ALBERT

Beschreibung: This paper explores temperature variability over southern South America. Four states of temperature variability are revealed in both winter and summer seasons. Synoptic‐scale meteorological patterns help diagnose the temperature variability states with low‐level temperature and moisture advection are closely related to patterns of temperature variability. Large‐scale modes of climate variability show some connection to temperature variability states, no single mode appears to be a primary driver. Abstract Key spatiotemporal patterns of monthly scale temperature variability are characterized over southern South America using k‐means clustering. The resulting clusters reveal patterns of temperature variability, referred to as temperature variability states. Analysis is performed over summer and winter months separately using data covering the period 1980–2015. Results for both seasons show four primary temperature variability states. In both seasons, one state is primarily characterized by warm temperature anomalies across the domain while another is characterized by cold anomalies. The other two patterns tend to be characterized by a warm north–cold south and cold north–warm south feature. This suggests two primary modes of temperature variability over the region. Composites of synoptic‐scale meteorological patterns (wind, geopotential height, and moisture fields) are computed for months assigned to each cluster to diagnose the driving meteorology associated with these variability states. Results suggest that low‐level temperature advection promoted by anomalies in atmospheric circulation patterns is a key process for driving these variability states. Moisture‐related processes also are shown to play a role, especially in summer. The El Niño–Southern Oscillation and the Southern Annular Mode exhibit some relationship with temperature variability state frequency, with some states more common during amplified phases of these two modes than others. However, the climate modes are not a primary driver of the temperature variability states.

Beschreibung: Abstract Abrupt swings in temperature can exert negative impacts, ranging from human health to agricultural production. Here, we focus on a global assessment of the extremes in the temperature swings at sub‐daily scales using Modern‐Era Retrospective analysis for Research and Applications, Version 2 (MERRA‐2) data. Overall, the regions with extremely large swings in hourly temperature (i.e., 99th percentile) are located in desert or arid regions, and the land masses exhibit larger temperature swings than the oceans. In contrast, the first percentile of the hourly temperature swings exhibits a different spatial pattern, with the lowest values (i.e., largest negative swings) located in the Rocky Mountain, South Australia, South and North Africa and some regions in Northwestern China. We identify a significant downward/upward trend in the 99th/1st percentile of sub‐daily (i.e., hourly and 12 hr) temperature changes in the midlatitudes in the Northern Hemisphere, particularly during boreal summer. Overall, the regions with significant trends in the Northern Hemisphere are collocated with the paths of the jet streams and storm tracks. The significant downward/upward trends in the 99th/1st percentile of the sub‐daily temperature swings over the Northern Hemisphere can be explained by a weakening in the Northern Hemisphere's summer circulation, as suggested by the downward trend in the eddy kinetic energy. These results indicate that a weak/strong persistence in the circulation may lead to less/more abrupt temperature swings (i.e., increase or decrease) caused by horizontal temperature advection.

Beschreibung: Abstract The presence of a seasonal snowpack determines the hydrology, geomorphology and ecology of wide parts of the Iberian Peninsula, with strong implications for the economy, transport and risk management. Thus, reliable information on snow is necessary from a scientific and operational point of view. This is the case of the Iberian Peninsula where, lack of observation has impeded proper analysis of snowpack duration, magnitude and interannual variability. In this study we present the first snow climatology of the entire Iberian Peninsula. The scarcity of in situ observations has been overcome, using a newly developed remote sensing snow database from MODIS satellite sensors for the period 2000 ‐ 2014 and a physically based snow model (Factorial Snow Model‐ FSM), driven by a regional atmospheric model (Weather Research and Forecast model‐ WRF) over the Iberian Peninsula for the period 1980 ‐ 2014. The snowpack of the main mountain areas (Pyrenees, Cantabrian, Central, Iberian range and Sierra Nevada) are described, estimated from the generated databases. The information has been processed using a k‐means cluster algorithm, looking for similarities in snow indices at different elevation bands. Results show four different types of snowpack in terms of depth, duration and interannual variability, lying over different elevation bands in the different ranges, proving the variability of the snowpack over Iberia. Analyses reveal areas characterised by ephemeral snowpacks, while in some sectors snowpack lasts, on average, 198 days per year with 3.02 meters of peak snow depth. The coefficient of variation of interannual peak snow depth oscillated between 35.2% and 162.4%. All the analysed indices show that at common elevations the Cantabrian range and the Pyrenees host the deepest and longest lasting snowpacks, followed by the Central and Iberian ranges. The Sierra Nevada exhibits the shortest, shallowest snowpack and more year‐to‐year variability. This article is protected by copyright. All rights reserved.

Beschreibung: Abstract In this work, cobalt phosphide (CoP) nanoparticles were successfully decorated on an ultrathin g‐C3N4 nanosheet photocatalysts by in situ chemical deposition. The built‐in electric field formed by heterojunction interface of the CoP/g‐C3N4 composite semiconductor can accelerate the transmission and separation of photogenerated charge‐hole pairs and effectively improve the photocatalytic performance. TEM, HRTEM, XPS, and SPV analysis showed that CoP/g‐C3N4 formed a stable heterogeneous interface and effectively enhanced photogenerated electron‐hole separation. UV‐vis DRS analysis showed that the composite had enhanced visible light absorption than pure g‐C3N4 and was a visible light driven photocatalyst. In this process, NaH2PO2 and CoCl2 are used as the source of P and Co, and typical preparation of CoP can be completed within 3 hours. Under visible light irradiation, the optimal H2 evolution rate of 3.0 mol% CoP/g‐C3N4 is about 15.1 μmol h−1. The photocatalytic activity and stability of the CoP/g‐C3N4 materials were evaluated by photocatalytic decomposition of water. The intrinsic relationship between the microstructure of the composite catalyst and the photocatalytic performance was analyzed to reveal the photocatalytic reaction mechanism.

Beschreibung: Abstract High volume fraction SiC nanowires‐reinforced SiC composites (SiCNWs/SiC) were prepared by hybrid process of chemical vapor infiltration and polymer impregnation/pyrolysis in this research. SiCNWs networks are first to be made promising a high volume fraction (20 vol%), and the pyrolytic carbon (PyC) interphase with 5 nm is designed on SiCNWs surface to optimize the bonding condition between SiCNWs and SiC matrix. Nanoindentation shows a modulus of 494 ± 14 GPa of SiCNWs/SiC composites without interphase comparing to the one with PyC interphase of 452 ± 13 GPa. However, the 3‐point bending test shows a higher strength of the composite with PyC interphase (273 ± 32 MPa) comparing with the one without interphase (240 ± 38 MPa). The fracture surface is observed under SEM, which shows a longer SiCNWs pullout of the composite with PyC interphase. The energy dissipation during the 3‐point bending test is calculated by the length of nanowire pull‐out, it demonstrates that the SiCNWs with PyC interphase possess better performance for toughening composite. Further characterization proves that the PyC interphase can give SiCNWs/SiC composites higher fracture toughness (4.49 ± 0.44 MPa·m1/2) than the composites without interphase (3.66 ± 0.28 MPa·m1/2).

Beschreibung: Here, we report a multicolor PersL phosphor Sr Ga GeO :Pr .The PersL color can be tuned from deep red to blue. It reveals that the multicolor luminescence of the phosphor is essentially associated with the crossrelaxation effect of Pr . What's more,the PersL lifetime of the multicolor phosphor can be also tuned. Based on the unique features of Sr Ga GeO :Pr phosphor, some luminescent images are fabricated for dynamic multicolor anticounterfeiting. Abstract Persistent luminescence (PersL) phosphor is a glow‐in‐the‐dark material that has been widely applied. Here, we report a multicolor PersL phosphor Sr2Ga2GeO7:Pr3+. The PersL color can be tuned from deep red to blue. It reveals that the luminescent color modulation of the Sr2Ga2GeO7:Pr3+ phosphor is essentially associated with the cross‐relaxation effect of Pr3+ in the host with low‐phonon assistance energy. The PersL lifetime of the multicolor phosphors can be also tuned. Based on the unique features of Sr2Ga2GeO7:Pr3+ phosphor, some simple PersL images are fabricated to emit dynamic multicolor information, and it shows that the PersL image even depicts dynamic multicolor anticounterfeiting.

Beschreibung: Abstract Although great advance has been made in glass science, predicting luminescence properties of laser glass poses a significant challenge for scientists due to the complex relationship between the composition, structure, and properties of the rare earth ions doped laser glasses. The development of high‐performance laser glass usually relies on intuition and trial‐and‐error. Recently, with the proposal of the materials genome engineering, the “glass genome” has also attracted much attention. Here, the structure of the Nd3+ doped B2O3‐Li2O laser glasses was analyzed using Fourier transform infrared spectra and nuclear magnetic resonance, revealing that the glass contains similar glass‐forming ion‐centered coordination polyhedron structure groups to the neighbor congruent glassy compounds. The structure and properties of glass largely depend on the neighbor congruent glassy compounds. Therefore, the structure and luminescence properties of Nd3+ doped B2O3‐Li2O and B2O3‐MgO‐Li2O laser glasses can be quantitatively predicted via the neighbor congruent glassy compounds. The predictive values are in good agreement with the experimental data, which indicates that our approach is an effective way to predict the structure and luminescence properties of Nd3+ doped borate laser glasses.

Beschreibung: Abstract Ba2Ti9O20 single‐phase ceramics were prepared by reaction sintering method using TiO2 and BaCO3 as raw materials after heat treating at 1150°C for 10h. Furthermore, the formation mechanism and microstructure evolution of Ba2Ti9O20 ceramics prepared by reaction sintering method were investigated. The formation behavior of Ba2Ti9O20 phase was analyzed from the perspective of diffusion, where the reaction activation energy required for the process was calculated to be about 386.17kJ/mol. Combined with the scanning electron microscopy and the energy dispersive spectrometer, it was revealed that the pores on Ba2Ti9O20 grains in the process of reaction sintering might be caused by the absence of oxygen element. Meanwhile, the reason for the roughness of ceramic surface was that the local inhomogeneous distribution of barium on the surface of Ba2Ti9O20 grain leaded to the enrichment of titanium.

Beschreibung: Abstract Two dimensional (2D) SnS2/MoS2 heterojunction with a 2D/2D novel structure were used as electrodes materials for enhanced supercapacitor performance. Compared with the sole SnS2, the as‐prepared 2D/2D SnS2/MoS2 layered heterojunction has exhibited great improvement in supercapacitor properties. This novel structure can effectively prevent agglomeration and stacking in electrochemical process, and 2D/2D structure is beneficial to intercalation and desorption of ions in electrochemical processes. The experiment result shows that MoSn5 (Samples with 5% Mo:Sn mole ratios) display a specific capacitance of 466.6 F/g at the current Density of 1 A/g in 0.5M Potassium hydroxide solution, an impressive cycling stability with 88.2 % capacitance retention at current density of 4 A/g. In addition, the as‐fabricated symmetric supercapacitor exhibited high energy density of 115 Wh kg‐1 at the power density of 2230 W kg‐1. This work provides a fundamental investigation of 2D/2D layered material synergistic effect on the electrochemical process.

Beschreibung: Abstract Freeze casting is an established method for fabricating porous ceramic structures with controlled porosity and pore geometries. Herein, we developed a novel freeze casting and freeze drying process to fabricate tubular anode supports for solid oxide fuel cells (SOFCs). Freeze casting was performed by injecting aqueous anode slurry to a dual‐purpose freeze casting and freeze drying mold wrapped with peripheral coils for flowing a coolant. With the use of an ice barrier layer, proper control of the experimental setup, and adjustments in the drying temperature profile, complete drying of the individual anode tubes was achieved in four hours. The freeze‐cast anode tubes contained radially aligned columnar pore channels, thus significantly enhancing the gaseous diffusion. SOFC single cells with conventional Ni/yttria‐stabilized zirconia (YSZ)/strontium‐doped lanthanum manganite (LSM) materials were prepared by dip coating the thin functional layers onto the anode support. Single‐cell tests showed that the concentration polarization was low owing to the highly porous anode support with directional pores. With H2/N2 (1:1) fuel, maximum power densities of 0.47, 0.36, and 0.27 W/cm2 were recorded at 800, 750, and 700 °C, respectively. Our results demonstrate the feasibility of using freeze casting to obtain tubular SOFCs with desired microstructures and fast turn‐around times. This article is protected by copyright. All rights reserved.

Beschreibung: Abstract Defect engineering plays an important role in property modification for piezoelectric materials. In this work, we pay much attention to the effect of Nb non‐stoichiometry on structure and properties of typical 0.95(K0.45Na0.55)Nb1+xO3‐0.05Bi0.5Na0.5HfO3 ceramics. Large piezoelectric constant (d33~425 pC/N and d33*~ 482 pm/V) together with high Curie temperature (TC~315 ºC) have been achieved in the ceramics with excess Nb content (x=0.01). However, the ceramics with deficient Nb element have seriously suppressed cryogenic εr‐T curves and deteriorated electrical properties. Multi‐scale characterizations including phase structure, microstructure, defect structure and domain structure have been adopted to explain the corresponding phenomenon. Defect complex of VNb'''''‐Vo.. caused by deficient Nb induces clamped domain wall motion, leading to blocked polarization vector and poor electrical properties. On the contrary, the enhanced properties for the ceramics with excess Nb are attributed to easier domain switching due to the suppressed vacancies. We believe that defect engineering, for example non‐stoichiometry, can not only modulate electrical properties but also help us to understand some fundamental and critical problems about KNN‐based ceramics. This article is protected by copyright. All rights reserved.

Beschreibung: Abstract The paper by Lee et al (J Am Ceram Soc 102:4555‐4561, 2019) reports on semiconductor quantum dots (QDs) obtained in a silicate glass matrix by a novel modification of the solid‐state precipitation technique and characterized by a variety of techniques. Based on their experimental data, we critically discuss their assessment of the QDs obtained as CdSe/Cd1−xZnxSe core/shell structures. By analyzing their results (in particular, Raman scattering data) and comparing them to other data available in literature, we show that the data presented give no evidence for the formation of core/shell structures and conclude that the authors obtained rather homogeneous Cd1−xZnxSe QDs without any noticeable compositional gradient.

Beschreibung: Abstract Solid‐oxide fuel cells (SOFCs) have the potential to increase electricity generation efficiency, but traditional SOFCs supported by nickel cermets suffer from reliability challenges due to weaker mechanical strength caused by cracking after redox cycling. To solve this problem, a new ceramic anode material, SrFe0.2Co0.4Mo0.4O3−δ (SFCM) combined with Ce0.9Gd0.1O2 (GDC), was evaluated for conductivity and mechanical strength at SOFC operating conditions and after redox cycling. Fracture toughness of SFCM was determined to be (0.124 ± 0.023) MPa√m at room temperature in air, increasing to (0.286 ± 0.038) MPa√m at 600°C. A mixture of SFCM:GDC showed fracture toughness between the two materials, following SFCM's trend with temperature. The SFCM‐GDC anode supported half‐cell strength increases by 31% from room temperature to 600°C as intrinsic stresses remaining from sintering are relaxed and thermal expansion pushes existing cracks closed. Exposure to reducing gasses decreases strength by 29% compared to ambient, due to oxygen vacancy formation and microstructural flaw changes. It is found that SFCM‐GDC based cells tolerate cycling well because of phase stability but weaken from 34.3 to 22.4 MPa due to uniform growth of critical microstructural flaws.

Beschreibung: Abstract Photoluminescence of rare earth ions doped glasses could be enhanced by diverse Ag species such as Ag+ ions, Ag+‐Ag+ pairs, Ag nano‐clusters (NCs) and Ag nanoparticles (NPs). Selective preparation of silver species in rare earth ions doped glasses is a crucial step to obtain the luminescence enhancement of rare earth ions caused by the different silver species. In this work, the Ag+ ions and Ag NCs were selectively prepared in the Sm3+ doped borosilicate glass via the Ag+‐Na+ ion exchange. The influence of AgNO3/NaNO3 ratio in the molten salt on the Ag existing states was investigated. The results demonstrate the isolated Ag+ ions exist in the Sm3+ doped borosilicate glass when the ratio of AgNO3/NaNO3 is 1/1000. The Ag NCs are formed in the Sm3+ doped borosilicate glass when the AgNO3/NaNO3 ratio is 1/10. The influences of Ag+ ions or Ag NCs on the photoluminescence of Sm3+ were systematically investigated. The results show that the photoluminescence of Sm3+ was enhanced by the energy transfer from Ag+ ions or Ag NCs to Sm3+. This article is protected by copyright. All rights reserved.

Beschreibung: Journal of the American Ceramic Society, EarlyView.

Beschreibung: Abstract The Eu3+ ions doped (1‐x)Na0.5Bi0.5TiO3‐xSrTiO3 (Eu‐NBT‐xSTO) thin films were prepared on Pt/Ti/SiO2/Si substrates. Raman analysis reveals that the phase structure may undergo a phase evolution of rhombohedral → rhombohedral + tetragonal (morphotropic phase boundary) → tetragonal with increasing content of STO. The SEM images show that the uniformity and high density of Eu‐NBT‐xSTO films were increased by adding STO, resulting in a pronounced effect on energy‐storage properties. The ɛ‐T curves confirm that a high phase transition diffuseness of γ= 2.02±0.03 and 1.98±0.03 was achieved in Eu‐NBT‐0.24STO and Eu‐NBT‐0.3STO films, respectively. Further, a large recoverable energy‐storage density of 31.5 J/cm3 with an efficiency of 64% was obtained in Eu‐NBT‐0.3STO film, which also exhibited good thermal stability in the temperature range between ‐60 °C and 80 °C as well as long‐term stability up to 1×108 switching cycles. These results suggest that the Eu‐NBT‐xSTO films may be used in the novel and advanced energy‐storage capacitors. This article is protected by copyright. All rights reserved.

Beschreibung: ABSTRACT The understanding of past millennium climate change is very important. Due to the lack of continuously annual resolution records, the temperature characteristics in the low‐latitude regions of East Asia (LLREA) during past several centuries are still unknown. Using tree‐ring width chronology from Taiwan, an island located in the western Pacific region and in southeastern China, February–October mean temperature from 1380 to 2007 AD was reconstructed. Spatial correlation analysis indicated that the reconstructed temperature could represent the sea‐land temperature change in LLREA. During the past six centuries, both the warmest intervals and the largest variability of temperature appeared in the twentieth century. This is probably related to human activities. Temperature in LLREA provided good contrast with temperature changes in the Tibet Plateau and elsewhere in the Northern Hemisphere. The LLREA entered into the Little Ice Age around the year of 1450, approximately 100 years earlier than the Tibet Plateau. The 10‐year cycle contained in the reconstructed temperature is close to the 11‐year period of solar activity, which revealed there was a certain relationship between them. The temperature in LLREA significantly correlated with solar activity at the decadal to centennial scales. The strong/weak solar irradiance corresponded to the great/small temperature variability. This article is protected by copyright. All rights reserved.

Beschreibung: Abstract The Catskill Mountains and surrounding counties in south‐central New York State are home to almost 400,000 residents, and supply drinking water to over 9 million people in New York City and other municipalities. In this study, we identify a set of stations in this region that are appropriate for climatological analysis, and examine variations in precipitation, streamflow, and temperature between 1900 and 2016, extending the time domain of previous studies of the climatology of this region during both the early and recent portions of the record. Temperatures have increased since the mid‐20th century, in particular daily minimum temperatures, at rates that vary with season and elevation. As a result, diurnal temperature ranges have tended to decrease, particularly during the warm season at lower elevations. The most significant hydrological events include the cold drought of the 1960s (a year‐round phenomenon), and the wet period beginning in the late 1990s (primarily a warm season phenomenon). We also find evidence of a particularly wet period at the start of the 20th century. Cyclic behavior is found in both hydrological and temperature records, with the most prominent cycle in cold season precipitation and streamflow peaking at 28 years. This article is protected by copyright. All rights reserved.

Beschreibung: Abstract The monthly and seasonal variability and distribution of dust events over northern Saudi Arabia were studied using ground‐based measurements from 11 surface stations for the period of 1978‐2010. Additionally, to study the synoptic climatology of the dust variability, the aerosol index (AI) data from the Total Ozone Mapping Spectrometer (TOMS) satellite and meteorological data from the National Center for Environmental Prediction and National Center for Atmospheric Research (NCEP/NCAR) reanalysis datasets were used. The dust types observed at the surface stations are classified into two categories: weak dust and dust storms. A statistical study of the ground measurements demonstrated that weak dust category events are prevalent in the cold months, whereas storm category events are prevalent in the hot months. Additionally, the annual distribution distinguishes two periods for dust observations, before and after 1989, where the number of events in the first period is lower than the annual average but increases during the second period. The synoptic climate study indicated that two main atmospheric wind patterns, anticyclonic and northerly (shamal) patterns, accompany the dust events in the study area. The dust in winter and autumn is mainly affected by the anticyclonic pattern, while that in spring and summer is mainly affected by the shamal pattern. In addition, a synoptic study of selected cases confirmed the climate results and demonstrated the existence of two atmospheric patterns corresponding to winter and summer. Both patterns include troughs over the Red Sea and Arabian Gulf and a ridge or high‐pressure cell over the eastern Mediterranean region during the summer atmospheric pattern and over the mid‐Arabian Peninsula during the winter atmospheric pattern. The characteristic of non‐dust storm composition demonstrated that the storms exhibit pronounced synoptic systems (winter and summer) with the highest pressure/geopotential gradient near the Arabian Peninsula. This article is protected by copyright. All rights reserved.

Beschreibung: Abstract A unique feature of cordierite is the negative thermal expansion of its c‐axis, while the a‐ and b‐axes show positive thermal expansion behavior. The thermal expansion mechanism of cordierite has been investigated in many theoretical studies, but the effect of Ti or Ge doping has not yet been studied theoretically. Here, we investigate the thermal expansion behavior of Ti‐ and Ge‐doped cordierite by ab initio molecular dynamics (AIMD) simulation. The computational cost of AIMD simulation for cordierite doped with Ti or Ge is challenging due to the many different configurations of crystal models. We overcame this computational difficulty by separating the respective models into groups with identical symmetry, then we performed the MD simulation for each different symmetry crystal model. To understand the mechanism of the negative thermal expansion of the c‐axis, we investigated the changes of all the bond lengths and angles. We found that the negative thermal expansion of the c‐axis is coupled with the increase in the O‐Al‐O angle and the shrinkage of the O‐Si‐O angle at the T1 site in cordierite, which suggests rotation of the six‐membered ring. This studyprovides insight into the mechanism of thermal expansion of cordierite with Ti and Ge doping. Moreover, the approach presented here can be generally applied to investigate the thermal expansion behavior of other ceramic materials within reasonable accuracy and computational cost. This article is protected by copyright. All rights reserved.

Beschreibung: Abstract The impact of the Pacific multidecadal oscillation (PMO) on precipitation in April during the sowing season in Northeast China (NEC) was analyzed. According to the results, there was a significant interdecadal change in the relationship between the PMO in December of the previous year and the precipitation in NEC in April of the following year during different PMO phases. Before 1980, when the PMO was in a negative phase, there was no significant correlation between the PMO and NEC April precipitation. After 1980, when the PMO changed to a positive phase, the relationship between the two variables became significant. Based on further analysis, the main reason for this relationship is that as the PMO changes from a negative phase to a positive phase, the northern North Pacific warms, and the north–south temperature gradient in the mid‐ to high latitudes of the North Pacific decreases, which weakens the mid‐ to high‐level westerlies, thus increasing the impact of North Pacific water vapor transport on the April precipitation in NEC. When the PMO changes from a negative phase to a positive phase, the increased sea surface temperature (SST) significantly strengthens the Aleutian low (AL), which can enhance the Alaska warm current and further increase the sea temperature in the PMO region. This air‐sea interaction forms a positive feedback that maintains the SST signal from December of the previous year to April of the following year, which affects the circulation and water vapor conditions of NEC and ultimately affects NEC April precipitation. This positive feedback mechanism was further verified in the ECHAM5 model. When the positive anomalous SST appeared in the PMO region, as in the observations after 1980, the AL was significantly enhanced, which in turn affected the SST enhancement. This article is protected by copyright. All rights reserved.

Beschreibung: Abstract Lateral nanoindentation provides access to the scratch hardness of glass surfaces. The specific sensitivity of the scratching experiment to surface mechanical properties can be enhanced when the local load at the tip apex is reduced. Here, we report on ramp‐load scratch tests on a range of silicate glasses using a sphero‐conical tip shape. Similar as with regular scratching experiments using sharp indenters, such tests create a sequence of micro‐ductile, micro‐cracking, and micro‐abrasive regimes. Detailed investigation of the indenter displacement h and of the lateral force FL as recorded in situ, however, reveals pronounced deviations in comparison to Vickers or Berkovich scratching experiments. Most notably, this includes an abrupt increase in both h and FL at moderate normal load, marking the onset of ductile fracture, and a yield point at the transition from fully elastic deformation to the elastic‐plastic regime at low load. For the range of examined silicate glasses, we find that structural cohesion controls yielding, whereas scratch‐induced fracture and micro‐abrasion are dominated by the volume density of bond energy.

Beschreibung: Abstract Heat transfer at the interfacial contact is a dominant factor in the thermal behavior of glass during nonisothermal glass molding process. Recent research is developing reliable numerical approaches to quantify contact heat transfer coefficients. In most previous studies, however, both theoretical and numerical models of thermal contact conductance in glass molding attempted to investigate this factor by either omitting surface topography or simplifying the nature of contact surfaces. In fact, the determination of the contact heat transfer coefficient demands a detailed characterization of the contact interface including the surface topography and the thermo‐mechanical behavior of the contact pair. This paper introduces a numerical approach to quantify the contact heat transfer by means of a microscale simulation at the glass‐mold interface. The simulation successfully incorporates modeling of the thermo‐mechanical behaviors and the three‐dimensional topographies from actual surface measurements of the contact pair. The presented numerical model enables the derivation of contact heat transfer coefficients from various contact pressures and surface finishes. Numerical predictions of these coefficients are validated by transient contact heat transfer experiments using infrared thermography to verify the model. This article is protected by copyright. All rights reserved.

Beschreibung: Abstract In the (Bi1‐xCex)VO4 (0 ≤ x ≤ 1) system, we found that the (Bi1‐xCex)VO4 (0 ≤ x ≤ 0.1) belongs to the monoclinic scheelite phase and the (Bi1‐xCex)VO4 (0.7 ≤ x ≤ 1) belongs to the tetragonal zircon phase, while the (Bi1‐xCex)VO4 (0.1 〈 x 〈 0.7) belongs to the mixed phases of both monoclinic scheelite and tetragonal zircon structure. Interestingly, two components with near‐zero temperature coefficient of resonant frequency (TCF) appeared in this system. In our previous work, a near‐zero TCF of ~ +15 ppm/oC was obtained in a (Bi0.75Ce0.25)VO4 ceramic with a permittivity (εr) of ~ 47.9, a Qf (Q = quality factor = 1/dielectric loss; f = resonant frequency) value of ~18,000 GHz (at 7.6 GHz). Furthermore, in the present work, another temperature stable microwave dielectric ceramic was obtained in (Bi0.05Ce0.95)VO4 composition sintered at 950 °C and exhibits good microwave dielectric properties with a εr of ~ 11.9, a Qf of ~ 22,360 GHz (at 10.6 GHz), a near‐zero TCF of ~ +6.6 ppm/oC. The results indicate that this system might be an interesting candidate for microwave device applications. This article is protected by copyright. All rights reserved.

Beschreibung: Abstract BiFeO3‐BaTiO3 (BF‐BT) solid solutions are lead‐free candidates for high‐temperature piezoelectric applications. BF‐BT ceramics with compositions near the morphotropic phase boundary (MPB) separating rhombohedral (R) and pseudo‐cubic (PC) phases were fabricated by the conventional high temperature sintering method, and their thermal stability and aging properties were studied in detail. BF‐BT ceramics with rhombohedral (R) phase show much better thermal stability and aging properties than those with pseudo‐cubic (PC) or coexistence of PC and R phases. The thermal degradation and aging rates of BF‐BT ceramics with R phase are on the order of 1% and 1.2% per decade, respectively. X‐ray diffraction results reveal that the domain state of poled rhombohedral BF‐BT ceramics is stable up to its Curie temperature, which is responsible for the high thermal stability. The Rayleigh analysis shows that the low aging rate is attributed to the low domain wall contribution to the overall piezoelectric response. The high thermal stability and low aging rates indicate that the lead‐free BF‐BT ceramics with R phase are potential candidates for sensor and transducer applications over a broad temperature range.

Beschreibung: Abstract In this report, a mixed‐metal cation‐based halide perovskite (HP) CsPb1−xTixBr3 quantum dots (QDs) were first embedded in the B–Si–Zn glasses using a traditional approach of melt quenching and heat treating. A battery of test results such as photoluminescence, X‐ray diffraction, and time‐resolved attenuation prove that Ti ions do not destroy the properties of CsPbBr3, and they are successfully doped into CsPbBr3. At the same time, the doping of Ti ions also reduces the toxicity of lead. By altering the ratio of Pb/Ti, we determined the optimum ratio of CsPb0.7Ti0.3Br3 QDs through experimental data. Due to the excellent optical properties and stability of CsPb0.7Ti0.3Br3 QDs glass, it was designed to construct the white‐light emitting diode device with tunable color coordinate, color rendering index, correlated color temperature, and a high luminous efficiency compared with CsPbBr3 QDs glass, which may be a promising candidate for the field of lighting and displays.

Beschreibung: Abstract Statistical downscaling methods are extensively used to refine future climate change projections produced by physical models. Distributional methods, which are among the simplest to implement, are also among the most widely used, either by themselves or in conjunction with more complex approaches. Here, building off of earlier work we evaluate the performance of seven methods in this class that range widely in their degree of complexity. We employ daily maximum temperature over the Continental U. S. in a "Perfect Model" approach in which the output from a large‐scale dynamical model is used as a proxy for both observations and model output. Importantly, this experimental design allows one to estimate expected performance under a future high‐emissions climate‐change scenario. We examine skill over the full distribution as well in the tails, seasonal variations in skill, and the ability to reproduce the climate change signal. Viewed broadly, there generally are modest overall differences in performance across the majority of the methods. However, the choice of philosophical paradigms used to define the downscaling algorithms divides the seven methods into two classes, of better vs. poorer overall performance. In particular, the bias‐correction plus change‐factor approach performs better overall than the bias‐correction only approach. Finally, we examine the performance of some special tail treatments that we introduced in earlier work which were based on extensions of a widely used existing scheme. We find that our tail treatments provide a further enhancement in downscaling extremes. This article is protected by copyright. All rights reserved.

Beschreibung: Western Africa with three rainfall zones of the Guinea Coast (0°–10°N, 25°W–15°E), the Western Sudano Sahel (10°–20°N, 25°–5°W) and the Eastern Sudano Sahel (10°–20°N, 5°W–15°E). Abstract The interannual variability and trends of atmospheric moisture flux convergence (MFC) and the flux transport and their roles in wet season rainfall variability during the West Africa monsoon season have been investigated using the Climate Research Unit observational datasets and the National Center for Environmental Prediction reanalysis 2 from 1979 to 2016 and the Coordinated Regional Downscaling Experiment (CORDEX)‐Africa model outputs. Particular emphasis has been placed on the three rainfall zones: the Western Sudano Sahel, the Eastern Sudano Sahel and the Guinea Coast. The MFC shows largest variability and impact on rainfall in the Western Sudano Sahel, followed by the Guinea Coast, but there is no significant impact in the Eastern Sudano Sahel. Furthermore, the MFC shows significant positive trends at the Sahelian locations but not at the Guinea Coast. The CORDEX‐Africa models adequately simulate the climatology and spatial patterns of the mean June to September atmospheric moisture; however, differences exist in the magnitude and signs of the temporal trend. The model ensemble mean is presented, which better represents the atmospheric moisture during the monsoon rainfall variability. A mean bias‐corrected projection of the atmospheric moisture shows enhanced rainfall variability of the Guinea Coast in the representative concentration pathway (RCP) 4.5 and RCP 8.5 at the end of the 21st century.

Beschreibung: Abstract Due to their superior piezo‐responses (strain S〉0.3%), bismuth sodium titanate (BNT)‐based relaxor ferroelectrics have received much attention. Compared to other chemical elements, tantalum (Ta) doping provides superior electro‐strain for these ferroelectrics, while the effect of Ta2O5 as oxide additive has been rarely reported. Herein, lead‐free piezoceramics of Bi0.5(Na0.72K0.22Li0.06)0.5TiO3‐xTa2O5 (BNKLT‐xTa2O5, x=0‐0.015) are synthesized. We study the effects of Ta2O5 addition on the crystal structure, piezoelectric responses, dielectric properties, and ferroelectric properties of BNKLT ceramics. All of the ceramics exhibit a typical perovskite structure, and Ta2O5 diffuses into the BNKLT lattice to form a uniform solid solution. The addition of Ta2O5 can make the grains more regular and uniform, while excess Ta2O5 result in finer grains. The undoped BNKLT ceramics show good ferroelectric and piezoelectric properties (remnant polarization Pr=22.5 μC/cm2 and piezoelectric coefficient d33=250 pC/N); however, the addition of Ta2O5 leads to an clear degradation in d33 and Pr. Meanwhile, the addition of an appropriate Ta2O5 amount leads to an increase in the electro‐strain, and the unipolar strain reaches 0.385% under 60 kV/cm for x=0.003, together with a higher normalized strain (d33*=Smax/Emax) of 633 pm/V (x=0.003). The enhanced strain behaviors can be attributed to the coexistence of the ferroelectric and relaxor states, and an excellent electrostriction coefficient Q33 (Q33=S/P2) value of 0.038 m4C‐2 is obtained under 60 kV/cm for x=0.003. This article is protected by copyright. All rights reserved.

Beschreibung: Abstract The primary goal of this study is to characterize the influence of the pore saturated gas media and their physical properties on the elasticity of porous ceramic materials. Resonant ultrasound spectroscopic (RUS) measurements were performed on test specimens of alumina with ~40% porosity, zirconia with ~48% porosity and sintered fully dense zirconia to determine the hydrostatic pressure dependent macroscopic elasticity. Here we report the variation of elasticity of porous and full dense samples over approximately five orders of magnitude (800 ‐ 0.02 psi) in absolute pressure. The time evolution of mechanical equilibrium of the porous materials at low pressure and high temperature conditions will also be discussed. This article is protected by copyright. All rights reserved.

Beschreibung: Abstract Calcium‐Silicate‐Hydrates (C‐S‐H) gel, the main binding phase in cementitious materials, has a complex multiscale texture. Despite decades of intensive research, the relation between C‐S‐H's chemical composition and mesoscale texture remains experimentally limited to probe and theoretically elusive to comprehend. While the nanogranular texture explains a wide range of experimental observations, understanding the fundamental processes that control particles' size and shape are still obscure. This paper strives to establish a link between the chemistry of C‐S‐H nanolayers at the molecular level and formation of C‐S‐H globules at the mesoscale via the potential‐of‐mean‐force (PMF) coarse‐graining approach. We propose a new thermo‐mechanical load cycling scheme that effectively packs polydisperse coarse‐grained nanolayers and creates representative C‐S‐H gel structures at various packing densities. We find that the C‐S‐H nanolayers percolate at ~ 0% packing fraction, significantly below the percolation of ideal hard contact oblate particles and rather close to that of overlapping ellipsoids. The agglomeration of C‐S‐H nanolayers leads to the formation of globular clusters with the effective thickness of ~ 5nm, in striking agreement with small angle neutron and X‐ray scattering measurements as well as nanoscale imaging observations. The study of pore structure and local packing distribution in the course of densification shows a transition from a connected pore network to isolated nanoporosity. Furthermore, the calculated mechanical properties are in excellent agreement with statistical nanoindentation experiments, positioning nanolayered morphology as a finer description of C‐S‐H globule models. Such high‐resolution description becomes indispensable when investigating phenomena that involve internal building blocks of globules such as shrinkage and creep. This article is protected by copyright. All rights reserved.

Beschreibung: Abstract Calcium silicate hydrate (C–S–H) is the main hydration product of cement and the most important binder that plays a pivotal role in the mechanical properties of concrete. However, one of the major drawbacks of C–S–H is its high brittleness and low flexural strength due to its disordered structure at the nano‐ and micro‐scales. Therefore, this study adopts graphene oxide (GO) to modify the structure of C–S–H, and investigates the effects of synthetic methods on the structure of C–S–H–GO composites. In this study, the highly ordered C–S–H–GO composite is successfully synthesized and exhibits itself the high toughness. Moreover, the formation mechanism of the highly ordered C–S–H–GO composite is explored and discussed, which provides a new insight into the design of high‐toughness cement‐based materials.

Beschreibung: The Nowotny phase Mo Si C (x = 0.9‐0.764) was found to be catalytically active in electrochemical water splitting. The electrocatalytic activity of the Mo Si C /C/SiC nanocomposite with respect to the hydrogen evolution reaction was characterized by low overpotentials of 22 and 138 mV vs reversible hydrogen electrode for applying 1 and 10 m A cm of current density, respectively, which exceeds that of most Mo‐based electrocatalysts and shows a high stability (over 90 %) during 35 h. Abstract The ternary Nowotny phase (NP), with a composition Mo3+2xSi3C0.6 (x = 0.9‐0.764), is found to be catalytically active in the field of electrochemical water splitting. The NP embedded in a porous SiC/C nanocomposite matrix is synthesized via a single‐source‐precursor approach which involves the reaction of allylhydridopolycarbosilane with MoO2(acac)2. Thermal treatment of the single‐source‐precursor up to 1400°C in a protective atmosphere results in the in situ formation of nanocrystalline Mo3+2xSi3C0.6 immobilized in a thermally and corrosion‐stable SiC/C matrix. The weight fractions of the observed crystalline phases Mo3+2xSi3C0.6 and SiC amount to ca. 28 (26) and 72 (74) wt%, respectively, when prepared at 1400°C (1350°C). The porosity of the formed nanocomposite is adjusted by the addition of polystyrene (PS) as a pore former to the single‐source‐precursor resulting in a specific surface area up to 206 m2/g. The electrocatalytic activity of the Mo3+2xSi3C0.6/C/SiC nanocomposite with respect to the hydrogen evolution reaction (HER) is characterized by low over potentials of 22 and 138 mV vs reversible hydrogen electrode (RHE) for applying 1 and 10 mA cm−2 of current density, respectively. The analyzed electrocatalytic performance exceeds that of most Mo‐based electrocatalysts and shows high stability (over 90%) during 35 hours.

Beschreibung: Abstract Making illumination light sources become comfortable to the human eye is a long‐term effort, which justifies the current research on warm white‐light‐emitting diodes (w‐LEDs). In this work, a novel phosphor for w‐LEDs, namely SrGa12O19: Dy3+(SGO: Dy3+), with a low‐color temperature (CT) was designed and synthesized. The crystal structure, the luminescence properties, the thermoluminescence properties and the stability of SGO: Dy3+ were investigated. We demonstrate outstanding luminescent characteristics and excellent stabilities. The intensity of emission light keep remained when excited by a flickering light source with a chopping speed or off‐time of a few seconds, which indicates that the SGO: Dy3+ phosphor has anti‐flicker properties that will be useful for potential applications, as LEDs driven by alternating current (AC‐LED). The chromaticity coordinates and the correlated color temperature (CCT) of SGO: Dy3+ phosphors with different Dy3+ concentrations are close with an optimal doping at 4.00 mol% Dy3+ for chromaticity coordinate (0.4269, 0.4348) and a lowest CCT of 3361 K. The perfect weatherability of this phosphor was also confirmed since the phosphorescence intensity and the color were stable at high temperature and in a high humidity environment. The performance obtained shows that SGO: Dy3+ is a suitable candidate for illumination sources that are beneficial to human health.

Beschreibung: Both ERA‐20C and NOAA‐20CR with only the observed surface signal assimilated, could reproduce the observed MJO characteristics very well, with the former superior to the latter, regardless of MJO intensity. Abstract The Madden–Julian Oscillation (MJO), as a dominant mode of tropical intraseasonal oscillation, plays an important role in the variability of global weather and climate. However, current state‐of‐the‐art atmospheric circulation models have difficulty in reproducing observed MJO characteristics when forced by observed daily sea surface temperature alone. An important practical question is how much data a model needs in assimilation to reproduce real MJO events? By analysing ERA‐20C and NOAA‐20CR reanalysis data, the authors tried to figure out whether a model could reproduce observed MJO events by assimilating the observed surface signal alone. The phase propagation and vertical structure associated with MJO were compared between the reanalysis data and observations during 1979–2010. A total skill score considering both temporal correlation and spatial standard deviation were defined. The result showed that both ERA‐20C and NOAA‐20CR could reproduce the observed MJO characteristics very well, with the former superior to the latter, regardless of MJO intensity. Thus, a minimum requirement for an operational atmospheric model for MJO prediction is the assimilation of the observed surface signals.

Beschreibung: The temperature inversions are a common phenomenon occurring in the lower troposphere. Their temporal and spatial variability is, however, determined by the inversion type. Surface‐based inversions (SBI) indicate a clear diurnal cycle, while the day–night variability of elevated inversions (EI) is far less pronounced. The analysis conducted revealed that anticyclonic circulation is both an important factor supporting the subsidence leading to EI occurrence and a good precursor of the nocturnal radiation favourable for the development of deep SBI. Abstract Tropospheric temperature inversions are thought to be an important feature of climate as well as a significant factor affecting air quality and low‐level cloud formation. The aim of this study is to investigate the temporal and spatial variability of the tropospheric temperature inversions, in particular so‐called elevated inversions, over Europe. The analysis is based on data gained from ERA‐Interim reanalysis for the period 1981–2015. The data consist of air temperature, and geopotential height from the entire vertical cross‐section of the troposphere, that is, from 1,000 to 100 hPa. The study examines the temporal (intra‐ and inter‐annual) variability of the temperature inversions based on their frequency, base height, depth, and strength. The analysis conducted revealed that the temperature inversions are a common phenomenon occurring in the lower troposphere. Their temporal and spatial variability is, however, determined by the inversion type. Surface‐based inversions (SBI) indicate a clear diurnal cycle, while the day–night variability of elevated inversions (EI) is far less pronounced. Two main regions of the most frequent EI occurrence may be distinguished. These are: (a) a marine area west of the Iberian Peninsula and (b) Eastern Europe. Both of them are located in areas which are under the influence of extensive high‐pressure systems—the permanent Azores High and semipermanent Siberian High, respectively. The development of EI should be therefore attributed to the large‐scale subsidence and adiabatic heating of air parcels. EI are also quite common over the other parts of the Atlantic Ocean, which is closely linked to the development of marine inversions. SBI tend to be stronger than EI—the mean seasonal inversion strength is usually substantially higher for SBI. In turn, EI reach higher values of the mean seasonal inversion depth as compared with SBI.

Beschreibung: It is found that the climatology, interannual variation, spatial modes and characteristic indices of the winter North Pacific storm track (WNPST) are extremely sensitive to the choice of cumulus convection scheme (CCS). The Kuo scheme has a stronger ability to simulate the WNPST. We find that energy conversion from the eddy available potential energy to eddy kinetic energy among these CCSs may be one of the key reasons affecting the simulation results of the WNPST. Abstract Based on the regional climate model RegCM4.5 driven by National Centers for Environmental Prediction (NCEP) reanalysis, the influence of cumulus convection schemes (CCSs) on the winter North Pacific storm track (WNPST) is investigated. It is found that the climatology, interannual variation, spatial modes and characteristic indices of the WNPST are extremely sensitive to the choice of CCS. Among the selected CCSs, WNPST climatology and interannual variation in the Kuo scheme are better than in other CCSs, with a smaller root mean square error. The WNPST spatial modes and strength indices in the Kuo and Grell schemes are more consistent with NCEP reanalysis. The Kuo scheme has a stronger ability to simulate the WNPST latitude index and the interannual variation of winter characteristic indices. In addition, we attempt to reveal the possible reasons for the different performances of CCSs from the viewpoint of baroclinic energy conversion (BCEC). It is found that the energy conversion from the mean available potential energy to the eddy available potential energy (BCEC1) has no significant difference among the Kuo, Grell and Emanuel schemes, while energy conversion from the eddy available potential energy to eddy kinetic energy (BCEC2) in the Kuo scheme is obviously better than other CCSs, which means that the differences in BCEC2 among these CCSs may be one of the key reasons affecting the simulation results of the WNPST.

Beschreibung: 118‐year urban climate and extreme weather events of Metropolitan Manila, the capital of the Philippines. Observed temperature and precipitation are rising in this megacity. Temperature is driven by large and small scale forcing (i.e., ENSO, urbanization) while precipitation is heavily influenced by landfalling and distant tropical cyclones. Abstract Metropolitan Manila, the Philippines, is a megacity with a population of 12.9 million people. Unabated urbanization and disorganized infrastructure build‐up, coupled with a large urban poor population have made many of its population vulnerable to climate change. This study presents the 118‐year urban climate and extreme weather events of Metropolitan Manila. Daily average and minimum temperature are on the rise comparable to countrywide trends. Consequently, there are more warm and less cold nights. Total annual precipitation is also increasing at a rate of 77.99 mm/decade. Decreasing simple daily intensity index implies that higher observed precipitation is due to the increase in wet days count rather than intensity. Tropical cyclones (TCs) are critical in producing most extreme rainfall events in the metropolis. Extreme precipitation is induced either by a TC's immediate rainbands or remote precipitation effects by enhancing the prevailing summer monsoon flow. TC‐induced rain modulates annual rainfall variability and is estimated to contribute 45.2% to Metropolitan Manila mean total rainfall.

Beschreibung: Abstract Precipitation during the Ethiopian Kiremt (June–September) season has exhibited significant interannual and multidecadal variability over the 20th and early 21st century. We investigated the temporal variability in the strength of the teleconnections between sea‐surface temperatures in key global oceanic regions, including the Tropical Pacific, Indian Ocean, and Tropical Atlantic, and Kiremt season precipitation at subseasonal, interannual and multi‐decadal time scales. We also investigate the influence of the Madden‐Julian Oscillation (MJO). We performed a systematic analysis of 112‐year long (1901–2012) precipitation in the northern region of East Africa including the southern and central regions of Ethiopia and uncover interesting spatial, temporal and subseasonal variability and teleconnection patterns. Precipitation anomalies during wet and dry years extend throughout Northern Africa and also, during September extends over Indian subcontinent, suggesting large‐scale variability of wet/dry patterns. Wet (dry) years are accompanied by La Nina like (El Nino like) conditions in the tropical Pacific and extending into Atlantic and Indian Oceans. Through Bayesian dynamical linear modeling we find that temporal changes in seasonal precipitation correspond to changes in the strengths of SST teleconnections, and that the relative strengths of these teleconnections rather than one dominant teleconnection influences precipitation variability. During three precipitation epochs in this region, the mid‐century pluvial, the late‐century drought, and the early 21st century, we find that changes in precipitation are related to changes in the main dynamical features of precipitation. These findings suggest that Kiremt season precipitation is in a new regime, and is of key interest to the agricultural and water resources communities who rely on accurate forecasts of precipitation to make operational decisions. This article is protected by copyright. All rights reserved.

Beschreibung: The average annual precipitation for recent decades shows a downwards trend and is contrary to what was observed for the last decades of the 20th century over humid subtropical climate areas. Maximum daily precipitations over the Paraná River basin showed trends of decrease or increase, depending on the type of climate and season. In terms of monthly maximum trends, February, July, and October are the months with the highest probability of an extreme weather event occurring in the basin. Abstract The main objective of this study was to investigate the trends on average and extreme events in time series of daily precipitation from 1980 to 2010 in the Paraná River basin, Brazil. The nonparametric Mann–Kendall test was applied to detect monotonic trend in the precipitation series. The occurrence of extreme values was analysed based on three generalized extreme values (GEV) models: Model 1 (stationary), Model 2 (non‐stationary for location parameter), and Model 3 (non‐stationary for location and scale parameters). The GEV parameters were estimated by the Generalized Maximum Likelihood method (GMLE) and for the non‐stationary models, the parameters were estimated as linear functions of time. To choose the most suitable model, the maximum likelihood ratio test (D) was used. From the results observed at the monthly scale, it was possible to infer that the months with the highest probability of an extreme weather event occurrence are February (climates Aw and Cfa), July (Cfa and Cfb), and October (Aw, Cfa, and Cfb). Approximately 90% of the 1,112 stations presented no trend regarding the GEV parameters. The non‐stationarity showed by other stations (Models 2 and 3) might be associated with several factors, such as the alteration of land use due to the north expansion of the agricultural border of the Paraná River basin.

Beschreibung: Abstract This article presents a review of the scientific literature on detection, sources of variability, and predictability of the timing of monsoons. The timing of monsoons is characterized by the beginning (commonly referred to as onset) and end (commonly referred to as demise, cessation, retreat, or withdrawal) dates of the summer monsoons. The main methods used to detect the timing of monsoons are divided into two categories: local‐scale methods and regional‐to‐large‐scale methods. The sources of variability of the timing of monsoons are also separated into two categories: local‐scale and large‐scale sources. Finally, the article presents a summary of the literature on the predictability of the timing of monsoons using both dynamical and statistical approaches. We show that all methods are parameterized in some way. A comparison between two different methods shows that while there might be large differences in the definition of onset and demise dates at the local level, spatial aggregation usually reduces the noise and enhances the regional monsoonal signal, which may be predictable. This article is protected by copyright. All rights reserved.

Beschreibung: Abstract The Australian Alpine region is highly vulnerable to extreme climate events such as heavy rainfall and snow falls, these events subsequently impact rainfall erosivity and hillslope erosion in the region. In this study, the relationship between extreme rainfall indices and rainfall erosivity was examined across the Alpine region in New South Wales (NSW) and Australian Capital Territory (ACT) and the surrounding areas including Murray Murrumbidgee and South East and Tablelands (SET). Rainfall erosivity, hillslope erosion and their changes were estimated in the future periods using the revised universal soil loss equation and the NSW/ACT Regional Climate Modeling (NARCliM) projections. Results from the study demonstrate a good relationship between extreme rainfall indices (especially Rx5Day) and rainfall erosivity. The rainfall erosivity and hillslope erosion are projected to increase about 2% and 8% for the near future (2020–2039), further increase to 8% and 18% for the far future (2060–2079) in the Alpine region assuming the groundcover is maintained at the current condition. The change in rainfall erosivity and erosion risk is highly uneven in space and in season with the highest erosion risk in summer with an increase about 33% in the next 50 years. The highest erosion risk area is predicted within SET (maximum rate 19.95 Mg ha−1 year−1), but on average, the ACT has the highest erosion rate, which is above 1.36 Mg ha−1 year−1 in all periods. The snowmelt in spring in the Alpine region is estimated to increase the rainfall erosivity by 13% in the baseline period, up to 24% in the near future, but far less (about 1%) in the far future due to predicted temperature rise and less snow available in the Alpine region in the next 50 years. This article is protected by copyright. All rights reserved.

Beschreibung: International Journal of Climatology, Volume 39, Issue 10, Page i-iv, August 2019.

Beschreibung: Abstract The exhibited geometry of catalytic substrates can have a significant influence on the chemical activity and efficiency. Controlling their geometry can be challenging using the traditional techniques. In this work, we propose new and novel catalytic substrates with architected and controllable topologies based on the minimal surfaces framework. A novel design approach and an additive manufacturing (AM) technique were proposed to manufacture the catalytic substrates using ceramic materials. After 3D printing, their mechanical and flow properties were investigated experimentally. An elastic‐plastic‐damage coupled model was employed to investigate the underlying deformation mechanism of the investigated substrates. Results showed that the CLP substrate exhibited the highest mechanical properties as well as the least pressure drop among the tested substrates. Also, numerical simulations showed that the strut‐based substrates exhibit stress localization which leads to faster failure, while stress is distributed more homogeneously in the sheet‐based substrates. While the model showed to have a good agreement in the experimental and simulation stress‐strain responses, the damage mechanism was not fully captured by the numerical simulations. This was attributed mainly to the process‐induced defects in the form of microcracks and microvoids that can alter the nature of deformation and damage.

Beschreibung: Abstract The degradation of mechanical properties due to sintering is one of the major issues during high temperature service of thermal barrier coating system for advanced gas turbines. In this study, a constitutive model was developed by the variational principle, based on the experimentally observed microstructure features of suspension plasma‐sprayed thermal barrier coatings. The constitutive model was further implemented in finite element analysis software, in order to investigate the effect of vertical cracks. The evolution of microstructure during sintering, coating shrinkage and mechanical degradation were predicted. The numerical predictions of Young's modulus were generally in agreement with experimental results. Furthermore, the effect of vertical cracks on the strain tolerance and sintering resistance were discussed. It was confirmed that the introduction of vertical cracks contributed to the improvement of both properties.

Beschreibung: Abstract Hollandite has been studied as a candidate ceramic waste form for the disposal of high‐level radioactive waste due to its inherent leach resistance and ability to immobilize alkaline‐earth metals such as Cs and Ba at defined lattice sites in the crystallographic structure. The chemical and structural complexity of hollandite‐type phases developed for high‐level waste immobilization limits the systematic experimental research that is required to understand phase development due to the large number of potential additives and compositional ranges that must be evaluated. Modeling the equilibrium behavior of the complex hollandite‐forming oxide waste system would aid in the design and processing of hollandite waste forms by predicting their thermodynamic stability. Thus, a BaO–Cs2O–TiO2–Cr2O3–Al2O3–Fe2O3–FeO–Ga2O3 thermodynamic database was developed in this work according to the CALPHAD methodology. The compound energy formalism was used to model solid solution phases such as hollandite while the two‐sublattice partially ionic liquid model characterized the oxide melt. Results of model optimizations are presented and discussed including a 1473 K isothermal BaO–Cs2O–TiO2 pseudo‐ternary diagram that extrapolates phase equilibrium behavior to regions not experimentally explored.

Beschreibung: Abstract Suppression of charge recombination by thin amorphous alumina layers on metal oxide semiconductors has demonstrated a vital role in electronic appliances beside its role as an insulator. This study reports effect of amorphous alumina (Al2O3) on the structural, electrical, and optical properties of stannous oxide (SnO2). The samples for the present study are prepared as nanofibers by electrospinning a polymeric solution containing aluminum and stannous precursors and subsequent annealing; six samples with varying concentrations of aluminum and stannous are considered. A crystal‐amorphous SnO2/Al2O3 hybrid system was confirmed by both XRD and XPS analysis. Both BET and Mott‐Schottky analysis showed increase in the surface area and conduction band minimum of the sample with increase in the Al content, however, at the expense of its electrical conductivity. The electron lifetime of the sample increased with increase in the Al content, but the electron transport time increase with decrease in the electrical conductivity of the sample. Both Urbach energy measurement and Stoke's shift showed generation of deeper trap state with increase in the Al content. Investigation on sample photovoltaic performance showed that the loss in electrical conductivity of the sample can be compensated by the improved surface area to a certain extent. Interestingly, a composite nanofiber containing equal molar fraction of aluminum and stannous showed orders of magnitude higher photocurrent despite its similar resistivity as that of pure alumina fibers, which is shown to originate from a Fermi energy gradient at the Al2O3/SnO2 interface.

Beschreibung: Abstract Ba0.875Ca0.125Ti0.95Sn0.05O3 (BCT‐Sn) was examined for photocatalytic, piezocatalytic, and piezo‐photocatalytic effects. BCT‐Sn powder was poled through corona poling and it was found that poling induces significant impact on photocatalysis. This material was also able to degrade dye (Methylene blue) using poled powder under ultrasonication (piezocatalysis). There was a remarkable effect in dye degradation which is a clear indication of the importance of piezocatalytic behavior in catalytic reactions. Moreover, the piezo‐photocatalytic effect (piezocatalysis + photocatalysis) was also investigated. Results suggested an enormous scope of ferroelectric materials in the field of catalysis.

Beschreibung: Abstract A novel pale‐yellow Ba2ZnGe2O7:Bi3+ phosphor with site‐selected excitation and small thermal quenching was synthesized by conventional solid‐state sintering. The crystal structure and luminescence properties have been investigated in detail for the first time using XRD patterns, photoluminescence spectra, diffuse reflection spectra, decay curves, and temperature‐dependent emission spectra. The results reveal that the excitation spectrum of Ba2ZnGe2O7:Bi3+ phosphor locates in the near‐ultraviolet region of 300‐400 nm, and its emission shows an obvious site‐selective excitation phenomenon since Bi3+ ions occupy two different crystallographic sites in the Ba2ZnGe2O7 host. When excited under 360 nm, the phosphors show a pale‐yellow emission in the range of 400‐700 nm with the maximum peaking at 520 nm, while when excited under 316 nm, the phosphors show a blue emission in the range of 400‐700 nm with the maximum peaking at 480 nm. In addition, the emission of Ba2ZnGe2O7:Bi3+ can also be easily controlled by changing the Bi3+ concentration. The Ba2ZnGe2O7:Bi3+ phosphor has small thermal quenching, and its emission intensity only decreases by 2% at 200°C. The results indicate that this novel pale‐yellow Ba2ZnGe2O7:Bi3+ phosphor could be conducive to the development of white light‐emitting diodes.

Beschreibung: Abstract The binding of Na+, K+, and Li+ by magnesium silicate hydrate (M–S–H) was investigated in batch sorption experiments. Sorption isotherms and cation exchange measurements indicated the binding of alkalis in cation exchange sites compensating the negative surface charge of M–S–H. Higher pH values led to further deprotonation of the silanol groups and a higher alkali uptake by M–S–H. No significant incorporation of alkalis in the main silica or magnesium oxide sheets was observed. However, the silica sheets were less polymerized in the presence of higher alkali hydroxide concentrations.

Beschreibung: Abstract Large‐strain multilayer actuators (MLAs) were fabricated by tape‐casting 0.91(Na1/2 Bi1/2)TiO3–0.06BaTiO3–0.03AgNbO3 (NBT‐BT–3AN) lead‐free incipient piezoceramics co‐fired with Pt inner electrodes. Microstructures, dielectric properties, unipolar and bipolar strain, as well as fatigue properties of the MLAs were investigated. It was found that the actuator consisting of 15 ceramic layers with individual thicknesses of 114 μm could output a large unipolar strain of 0.3% and a dynamic displacement of 5 μm at 6 kV/mm at room temperature. It exhibited excellent cycling stability and provided a high strain of 0.23% after 107 cycles at 6 kV/mm. Moreover, these MLAs still can deliver a strain of 0.20% at 125°C.

Beschreibung: Abstract (0.96‐x)K0.48Na0.52NbO3‐0.04Bi0.5Na0.5ZrO3‐xLaFeO3 ceramics (abbreviated as KNN‐BNZ‐LF1000x) with enhanced piezoelectric performance and temperature stability were prepared by the conventional solid‐state sintering method. It was found that the incorporation of LaFeO3 gradually shifted the O‐T phase boundary toward room temperature, while maintaining the Curie temperature above 300°C. The optimal piezoelectricity was found at x = 0.006, with relatively high piezoelectric constant d33 of 345 pC/N as well as a high level of unipolar strain (0.126% at 3 kV/mm). Benefiting from the diffused phase transition induced by appropriate amount of LaFeO3 content, the KNN‐BNZ‐LF6 sample possessed greatly enhanced the temperature stability of , which varied less than 8% in the temperature range of 20°C‐100°C.

Beschreibung: Abstract Degradation of thermal barrier coatings (TBCs) in gas‐turbine engines due to calcium–magnesium–aluminosilicate (CMAS) glassy deposits from various sources has been a persistent issue since many years. In this study, state of the art electron microscopy was correlated with X‐ray refraction techniques to elucidate the intrusion of CMAS into the porous structure of atmospheric plasma sprayed (APS) TBCs and the formation and growth of cracks under thermal cycling in a burner rig. Results indicate that the sparse nature of the infiltration as well as kinetics in the burner rig are majorly influenced by the wetting behavior of the CMAS. Despite the obvious attack of CMAS on grain boundaries, the interaction of yttria‐stabilized zirconia (YSZ) with intruded CMAS has no immediate impact on structure and density of internal surfaces. At a later stage the formation of horizontal cracks is observed in a wider zone of the TBC layer.

Beschreibung: An effective and facile dip‐loading approach was adopted to fabricate Au nanoparticle (NPs) @TiO2 nanotube arrays (NTAs) heterostructured films with improved H2 generation rate under visible light. Abstract Au nanoparticle (NPs)@TiO2 nanotube arrays (NTAs) heterostructured films with enhanced H2 generation rate under full spectrum were synthesized, by using a controllable and facile dip‐loading approach. Size of the Au NPs was well‐distributed around 7 nm, and the TiO2 NTAs were found vertically aligned. Due to LSPR effect and Schottky contact, the as‐prepared Au NPs@TiO2 NTAs heterostructured films exhibited improved H2 generation abilities as well as photocatalytic degradation abilities. H2 evolution rate of the obtained samples (effective area: 5.25 cm2) reached 74.56 μmol/h, which was 38 times higher than that of the raw TiO2 NTAs. And the Au NPs@TiO2 NTAs samples also showed an obvious advantage over the raw TiO2 NTAs, in methyl orange degradation under UV illumination. Repetition experiments were further carried out to ensure the dip‐loading method was a reliable fabrication process, and the amount of Au particles attached on TiO2 tube walls could be manipulated by changing the dip‐loading cycle times.

Beschreibung: Abstract In this study, TiO2 nanorod arrays (TNR), Ag quantum dots (QDs) sensitized with TNR TiO2/Ag, bismuth oxyhalide (BiOI) nanosheets, and Ag QDs co‐modified with TNR and TiO2/BiOI/Ag (TBA) were prepared by a stepwise process. The morphological, structural, compositional, optical, photocatalytic (PC), and photoelectrochemical (PEC) properties of the samples were investigated. The TBA‐2 sample exhibited the highest photocurrent density (281.8 μA/cm2) and photodegradation efficiency (93.3%), with values 9.7 times and 2.25 times higher than those for TNR, respectively. The improvement in sample performance can be attributed to the formation of a heterojunction between BiOI and TiO2, thereby enhancing the absorption of visible light and improving the charge separation efficiency; Ag QDs limit interfacial electron‐hole pair recombination. The experimental results show that TBA can effectively promote light‐induced carrier transport and visible light absorption, while inhibiting the recombination rate of the electron‐hole pairs, PEC, and PC.

Beschreibung: Abstract The drastic reduction in dimensions in thin films, together with the low crystallization temperatures used, normally results in a large reduction in the grain size. It has been reported that relaxor ferroelectric states are stabilized at room temperature for fine‐grained ceramics and films that behave as normal ferroelectrics for large grains. In this work, the effects of the grain size reduction on the relaxor characteristics are analyzed for a composition that is already a canonical relaxor with a nonergodic state at room temperature: (Bi0.5Na0.5)1‐xBaxTiO3 (BNBT). The comparison of the local polar ordering within BNBT grains studied with piezoresponse force microscopy on large‐grained ceramics and fine‐grained thin films shows that the development of stable long‐range ferroelectric order with the application of an electric field is hampered due to the small grain size of the grains. The ergodic character of the high‐temperature phase is thus stabilized at room temperature, following a similar mechanism as the one discussed for other noncanonical relaxors.

Beschreibung: Abstract In this work, we have prepared a novel (K0.5Na0.5)0.99‐xPrxYb0.01NbO3 (abbreviated as KNN:xPr3+/0.01Yb3+, x = 0.0006, 0.0008, 0.001, 0.002, 0.003, and 0.004) ceramics, which possess visible UC emissions, photochromic (PC) and optical thermometric properties. Under the excitation of a 980‐nm diode laser, all the samples show the featured emissions of Pr3+ ions and the UC emission intensity is greatly dependent on the Pr3+ doping content. The optimal UC luminescence intensity is obtained at x = 0.001. All the prepared samples show a strong PC reaction, and a large luminescence quenching degree (ΔRt) of 74.94% is found. The optical thermometric properties of both the irradiated and unirradiated KNN:0.001Pr3+/0.01Yb3+ ceramics in the temperature range of 123‐573 K have been investigated via measuring the temperature‐dependent UC emission spectra of green emissions, which originate from the two 3P1 and 3P0 thermally coupled levels. It has been found that the prepared samples have both excellent PC behaviors and temperature‐sensing performances. These results suggest that the KNN:xPr3+/0.01Yb3+ ceramics are promising candidates for the applications in PC reaction and thermometers.

Beschreibung: Abstract In this work, we present a general sol‐gel protocol for the synthesis of highly porous monolithic transition metal borides via carbothermal conversion of the organic/inorganic interpenetrating networks (IPNs). The formation of organic/inorganic IPNs is clearly demonstrated by simple oxidation and boiling water treatment. A series of transition metal boride porous monoliths, including CrB2, ZrB2, TiB2, Cr3C2/CrB, and ZrB2/ZrC with porosities ranging from 70% to 85% and pore sizes ranging from 0.5 to 35 μm, have been prepared. In each case, a porous hybrid monolith is obtained by drying the wet gel under ambient pressure. It is believed that the formation of organic/inorganic IPNs strengthens the gel network, so that it can withstand the severe changes during desiccation to give out a monolithic xerogel. Samples are characterized by TG‐DSC, XRD, SEM, EDS, TEM, BET, and MIP, and the ceramic monoliths are shown to be well defined and rather homogeneous.

Beschreibung: Abstract Sr2[Ti1−x(Al0.5Nb0.5)x]O4 (x = 0, 0.10, 0.25, 0.30, 0.5) ceramics were synthesized by a standard solid‐state reaction process. Sr2[Ti1−x(Al0.5Nb0.5)x]O4 solid solutions with tetragonal Ruddlesdon‐Popper (R‐P) structure in space group I4/mmm were obtained within x ≤ 0.50, and only minor amount (1‐2 wt%) of Sr3Ti2O7 secondary phase was detected for the compositions x ≥ 0.25. The temperature coefficient of resonant frequency τf of Sr2[Ti1−x(Al0.5Nb0.5)x]O4 ceramics was significantly improved from 132 to 14 ppm/°C correlated with the increase in degree of covalency (%) with increasing x. The dielectric constant ɛr decreased linearly with increasing x, while high Qf value was maintained though it decreased firstly. The variation tendency of Qf value was dependent on the trend of packing fraction combined with the microstructure. Good combination of microwave dielectric properties was achieved for x = 0.50: ɛr = 25.1, Qf = 77 580 GHz, τf = 14 ppm/°C. The present ceramics could be expected as new candidates of ultra‐high Q microwave dielectric materials without noble element such as Ta.

Beschreibung: A small addition of TaC into HfC (or vice versa) induces a great improvement in materials properties of (Hf1‐xTax)C. Abstract Bond characteristics, mechanical properties, and high‐temperature thermal conductivity of ultrahigh‐temperature ceramics (UHTCs), hafnium carbide (HfC), tantalum carbide (TaC), and their solid solution composites, were investigated using first‐principles calculations. Mulliken analyses revealed that Ta formed stronger covalent bonds with C than did Hf. Bond overlap analyses indicated that the Hf–C bond possessed mixed covalent and ionic bond characteristics, compared with the more covalent character of the Ta–C bond. Consequently, the overall elastic properties were enhanced with increasing number of Ta–C bonds in the composites. The overall metallicity of the composites also increased with increasing TaC content; thus, the mechanical properties did not improve monotonically. Our results indicate that adding a small amount of TaC to HfC or vice versa to produce a composite would create a new UHTC with greatly improved elastic and mechanical properties as well as high‐temperature thermal conductivity.

Beschreibung: Abstract The charge compensation mechanisms that occur when Li+ substitutes a 2+ element in superionic conductor (MgCoNiCuZn)O high‐entropy oxide have been studied using a combination of thermogravimetric analysis and X‐ray photoemission spectroscopy. Depending on the concentration of Li+ in the compound, the charge compensation involves first partial oxidation of Co2+ into Co3+ for low fraction of Li+, and then a combination of both the oxidation of cobalt and the formation of oxygen vacancies for large fraction of Li+.

Beschreibung: Abstract HBO2‐II ceramics were prepared by cold sintering with 10wt% dehydrated ethanol as the transient liquid phase. When the processing temperature is 30°C, the relative density of the mechanically robust HBO2‐II ceramics increases from 77.5% to 84.5% with increasing the uniaxial pressure from 200 to 500 MPa. It changes less than 0.2% for higher pressure up to 700 MPa. Under a constant uniaxial pressure of 500 MPa, the relative density further increases to 94.7% for the processing temperature of 120°C. HBO2‐I is observed as the secondary phase when the processing temperature is 150°C. In comparison, the compacts prepared in the absence of ethanol are fragile, and the relative densities are 78.5%‐84.5% for the processing temperatures of 30‐120°C and uniaxial pressure of 500 MPa. It is indicated that ethanol promotes the densification significantly through the dissolution‐precipitation mechanism. The permittivity increases with increasing the processing temperature, while the Qf value decreases. The optimal properties with the relative density of 94.7%, εr = 4.21, Qf = 47 500 GHz, and τf = −70.0 ppm/°C were obtained in the single‐phase HBO2‐II ceramics cold sintered at 120°C under 500 MPa for 10 minutes. The relative density and Qf value are significantly higher than those of the HBO2‐II ceramic prepared by sintering the H3BO3 compact at 180°C for 2 hours (70.3% and 32 700 GHz, respectively). The results indicate that the nonaqueous solvent can also be used as the transient liquid phase for cold sintering, so that more materials that are unstable or insoluble in water can be densified by this method.

Beschreibung: Abstract Self‐healing capability in wet oxygen atmospheres is the key issue for long term service of SiC/SiC composites in aero‐engines. Polymer derived SiBCN ceramic (PDC SiBCN) was introduced into SiC fiber reinforced SiC as a self‐healing component to obtain SiC/(SiC‐SiBCN)x composites by a newly developed method, namely chemical vapor infiltration combined with polymer infiltration online pyrolysis (CVI + PIOP) process. The weight loss behavior and three‐point bending performance of the samples under different temperatures (1200, 1300 and 1400°C) and different wet oxygen partial pressures were tested up to 100 hours to demonstrate the oxidation behavior of the samples in wet oxygen environments. According to these tests, the antioxidant capacities of samples prepared from different preforms were compared. It has been found that the 2D plain weave samples with higher density have the best resistance to wet oxygen corrosion while the 2D plain weave samples have the worst resistance to wet oxidation and the antioxidant capacities of 2D satin weave samples is between them.

Beschreibung: Abstract Low‐permittivity ZnAl2‐x(Zn0.5Ti0.5)xO4 ceramics were synthesized via conventional solid‐state reaction method. A pure ZnAl2O4 solid‐state solution with an Fd‐3m space group was achieved at x ≤ 0.1. Results showed that partial substitution of [Zn0.5Ti0.5]3+ for Al3+ effectively lowered the sintering temperature of the ZnAl2O4 ceramics and remarkably increased the quality factor (Q × f) values. Optimum microwave dielectric properties (εr = 9.1, Q × f = 115,800 GHz and τf = −78 ppm/°C) were obtained in the sample with x = 0.1 sintered at 1400°C in oxygen atmosphere for 10 h. The temperature used for the sample was approximately 250°C lower than the sintering temperature of conventional ZnAl2O4 ceramics.

Beschreibung: Abstract A series of Dy3+/Eu3+ single‐ and co‐doped calcium borosilicate luminescent glasses were prepared by the conventional high temperature melt‐quenching method. A compact glass structure is obtained by the addition of Dy3+/Eu3+ ions, which is verified by the physical properties of synthetic glasses. As network modifiers, Dy3+/Eu3+ fill in the interspaces of glass network and contribute to the conversion of [BO3] to [BO4]. Dy3+/Eu3+ co‐doped calcium borosilicate glasses can emit white light, which consists of blue, yellow, and red light under 387 nm excitation. The emission spectra and decay curves of the white‐emitting glasses have proved the existence of energy transfer. The average lifetime of Dy3+ decreases from 0.251 to 0.165 ms with the increasing Eu3+ concentration. Changing rare earth ions concentration, CIE color coordinates of Dy3+/Eu3+ co‐doped glass shifts from cyan to white with increasing excitation wavelength. A white‐light emission is obtained when the concentration of Dy3+ and Eu3+ equals to 4% and 2%, respectively. Moreover, the Dy3+/Eu3+ co‐doped calcium borosilicate glass shows high‐thermal stability and it may be applicable for high‐quality white LEDs based on high power near ultraviolet (n‐UV) LED chip in the future.

Beschreibung: Abstract Freeze‐casting is a technique used to produce structures with anisotropic porosity in the form of well‐defined microchannels throughout a sample. Here, this technique is used on the magnetocaloric ceramic La0.66Ca0.26Sr0.07 Mn1.05O3. We show that a dynamic freezing profile, where the temperature is decreased continuously at −10 K/min, results in homogeneous, lamellar channels with widths of ∼15 µm, while static freezing, where the temperature is kept constant at 177 K, results in channels of increasing size away from the initial ice crystal nucleation site. The effect of gelation before freeze‐casting is also investigated. Gelation inhibits ice crystal growth, which significantly changes the morphology by making channel cross sections less elongated, while additionally introducing more dendrites and ceramic bridges in the structure. The latter significantly dominates the flow path through the gelated structures, affecting the calculated tortuosity, which increases to τ ≈ 4 when compared to non‐gelated samples where calculated tortuosities are in the range of ∼1.3 to ∼3. Finally, we present a systematic and automatic approach for evaluating channel and wall sizes and calculating tortuosities. This is based on analysis of images obtained by scanning electron microscopy using a continuous particle size distribution method and the TauFactor application in MATLAB®.

Beschreibung: Location of the GHAS and GHAN regions Abstract Regional‐scale seasonal climate outlooks are typically produced using forecast information either local to the region or from another area with teleconnections to the region. Dynamical global long‐range forecast (LRF) systems can provide both types of information, and these two approaches are compared in the context of seasonal rainfall forecasts for two adjoining areas in the Greater Horn of Africa region in tropical East Africa. The direct method utilizes the unprocessed LRF outputs for the region. For the “indirect” method, canonical correlation analysis is used and works by identifying patterns in historical LRF predictions over large tropical domains that relate to observed variability in the East Africa regions. For a given year, projections of the LRF forecasts onto those patterns can then be employed to construct the regional forecasts. This approach takes advantage of the tendency for LRF systems to have greater skill for large‐scale variability than for smaller regional‐scale features. Using case studies, it is found the two approaches contain complementary information: the indirect approach can provide notable skill benefits in years with strong large‐scale forcing while in some years, particularly when large‐scale signals are weak, the “direct” forecast are superior. Skill comparisons over many years found that, although results are region/season dependent, in general the indirect approach has higher skill overall—with improvements equal to or greater than those afforded by a 1‐month reduction in lead time with the direct approach. Results for both methods used separately and in combination are provided for the March–April–May and September‐to‐December seasons in the two regions, using data from currently operational dynamical LRF systems. Skill was best for the September‐to‐December season in the southern region, using “indirect” forecasts. The “direct” approach was better than “indirect” for the March‐to‐May season in the northern region. In general, combination did not produce a substantial benefit.

Beschreibung: Topography elevation (m) map of Mediterranean Sea, central North Africa and Southwest Asia. The EMED, wISM and BoB regions are denoted. The cross corresponds to the reference point. Data are available from NOAA US Department of Commerce under data announcement 88‐MGG‐02. Abstract Etesians are north to south direction winds in the lower atmosphere, blowing over the Aegean basin from early summer to early autumn. They are an important circulation component for the East Mediterranean (EMED) area, linked to the subsidence and ascent circulation over EMED and the extended Indian monsoon region, respectively. In this study we investigate the evolution of Etesian days and the associated wind speed (10 m) over the recent past (1979–2005) in simulations from Earth System Models (ESMs) available from the Coupled Model Intercomparison Project Phase 5. Results from this analysis are compared to the ERA‐Interim reanalysis. Moreover, we study the connection of the Etesians to the atmospheric circulation over EMED and the wider Indian monsoon area, in particular over the west Indian summer monsoon (wISM) and the Bay of Bengal (BoB). Our findings suggest that while the ESMs underestimate the wind speed of the Etesians, their frequency and summer cycle are in good agreement to reanalysis. ESMs can accurately represent the summer atmospheric circulation and depict the connection between EMED and Indian summer monsoon (ISM), capturing the link between them. Finally, we highlight here the capability and efficiency of ESMs in representing the climatology of Etesians and related atmospheric circulation.

Beschreibung: Abstract This study investigates the relative contribution of internal variability and external forcings on summer (June–August) surface air temperature (SAT) over the Central Indian landmass. Here we use Community Earth System Model Large Ensemble (CESM‐LE) data to assess the historical (1966–2005) and future (2010–2060) climate change in presence of internal climate variability. The summer SAT trend during the historical period exhibit an amplified cooling (〈−3°C), whereas, a warming trend (〉= 4°C) is projected in all the ensemble members under RCP8.5 scenario. The total trend is then partitioned into contributions from the externally forced response and internal climatic variability. Over the Indian region, the external forcing displays a strong cooling trend during the historical period and warming trend under RCP8.5 scenario. On the other hand, natural variability displays mainly cooling trends and it introduces a wide range of uncertainty to the future projection in climate models. In historical period, the signal to noise ratio (SNR) i.e. ratio of external forcings and internal variability is less than 1, which indicates that the internal climatic variability dominates over the forced response. But in future decades the SNR is much higher than 1 i.e. external forcing overrides the internal variability. However, to a greater extent natural variability will mask the warming trend over the Indian region, even under RCP8.5 scenario. This article is protected by copyright. All rights reserved.

Beschreibung: Abstract Here, we select simple Er3+‐doped tellurite glass as model system to systematically explore the up‐conversion, down‐shifting mechanisms with different excitations (980 nm and 447 nm), respectively. We observe for the first time, to the best of our knowledge, that tunable photo‐luminescence occurs from green to red & NIR region, rather than merely from the long‐accepted green to red region. Direct evidence of selective energy transfer mechanism is expounded in detail, and its potential applications are demonstrated. In addition, we provide evidence that the cross‐relaxation process between dopant ions can enhance photo‐luminescence in Er3+ doped tellurite glasses with high dopant concentrations, whereas the crucial reason for emission decrease is the energy loss long‐distance energy migration. These fundamental insights into the photophysical processes in heavily doped photonic glasses will broaden the applications of rare‐earth‐doped materials ranging from optical communications to medical imaging. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.

Beschreibung: Abstract An intercomparison of three regional climate models (PRECIS‐HadRM3P, RCA4, and RegCM4) was performed over the Coordinated Regional Dynamical Experiment (CORDEX) ‐ Central America, Caribbean and Mexico (CAM) domain to determine their ability to reproduce observed temperature and precipitation trends during 1980‐2010. Particular emphasis was given to the North American monsoon (NAM) and the mid‐summer drought (MSD) regions. The three RCMs show negative (positive) temperature (precipitation) biases over the mountains, where observations have more problems due to poor data coverage. Observations from the Climate Research Unit (CRU) and ERA‐Interim show a generalized warming over the domain. The most significant warming trend (≥ 0.34°C decade‐1) is observed in the NAM, which is moderately captured by the three RCMs, but with less intensity; each decade from 1970 to 2016 has become warmer than the previous ones, especially during the summer (mean and extremes); this warming appears partially related to the positive Atlantic Multidecadal Oscillation (+AMO). CRU, GPCP and CHIRPS show significant decreases of precipitation (less than ‐15% decade‐1) in parts of the Southwest United States and Northwestern Mexico, including the NAM, and a positive trend (5% to 10% decade‐1) in June‐September in eastern Mexico, the MSD region, and northern South America, but longer trends (1950‐2017) are not statistically significant. RCMs are able to moderately simulate some of the recent trends, especially in winter. In spite of their mean biases, the RCMs are able to adequately simulate interannual and seasonal variations. Wet (warm) periods in regions affected by the MSD are significantly correlated with the +AMO and La Niña events (+AMO and El Niño). Summer precipitation trends from GPCP show opposite signs to those of CRU and CHIRPS over the Mexican coasts of the southern Gulf of Mexico, the Yucatan Peninsula, and Cuba, possibly due to data limitations and differences in grid resolutions. This article is protected by copyright. All rights reserved.

Beschreibung: Abstract This study has addressed the spatiotemporal distribution of the daily rainfall concentration and its relation to the teleconnection patterns across the Mediterranean (MR). Daily Concentration Index (CI) and the ordered n index (nor) are used at annual time scale to reveal the statistical structure of precipitation across the MR based on 233 daily rainfall series for the period 1975–2015. Eight teleconnection patterns, North Atlantic Oscillation (NAO), Mediterranean Oscillation (MO), Western Mediterranean Oscillation (WeMO), Upper Level Mediterranean Oscillation index (ULMO), East Atlantic (EA) pattern, East Atlantic/West Russia (EATL/WRUS) pattern, Scandinavia (SCAND) pattern and Southern Oscillation (SO) at annual time scale are selected. The spatiotemporal patterns in precipitation concentration indices, annual precipitation and their teleconnections with previous large‐scale circulations are investigated. Results show a strong connection between the CI and the nor (r = 0.70, p〈0.05) which present the same relative areas of high and low concentration. The annual values range from 0.57 to 0.70 for CI and 0.49 to 0.71 for nor index which show a high daily precipitation concentration across the MR. Trend analysis demonstrated mostly significant increasing trends for both indices. This increase is mainly found in south France, northern coastlands of the Iberian Peninsula (IP), Greece and Tunisia. An inverse relationship between the number of rainy days and concentration indices is evident. Both of WeMO and MO can play an important role in modulating rainfall in the northwest Mediterranean. The positive EATL/WRUS phase is mainly connected with positive precipitation mean anomalies in the Eastern Mediterranean and vice versa in the west. The high daily precipitation concentration values over south France, northeast Spain, Croatia and Tunisia are linked to the low values of WeMO and high values of EA. These results could pave the way for new possibilities regarding the projection of precipitation concentration and precipitation irregularity in downscaling techniques. This article is protected by copyright. All rights reserved.

Beschreibung: Abstract In this work, the influence of starting particle size and sintering conditions on the microstructures and dielectric properties of BaTiO3‐based ceramics coated with 0.3Bi(Zn1/2Ti1/2)O3‐0.7BaTiO3 were investigated to reveal the core‐shell structure by using high resolution transmission electron microscopy technique coupled with energy‐dispersive spectrometer analysis. The ion‐diffusion behavior plays a critical role in the formation and evolution of the core‐shell structure and, therefore, significantly influences the dielectric properties. When using starting powders containing BaTiO3 particles larger than 100 nm in size and sintering for shorter dwelling times (0.5‐2.0 hours), a core‐shell structure could be formed and retained owing to the limited diffusion behavior, enabling BaTiO3‐based ceramics to meet the X8R specification for multilayer ceramic capacitors applications at high temperatures. However, when using 80 nm BaTiO3 nanopowders and further extending the dwelling time to 6.0 hours, more driving energy was provided to prompt ion diffusion, which led to the compositional inhomogeneity becoming homogenized.

Beschreibung: Abstract The combined impact of Greenland sea ice, Eurasian snow, and the El Niño–Southern Oscillation (ENSO) on the out‐of‐phase relationship between the Indian summer monsoon (ISM) and Korean summer monsoon (KSM) were investigated through numerical experiments. The results revealed that Indian and Korean summer rainfalls showed nonlinear responses to ENSO and Greenland sea ice forcing when the events co‐occurred. Above‐normal Greenland sea ice and a concurrent La Niña showed a distinct in‐phase relationship with ISM and out‐of‐phase relationship with KSM. Below‐normal and above‐normal Greenland sea ice during boreal autumn surrounded the Greenland region with anomalous low pressure and high pressure, respectively. These were associated with a barotropic +west/−east or –west/+east dipole pattern, respectively, over Eurasia during the subsequent winter and spring seasons. Furthermore, these patterns led to positive and negative snow depth anomalies, respectively, over western Eurasia and the opposite snow tendency over eastern Eurasia during the subsequent spring. This variability in Eurasian snow patterns may play a crucial role in ISM and KSM. The co‐occurrence of ENSO variability also generates high‐ and low‐pressure anomaly patterns over the Indian Ocean that may be related to unfavorable or favorable ISM, respectively, while influencing the negative or positive phases of a Pacific Japan (PJ)‐like teleconnection pattern that may be related to unfavorable or favorable KSM, respectively. Therefore, coexisting ENSO forcing may play a dominant role in ISM and KSM, but Greenland sea ice forcing and Eurasian snow variation intensify the out‐of‐phase relationship between ISM and KSM. This article is protected by copyright. All rights reserved.

Beschreibung: Abstract Ba{[Gax,Tax]Ti(1−2x)}O3 ceramics with x equal to 0, 0.0025, 0.005, 0.01, 0.025, and 0.05 have been prepared by conventional solid‐state reaction. Structural and dielectric characterization have been performed to investigate the effect of dipole‐pair substitution concentration on the macroscopic dielectric properties. Ba{[Gax,Tax]Ti(1−2x)}O3 evolves from a classic ferroelectric to a diffuse phase transition (DPT) as x increases. Ba{[Gax,Tax]Ti(1−2x)}O3 for x ≥ 0.01 possesses diffuseness parameters comparable to Pb(Mg1/3Nb2/3)O3‐PbTiO3 (PMN‐PT) and recently reported (Ba0.97Pr0.03)(Ti0.9425Ce0.05)O3 (BPTC), yet it lacks the frequency and temperature dependence of Tm necessary to be a strictly defined relaxor ferroelectric. Additionally, Ba{[Ga0.05,Ta0.05]Ti0.9}O3 possesses a relative permittivity, ɛr, of 700 ± 16% and dissipation factor less than 0.05 at 10 kHz within the temperature range [−75°C, 120°C]. In comparison to BaTiO3, Ba{[Gax,Tax]Ti(1−2x)}O3 possesses enhanced electrical resistivity at and above room temperature. In situ XRD, including Rietveld refinement, have been performed to determine the lattice parameter, coefficient of thermal expansion, and phase transition temperature (Tc) of each composition within the temperature range [RT, 1000°C], thus linking the dielectric properties with the material's structure. These studies have been corroborated by temperature‐dependent Raman spectroscopy to compare the Tc determined by electrical and structural characterization. The properties of Ba{[Gax,Tax]Ti(1−2x)}O3 are discussed in context with available models that describe donor and acceptor dopants spatially separated in the parent matrix, inter‐relating lattice parameter, Curie temperature, and other material properties.

Beschreibung: Abstract Ab initio molecular dynamics simulations are executed to probe the short‐range order and the electrical features of the liquid and amorphous boron subarsenide (B12As2). A drastic volume swelling of ~40% is witnessed for the liquid state, relative to the crystal. The density of the melt is found to be close to that of liquid boron. As the temperature applied is gradually decreased, the volume progressively decreases and a glass‐transition zone at around 1400 K is observed. About 14% volume expansion is perceived for the amorphous phase. Due to the drastic density (volume) difference between the liquid and amorphous forms, their atomic structure is found to be different from each other. In the liquid phase at 2500 K, the mean coordination number (CN) of B and As atoms is 4.4 and 2.5, correspondingly. During the solidification process, both average CNs steadily increase and reach values of 5.5 (B‐atom) and 4.14 (As‐atom) at 300 K. The pentagonal pyramid‐like motifs barely survive at 2500 K but during the quenching process they develop progressively and some of which lead to the formation of B12 clusters. In the amorphous state, the chain‐like and A7‐like As‐As clusters are observed. Nonetheless, the noncrystalline state is proposed to be partially similar to the crystalline structure. The liquid state shows a metallic character while the amorphous form presents a semiconducting nature having an energy band gap much smaller than that of the crystalline phase.

Beschreibung: A Landsat‐7 image (07 July, 2001) of the study area, known as the Sermeq Kajulleq ablation region, commonly referred to as the Jakobshavn ablation region, or JAR (within red box). The study area is north of the glacier (red dashed line) in west‐central Greenland. In the region surrounding the melt‐lakes is a linear transect of three automated weather stations, JAR‐2 (568 m), JAR‐1 (962 m), and Swiss Camp (1,149 m) that are part of the Greenland Climate Network Abstract Along the west‐central Greenland ice sheet (GrIS) ablation zone, the time of annual maximum occurrence of surface melt‐lakes, or peak lake period (PLP) averages June 18–July 3. This study combines atmospheric reanalysis and automatic weather station data from the Greenland Climate Network to assess the roles of synoptic circulation patterns and local climate variables, respectively, in the total melt‐lake area and count in the Sermeq Kujalleq ablation region (SKAR) for the PLPs of 2000–2016. Melt‐lake information is obtained from analysis of Landsat‐7 images. Two surface climate parameters (e.g., temperature, incoming shortwave radiation) having a strong combined effect on melt‐lake area in the SKAR are the June mean temperature, and May mean incoming solar radiation (r = .96). Incorporating the May insolation into a regression equation permits predictability of total melt‐lake area for the study area into late June. June months classified as high melt correlate regionally with mid‐tropospheric ridging, warm air advection, and reduced cloud cover, while low melt June months are associated with a trough, cold advection, and greater cloud amount. A localized feature that we found to be prevalent during the high‐melt years are piteraq, or downsloping winds, which provide additional warming to the SKAR from adiabatic compression. Atmospheric circulation indices comprising the North Atlantic Oscillation index (NAOI) teleconnection and Greenland blocking index (GBI) pattern augment the reanalysis gridded data. We find statistically significant correlations of the NAOI and GBI with melt‐lake area (r = −.62 and r = .77, respectively). The correlations with melt‐lake count however, are not significant; greater combined lake area and count tend to accompany the meridional mode of high amplitude Rossby waves and/or anti‐cyclonic blocking in the Greenland sector. Determining the local and synoptic‐scale atmospheric controls on supraglacial lake variability helps clarify the role of climate in the surface hydrology of the GrIS.

Beschreibung: Abstract We have used digital holographic tomography (DHT) to study the refractive index (density) changes occurring under Vickers indentations in silica, soda‐lime, and non‐alkaline aluminoborosilicate glasses. The measurements confirm that the maximum refractive index (density) is not constant but increases with load up to 300 gf. At higher loads (500 gf and 1 kgf), a subsurface (median) crack in soda‐lime glass is observed with no apparent surface trace. The appearance of this crack reduces the maximum refractive index (density) observed. In addition, the vertical cross section of the 3D refractive index (density) map has been successfully obtained using a square fiber sample and lateral observation. These results clearly demonstrate a promising potential of DHT to evaluate the shape and the density distribution of the structurally modified zone in a Vickers‐indented glass.

Beschreibung: Abstract Weakly coupled relaxors based on compositions (1‐x) BaTiO3‐xBiMeO3, where Me is a metal ion, have attracted attention as potential candidates for high‐temperature high‐energy density capacitors. However, the necessary Bi content is typically high with x = 0.3‐0.4. In order to reduce problems associated with compatibility for base metal electrodes and due to additional problems due to Bi volatility, it is desirable to lower the Bi content in the overall composition for these materials. Here, we have explored a possible way to reduce BiMeO3 content through additional A‐site substitutions viz. Ca and Sn. The relaxor nature and energy storage properties of Sn‐modified (Ba,Ca)(Ti)O3‐BiScO3 ceramics were determined from their dielectric and ferroelectric behaviors. The material showed attractive properties in terms of a frequency‐independent (200 Hz‐1 MHz) dielectric response from room temperature to 200°C, extremely low loss and high‐energy storage efficiency. The structural phenomena underlying the functional properties of Sn‐modified (Ba,Ca)TiO3‐BiScO3 are characterized from temperature‐dependent X‐ray diffraction and pair distribution function analysis. In broader terms, the study illustrates the potential for tailoring relaxor behavior in Pb‐free ferroelectrics by combining phenomena, such as quantum fluctuations and lone pair stereochemical effect associated with different solid‐solution substitutions.

Beschreibung: Steps involved for investigation of the effect of AD processing at the substrate interface using NaCl coating. Abstract Aerosol deposition is a feasible method of fabricating dense ceramic films at room temperature by the impact consolidation of submicron‐sized particles on ceramic, metal, glass, and polymer substrates at a rapid rate. Despite the potential usefulness of the aerosol deposition process, there are issues, such as deposition mechanisms and structure of the film‐substrate interface, that are not well understood. We have used complementary structural and microstructural analysis to capture the state of the substrate surface after the aerosol deposition process. The results reveal that modification of the substrate surface by the ejected submicron‐sized particles is essential for the formation of anchoring layer, thereby, a change in internal residual stress state and surface free energy of the substrate is required to deposit film using AD process. Our analysis also suggests that the adhesion between the metal substrate and ceramic particles is possibly contributed by both physical bonding and mechanical interlocking.

Beschreibung: Abstract Silicon carbide fiber reinforced MoSi2 matrix composite (SiCf/MoSi2) is prepared by liquid silicon infiltration at 1450°C. SiC fiber preform is first impregnated with phosphomolybdic acid (PMA) solution in ethyl alcohol. After calcinations, the PMA is converted into MoO3. Following the heating in hydrogen atmosphere, the MoO3 is reduced into metallic Mo, leading to a porous SiCf/Mo. The porous preform is then infiltrated with liquid silicon above silicon melting point to produce SiCf/MoSi2. The microstructure evolution and the underlying mechanism are studied. It is found that MoSi2 is formed by dissolution‐precipitation. Through multiple impregnation‐calcination cycles, a fully dense SiCf/MoSi2 can be obtained with MoSi2 as the continuous matrix phase. The presence of Mo is found to significantly reduce the attack of liquid silicon the silicon carbide fiber reinforcements.

Beschreibung: Abstract 8 mol% yttria‐stabilized zirconia (8YSZ) ceramic is an oxide ion conductor at atmospheric pressure but shows the onset of p‐type semiconduction, in addition to the preexisting oxide ion conduction, on application of a dc bias in the range 4‐66 Vcm−1 and at temperatures in the range 150°C‐750°C. The p‐type behavior is attributed to the location and hopping of holes on oxygen. This contrasts with the commonly observed introduction of n‐type conduction under reducing conditions and high fields. The hole conductivity increases with both dc bias and pO2. Its occurrence may contribute to the early stages of flash phenomena in 8YSZ ceramics.

Beschreibung: Abstract BiMn3Cr4O12 shows an unusual joint multiferroicity, which facilitates the coexistence of considerable ferroelectric polarization and remarkable magnetoelectric coupling in a single‐phase multiferroic material. Based on first‐principles calculations, we investigate the two different types of ferroelectric phase transitions in the BiMn3Cr4O12 material. Our results show that the first ferroelectric phase transition is driven by soft mode and leads BiMn3Cr4O12 into the Cm space group. The predicted ferroelectric polarization in single crystal is about ~9.8 μC/cm2. With the emergence of spin order on both Mn and Cr sublattices, it is the polar Cm structure that triggers the exchange striction mechanism and therefore results in a large type‐II multiferroicity (~1.1 μC/cm2). In addition, the intrinsic direction of the spin‐driven ferroelectric polarization is always opposite to that of the existing Cm phase structure. Our results imply a feasible strategy in searching/designing novel type‐II multiferroics with large ferroelectric polarization.

Beschreibung: The crystal structure of Li5La3Ta2O12 and PL spectrum of Li5La3Ta2O12:Mn4+ phosphor with the chromaticity diagram and picture under UV 365 nm lamp. Abstract Li5La3Ta2O12:Mn4+ (LLTO:Mn4+) phosphors are prepared in air via high‐temperature solid‐state method and investigated for their crystal structures and luminescence properties. LLTO:Mn4+ phosphor under excitation at 314 nm shows deep‐red emission peaking at 714 nm due to the 2E→4A2 transition of Mn4+ ion. The excitation bands in the range 220 ‐ 570 nm are attributed to the Mn4+ ‐ O2‐ charge‐transfer band and the 4A2g→4T1g, 2T2g, and 4T2g transitions of Mn4+, respectively. The optimal Mn4+ ion concentration is ~0.4 mol%. The concentration quenching mechanism in LLTO:Mn4+ phosphor is electric dipole‐dipole interaction. The luminous mechanism and temperature quenching phenomenon are explained by the Tanabe‐Sugano energy level diagram and the configurational coordinate diagram of Mn4+ in the octahedron, respectively. The experimental results indicate that LLTO:Mn4+ phosphor has a potential application prospect as candidate of deep‐red component in light‐emitting diode (LED) lighting.

Beschreibung: Abstract The effect of the substitution of Na2O with K2O on the viscosity and structure of molten CaO‐SiO2‐CaF2‐based mold fluxes containing alkali‐oxides at high temperatures has been studied. The CaO/SiO2 mass ratio (C/S) and CaF2 were fixed at 0.8 and 10 mass pct., respectively. The total alkali‐oxide was fixed at 20 mass pct. By systematically substituting the Na2O with K2O, the K2O/(Na2O + K2O) mass ratio was modified between 0.0 and 1.0. Using the rotating spindle method to measure the viscosity at high temperatures, the viscosity was found to increase with higher K2O/(Na2O + K2O). From the slope of the temperature dependence of the viscosity, an apparent activation energy was calculated and increased with higher K2O/(Na2O + K2O), from 96 to 154 kJ/mol, due to the cation size effect on the resistance to shearing. Using Raman spectroscopy of as‐quenched fluxes, the mole fraction of Q3 was found to increase, while the mole fractions of Q2 and Q0 decreased with higher K2O/(Na2O + K2O). The nonbridged oxygen per silicon cation (NBO/Si) decreased from 1.97 to 1.58 with increasing K2O/(Na2O + K2O), suggesting greater complexity of the flux structure with higher K2O/(Na2O + K2O), resulting in a higher viscosity.

Beschreibung: Abstract A novel tantalate red‐emitting phosphors NaCa1‐xEuxTiTaO6 (x = 0.02‐0.50) is synthesized via the traditional solid‐state reaction sintering. The photoluminescence properties, X‐ray diffraction (XRD), scanning electron microscopy (SEM), and thermal stability are characterized in detail. Photoluminescence spectra show strong red emission monitored at 614 nm at λex = 395 nm. The spectral properties exhibit excellent color purity and chromaticity coordinate (CIE) characteristics. White light‐emitting diodes (w‐LEDs) device are fabricated by the prepared phosphors and show high quality of color‐rendering index. The investigated results suggest that the Eu3+‐doped NaCaTiTaO6 phosphors can be as potential substitute red phosphors for w‐LEDs.

Beschreibung: Abstract Piezoceramics are widely‐used in high‐power applications, whereby the material is driven in the vicinity of the resonance frequency with high electric fields. Evaluating material's performance at these conditions requires the consideration of inherent nonlinearity, anisotropy, and differences between individual vibration modes. In this work, the relation between electromechanical properties at large vibration velocity and the utilized vibration mode is investigated for a prototype hard piezoceramic. The nonlinear behavior is determined using a combined three‐stage pulse drive method, which enables the analysis of resonant and antiresonant conditions and the calculation of electromechanical parameters. The deviations of coupling coefficients, compliances, and piezoelectric coefficients at high‐power drive were found to be strongest for the transverse length vibration mode. Differences in the mechanical quality factors were observed only between the planar and transverse length modes, which were rationalized by the different strain distribution profiles and the contribution of different loss tensor components. In addition, the influence of the measurement configuration was investigated and a correction method is proposed. The differences between vibration modes are further confirmed by heat generation measurements under continuous drive, which revealed that the strongest heat generation appears in the radial mode, while transverse and longitudinal length modes show similar temperature increase. Piezoceramics are widely‐used in high‐power applications, whereby the material is driven in the vicinity of the resonance frequency with high electric fields. Evaluating material's performance at these conditions requires the consideration of inherent nonlinearity, anisotropy, and differences between individual vibration modes. In this work, the relation between electromechanical properties at large vibration velocity and the utilized vibration mode is investigated for a prototype hard piezoceramic. The nonlinear behavior is determined using a combined three‐stage pulse drive method, which enables the analysis of resonant and antiresonant conditions and the calculation of electromechanical parameters. The deviations of coupling coefficients, compliances, and piezoelectric coefficients at high‐power drive were found to be strongest for the transverse length vibration mode. Differences in the mechanical quality factors were observed only between the planar and transverse length modes, which were rationalized by the different strain distribution profiles and the contribution of different loss tensor components. In addition, the influence of the measurement configuration was investigated and a correction method is proposed. The differences between vibration modes are further confirmed by heat generation measurements under continuous drive, which revealed that the strongest heat generation appears in the radial mode, while transverse and longitudinal length modes show similar temperature increase.

Beschreibung: Abstract ZnO thin films were deposited via atomic layer deposition (ALD) using H2O and H2O2 as oxidants with substrate temperatures from 100°C to 200°C. The ZnO films deposited using H2O2 (H2O2‐ZnO) showed lower growth rates than those deposited with H2O (H2O‐ZnO) at these temperature range due to the lower vapor pressure of H2O2, which produces fewer OH− functional groups; the H2O2‐ZnO films exhibited higher electrical resistivities than the H2O‐ZnO films. The selection of H2O2 or H2O as oxidants was revealed to be very important for controlling the electrical properties of ALD‐ZnO thin films, as it affected the film crystallinity and number of defects. Compared to H2O‐ZnO, H2O2‐ZnO exhibited poor crystallinity within a growth temperature range of 100‐200°C, while H2O2‐ZnO showed a strong (002) peak intensity. Photoluminescence showed that H2O2‐ZnO had more interstitial oxygen and fewer oxygen vacancies than H2O‐ZnO. Finally, both kinds of ZnO thin films were prepared as transparent resistive oxide layers for CIGS solar cells and were evaluated.

Beschreibung: Cu2O particles can be produced along with siloxene formation by simply dispersing layered CaSi2 into CuCl2 + HCl aqueous solution through the comproportionation reaction between Cu and [Cu(OH)4]2‐ ions. Abstract We demonstrate that Cu2O particles can be produced along with siloxene formation by simply dispersing layered CaSi2 into an aqueous solution of CuCl2 and HCl at room temperature. The Cl− ions induce oxidative extraction of Ca from CaSi2 to form siloxene and trigger the reductive deposition of Cu particles. All particles are then gradually oxidized to form Cu2O particles under optimized conditions as follows. A trace amount of residual CaSi2 is dissolved in the solution, which provides OH− ions, and a portion of the formed Cu particles are dissolved as [Cu(OH)4]2− ions. Accordingly, Cu2O particles would be formed through the comproportionation reaction between Cu and [Cu(OH)4]2− ions in the solution. However, under conditions with an excess amount of Cl− ions results in further oxidation of Cu to also form Cu2Cl(OH)3. Thus, CaSi2 acts as an effective reduction and/or oxidation mediator to tune the number of Cl− and OH− ions and control the oxidation state of Cu.

Beschreibung: The tunable color was obtained via the substitution of Sr2+, Ca2+, Zn2+ and Mg2+ ions for Ba2+ ions under the same excitation conditions. The emission color can be tuned from deep blue (0.15, 0.12) to cyan (0.16, 0.27) due to the variation of crystal field and distortion of the unit cell by replacing part of the host lattice cation Ba2+ with Sr2+, Ca2+, Zn2+ and Mg2+. The emission bands of BMBO:Ce3+, BZBO:Ce3+, BCBO:Ce3+ and BSBO:Ce3+ can be influenced by two factors: the crystal field splitting and centroid shifts. Abstract In this study, Sr2+, Ca2+, Zn2+, and Mg2+ ions act to tune the emission band to the blue‐cyan region in BaxSryB2O5:Ce3+ (BSBO), BaxCazB2O5:Ce3+ (BCBO), BaxZnuB2O5:Ce3+ (BZBO), and BaxMgvB2O5:Ce3+ (BMBO) phosphors. A red shift occurs with the increase of Sr2+, Ca2+, Zn2+, and Mg2+ concentration, and a blue shift occurs when the concentrations of Sr2+, Ca2+, Zn2+, and Mg2+ exceed the critical value. The emission color can be tuned from deep blue (0.15, 0.12) to cyan (0.16, 0.27) upon 365 nm UV lamp excitation due to the crystal field splitting and centroid shifts. The excitation band shift to long wavelength by introducing ions, so that the synthesized phosphor can be better matched with the n‐UV chip. The emission intensity slowly decreases with the temperature increasing. Therefore, the BMBO:Ce3+, BZBO:Ce3+, BCBO:Ce3+, and BSBO:Ce3+ phosphors with relatively good thermal stability were synthesized, which could have potential applications in the n‐UV white LEDs.

Beschreibung: Abstract We investigate the thermoelectric properties of bulk polycrystalline samples of WSe2‐based compounds with partial substitutions in the cationic (W) and the anionic (Se) sublattices in the temperature range from 4.2 to 650 K. The substitution of W for Nb leads to a significant increase in the charge carrier concentration, however, deteriorates the charge carrier mobility. In contrast, the substitution of selenium for sulfur increases the charge carrier mobility, the thermal conductivity, and the Seebeck coefficient but conductivity changes non‐monotonical. We show that the addition of sulfur in anionic sublattice affects the grain sizes in the polycrystalline material. Using substitutions in the anionic and cationic sublattices, we find the optimal ratio of the elements for better thermoelectric efficiency. The W0.98Nb0.02Se1.7S0.3 sample showed the best value of the figure of merit ZT = 0.26 (T = 650 K).

Beschreibung: Abstract Although heat‐cured concrete (HCC) has received extensive research interests in recent years, it still suffers from problems including coarsened microstructure, low cement hydration degrees, etc, which limited its application. Some of these problems can be solved by internal curing method resulting in low early strength of HCC and low‐production efficiency. This study addressed this issue by activating the aluminosilicate internal curing agent (lightweight fine aggregate, LWFA) with triisopropanolamine (TIPA). The results indicated that more Al3+ and Fe3+ ions were dissolved from LWFA by TIPA, which assisted the formation of hydrates with cement ions in interfacial transition zone (ITZ), and enhanced the density of ITZ in the early stage. The introduction of TIPA was found to increase the early compressive strength of HCC, by approximately 15.3%, 25.9% and 28.0%, respectively for the cement cured for 1, 3, and 7 days compared with control samples. Moreover, the results of rapid chloride migration and water absorption depth also suggested that coupling the aluminosilicate internal curing agent with TIPA improved the pore structure of HCC.

Beschreibung: Abstract Rare earth (RE) ions‐doped luminescent nanocrystals (NCs) with numerous unique advantages have attracted tremendous interest for the wide applications from science to engineering, yet suffering from the shortcoming of thermal quenching coming from surface organic ligands. We propose utilizing a facile acid‐base reaction to remove surface organic ligands introduced choosing carboxylic acids as stabilizing agent and weaken thermal quenching. The results showed that the acid‐base reaction displayed an outstanding cleaning effect. After acid‐treatment, most surface organic ligands were removed, and there was no influence on crystal structure and morphology of as‐prepared β‐NaYF4:Er3+ NCs. Meanwhile, with no surface organic ligands capping, β‐NaYF4:Er3+ NCs preferred brighter emission after thermal treatment, including up‐conversion (UC), near‐infrared (NIR), and mid‐infrared (MIR) emission. When calcined the acid‐treated β‐NaYF4:Er3+ NCs in different atmosphere, such as oxygen and reducing atmosphere (15%H2 + 85%N2), an unexpected enhancement of all emission bands in Er3+ was determined under phase transformation temperature, especially in oxygen atmosphere. Furthermore, all the fluorescence lifetimes of Er3+ also exhibited obvious extension. Our results supposed that the β‐NaYF4:Er3+ NCs have promising applications in safety ink, and the acid‐treatment by diluted hydrochloric acid is a general approach to remove deleterious organic ligands on NC surface further to weaken thermal quenching.

Beschreibung: Abstract Multicomponent boron‐containing carbide (ie, Zr‐Ti‐C‐B) composites show good ablation resistance. The present work is the first report to introduce the powder fabrication of Zr‐Ti‐C‐B using a new method for solid‐state diffusion of boron atoms. First, the nonstoichiometric carbide (ie, Zr0.8Ti0.2C0.8) with carbon vacancies was fabricated by free‐pressureless spark plasma sintering. Different boron sources such as B2O3, B, and B4C were used to react with the nonstoichiometric carbide. The Zr0.81Ti0.19C0.86B0.14 can be finally generated through the solid‐state diffusion of boron atoms using the B2O3 boron source at 1300°C followed by carbon thermal reduction using the phenolic resins at 1600°C.

Beschreibung: Abstract The influence of synoptic‐scale circulation on air temperature variation in the ice‐free and glaciated areas on the eastern side of the Antarctic Peninsula have been analysed. For this purpose, a new classification of atmospheric circulation with fifteen synoptic patterns in the Antarctic Peninsula region was developed using the self‐organizing maps technique. The synoptic patterns were compared with air temperature observations from coastal and glacial sites on James Ross Island, north‐eastern Antarctic Peninsula, in the period 2005–2015. The most frequent synoptic pattern with a frequency of 13.7% was dominated by a low‐pressure centre in the north‐western Bellingshausen Sea, which extended over the Antarctic Peninsula to the Weddell Sea. On the other hand, the largest interannual variability was observed for a synoptic pattern with a low‐pressure centre in the southern Bellingshausen Sea. This synoptic pattern also had the highest air temperature anomalies at both investigated sites year‐round. Air temperature anomalies at the lower lying site (Mendel station) were the lowest during a high‐pressure ridge dominating the AP region due to a combination of local and synoptic‐scale processes. At Davies Dome, the glacial site, southerly barrier winds advecting cold air from the ice‐covered Weddell Sea during a strong low‐pressure system in the Weddell Sea ensured the coldest air temperature anomalies. This article is protected by copyright. All rights reserved.

Beschreibung: An intense green long‐persistent phosphor LaSrAl3O7:Eu2+, was synthesized. Optical data can be encoded on a flexible film by 405 nm laser and decoded by heating or by 980 nm laser, which opens new opportunities for information security system. Abstract Here, a green emission persistent luminescent phosphor LaSrAl3O7:Eu2+ which is chargeable by UV light, was synthesized by solid‐state reaction method. Elemental mapping and fluorescence microscopy photoluminescence of the sample demonstrated the homogeneous distribution of La, Sr, Al, O, and Eu in the phosphor. Rietveld refinement shows that the as‐prepared sample belongs to the tetragonal crystalline structure with space group of P421m. The Eu2+:5d‐4f broad persistent luminescence with maximum emission peaking at 518 nm can be effectively obtained after irradiating in the UV light. A series of excitation temperature‐dependent thermoluminescence measurements were conducted to gain some insight into the information of traps. Additionally, to verify its feasibility of optical data storage, specific information letters were encoded on the LaSrAl3O7:Eu2+ phosphor films using the laser of 405 nm, then the stored information could indeed be read out by thermal stimulation as expected. Meanwhile, NIR photo‐stimulated red persistent luminescence was also obtained, which holds great potential for optical information storage. Finally, combined with the experimental and density functional theory calculation results, we proposed a tentative schematic diagram to account for the PersL and photo‐stimulated persistent luminescence mechanism in LaSrAl3O7:Eu2+ phosphor.

Beschreibung: Abstract The influence of different SPS‐based methods, that is, conventional spark plasma sintering (SPS), flash SPS (FSPS), and reactive SPS (RSPS) on the properties of Al2O3/SiC composite was investigated. It was shown that the application of preliminary high energy ball milling of the powders significantly enhances the sinterability of the ceramics. It was also demonstrated that FSPS provides unique conditions for rapid, that is, less than a minute, consolidation of refractory ceramics. The Al2O3‐20 wt% SiC composite produced by FSPS possesses the highest relative density (~99%), fracture toughness (7.5 MPa m1/2), hardness (20.3 GPa) and wear resistance among all ceramics produced by other SPS‐based approaches with dwelling time 10 minutes. The RSPS ceramics hold the highest Young's modulus (390 GPa). Substitution of micron‐sized Al2O3 particles by nano alumina does not lead to measurable enhancement of the mechanical properties.

Beschreibung: Abstract The effect of the structural environment on the Cl− ion conductivity was demonstrated in LaOCl‐based solid electrolytes. By replacing the La3+ site with lower‐valent Mg2+ or Ca2+ ions, the conductivity was enhanced owing to the formation of a Cl− ion vacancy. Despite the same dopant content, the conductivity of La0.8Ca0.2OCl0.8 was considerably greater than La0.8Mg0.2OCl0.8. This enhancement of the conductivity was influenced by the high ionicity of the Cl− ions, which facilitated the weakening of the La‐Cl bond cleavage to conduct inside the lattice. The elongation of the La‐La distance, associated with the Cl− ion conduction, could also cause an increase of the conductivity.

Beschreibung: Abstract The diminished conductivity of pristine grain boundaries in oxide‐ion conducting electrolytes, such as (Ce,Gd)O2 and (Zr,Y)O2, is widely interpreted with the Mott–Schottky space‐charge model, or less frequently, with the Gouy–Chapman space‐charge model. Although routinely applied to the entire compositional range of solid solutions, from dilute to concentrated, these models, being based on the Poisson–Boltzmann formalism, are limited in their range of validity to dilute solutions of point defects. Analysing the grain‐boundary properties of concentrated solid solutions with such models is expected to lead to errors and inconsistencies. In this study we employ Poisson–Cahn theory to analyse literature data for the grain‐boundary resistance of CeO2–Gd2O3 materials as a function of Gd concentration. Poisson–Cahn theory combines the Cahn–Hilliard theory of inhomogeneous systems with the Poisson equation of electrostatics and it is valid over the entire compositional range. We treat the realistic case of a restricted equilibrium: Gd accumulation profiles are frozen‐in from sintering temperatures, while the oxygen‐vacancy distributions are in equilibrium at sintering and (much lower) measurement temperatures. Data for the grain‐boundary resistance are also analysed with the standard analytical expressions from the Mott–Schottky and Gouy–Chapman models. Outside the domain of their validity, these expressions are found to perform poorly. In general, we emphasise the importance of treating the interfacial properties of concentrated solid solutions with physically appropriate theories. This article is protected by copyright. All rights reserved.

Beschreibung: Abstract In the diffusion couple of Ti3SiC2 and Ti3AlC2, only interdiffusion of Si and Al occurred during diffusion treatment process. Based on the concentration profiles of Si and Al measured by electron probe microanalysis (EPMA), the interdiffusion coefficients of Si and Al at 1373‐1673 K in Ti3SiC2–Ti3AlC2 diffusion couple were determined by both the Boltzmann‐Matano (B‐M) method and the Saucer‐Freise (S‐F) method. At the position of Matano plane with the composition of Ti3Al0.5Si0.5C2, the interdiffusion coefficient could be expressed as Dint (m2/s) = 5.6 × 10−4⋅exp [−246 ± 14 (kJ/mol)/RT]. Based on the two methods, the calculated interdiffusion coefficients increased with increasing temperature, and the magnitudes of their absolute values were on the order of 10–13‐10–11 m2/s at 1373‐1673 K. At 1373‐1573 K, the calculated interdiffusion coefficients decreased monotonously with the increase of Si concentration, that is, xSi/(xAl + xSi). But at 1673 K, the variation trend of interdiffusion coefficients with xSi/(xAl + xSi) was no longer monotonous, probably due to the presence of Ti5Si3 phase and voids on Ti3AlC2 side.