Various Types Of Precipitation Research Articles

Effect of Ag and Ge on the precipitation behavior and resultant properties of AA6061 alloys

This study investigated the effects of Ag and Ge on the precipitation behavior and resultant properties of AA6061 alloys using hardness measurements, electrical conductivity tests, transmission electron microscopy (TEM), and atom probe tomography (APT). Trace addition of Ge can increase the electrical conductivity and thermal stability, but slightly deteriorates the hardness during the early- and peak-aging stages. Trace addition of Ag can enhance the hardness during aging, especially in the over-aging stage, but it deteriorates the electrical conductivity. For the Ag-added alloys, the Ag atoms provide more nucleation sites and are substantially incorporated into the clusters, suggesting the formation of various types of precipitates with increasing aging time. During the peak- and over-aging stages, the Ag atoms not only segregate but also incorporate into the precipitates, resulting in the disordering of the precipitates and suppression of the coarsening of the precipitates. For the Ge-added alloys, the formation and evolution of the clusters are suppressed by Ge addition, owing to the high binding energy between the Ge and Mg atoms. With the aging time increasing, the Ge atoms are incorporated into the precipitates and suppress the ordering process of the precipitates, resulting in better thermal stability of the Ge-added alloys in the over-aging stage. The addition of both Ag and Ge shows potential for elevated temperature component applications.

Effect of High-Temperature Tempering on Microstructure and Mechanical Strength of Laser-Welded Joints between Medium-Mn Stainless Steel and High-Strength Carbon Steel

The strengthening effect due to high-temperature tempering (HTT) at 700 °C on the microstructure and mechanical properties of welded joints between medium-Mn stainless steel (MMnSS) and high-strength carbon steel (CS) was studied. The microstructure of the weldments was investigated using Laser and scanning electron microscopes. An Electron probe microanalyzer (EPMA) was used to assess quantitatively the elemental distribution profiles of alloying elements within the weld zone. The strengthening precipitates induced during welding and HTT were characterized by transmission electron microscopy (TEM). Uniaxial tensile tests and microindentation hardness (HIT) measurements of the weld joints were conducted to evaluate the strengthening effect. Fully fresh-martensite and fine-tempered martensitic structures were promoted in the as-weld and HTT processes, respectively. The HTT structure exhibited a remarkable improvement in mechanical properties (a better combination of yield and tensile strength together with moderate ductility) compared to its weld counterpart. TEM investigation revealed that various types of precipitates have been promoted in the structures of the weld and HTT, e.g., nanosized vanadium and chromium carbides. It is apparent that the proposed HTT of the joints is an effective treatment for improving the mechanical properties due to inducing the formation of fine interphase precipitates, resulting in enhanced mechanical strength of the joints.

Simultaneous enhancement of mechanical properties and resistance to hydrogen-assisted degradation by multiple precipitation and nano-twinning in medium manganese steel

The microstructure, mechanical properties and resistance to hydrogen-assisted degradation of a medium manganese stainless steel (Fe-0.17C–10Mn–18Cr–5Ni-0.9V-0.26 N, in wt. %) were investigated. The investigated steel was 65% cold rolled and subsequently annealed at 1000 °C for 3 min to promote a very fine-grained austenitic microstructure of ∼1.3 μm with various V/Cr-rich precipitates in the size range of 20–400 nm. This steel took up 2.48 ppm hydrogen during in-situ immersion slow strain rate tensile (SSRT) testing at a strain rate of 10−6 s−1 in 5% NaCl. Insignificant changes in its strength and ductility values were observed, which demonstrates a high resistance to hydrogen-assisted degradation. The analysis of thermal desorption spectroscopy (TDS) curves of the SSRT specimens revealed that hydrogen uptake occurs on irreversible hydrogen traps (precipitates), which inferred from the corresponding high temperature desorption peaks. Transmission electron microscopy conducted on interrupted tensile samples revealed the formation of nano-deformation twins of ∼20 nm, which explains the outstanding strain hardening behavior. The findings demonstrate an excellent hydrogen trapping ability due to multiple types of precipitates in the fine-grained austenitic microstructure, and an outstanding strength-ductility balance (yield strength: 600 MPa, ultimate tensile strength: 975 MPa, total elongation: >45%) that is explained by deformation-induced nano-twins. The synergetic effects of various types of precipitates, fine grain size and deformation mechanism on the resistance to hydrogen-assisted degradation and mechanical behavior are discussed.

Investigation of Microstructure and Mechanical Properties of AlSi7Mg0.3Cu0.5 Alloy with Addition of Zr, Ti and Sr

The main objective of this paper is to investigate the effect of Zr and its synergistic effect together with the addition of an inoculant (Ti) and a modifier (Sr) in terms of structural analysis and mechanical characteristics of AlSi7Mg0.3Cu0.5 alloy. In accordance with the objectives of the paper, in the experimental part, eight material variants were cast by the investment casting method. The presence of Zr in the experimental alloys was manifested by the crystallization of phases with different chemical compositions mainly (AlSi)3(TiZr) and (AlSi)2(TiZr). The graded addition of Ti in the alloys resulted in a higher number of nucleation grains of Zr-rich phases, and alloys with a combination of Zr and Sr were characterized by the formation of (AlSi)2(TiZr) phases. Various types of precipitates based on Zr (Al3(ZrTi)) and Cu (Al2Cu) were observed in the substructure of the alloys. The addition of Zr and its synergistic effect with Ti and Sr led to an increase in the conventional yield strength, hardness and partly tensile strength with reduced elongation of the experimental alloys.

Model Estimate of the Acidity of Atmospheric Precipitation Acidity Due to Anthropogenic Sulfur Compounds in the 20th Century

An analysis of the acidity of precipitation is carried out by using the ChAP-1.0 (Chemistry and Aerosol Processes) atmospheric sulfur cycle scheme developed for Earth System Models of Intermediate Complexity (EMICs)These calculations are forced by monthly mean anthropogenic emissions of sulfur dioxide to the atmosphere in 1850–2000 adapted from the CMIP5 (Coupled Models Intercomparison Project, phase 5) database and by long-term means (taking into account annual variations) of meteorological variables adapted from the ERA-Interim reanalysis for 1979–2015. It was revealed that significant acidity of precipitation (minimum pH of hydrometeors) is typical for regions with high anthropogenic loading of sulfur compounds in atmosphere – Europe, southeast Asia, east North America, southern Africa, and western South America. In these regions in the last decades of the 20th century, typical precipitation values of pH amount from 2.5 to 3.5, which agrees well with the available measurements. The maximum acidity of precipitation (the minimum pH of hydrometeors, which is close to 2) due to anthropogenic sulfur are noted in the eastern Mediterranean region. Atmospheric transport leads to regions with pH 3.5 covering almost all of Eurasia in the last decades of the 20th century. The influence of this transport is also noticeable in other midlatitudinal regions – south of North America and western South America. In general, the ChAP scheme can be used in EMICs, but after a refinement to account for the effect of various types of precipitation on the wet deposition of sulfur compounds from the atmosphere and the effects of orography on the transport of chemical species in the atmosphere

Microstructure characteristics and mechanical performance of Fe-Cr-Ni-Al-Ti superalloy fabricated by powder metallurgy

Fe-Cr-Ni-Al-Ti ferritic superalloy was fabricated by hot isostatic pressing (HIP) of Fe-Cr-Ni-Al-Ti gas-atomized powders. Three types of precipitates with difference in particle size, composition and morphologies have been identified in the as-HIPed ferritic alloy. Micron-sized B2-NiAl distributed in the bulk together with L2 1 -Ni 2 TiAl and Fe(Cr) sub-precipitations are the dominant precipitates. Submicron-sized B2/L2 1 composite precipitates with Fe(Cr)-enriched outer layer and nano-scaled single B2 particles are distributed around the micron-sized B2/ L2 1 / Fe(Cr) composite precipitates. After solution treatment at 1100 °C, various types of precipitates in as-HIPed alloy can be completely dissolved, while dense spherical B2/L2 1 particles are precipitated rapidly even upon water quenching. During aging at 700 °C, the spherical particles evolve into cuboidal morphology and then coarsen and coalesce into large plates. The loss of coherency between the particle and the matrix would produce dense dislocation network at the particle/matrix interface. The measured tensile strength of as-HIPed ferritic superalloy at 700 °C is up to 198 MPa with a total elongation of 47.6%, and the cracks are found to be initiated at the prior particle boundaries, which leads to the failure. To fabricate the high-performance Fe-Cr-Ni-Al-Ti superalloy by powder metallurgy, we suggest that the prior particle boundaries should be avoided during consolidation process. • L2 1 -Ni 2 TiAl and Fe(Cr) sub-precipitations are formed within micron-sized B2-NiAl precipitates. • Outer layer of submicron-sized B2/L2 1 precipitates is enriched in Fe(Cr). • During aging at 700 °C, dense dislocation network is formed at the particle/matrix interface. • Cracks are initiated at prior particle boundaries upon tensile deformation of HIPed Fe-Cr-Ni-Al-Ti superalloy.

Interactive transformation mechanisms of multiple metastable precipitates in a Si-rich Al-Mg-Si alloy

ABSTRACT The precipitate evolution mechanism of the Al-Mg-Si alloys with a Si-rich composition have been a long-term challenge due to the complex transformation paths among multiple precipitates. In the present work, the interactive transformation process of multiple metastable precipitates in a Si-rich Al-Mg-Si alloy were thoroughly studied by atomic resolution high angle annular dark field scanning transmission electron microscopy (HAADF-STEM), in-situ heating TEM and first-principles calculation. It was revealed that the β″ phase transforms simultaneously to various types of precipitates in the over-aged stage. Two different evolution paths are proposed. Firstly, the β″ phase transforms directly to the U1, U2 and β′ phases. Secondly, the U2 phase, as an intermediate phase, transforms to the U1, β′ and B′ phases during the prolonging aging. The formation and evolution of substructures, including the QP lattice and Al–Si columns, are the key for structural transformation of precipitates. During the severe over-aging, the evolution of precipitates is governed by the dissolution of small precipitates (β′ and B′ phases) and the growth of the large ones (U1 phase). These results provide scientific basis for both property improvement of the commercial Al-Mg-Si alloys and development of new 6xxx aluminum alloys.

Application of geotextile containers for removal of silt layers of the Krasnodar reservoir

The article deals with the issues of improving the methods of removing silt layers of the Krasnodar reservoir using geotextile containers. The new technology exceeds all the characteristics of the dewatering facilities available in Russia. The necessary stage of preparation of wastes for disposal is dewatering to a humidity of 50-60%, which allows you to reduce their volume tenfold and improve the structure of raw materials. For these purposes, Russia has quite a lot of different structures and a large number of sludge dewatering methods. For the construction of sludge dewatering facilities and various types of precipitation of sewage, much less time and economic costs are required than for the construction of mechanical cleaning facilities. Also, new technologies occupy quite a little free land area compared to silt sites and they do not depend on climatic factors because atmospheric precipitation falling on the container drains from its surface. The impact of negative temperatures provides the deep moisture drainage after thawing of organogenic silts and hydroxide slimes. Also, new technologies occupy. Geotextile container technology is ideal for silt maps cleaning, sludge storage facilities and reservoirs, for temporary storage of dewatered sludge on a site, and, most importantly, for disposal of wastes directly at the dewatering site in the form of a highly loaded landfill that is resistant to wind and water erosion. When reducing the area of silt maps, the containers can be used as an emergency reserve, since their guaranteed storage period is 25 years. The main principle of the technology is to provide the sludge into the container through a pulp pipeline and then wait for the free water to drain. When dewatering granular suspensions (from sand to dense slimes), the container is filled with natural pulp. When fine silts and hydroxide slimes are dewatered, a flocculant is added to the pulp. After the initial filling of the container with pulp, its subsequent pumping is carried out from 1 to 5 times, after which the process of consolidation of the dehydrated material to the limit of free water release occurs, the duration of which depends on the properties of the solid phase. The main thing is that waiting does not consume any resources, except for the area provided for containers. After consolidation, a loose or refractory material is formed, the size of which depends on the size of the geotextile container used.

Trends and Variability of North American Cool-Season Extratropical Cyclones: 1979–2019

AbstractExtratropical cyclones are the primary driver of sensible weather conditions across the mid-latitudes of North America, often generating various types of precipitation, gusty non-convective winds, and severe convective storms throughout portions of the annual cycle. Given ongoing modifications of the zonal atmospheric thermal gradient due to anthropogenic forcing, analyzing the historical characteristics of these systems presents an important research question. Using the North American Regional Reanalysis, boreal cool-season (October–April) extratropical cyclones for the period 1979–2019 were identified, tracked, and classified based on their genesis location. Additionally, bomb cyclones—extratropical cyclones that recorded a latitude normalized pressure fall of 24 hPa in 24-hr—were identified and stratified for additional analysis. Cyclone lifespan across the domain exhibits a log-linear relationship, with 99% of all cyclones tracked lasting less than 8 days. On average, ≈ 270 cyclones were tracked across the analysis domain per year, with an average of ≈ 18 year−1 being classified as bomb cyclones. The average number of cyclones in the analysis domain has decreased in the last 20 years from 290 year−1 during the period 1979–1999 to 250 year−1 during the period 2000–2019. Spatially, decreasing trends in the frequency of cyclone track counts were noted across a majority of the analysis domain, with the most significant decreases found in Canada’s Northwest Territories, Colorado, and east of the Graah mountain range. No significant interannual or spatial trends were noted with bomb cyclone frequency.

Quantitative microstructural characterization of nuclear grade bainitic steel: Influence of macrosegregations in full-scale forgings

Large forgings used for the fabrication of nuclear reactor components often present chemical macrosegregations as a result of the solidification processes in the initial ingot. This paper presents an extensive microstructural characterization of both the macrosegregated area (up to 0.28 wt% of carbon) and a reference non-segregated area (0.18 wt% of carbon) from 16MND5 steel full-scale large forgings after the final heat treatments and tempering. Inside the macrosegregated areas, significant microhardness variations are observed, corresponding to millimetric microsegregations observed by optical microscopy. At a finer scale, the microstructures of the reference non-segregated area and the macrosegregated area are quite similar, as revealed by Scanning Electron Microscope (SEM) and Electron BackScattered Diffraction (EBSD). In both cases, the microstructure is mostly made up of granular bainite and upper bainite. Various types of precipitates were observed by either SEM or Transmission Electron Microscopy (TEM), such as Fe(Cr,Mn)3C, Mo2C, AlN and AlMnSiN precipitates. The main difference between unsegregated and segregated areas is the significantly higher precipitate number density in the segregated area, as a result of the increase in C, Cr, Mn and Mo content, which can explain the lowered fracture toughness in these areas. Thermodynamic calculations confirm that Cr and Mn enrich cementite precipitates after tempering.

Evolution of Sulfides in Nonoriented Silicon Steels during Heating Process

The evolution of sulfides in nonoriented silicon steels during the heating process is investigated through chemical composition analysis and thermodynamic calculation. Evolution behaviors of sulfides are analyzed using field emission scanning electron microscope (FESEM) and automatic scanning electron microscope (ASPEX). A homogeneous complex sulfide is detected containing magnesium and manganese. The different proportions of MgS and MnS in the complex sulfide are due to the competition between Mg, Mn, and S in low‐sulfur steel. Sulfides and compounds containing sulfides, oxides, and nitrides are mainly formed during the heating temperature of 1000 °C. The presence of sulfides and compounds with sulfide and oxide is at the temperature of 1300 °C. Sulfides reach equilibrium in less time than AlN at 1000 °C, while the time for sulfides to reach the theoretical equilibrium value takes precedence over oxides at 1300 °C. In addition, the proportions of various types of precipitation at 1300 and 1000 °C are discussed through the theoretical calculation and the observation results.

Investigation of secondary phases and tensile strength of nitrogen-containing Alloy 718 weldment

The influence of nitrogen content on the precipitation of secondary phases and the tensile strength of Alloy 718 during gas tungsten arc welding was investigated. Various types of precipitates were characterized using scanning electron microscopy and transmission electron microscopy. The results showed that in the fusion zone, the volume fraction of Nb-rich phases such as Laves, (Nb,Ti)C, and δ phases, as well as Ti-rich phases such as (Ti,Nb)CN and (Ti,Nb)N, increased with increase in the nitrogen content due to the microsegregation of Nb and Ti within interdendritic areas. Nitrogen was also found to decrease the size of γ″ particles within γ dendrites. For precipitates in the partially melted zone, constitutional liquation was observed for both (Nb,Ti)C and (Ti,Nb)N particles. Based on the results of tensile tests, the weld containing 0.015wt% nitrogen exhibited the highest ultimate tensile strength (UTS), whereas more addition of nitrogen led to a decrease in both the UTS and yield strength due to the increased content of brittle Laves phases and decreased size of γ″.

Глаголы падения в казахском языке

The article is devoted to the semantic analysis of verbs of falling in Kazakh language. In particular, the composition of a group of verbs is revealed, their semantic features were described, the usage as part of serial constructions and the main directions of metaphor construction. The article has used the method of analysis, which was created by the Moscow Lexical Typology Group. Data collection was performed through the dictionaries, corpus data, speech observation, a survey of Kazakh speakers, etc. The main verb of falling in Kazakh is the verb құлау. It means falling from above, losing a vertical orientation, crashing down. In contrast to this, the separation of one object from another or the part of a whole is expressed by the verb түсу ‘to descend / fall’, as well as ұшу ‘to fl y’, шығу ‘to go out’. Moreover, the Kazakh language has a number of verbs,which are detailing the process of falling by its nature, the type of subject of falling, etc. The process of falling is detailed by a number of verbs: аударылу ‘to turn over’; ауу ‘to overturn / to tumble/ to turn over / hang on one side’; жығылу ‘to be dumped/ to be dropped’; сүріну ‘to stumble’; төмендеу ‘to lower/ to fall’ etc.In addition, verbs of falling are often found by the type of subject of falling. Viaverbs can be detected various types of precipitation, falling drops, small objects, liquid and loose substances, etc. Kazakh verbs of falling are used as part of serial constructions: in combination with auxiliary verbs қалу ‘to stay’ and кету ‘to go away’, they express the meaning of suddenness, brevity or completeness of action. The verb of falling түсу ‘to go down/ to get down/ to fall’ can also stand out as an auxiliary verb. Verbs of falling develop metaphorical meanings of decrease, the loss of functionality by objects and disability by a person, a sudden and uncontrolled process, etc. At the same time, this or that type of metaphor, as a rule, is expressed by any verb of falling.

Near-0 °C surface temperature and precipitation type patterns across Canada

Abstract. The 0 ∘C temperature threshold is critical for many meteorological and hydrological processes driven by melting and freezing in the atmosphere, surface, and sub-surface and by the associated precipitation varying between rain, freezing rain, wet snow, and snow. This threshold is especially important in cold regions such as Canada, because it is linked with freeze–thaw, snowmelt, and permafrost. This study develops a Canada-wide perspective on near-0 ∘C conditions using hourly surface temperature and precipitation type observations from 92 climate stations for the period from 1981 to 2011. In addition, nine stations from various climatic regions are selected for further analysis. Near-0 ∘C conditions are defined as periods when the surface temperature is between −2 and 2 ∘C. Near-0 ∘C conditions occur often across all regions of the country, although the annual number of days and hours and the duration of these events varies dramatically. Various types of precipitation (e.g., rain, freezing rain, wet snow, and ice pellets) sometimes occur with these temperatures. Near-0 ∘C conditions and the reported precipitation type occurrences tend to be higher in Atlantic Canada, although high values also occur in other regions. Trends of most temperature-based and precipitation-based indicators show little or no change despite a systematic warming in annual surface temperatures over Canada. Over the annual cycle, near-0 ∘C temperatures and precipitation often exhibit a pattern: short durations occur around summer, driven by the diurnal cycle, and a tendency toward longer durations around winter, associated with storms. There is also a tendency for near-0 ∘C surface temperatures to occur more often than expected relative to other temperature windows at some stations due, at least in part, to diabatic cooling and heating that take place with melting and freezing, respectively, in the atmosphere and at the surface.

Macro- and Microphysical Characteristics of Precipitating and Non-Precipitating Stratocumulus Clouds over Eastern China

Stratocumulus (Sc) is the most common cloud type in China. Sc clouds may or may not be accompanied by various types of precipitation that are representative of different macro- and microphysical characteristics. The finely resolved CloudSat data products are used in this study to quantitatively investigate the macro- and microphysical characteristics of precipitating and non-precipitating Sc (PS and NPS, respectively) clouds over Eastern China (EC). Based on statistical information extracted from the CloudSat data, Sc clouds are highly likely to occur alone, in association with liquid precipitation, or in association with drizzle over 25% of EC. The cloud bases of NPS clouds are higher than those of PS clouds, although the latter display higher cloud top heights and thicker cloud thicknesses. The spatial distributions of microphysical characteristics differ between PS and NPS clouds. The magnitudes of microphysical characteristics in NPS clouds are relatively small, whereas the magnitudes of microphysical characteristics in PS clouds are relatively large and peak in response to certain circulation patterns and over certain terrain. In NPS clouds, condensation is the primary mechanism for hydrometeor particle growth, and the liquid water content and effective radius increase with height. Once the particles are too large to be supported by the updrafts, cloud droplets form raindrops. In PS clouds, raindrops increase continuously in size via collision-coalescence processes as they fall, leading to an increase in the liquid water content and effective radius from cloud top to cloud base. The CFRHDs (contoured frequency by relative height diagrams) of radar reflectivity in different cloud thickness indicate the cloud evolution and the precipitation formation process. In thinner clouds, downward particle growth by coalescence and upward particle growth by condensation occur in the upper and lower layers of clouds, respectively. With the increases in cloud thickness, the collision-coalescence process becomes apparent in all cloud layers, and the upward condensation process is less pronounced near the cloud base. Particles can grow for a long period of time and increase to larger sizes in thicker clouds, resulting in increased precipitation frequency. In clouds thicker than 1.92 km, the continuous transition from cloud to drizzle to rain by the collision-coalescence process takes place mostly in the upper layers.

The Effect of Precipitate Evolution on Austenite Grain Growth in RAFM Steel.

To study the effects of various types of precipitates and precipitate evolution behavior on austenite (size and phase fraction) in reduced activation ferritic/martensitic (RAFM) steel, RAFM steel was heated to various austenitizing temperatures. The microstructures of specimens were observed using optical microscopy (OM) and transmission electron microscopy (TEM). The results indicate that the M23C6 and MX precipitates gradually coarsen and dissolve into the matrix as the austenitizing temperatures increase. The M23C6 precipitates dissolve completely at 1100 °C, while the MX precipitates dissolve completely at 1200 °C. The evolution of two types of precipitate has a significant effect on the size of austenite. Based on the Zener pinning model, the effect of precipitate evolution on austenite grain size is quantified. It was found that the coarsening and dissolution of M23C6 and MX precipitates leads to a decrease in pinning pressure on grain boundaries, facilitating the rapid growth of austenite grains. The austenite phase fraction is also affected by the coarsening and dissolution of precipitates.

On the seasonal variation of various types of precipitation over global tropical ocean region: A perspective from TRMM measurements

The radar reflectivity and precipitation rate from Precipitation Radar (PR) onboard Tropical Rainfall Measuring Mission (TRMM) are obtained over the global tropical regions (35°S–35°N) during the period from 2007 to 2012, combined with coincident vertical velocity at 400 hPa ( ω 400 hPa), relative humidity at 850 hPa (RH850 hPa) and lower tropospheric stability (LTS) from European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis. First of all, the seasonal and spatial distribution of meteorological factors, including ω 400hPa, RH850 hPa, and LTS, together with rain rate are investigated. Next, four typical Regions of Interest (ROIs) and their individual seasons (i.e., favorable and non-favorable seasons for rainfall) are identified for further analysis by determining whether there exist most pronounced seasonal differences observed in ω 400 hPa. Meanwhile, rainy area, and rainfall of three precipitation types (i.e., shallow, stratus, and convection precipitation regimes) over the ROIs has been calculated. The three dimensional structures of individual precipitating system are analyzed, based on normalized contoured frequency by altitude diagram (NCFAD) and other statistical methods. Finally, with a focus on convection precipitation system, we give a quantitative description of the response of precipitation vertical structure to meteorological factors. Namely, how the rain echo top height (RTH), echo top height with reflectivity of 30 dBZ (ZTH30 dBZ), and reflectivity center of gravity (ZCOG) vary with ω 400 hPa, RH850 hPa, and LTS. In particular, (1) high rain rate dominates over intertropical convergence zone, which is characterized by strong updraft, sufficient moisture, and low LTS, showing the average rain rate is negatively associated with ω 400 hPa at both temporal and spatial scales. That is to say, lower ω 400hPa comes with more intensive rain rate. (2) The meteorological factors, along with average rain rate, exhibit appreciable seasonal variation. To be specific, negative (positive) ω 400 hPa anomalies is mostly found over the northern (southern) hemisphere in summer and autumn, as opposed to the patterns found in winter and spring. (3) In terms of the area with rainfall, the stratiform precipitating system accounts for more than 50% of the total area under investigation, followed by the convective precipitating system (about 30%), and the shallow precipitating system (less than 20%). In contrast, convective precipitating system, among others, takes the lead (about 65%) in contributing to the accumulated rainfall amount in the ROIs studied, followed by stratiform precipitating system (about 25%), and the shallow precipitating system (about 10%). (4) In the season with relatively higher ω 400 hPa, both rainy area and accumulated rainfall amount for all three types of precipitation show a increasing trend, irrespective of ROI. By comparison, rain rate and its vertical structures show large discrepancy, i.e., the intensity of convective precipitation system in favorable season tends to systematically increase as compared with that in non-favorable season. (5) The bulk precipitation system parameters used to describe convective precipitating system, including RTH, ZTH30 dBZ, and ZCOG, are observed to be elevated sharply with increasing ω 400 hPa and RH850 hPa. The same holds for the increasing LTS but with a smaller magnitude in the elevated height. This implies that ω 400 hPa and RH850 hPa most likely play a dominant role in dictating the vertical development of convection.

Potential formation damage and mitigation methods using seawater-mixed acid to stimulate sandstone reservoirs

It has been a practice to use seawater to prepare hydrochloric acid for carbonate reservoir stimulation in the offshore operations where fresh water is relatively expensive or logistically impossible to use. However, compare with carbonate matrix stimulation, F− and secondary SiF62− are released into the solution using hydrofluoric acid to treat sandstone reservoirs. The released components will combine with Mg2+, Ca2+, Na+, and K+ ions in seawater. Large quantities and various types of precipitates are formed when critical scaling tendency was exceeded, which results in serious formation damage.In this research, artificial simulated seawater (salinity about 35‰) was mixed with mud acid (almost hydrofluoric acid) and multi-hydrogen acid (an organophosphonic acid complex). Chemical effects of current seawater-mixed acid were investigated using spectrophotometry methods. The chemical effects include acid composition and concentration, HCl volume, seawater dilution ratio, and inorganic salt on damage quantities during acid preparation and reaction. Effective mitigation methods favorable to the inhibition of precipitation were provided.Results show that fluoride precipitates including CaF2 and MgF2 can be effectively mitigated by decreasing the free F− concentration and the pH value, increasing the seawater dilution and adding the inorganic electrolytes to elevate the ionic strength of solution. Because the organic phosphonic acid forms complexes with the metal ions, precipitation mitigation capacity of the multi-hydrogen acid is stronger than that of the mud acid. A special and abnormal common-ion effect was discovered based on the multi-hydrogen acid system. The addition of calcium ions in the seawater-mixed multi-hydrogen acid solution produces a super-clear liquid system with the turbidity <30 FTU. Static simulation shows that fluorosilicate precipitates as products of the secondary reaction in acidizing are mainly determined by the dissolution ratio. The precipitates can be mitigated by adding proper amount of hydrochloric acid, increasing the concentration of ammonium chloride in acid, and using appropriate inhibitors such as organophosphonic acid HA and DA. According to a parametric analysis, a seawater-mixed acid system based on the synergistic reactions of acid effect, salt effect and complex effect was proposed to mitigate formation damage for the sandstone reservoir stimulation using seawater-mixed acid. Reactions between the acid and different minerals indicate that this acid system could remain clear and eliminate secondary deposition during acidizing treatment.

Formation and evolution of precipitates in high Cr ferritic heat-resistant steels

For high Cr ferritic heat-resistant steels, dispersion hardening has played a vital role in improving creep strength at high temperatures. In this paper, the various types of precipitates in high Cr ferritic steels are reviewed, concerning M3C, M23C6, MX, M2X, Laves phase and Z phase. The evolution of these precipitates is a complicated process, since the dissolution of one type of precipitate may be overlapped with the precipitation of another type or other types. The composition of some precipitations varies towards the equilibrium composition under certain conditions, which is relevant to the solubility and diffusivity of the alloying element, while the composition of some other precipitates changes slightly. For the precipitates in high Cr ferritic steels, the preferred nucleation sites involve prior austenite grain boundaries, lath boundaries, dislocations and the interfaces between the precipitates and the matrix.

Cross Validation of TRMM PR Reflectivity Profiles Using 3D Reflectivity Composite from the Ground-Based Radar Network over the Korean Peninsula

Abstract The Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) measures reflectivity downward from space and provides observations of the vertical distributions of precipitation over land as well as the ocean. It overpasses the southern part of the Korean Peninsula where (i) a dense network of operational S-band scanning radars is available and (ii) various types of precipitation occur. By utilizing a 3D reflectivity composite from the ground S-band radar (GR) observations, this paper shows a comparison of reflectivity profiles observed with both PR and GR focusing on their vertical structure. For four cases of widespread rain, visual and statistical analyses show that PR attenuation-corrected reflectivity agrees closely with reflectivity observed from the GR composite below the melting layer. Above and within the melting layer, PR is affected critically by its sensitivity while GR beam broadening at far ranges causes systematic differences in the PR–GR comparisons. For four cases of convective rain, PR underestimates the mean reflectivities by 1–3 dB compared with those from GR at low levels where precipitation attenuation is significant toward the ground. In these cases, the low sensitivity of PR results in a small number of matched points for weak echoes. Also, the PR–GR discrepancy for the convective case is more affected by time mismatching.