Virtual Simulation of Blast Behind-Armor Blunt Trauma and Projectile Penetration Leading to Injury of Life-Critical Organs in the Human Torso.
Abstract not provided.
Cooper, Candice Frances↗
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A Pitzer Model for Lead Oxide Solubilities in the Pressence of Borate to High Ionic Strength.
Abstract not provided.
Xiong, Yongliang↗
Disruption of polyubiquitin gene Ubc leads to defective proliferation of hepatocytes and bipotent fetal liver epithelial progenitor cells
Highlights: •Proliferation capacity of Ubc{sup −/−} FLCs was reduced during culture in vitro. •Ubc is required for proliferation of both hepatocytes and bipotent FLEPCs. •Bipotent FLEPCs exhibit highest Ubc transcription and proliferation capacity. •Cell types responsible for Ubc{sup −/−} fetal liver developmental defect were identified. -- Abstract: We have previously demonstrated that disruption of polyubiquitin gene Ubc leads to mid-gestation embryonic lethality most likely due to a defect in fetal liver development, which can be partially rescued by ectopic expression of Ub. In a previous study, we assessed the cause of embryonic lethality with respect to the fetal liver hematopoietic system. We confirmed that Ubc{sup −/−} embryonic lethality could not be attributed to impaired function of hematopoietic stem cells, which raises the question of whether or not FLECs such as hepatocytes and bile duct cells, the most abundant cell types in the liver, are affected by disruption of Ubc and contribute to embryonic lethality. To answer this, we isolated FLCs from E13.5 embryos and cultured them in vitro. We found that proliferation capacity of Ubc{sup −/−} cells was significantly reduced compared to that of control cells, especially during the early culture period, however we did not observe the increased number of apoptotic cells. Furthermore, levels of Ub conjugate, but not free Ub, decreased upon disruption of Ubc expression in FLCs, and this could not be compensated for by upregulation of other poly- or mono-ubiquitin genes. Intriguingly, the highest Ubc expression levels throughout the entire culture period were observed in bipotent FLEPCs. Hepatocytes and bipotent FLEPCs were most affected by disruption of Ubc, resulting in defective proliferation as well as reduced cell numbers in vitro. These results suggest that defective proliferation of these cell types may contribute to severe reduction of fetal liver size and potentially mid-gestation lethality of Ubc{sup −/−} embryos.
60 APPLIED LIFE SCIENCES↗
An Experimental and Numerical Investigation to Characterize the Low-Temperature Heat Release in Stoichiometric and Lean Combustion
This work reports on an experimental and modeling study on the low-temperature heat release (LTHR) characteristics for three RON 90 binary blends (n-heptane blended with isooctane, toluene and ethanol) in a Cooperative Fuel Research (CFR) engine at lean and stoichiometric conditions that are representative of homogeneous charge compression ignition (HCCI) and spark-ignition (SI) end-gas combustion conditions, respectively. An analysis of the end-gas temperature-pressure (T-P) trajectories was performed to identify the intake conditions leading to similar T-P trajectories between the two lambdas for each fuel blend. A heat release analysis was then conducted for the identified cases, where fuel-to-fuel differences in LTHR were identified and found to be sensitive to the operating condition. Simulations were conducted for these cases using a recently updated chemical kinetic model and a 0-D engine model, where good qualitative and reasonable quantitative agreements in LTHR were obtained. Sensitivity analysis was also performed directly on the rates of LTHR, to understand the controlling chemical reactions of LTHR, providing further insights into the fuel-to-fuel differences. The results demonstrate the significant promoting effect of n-heptane on LTHR rates, while inhibiting effects were seen for ethanol and toluene. Also highlighted was the importance of H atom abstraction reactions from the chemistry of each fuel component, which could lead to contradictory fuel behavior depending on the locations of the H site of the abstraction reaction due to the different ensuing pathways for the primary fuel radicals.
LTHR, RON 90 binary blends, sensitivity analysis↗
Nanofilm Composite Membranes of Bottlebrush Poly(1,3‐Dioxolane) Plasticized by Poly(Ethylene Glycol) for CO 2 /N 2 Separation
Abstract Poly(1,3‐dioxolane) has emerged as a leading membrane material for post‐combustion CO 2 capture due to its high ether oxygen content and strong affinity toward CO 2 . However, they are often cross‐linked to inhibit crystallization, which makes them impossible to fabricate into industrial thin‐film composite membranes. Herein, soluble and high molecular weight bottlebrush polymers ( b PDXLA) are synthesized using reversible addition‐fragmentation chain transfer polymerization and demonstrate the feasibility of fabricating nanofilm (≈100 nm) composite membranes (NCMs). Furthermore, b PDXLA can be plasticized using a miscible additive of poly(ethylene glycol) dimethyl ether (PEGDME) to improve CO 2 permeability while retaining good CO 2 /N 2 selectivity. For example, adding 20 mass% PEGDME improves CO 2 permeance from 930 to 1300 GPU and decreases CO 2 /N 2 selectivity from 74 to 53 at 25 °C; the membrane exhibits stable separation performance competitive with state‐of‐the‐art commercial membranes. This work unveils a practical approach to designing uncross‐linked, highly polar polymers for practical membrane gas separation and highlights a facile way to enhance performance by incorporating miscible plasticizers using industrial manufacturing processes.
Zhang, Gengyi [Department of Chemical and Biologic↗
Representative Phenomena of Cyclic Turbulent Combustion in High-Pressure Fuel Sprays
Abstract Cyclic variations in conventional diesel combustion engines can lead to large differences in engine out emissions even at steady operation. This study uses an optically accessible constant-pressure flow chamber to acquire fuel injections in quick succession to analyze mixing, auto-ignition, and combustion of diesel-surrogate n-heptane using multiple high-speed optical diagnostics. Prior studies have utilized fewer injections and/or they rely on analysis of ensemble average behavior. These approaches do not yield information on injection-to-injection variation or provide confidence in utilizing individual injection measurements for high-fidelity computational fluid dynamics(CFD) model validation. In this study, a large set of 500 injections is used to obtain global parameters including liquid length, vapor penetration length, ignition delay time, and lift-off length. Results for multiple injections are presented to illustrate large injection to injection variations. Potential sources for these variations are analyzed to conclude localized, small scale turbulence and rate of injection variations as the likely sources. Then, a statistical method based on z-scores is proposed and implemented to identify instantaneous injections that best represent the bulk data-set of jet boundaries measured independently by three different diagnostics. This synthesis of statistics-guided screening of data set and ensemble-average analysis offers higher confidence for CFD model validation relying upon both a representative single and average injection results.
42 ENGINEERING↗
Noninvasive PET quantitative myocardial blood flow with regadenoson for assessing cardiac allograft vasculopathy in orthotopic heart transplantation patients
Background: Risk stratification and early detection of cardiac allograft vasculopathy (CAV) is essential in orthotopic heart transplantation (OHT) patients. This study assesses the changes in myocardial blood flow (MBF) noninvasively in OHT patients using quantitative cardiac PET with regadenoson. Methods: Twelve patients (Group 1) (8 males, 4 females, mean age 55 ± 7 years) with no history of post OHT myocardial ischemia were enrolled 5.4 ± 2.0 years after OHT. Fifteen patients (Group 2) (9 males, 6 females, mean age 71 ± 9 years) with intermediate pretest probability but not documented evidence for coronary artery disease (CAD) were also included to serve as control. Global and regional MBFs were assessed using dynamic {sup 13}N-NH{sub 3} PET at rest and during regadenoson-induced hyperemia. The coronary flow reserve (CFR) was also calculated as the ratio of hyperemic to resting MBF. Results: Mean regadenoson-induced rate-pressure products were similar in both groups, while there was an increase in resting rate-pressure product in Group 1 patients. Both mean and median values of resting MBF were higher in Group 1 than Group 2 patients (1.33 ± 0.31 and 1.01 ± 0.21 mL/min/g for Groups 1 and 2, respectively, P < .001), while mean hyperemic MBF values were similar in both Groups (2.68 ± 0.84 and 2.64 ± 0.94 mL/min/g, P = NS) but median hyperemic MBF values were lower in Group 1 than Group 2 patients (2.0 vs. 2.60 mL/min/g, P = .018). Both mean and median CFR values demonstrated a significant reduction for Group 1 compared to Group 2 patients (2.07 ± 0.74 vs 2.63 ± 0.48, P = .025). Conclusions: This study suggests that the MBF in OHT patients may be abnormal at resting state with diminished CFR. This hints that the epicardial and microvascular coronary subsystem may be exacerbated after OHT leading to the gradual progression of CAV. [French] French Abstract: Contexte: Cette étude pilote par tomographie a positrons évalue de manière quantitative les changements de perfusion myocardique et le risque de vasculopathie coronaire après transplantation cardiaque chez l’être humain. Méthodes: Douze patients (groupe 1) (8 hommes, 4 femmes, âge moyen 55 ± 7 ans) sans antécédents d'ischémie myocardique post-chirurgicale ont été étudiés après 5,4 ± 2,0 ans après transplantation cardiaque. Quinze patients (groupe 2) (9 hommes, 6 femmes, âge moyen 71 ± 9 ans) avec une probabilité intermédiaire mais sans signes objectifs de maladie coronarienne ont servi de contrôles. Les donnes de perfusion myocardique globales et régionales ont été évaluées par tomographie à positrons l'aide de{sup 13}N-NH3 au repos et durant l'hyperémie induite par le vasodilatateur coronarien régadénoson. La réserve de flux coronarien a été calculée sur base du rapport entre le flux myocardique hyperhémique induit par le régadénoson et le flux myocardique au repos. Résultats: les double produits (fréquence cardiaque x tension artérielle) moyens après régadénoson furent similaires chez les deux groups de patients. Par contre le double produit au repos était plus élevé dans le groupe de patient transplantés. Les valeurs moyennes et médianes de perfusion myocardique globale au repos ont été calculées à 1.33 ± 0.31 ml/min/g dans le groupe de patients transplantés et 1.01 ± 0.21 ml/min/g dans le groupe control (P < 0.001). Après régadénoson, les valeurs moyennes de perfusion myocardique se sont avérées similaires dans les deux groupes (2,68 ± 0,84 et 2,64 ± 0,94 ml/min/g, P > 0.05). Néanmoins les valeurs médianes se sont avérées inferieures dans le groupe 1 comparativement au groupe control (2,0 versus 2,60 ml/min/g; P = 0,018). Les valeurs moyennes et médianes de réserve de flux myocardique mesurées étaient significativement réduites chez les patient transplantés (2,07 ± 0,74) en comparaison aux patients du groupe 2 (2,63 ± 0,48; P = 0.025). Conclusion: La perfusion myocardique au repos peut s’avérer anormale après transplantation cardiaque et s’accompagner d’une diminution de la réserve du flux coronaire. Cette étude pilote suggère que les vaisseaux épicardiques et la micro-vascularisation du myocarde peuvent être atteints après transplantation et conduire à la maladie coronaire du greffon. [Spanish] Spanish Abstract: Antecedentes: la estratificación de riesgo y detección temprana de la vasculopatía del aloinjerto cardiaco (VAC) es esencial en los pacientes con trasplante cardiaco ortotópico (TCO). El presente estudio evalúa de forma no invasiva los cambios en el flujo sanguíneo miocárdico (FSM) en pacientes con TCO utilizando el PET cardiaco cuantitativo con regadenoson. Métodos: Doce pacientes (Grupo 1) (8 hombres, 4 mujeres, edad promedio 55 ± 7 años) sin historia de isquemia miocárdica posterior al TCO fueron incluidos después de 5.4 ± 2.0 años de ser trasplantados. Quince pacientes (Grupo 2) (9 hombres, 6 mujeres, edad promedio 71 ± 9 años) con probabilidad pre-prueba intermedia pero sin evidencia documentada de enfermedad arterial coronaria (EAC) fueron incluidos como grupo control. El FSM global y regional fueron evaluados utilizando el estudio PET dinámico con {sup 13}N-NH{sub 3} en reposo y durante la inducción de hiperemia con regadenoson. La reserva de flujo coronario (RFC) también fue calculada como la proporción entre el FSM hiperémico y el de reposo. Resultados: el producto de velocidad-presión promedio inducido por regadenoson fue similar en ambos grupos, mientras que existió un incremento de este producto velocidad-presión durante el reposo en el Grupo 1 de pacientes. Los valores de la media y mediana del FSM de reposo fueron mayores en el Grupo 1 que el Grupo 2 de pacientes (1.33 ± 0.31 y 1.01 ± 0.21 mL/min/g para los Grupos 1 y 2, respectivamente, P < 0.001). La media de los valores del FSM hiperémico fueron similares en ambos grupos (2.68 ± 0.84 and 2.64 ± 0.94 mL/min/g, P = NS), sin embargo la mediana fue menor en el Grupo 1 que en el Grupo 2 (2.0 vs. 2.60 mL/min/g, P = .018). Tanto la media como la mediana para los valores de la RFC demostraron una disminución significativa en el Grupo 1 comparada con el Grupo 2 (2.07 ± 0.74 vs. 2.63 ± 0.48, P = 0.025). Conclusiones: El presente estudio sugiere que el FSM en pacientes con TCO puede estar alterado en reposo con una RFC disminuida. Esto indica que los sistemas coronarios epicardico y microvascular pudieran estar inflamados posterior al TCO conduciendo a una progresión gradual de la VAC. [Chinese] Chinese Abstract: 背景: 对于原位心脏移植 (OHT) 病人, 早期检测移植心脏血管病变 (CAV) 和进行危险分层是必要的。 本研究拟通过类伽腺苷定 心脏 PET 显像, 非侵入性地评估 OHT 病人心肌血流 (MBF) 的变化。 方法: 研究对象分为两组。 第一组, 12个病人 (8 男, 4女, 平均 55 ± 7岁), OHT 后 5.4 ± 2.0 年, 没有 OHT 后心肌缺血。 第二组 (对照组), 15 个病人 (9 男, 6 女, 平均 71 ± 9 岁), 中等冠心病可能, 但尚未确诊。 分别于静息及类伽腺苷药物负荷下, 动态采集 {sup 13}N-NH{sub 3} PET 图像, 获得整体和局部 MBF。冠脉血流储备 (CFR) 通过负荷 MBF /静息 MBF 计算而得。 结果: 类伽腺苷负荷时, 反映心肌耗氧 的心率血压乘积在两组间没有差异, 但在静息时, 第一组明显高于第二组。静息时, 第一组 MBF 的平均值高于第二组 (1.33 ± 0.31 vs. 1.01 ± 0.21 mL/min/g, P < 0.001); 负荷时, 两组 MBF 的平均值无差异 (2.68 ± 0.84 vs. 2.64 ± 0.94 mL/min/g, P = NS), 但 MBF 的中位数第一组要低于第二组 (2.0 vs. 2.60 mL/min/g, P = 0.018), 且第一组 CFR 的平均值明显低于第二组 (2.07 ± 0.74 vs. 2.63 ± 0.48, P = 0.025)。 结论: 在原位心脏移植病人中, 冠脉血流储备以及静息心肌血流 均呈现明显异常。提示原位心脏移植后, 冠状动脉心外膜血管与微小血管功能均受损, 进而将逐渐导致移植心脏血管病变。 关键词: 动态PET, 类伽腺苷, 冠状动脉血流储备, 原位心脏移植, 移植心脏血管病变。.
62 RADIOLOGY AND NUCLEAR MEDICINE↗
Ex-vivo assessment and non-invasive in vivo imaging of internal hemorrhages in Aga2/+ mutant mice
Highlights: ► Aga2/+ mice, model for Osteogenesis imperfecta, have type I collagen mutation. ► Aga2/+ mice display both moderate and severe phenotypes lethal 6–11th postnatal. ► Internal hemorrhages studied in Aga2/+ vs. control mice at 6 and 9 days postnatal. ► Anatomical and functional findings in-vivo contrasted to the ex-vivo appearance. -- Abstract: Mutations in type I collagen genes (COL1A1/2) typically lead to Osteogenesis imperfecta, the most common heritable cause of skeletal fractures and bone deformation in humans. Heterozygous Col1a1{sup Aga2/+}, animals with a dominant mutation in the terminal C-propeptide domain of type I collagen develop typical skeletal hallmarks and internal hemorrhages starting from 6 day after birth. The disease progression for Aga2/+ mice, however, is not uniform differing between severe phenotype lethal at the 6–11th day of life, and moderate-to-severe one with survival to adulthood. Herein we investigated whether a new modality that combines X-ray computer tomography with fluorescence tomography in one hybrid system can be employed to study internal bleedings in relation to bone fractures and obtain insights into disease progression. The disease phenotype was characterized on Aga2/+ vs. wild type mice between 6 and 9 days postnatal. Anatomical and functional findings obtained in-vivo were contrasted to the ex-vivo appearance of the same tissues under cryo-slicing.
60 APPLIED LIFE SCIENCES↗
Hydrogen peroxide impairs autophagic flux in a cell model of nonalcoholic fatty liver disease
Highlights: •Free fatty acids exposure induces elevated autophagy. •H{sub 2}O{sub 2} inhibits autophagic flux through impairing the fusion between autophagosomes and lysosomes. •Inhibition of autophagy potentiates H{sub 2}O{sub 2}-induced cell death. -- Abstract: Nonalcoholic fatty liver disease (NAFLD) has become the leading cause of chronic liver disease, but the pathogenesis of NAFLD is not fully clear. The aim of this study was to determine whether autophagy plays a role in the pathogenesis of NAFLD. We found that the levels of autophagy were elevated in hepatoma cells upon exposure to free fatty acids, as confirmed by the increase in the number of autophagosomes. However, exposure of hepatoma cells to H{sub 2}O{sub 2} and TNF-α, two typical “second hit” factors, increased the initiation of autophagy but inhibited the autophagic flux. The inhibition of autophagy sensitized cells to pro-apoptotic stimuli. Taken together, our results suggest that autophagy acts as a protective mechanism in the pathogenesis of NAFLD and that impairment of autophagy might induce more severe lesions of the liver. These findings will be a benefit to the understanding of the pathogenesis of NAFLD and might suggest a strategy for the prevention and cure of NAFLD.
60 APPLIED LIFE SCIENCES↗
Liquid crystallinity driven highly aligned large graphene oxide composites
Graphene is an emerging graphitic carbon materials, consisting of sp{sup 2} hybridized two dimensinal honeycomb structure. It has been widely studied to incorporate graphene with polymer to utilize unique property of graphene and reinforce electrical, mechanical and thermal property of polymer. In composite materials, orientation control of graphene significantly influences the property of composite. Until now, a few method has been developed for orientation control of graphene within polymer matrix. Here, we demonstrate facile fabrication of high aligned large graphene oxide (LGO) composites in polydimethylsiloxane (PDMS) matrix exploiting liquid crystallinity. Liquid crystalline aqueous dispersion of LGO is parallel oriented within flat confinement geometry. Freeze-drying of the aligned LGO dispersion and subsequent infiltration with PDMS produce highly aligned LGO/PDMS composites. Owing to the large shape anisotropy of LGO, liquid crystalline alignment occurred at low concentration of 2 mg/ml in aqueous dispersion, which leads to the 0.2 wt% LGO loaded composites. - Graphical abstract: Liquid crystalline LGO aqueous dispersions are spontaneous parallel aligned between geometric confinement for highly aligned LGO/polymer composite fabrication. - Highlights: • A simple fabrication method for highly aligned LGO/PDMS composites is proposed. • LGO aqueous dispersion shows nematic liquid crystalline phase at 0.8 mg/ml. • In nematic phase, LGO flakes are highly aligned by geometric confinement. • Infiltration of PDMS into freeze-dried LGO allows highly aligned LGO/PDMS composites.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
On the “alpha-phase” of Ca{sub 2−x}Sr{sub x}MnO{sub 4} and extending the chemistry of Sr{sub 7−y}Ca{sub y}Mn{sub 4}O{sub 15} to y>1
There has been renewed interest in the Ruddlesden-Popper phase (n=2) of composition Ca{sub n+1}Mn{sub n}O{sub 3} {sub n+1} in the light of recent research that has highlighted the nature of the improper ferroelectric ground state, which arises due to the couplings between specific combinations of MnO{sub 6} octahedral rotations and tilts. A fruitful route to control these octahedral degrees of freedom, and hence such desired physical properties, is through chemical substitution on the A–site cation i.e. Ca{sub 2−x}Sr{sub x}MnO{sub 4} for n =1, and in light of this, we have reinvestigated the chemistry of this solid solution. Here we focus on a common impurity phase observed during this synthesis which has been termed the “alpha-phase” in the literature. We show that this impurity phase is actually comprised mainly of a structure related to Sr{sub 7}Mn{sub 4}O{sub 15} but is found here with significantly higher Ca substitution than previously believed possible. Sr{sub 7}Mn{sub 4}O{sub 15} is an interesting structural type in its own right, but has been mainly overlooked to date, exhibiting interesting physics related to low dimensional magnetic ordering and dimer interactions, and we show here that the structural type is a likely candidate for exhibiting a multiferroic ground state. The prospect of being able to tune the lattice and the exchange interactions through further chemical substitution is likely to lead to a renewed interest in this material. - Graphical abstract: Extending the chemistry of Sr{sub 7−y}Ca{sub y}Mn{sub 4}O{sub 15} beyond y>1, revealing highly anisotropic cation ordering and tunable magnetic properties. - Highlights: • Chemistry of the unique structural type Sr{sub 7}Mn{sub 4}O{sub 15} is extended to high Ca concentrations. • Cation occupancy model is determined, showing highly anisotropic solubility of Ca on the 7 unique Sr crystallographic sites. • Anomalies in the magnetic susceptibility data are discussed with reference to symmetry arguments pointing towards a possible novel multiferroic mechanism in this material.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Through-thickness microstructural evolution during grain boundary engineering type thermomechanical processing and its implication on sensitization behavior in austenitic stainless steel
Highlights: • GBE-treated 304L steel exhibits thickness-dependent microstructural evolution. • Degree of sensitization increases from surface to interior in GBE specimen. • Low fractal dimension and large TRD size lead to lesser sensitization at surface. • As-received specimen shows high albeit thickness-independent sensitization behavior. • Higher residual strain leads to higher sensitization at surface of deformed sample. - Abstract: Through-thickness microstructural variations and their synergistic influence on degree of sensitization in grain boundary engineering (GBE) treated 304L stainless steel was compared with solution-annealed and marginally cold-worked (~ 3% thickness reduction) specimens. The solution-annealed specimen has shown higher degree of sensitization due to the presence of lower fraction of Σ3 (as well as other low Σ CSL) boundaries and dominant random high-angle boundaries (RHAGBs) connectivity. However, it has shown thickness-independent sensitization behavior as grain boundary character distribution, residual strain and grain boundary network topology towards thickness direction are similar. Owing to higher residual strain, as revealed by local misorientation analysis, the cold-worked specimen showed maximum degree of sensitization (higher than solution-annealed condition) at surface. The GBE specimen has shown much lower degree of sensitization at surface due to higher-fraction of Σ3 boundaries and discontinuous RHAGBs connectivity. However, increasing fraction of RHAGBs and their connectivity, as confirmed by twinning-related domain and fractal analysis, cause more sensitization at interior of this specimen. In spite of this, the degree of sensitization at the interior of GBE specimen is lower than the solution-annealed or cold-worked specimen. Even though the residual strain in GBE specimen is higher than the solution-annealed condition, the lower degree of sensitization indicates that the grain boundary character distribution and grain boundary network topology have higher implication than residual strain in controlling sensitization.
36 MATERIALS SCIENCE↗
Effect of Bi on the microstructure and mechanical properties of Sn-Zn alloys processed by rolling
Highlights: • Sn-Zn-Bi is proposed for the first time as the cladding in linear explosive device. • Bi can significantly refine the microstructure of Sn-Zn. • Bi can enhance both strength and ductility of Sn-Zn processed by rolling. • The 5 wt% Bi in Sn-3Zn leads to finest and most homogenous grains after rolling. - Abstract: Sn-Zn based alloys including Sn-3Zn, Sn-3Zn-1Bi, and Sn-3Zn-5Bi were prepared by casting and rolling, in efforts to assess their feasibility for the application as cladding materials in detonating and explosive cords. It was found that Bi significantly refined the solidification microstructure, changing the configuration of Sn-Zn eutectic from well-aligned Zn-rich precipitates/needles to misaligned Zn-rich flakes. During deformation, second phases like Zn-rich precipitates and Bi particles, and Bi solutes were effective in grain refinement since second phase particles provided more sites for nucleation and more obstacles to growth of new recrystallized grains. Tensile results revealed that Bi addition enhanced both strength and ductility of the rolled Sn-Zn-Bi alloys. The Sn-3Zn-5Bi alloy possessed superior strength and ductility (UTS: 84.4 MPa; Yield strength: 68.3 MPa; Elongation: 75.2%) due to its finest and most homogeneous equiaxed grains. Based on decent mechanical properties, the Sn-Zn-Bi alloys could be well qualified for the application as cladding materials.
36 MATERIALS SCIENCE↗
Distilling the Evolving Contributions of Anthropogenic Aerosols and Greenhouse Gases to Large‐Scale Low‐Frequency Surface Ocean Changes Over the Past Century
Abstract Anthropogenic aerosols (AER) and greenhouse gases (GHG)—the leading drivers of the forced historical change—produce different large‐scale climate response patterns, with correlations trending from negative to positive over the past century. To understand what caused the time‐evolving comparison between GHG and AER response patterns, we apply a low‐frequency component analysis to historical surface ocean changes from CESM1 single‐forcing large‐ensemble simulations. While GHG response is characterized by its first leading mode, AER response consists of two distinct modes. The first one, featuring long‐term global AER increase and global cooling, opposes GHG response patterns up to the mid‐twentieth century. The second one, featuring multidecadal variations in AER distributions and interhemispheric asymmetric surface ocean changes, appears to reinforce the GHG warming effect over recent decades. AER thus can have both competing and synergistic effects with GHG as their emissions change temporally and spatially.
Dong, Yue↗
An active site loop toggles between conformations to control antibiotic hydrolysis and inhibition potency for CTX-M β-lactamase drug-resistance enzymes
Abstract β-lactamases inactivate β-lactam antibiotics leading to drug resistance. Consequently, inhibitors of β-lactamases can combat this resistance, and the β-lactamase inhibitory protein (BLIP) is a naturally occurring inhibitor. The widespread CTX-M-14 and CTX-M-15 β-lactamases have an 83% sequence identity. In this study, we show that BLIP weakly inhibits CTX-M-14 but potently inhibits CTX-M-15. The structure of the BLIP/CTX-M-15 complex reveals that binding is associated with a conformational change of an active site loop of β-lactamase. Surprisingly, the loop structure in the complex is similar to that in a drug-resistant variant (N106S) of CTX-M-14. We hypothesized that the pre-established favorable loop conformation of the N106S mutant would facilitate binding. The N106S substitution results in a ~100- and 10-fold increase in BLIP inhibition potency for CTX-M-14 and CTX-M-15, respectively. Thus, this indicates that an active site loop in β-lactamase toggles between conformations that control antibiotic hydrolysis and inhibitor susceptibility. These findings highlight the role of accessible active site conformations in controlling enzyme activity and inhibitor susceptibility as well as the influence of mutations in selectively stabilizing discrete conformations.
59 BASIC BIOLOGICAL SCIENCES↗
Strong spin–orbit quenching via the product Jahn–Teller effect in neutral group IV qubits in diamond
Abstract Artificial atom qubits in diamond have emerged as leading candidates for a range of solid-state quantum systems, from quantum sensors to repeater nodes in memory-enhanced quantum communication. Inversion-symmetric group IV vacancy centers, comprised of Si, Ge, Sn, and Pb dopants, hold particular promise as their neutrally charged electronic configuration results in a ground-state spin triplet, enabling long spin coherence above cryogenic temperatures. However, despite the tremendous interest in these defects, a theoretical understanding of the electronic and spin structure of these centers remains elusive. In this context, we predict the ground-state and excited-state properties of the neutral group IV color centers from first principles. We capture the product Jahn–Teller effect found in the excited state manifold to second order in electron–phonon coupling, and present a nonperturbative treatment of the effect of spin–orbit coupling. Importantly, we find that spin–orbit splitting is strongly quenched due to the dominant Jahn–Teller effect, with the lowest optically-active 3 E u state weakly split into m s -resolved states. The predicted complex vibronic spectra of the neutral group IV color centers are essential for their experimental identification and have key implications for use of these systems in quantum information science.
Materials Science↗
Pulsed photoemission induced plasma breakdown
Abstract This article characterises the effects of cathode photoemission leading to electrical discharges in an argon gas. We perform breakdown experiments under pulsed laser illumination of a flat cathode and observe Townsend to glow discharge transitions. The breakdown process is recorded by high-speed imaging, and time-dependent voltage and current across the electrode gap are measured for different reduced electric fields and laser intensities. We employ a 0D transient discharge model to interpret the experimental measurements. The fitted values of transferred photoelectron charge are compared with calculations from a quantum model of photoemission. The breakdown voltage is found to be lower with photoemission than without. When the applied voltage is insufficient for ion-induced secondary electron emission to sustain the plasma, laser driven photoemission can still create a breakdown where a sheath (i.e. a region near the electrode surfaces consisting of positive ions and neutrals) is formed. This photoemission induced plasma persists and decays on a much longer time scale ( ∼ 10 s μ s) than the laser pulse length ( 30 ps). The effects of different applied voltages and laser energies on the breakdown voltage and current waveforms are investigated. The discharge model can accurately predict the measured breakdown voltage curves, despite the existence of discrepancy in quantitatively describing the transient discharge current and voltage waveforms.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗