experimental results are valuable for the interpretation of S and S-isotope signature in magmatic systems (e.g., in volcanic gasses or melt inclusions) and will help to elucidate, for instance, volatile transport processes across subduction zones and Earth's S cycle.

Change and Stability in Parent–Child Contact in Five Western Countries

Although much is known about changes in the conjugal family, little is known about trends in contact between parents and adult (independently living) children. Using unique survey data, we study changes in contact with the mother and the father in five western countries over a 15-year period (Austria, West Germany, Great Britain, the United States, and Italy). We describe changes and we examine the role of compositional changes in the trend. We find no evidence for a decline in intergenerational contact, in contrast to notions of individualism. In two countries, there has been an increase in contact with the mother and in three countries no net trend is observed. Contact with the father has not changed. Other forms of contact (e.g., telephone contact) have increased. Some compositional changes have had a downward pressure on the trend, leading to a decline in contact (i.e., rising education, declining church attendance), but these pressures have been compensated by counteracting compositional changes (declining sibsize) and by behavioral changes.

Freshwater supply by Korean rivers to the East Sea during the last glacial maximum: a review and new evidence from the Korea Strait region

This study presents a review of extensive literature and reports new findings extracted from previously collected cores. Globally lowered sea level during the last glacial maximum (LGM) reduced the cross-sectional area in the Korea Strait, minimizing volume transport of the paleo-Tsushima Current and increasing freshwater input to the East Sea. The higher supply of freshwater played an important role in compositional changes of surface water in the sea, indicated by low sea surface salinity (down to about 20‰) and light δ18O of planktonic Foraminifera (lighter than 1‰) recorded in core sediments. The Korean fluvial systems (Nakdong and Seomjin rivers) emptying into the southeastern sea of Korea may have contributed substantially to freshwater supply to the surface layer of the LGM East Sea, although Chinese paleo-river (Huanghe and Yangtze rivers) waters, together with the paleo-Tsushima Current, also seem to have supplied some freshwater to the sea. The higher supply of river waters to the East Sea is strongly evidenced by the high amount of terrigenous material (quartz, feldspar and rock fragments) in core sediments. In addition, high magnetic susceptibility, high grain density, and high C/N ratios were documented in cores MB98PC-11 and 95PC-1. In contrast with earlier studies, we propose that Korean rivers played a more substantial role in supplying freshwater to the East Sea during the LGM than previously thought.

Characterization of in-situ carbide coating of tungsten alloy

Tungsten alloys, produced by liquid phase sintering and subsequent swaging, are used commonly for engineering and defense applications. In this investigation the morphology of carburized coating on a series of specimens of tungsten alloy has been examined using electron metallographic and microanalytical techniques. The samples were pack carburized at 850 °C for 30 and 60 min to determine the surface properties. The role of compositional changes, formation of tungsten and iron carbides and the interfacial structure of the carburized samples were examined. It is found that the surface properties of the tungsten alloy have been improved by the formation of these carbides in the carburized specimens as compared with the as-received specimen.

Study of the structure and properties of Pb–Zn borophosphate glasses

Multicomponent oxide glasses of composition 25PbO–25ZnO– xB 2O 3–(50− x)P 2O 5, series A, and yPbO–(50− y)ZnO–20B 2O 3–30P 2O 5, series B, are investigated. The role of compositional changes on their density, chemical durability, thermomechanical properties and Raman scattering is examined. Structural changes are found to be more pronounced in the series A glasses affecting most thermomechanical properties of the glasses. Raman spectra reveal a continuous shift in frequency of the main vibrational band from 1170 cm −1 at x=0, to 960 cm −1 at x=40, explained in terms of a successive transformation of metaphosphate (Q 2) units into pyrophosphate (Q 1) and orthophosphate (Q 0) units. In the series B of glasses, results show that mixed Pb–Zn borophosphate glasses ( y=25) have better chemical durability than end point (y=0, y=50) composition single-cation glasses. With an increasing PbO content, T g is found to slowly decrease and the thermal expansion coefficient to increase. The frequency shift of the main Raman band from 1092 cm −1 (at y=0) to 1011 cm −1 (at y=50) is ascribed to differences in chemical bonding, coordination numbers and field strength of both cations.

イオン照射にともなう薄膜合金表面の濃度変化 イオン照射誘起偏析・拡散

Surface composition changes of Au-Cu alloys sputtered with 2 keV Ar ions were observed with low energy Auger spectra and ion radiation-enhanced diffusion (IRED) coefficiemts were obtained and Ion radiation-enhanced segregation (IRES) at the surface was estimated.The simulation of sputtering including IRED and IRES was also perfomed using experimental results. This shows clearly that the IRES plays an important role in composition changes at the surface and subsurface of ion sputtered alloys.Composition changes of Au-Cu thin film alloys prepared by the co-evaporation technique were also observed following sputtering with Ne, Ar and Kr. The coevaporated film composition was preserved during sputtering at low temperature (< -120°C).

Subsurface compositional modification of Au-Cu alloys sputtered with Ar, Xe, Ne and Kr ions

Surface and subsurface compositional changes in Au-Cu alloys and thin films sputtered with 2 keV Ar, Xe, Ne and Kr ions were observed with low energy (60 eV for Cu and 69 eV for Au) and high energy (239 eV for Au and 920 eV for Cu) Auger peaks at temperatures between liquid nitrogen and room temperature. For a Au 0.56Cu 0.44 alloy, Au enrichment at the surface and depletion beneath the surface was observed with high energy as well as low energy Auger peaks. But the compositional change assessed with low energy Auger peaks is greater than that assessed with high energy peaks. This was also calculated with the simulation of sputtering including ion radiation-enhanced segregation and diffusion. This shows clearly that the Gibbsian segregation plays an important role in composition changes at the surface and subsurface of the ion-sputtered alloy. Compositional changes of Au-Cu thin film alloys prepared by the co-evaporation technique were also observed following sputtering with Ar, Xe, Ne and Kr. Except in the case of Xe, the coevaporated composition was preserved during sputtering at low temperatures (<-120°C).