Frustrated metastable-to-equilibrium grain boundary structural transition in NbMoTaW due to segregation and chemical complexity

Grain boundary structural transitions can lead to significant changes in the properties and performance of materials. In multi-principal element alloys, understanding these transitions becomes complex due to phenomena such as local chemical ordering and multi-component segregation. Using atomistic simulations, we explore a metastable-to-equilibrium grain boundary structural transition in NbMoTaW. The transition, characterized by structural disordering and reduced free volume, shows high sensitivity to its local chemical environment. Most notably, the transition temperature range of the alloy is more than twice that of a pure metal. Differences in composition between coexisting metastable and equilibrium structures highlight the change in local site availability due to structural relaxation. Further examination of grain boundaries with fixed chemical states at varying temperatures reveals that the amount of segregation significantly influences the onset temperature yet has minimal effect on the transition width. These insights underscore the profound effects of chemical complexity and ordering on grain boundary transitions in complex concentrated alloys, marking a meaningful advancement in our understanding of grain boundary behavior at the atomic level

Influence of chemistry and structure on interfacial segregation in NbMoTaW with high-throughput atomistic simulations

Refractory multi-principal element alloys exhibiting promising mechanical properties such as excellent strength retention at elevated temperatures have been attracting increasing attention. Although their inherent chemical complexity is considered a defining feature, a challenge arises in predicting local chemical ordering, particularly in grain boundary regions with enhanced structural disorder. In this study, we use atomistic simulations of a large group of bicrystal models to sample a wide variety of interfacial sites (grain boundary) in NbMoTaW and explore emergent trends in interfacial segregation and the underlying structural and chemical driving factors. Sampling hundreds of bicrystals along the [001] symmetric tilt axis and analyzing more than one hundred and thirty thousand grain boundary sites with a variety of local atomic environments, we uncover segregation trends in NbMoTaW. While Nb is the dominant segregant, more notable are the segregation patterns that deviate from expected behavior and mark situations where local structural and chemical driving forces lead to interesting segregation events. For example, incomplete depletion of Ta in low-angle boundaries results from chemical pinning due to favorable local compositional environments associated with chemical short-range ordering. Finally, machine learning models capturing and comparing the structural and chemical features of interfacial sites are developed to weigh their relative importance and contributions to segregation tendency, revealing a significant increase in predictive capability when including local chemical information. Overall, this work, highlighting the complex interplay between local grain boundary structure and chemical short-range ordering, suggest tunable segregation and chemical ordering by tailoring grain boundary structure in multi-principal element alloys

Thoracoscopic Repair of Recurrent Bochdalek Diaphragmatic Hernias in Children

Abstract Background: Recurrent herniation is a well-known complication following the initial repair of congenital diaphragmatic hernias (CDHs). The role of minimally invasive surgical techniques in recurrent CDH remains undefined. The purpose of this study was to evaluate our early experience with thoracoscopic repair compared with traditional open repair in children with recurrent CDH. Subjects and Methods: We retrospectively reviewed all recurrent Bochdalek CDH cases (n=24) managed at a single tertiary-care referral center between January 1990 and March 2011. Children who underwent thoracoscopic repair for recurrent CDH were identified, and their data were compared by the unpaired t test and the two-sided Fisher's exact test, as appropriate, with those of children who underwent open repair. Significance was defined as P<.05. Results: Thoracoscopic repair was attempted in 6 (25%) children with recurrent CDH. Four (67%) repairs were successfully completed without conversion to an open procedure. The mean age at thoracoscopic repair was 11.5 months (range, 8.1?16.1 months). The mean operative time was 191 minutes (range, 94?296 minutes), and all children were extubated within 24 hours. The mean hospital length of stay was 3.75 days (range, 1?6 days). There were no deaths or subsequent recurrences after a mean follow-up of 26.5 months (range, 14.3?41.3 months). There were no statistical differences in any of the measured outcome variables when compared with the open repair group. Conclusions: Our initial experience suggests that thoracoscopic repair is a feasible alternative to open repair in selected children with recurrent Bochdalek diaphragmatic hernias.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98467/1/lap%2E2012%2E0048.pd

Jelenkori és múltbeli hidrogeológiai folyamatok sztochasztikus modelljei, ezek értékelése és földtani értelmezése = Stochastic models of recent and paleo- hydrogeological processes, their evaluation and geological interpretation

A felszín alatti vizek hidrográfjait alakító látens hatások hatások azonosítására, és ezek intenzitásának számszerűsítésére szolgáló dinamikus faktoranalízis (DFA) alkalmazási körét szélesítettük. Tettük ezt karsztos viszonyok között területi kiterjesztéssel, valamint nem-karsztos üledékes környezet talajvízszint adatainak elemzésével. A DFA a víztartó sérülékenységének hatékony mérőszámát nyújtja a látens hatások intenzitását reprezentáló faktorsúlyok segítségével. A Szigetközben a faktorsúlyok változása jól kimutatja a Duna betáplálási helyének az elterelés következtében kialakuló mintegy 15 km-es elmozdulását. Két fontos modellt alkottunk folyók napi vízhozam idősorának leírására, elemeztük becsléseik tulajdonságát, és illesztettük a Tisza és a Duna adataira. Az első modellben egy általánosított béta-ARCH zajt bocsátunk át egy ARMA szűrőn, míg a másikban egy szemi-Markov rezsimindikátor folyamat vezérli gamma bolyongások és Gauss AR(1) folyamatok váltakozásait a fel- és leszálló rezsimeknek megfelelően. A modellek extrém érték tulajdonságait vizsgáltuk elméletileg és szimulációval, majd összvetettük a valós adatokkal, jó egyezést nyerve. Eredményeinket felhasználtuk biztosítók árvízkockázatának elemzésében. Az aggteleki karszton repedésrendszerek kiürülési idejét határoztuk meg 5 forrás log-vízhozam görbéjének töréspontjai segítségével. | We tested the adequacy and power of dynamic factor analysis (DFA) in determining latent effects that shape the hydrographs of groundwater monitoring wells. Within the karstic environment, we extended the monitoring area of our previous project. We successfully applied DFA in sedimentary environments, other than karst. DFA provides a powerful indicator of the vulnerability of the aquifer by measuring the intensity of the major latent effects at a given location. In the Szigetköz area the changes of the factor loadings trace back the migration of water supply from Danube into the aquifer caused by the construction of the Bős dam. We gave two important models for diurnal discharge time series of rivers, analysed the properties of their estimators, and fitted them to the data of Tisza and Danube. In the first model a generalised beta-ARCH type noise passes through an ARMA filter, whereas in the second a semi-Markov hidden regime indicator process governs the swithches of a gamma random walk and a Gaussian AR(1) process in the ascending and descending regimes. We analysed the extreme value properties of the models both in theory and by means of simulations, and compared it with the real data. The results were used in flood risk estimations for insurance companies. We determined the depletion-time of various crack-systems in the Aggtelek karst from the break-points of the log-runoff curves of 5 springs in the area

Chemical order transitions within extended interfacial segregation zones in NbMoTaW

Interfacial segregation and chemical short-range ordering influence the behavior of grain boundaries in complex concentrated alloys. In this study, we use atomistic modeling of a NbMoTaW refractory complex concentrated alloy to provide insight into the interplay between these two phenomena. Hybrid Monte Carlo and molecular dynamics simulations are performed on columnar grain models to identify equilibrium grain boundary structures. Our results reveal extended near-boundary segregation zones that are much larger than traditional segregation regions, which also exhibit chemical patterning that bridges the interfacial and grain interior regions. Furthermore, structural transitions pertaining to an A2-to-B2 transformation are observed within these extended segregation zones. Both grain size and temperature are found to significantly alter the widths of these regions. Analysis of chemical short-range order indicates that not all pairwise elemental interactions are affected by the presence of a grain boundary equally, as only a subset of elemental clustering types are more likely to reside near certain boundaries. The results emphasize the increased chemical complexity that is associated with near-boundary segregation zones and demonstrate the unique nature of interfacial segregation in complex concentrated alloys

Droplet fragmentation: 3D imaging of a previously unidentified pore-scale process during multiphase flow in porous media

Using X-ray computed microtomography, we have visualized and quantified the in situ structure of a trapped nonwetting phase (oil) in a highly heterogeneous carbonate rock after injecting a wetting phase (brine) at low and high capillary numbers. We imaged the process of capillary desaturation in 3D and demonstrated its impacts on the trapped nonwetting phase cluster size distribution. We have identified a previously unidentified pore-scale event during capillary desaturation. This pore-scale event, described as droplet fragmentation of the nonwetting phase, occurs in larger pores. It increases volumetric production of the nonwetting phase after capillary trapping and enlarges the fluid−fluid interface, which can enhance mass transfer between the phases. Droplet fragmentation therefore has implications for a range of multiphase flow processes in natural and engineered porous media with complex heterogeneous pore spaces

Keratin K15 as a Biomarker of Epidermal Stem Cells

Keratin 15 (K15) is type I keratin protein co-expressed with the K5/K14 pair present in the basal keratinocytes of all stratified epithelia. Although it is a minor component of the cytoskeleton with a variable expression pattern, nonetheless its expression has been reported as a stem cell marker in the bulge of hair follicles. Conversely, suprabasal expression of K15 has also been reported in both normal and diseased tissues, which is inconsistent with its role as a stem cell marker. Our recently published work has given evidence of the molecular pathways that seem to control the expression of K15 in undifferentiated and differentiated cells. In this article, we have critically reviewed the published work to establish the reliability of K15 as an epidermal stem cell marker