Virtual memory T cells are foreign antigen‐inexperienced T cells that have acquired memory‐like phenotype and constitute 10–20% of all peripheral CD8+ T cells in mice. Their origin, biological roles, ...and relationship to naïve and foreign antigen‐experienced memory T cells are incompletely understood. By analyzing T‐cell receptor repertoires and using retrogenic monoclonal T‐cell populations, we demonstrate that the virtual memory T‐cell formation is a so far unappreciated cell fate decision checkpoint. We describe two molecular mechanisms driving the formation of virtual memory T cells. First, virtual memory T cells originate exclusively from strongly self‐reactive T cells. Second, the stoichiometry of the CD8 interaction with Lck regulates the size of the virtual memory T‐cell compartment via modulating the self‐reactivity of individual T cells. Although virtual memory T cells descend from the highly self‐reactive clones and acquire a partial memory program, they are not more potent in inducing experimental autoimmune diabetes than naïve T cells. These data underline the importance of the variable level of self‐reactivity in polyclonal T cells for the generation of functional T‐cell diversity.
Synopsis
Virtual memory T cells are formed from self‐reactive CD8+ T cells in a process regulated by CD8‐Lck. Despite their self‐reactivity and features of memory T cells, virtual memory T cells did not show a strong potential to trigger an autoimmune pathology.
Virtual memory CD8+ T cells are formed from relatively highly self‐reactive peripheral T cells.
Virtual memory T cells exhibit an intermediate stage between naïve and true antigen‐experienced T cells.
Virtual memory, true antigen experienced memory, and naïve T cells show functional differences upon activation.
Virtual memory T cells do not show higher potential to induce experimental tissue pathology than naïve T cells on a per cell basis.
T‐cell receptor signalling can induce formation of self‐reactive CD8+ cells with features of memory T cells, which however do not show strong potential for triggering autoimmune pathology.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
This study offers a kinetic exploration of the Hydrogen Evolution Reaction (HER) in an acidic environment using a catalyst of MoS x modified with electrodeposited platinum atoms (Pt-MoS x ). Scanning ...electron microscopy and high-resolution transmission electron microscopy images revealed a two-dimensional network structure of Pt-MoS x . The linear sweep voltammetries in a 0.5 mol/L H2SO4 solution demonstrated a high catalytic activity of the modified catalyst: an onset potential for hydrogen reduction reaction much more positive than that observed for MoS x , high mass activity (16.5 A/mg at an overpotential of −50 mV), a turnover frequency of 50 H2/s per surface site at a kinetic current density of 10 mA/cm2, and an overpotential of −39 mV. Based on classical models, including the Butler–Volmer equation, Kouteck-Levich equation, and Langmuir isotherm, essential kinetic parameters were obtained. The models in the frequency domain allowed the determination of the surface concentration of molecular hydrogen and the proposition of a transfer function for both dc frequency and infinite rotating disk speed conditions, enabling the determination of the exchange current density (8.51 × 10–4 A/cm2) and Tafel slope (40 mV/dec); the latter value suggested that the reaction proceeds through a Volmer–Heyrovsky pathway, predominantly limited by the Heyrovsky step. Based on the observed electrocatalytic behavior and the measured and calculated parameters, our findings suggest that the electrodeposition of small amounts of Pt on MoS x may represent a promising strategy for molecular hydrogen production.
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IJS, KILJ, NUK, PNG, UL, UM
By integrating an updated multi-dimensional model and the NSGA-II (non-dominated sorting genetic algorithm II), the combustion of a RCCI (reactivity controlled compression ignition) engine fueled ...with methanol/diesel was optimized. Based on the optimization results, parametric study was performed by varying energy fraction of methanol, EGR (exhaust gas recirculation rate, initial in-cylinder pressure at IVC (intake valve closing), initial in-cylinder temperature at IVC, and SOI (start of injection). Furthermore, the sensitivities of these five parameters on fuel efficiency, emissions, ignition timing and RI (ringing intensity) were analyzed. The results indicated that initial temperature and EGR rate exhibited the most significant effect on engine performance and emissions for their obvious effect on combustion temperature. By varying the local fuel-rich and high-temperature regions, methanol fraction and SOI could dramatically affect NOx (nitrogen oxide) emission. Overall, the RCCI combustion with high methanol fraction and advanced SOI exhibited higher fuel efficiency and lower emissions. Moreover, it was found that both decreasing EGR rate and increasing initial temperature led to the monotonously increased RI. While decreasing methanol fraction and increasing initial pressure demonstrated the negligible effect on RI at CA50 earlier than 4.3 degree CA ATDC, which was contributed to their obvious effect on fuel spatial distributions.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
34.
Equilibrium Acidities of Superacids Kütt, Agnes; Rodima, Toomas; Saame, Jaan ...
Journal of organic chemistry,
01/2011, Volume:
76, Issue:
2
Journal Article
Peer reviewed
In this paper, we report the most comprehensive equilibrium superacidity scale that is available to date. Contrary to most of the past works, this scale is set up in a medium of constant composition ...and the obtained acidity values characterize the acidities of molecules rather than acidities of media. The current scale is thus complementary to the well-known H 0 scale in the information that it provides. The solvent used is 1,2-dichloroethane (DCE). DCE has very weak basic properties (but sufficiently high polarity) and is an appropriate solvent for measuring acidities of very strong acids of diverse chemical nature. DCE acidities of well-known superacids (CF3SO2OH, (CF3SO2)2NH, cyanocarbon acids, etc.) as well as common mineral acids (H2SO4, HI, HBr, etc.) are reported. Acidities of altogether 62 acids have been determined from 176 interlinked relative acidity measurements. The scale spans 15 orders of magnitude (from picric acid to 1,1,2,3,3-pentacyanopropene) and is expected to be a useful tool in design, use, and further acidity measurements of superacidic molecules.
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The potential of zero charge (U PZC) is an important quantity of metal–water interfaces that are central in many electrochemical applications. In this work, we use ab initio molecular dynamics (AIMD) ...simulations to study a large number of (111), (100), (0001), and (211) and overlayers of transition metal–water interfaces to identify simple descriptors to predict their U PZC. We find a good correlation between water coverage and the work function reduction Δϕ which is defined by the difference of the work function in a vacuum and in the presence of water. Furthermore, we determine the vacuum binding energies of H2O and *OH species as good descriptors for the prediction of water coverage and thereby of Δϕ. Our insights unify different facet geometries and mixed metal surfaces and thereby generalize recent observations. We further present a scheme to predict U PZC based only on the *OH binding and the vacuum work function estimated from static DFT calculations. This formalism is applicable to all investigated metals and mixed metal surfaces including terrace and step geometries and does not require expensive AIMD simulations. To evaluate physical influences to U PZC, we decompose Δϕ into its orientational (Δϕorient) and electronic (Δϕel) component. We find Δϕorient to be a facet-dependent property and a major contributor to Δϕ on (211) surfaces, while Δϕel strongly depends on the metal identity.
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Alkali oxides are typically used as promoters of heterogeneous catalysts for the water–gas shift (WGS; H2O + CO → H2 + CO2) reaction. On Au(111), CsO x exhibits diverse nanostructures at varying ...coverages, as revealed by scanning tunneling microscopy. Clusters of cesium oxide (Cs2O2) nucleate at elbow sites of the Au(111) herringbone when θCs is less than 0.1 ML. Subsequently, these clusters transform into two-dimensional (2D) islands (Cs2O, Cs2O2, CsO2) as the cesium coverage increases (θCs > 0.1 ML). Both types of CsO x nanostructures enable the WGS process on Au(111). The highest activity was seen for the cesium oxide clusters which facilitated the partial dissociation of water and binding of CO. The COads and OHads groups were not strongly bound and probably reacted to yield a short-lived HOCO intermediate that led to gaseous H2 and CO2. The 2D islands of CsO x also enabled the WGS but their efficiency was reduced due to the formation of cesium hydroxide compounds (limiting mobility of OH groups) and the generation of CO3 and C species (blocking of active centers). The fact that the performance of the CsO x /Au(111) catalysts changed dramatically with variations in the chemical properties of the CsO x nanostructures indicates that the alkali oxide was an integral part of the active phase, playing a central role in the activation and conversion of the reactants. To attach the label of “promoter” to CsO x is a simplification that does not help in the design and optimization of catalysts for C1 chemistry. To achieve a rational design, one must consider the structural and chemical properties of the alkali oxide.
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Hematite is a promising catalyst to remove nitrogen oxide (NO x , x = 1 and 2) pollutants from the atmosphere. Improving its catalytic performance requires a clear understanding of the relevant ...surface processes, including NO x adsorption. Prior theoretical simulations were limited to isolated adsorbates at static conditions, with results not fully consistent with experiments. Here, we investigate the adsorption of NO x molecules on the hematite (0001) surface by using the density functional theory + U method with van der Waals corrections. We find that, at static conditions, NO x prefer to occupy two neighboring surface Fe and O sites simultaneously, due to a cooperative effect between two open-shell NO x molecules J. Phys. Chem. B 2002, 106, 7405–7413. In contrast, isolated adsorbates are favored at high temperatures (T) or low NO x partial pressures (P NO x ) due to their higher configurational entropy. A surface phase diagram is constructed for the NO x adsorbates, delineating both their stability fields and equilibrium coverages. As the structure and abundance of NO x adsorbates depend strongly on T and P NO x , surface reactions at different T-P NO x conditions may follow quite different pathways.
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DFT simulations are performed to understand the impact of H2O and CO on the NO interaction with Pd sites present at various locations in Pd/CHA passive NO x adsorbers. The presence of H2O facilitates ...the reduction of PdOH–PdOH+2 and Pd–O–Pd+2 by NO in 8-membered rings (8MR) but increases the activation barrier in 6MR. Bidentate nitrates are formed in the absence of H2O, whereas monodentate nitrates are formed in the presence of H2O, which transform to bidentate nitrates upon H2O desorption. The detrimental effect of H2O on NO binding over PdOH–PdOH+2 and PdOH+ is mitigated in the presence of CO. Additionally, CO preferentially reduces the Pd(II) species when both CO and NO are coadsorbed on Pd–O–Pd+2, resulting in the formation of Pd+1 for further NO uptake. H2O does not significantly impact the reduction of Pd(II) species by CO. Pd+1 sites can also reoxidize to Pd(II) species under an oxidizing atmosphere. However, the reoxidation of Pd+1 is inhibited in the presence of H2O in 6MR and 8MR, which could explain the reported increase in the NO x desorption temperature. The operating cycle of NO, including the transformation of Pd species and the effect of H2O and CO on NO x uptake and release, is proposed.
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•The neutronic parameters for the ARGUS reactor are calculated.•The 6 group effective delayed neutrons fractions are obtained.•The hot full power keff and fuel burnup are calculated.•The control rods ...worth, the shot down margin and the safety reactivity factor are calculated.•The temperature coefficient of reactivity and void coefficient of reactivity are calculated.•Two different types of radiation shield for gamma and neutron radiations are designed.
In this research, an aqueous homogeneous reactor is simulated and its neutronic parameters are investigated. Due to the negative reactivity caused by temperature change and void formation, the cold excess reactivity is considered equal to 4 βeff. Also, calculations of radiation shielding and neutronic characterization of the reactor are performed. For different heights of uranyl sulfate fuel, the effective multiplication factor (keff) of the reactor is calculated under cold zero power and hot full power conditions to assess the required excess reactivity. The amount of fuel burnup and changes in the keff are investigated for 500 days, finally 200 operating days are chosen as the working duration of the reactor. The control rods worth (CRW) for different diameters of boron carbid and reactor safety parameters including shot down margin (SDM) and safety reactivity factor (SRF), temperature and void coefficients of reactivity are analyzed. In order to design a suitable radiation shield for this reactor, two different shields are considered. The first shield is a combination of polyethylene thicknesses and barite concrete, and the second shield is made only of barite concrete. The total thickness of the first and second shield was 230 and 180 cm, respectively. Due to the problems of using polyethylene (e.g. problems related to machining, shield dimensions and low melting temperature), the second shield is chosen as the suitable radiation shield for this reactor. Using this radiation shield, the total dose rates of neutron and gamma rays satisfy the ICRP dose limits.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Research on reactivity, syngas production and synergy of petcoke-coal/biomass co-gasification are reviewed.•Catalytic/non-catalytic synergy mechanisms of co-gasification reactivity and syngas ...production are discussed.•Future perspectives on petcoke and coal/biomass co-gasification are proposed based on the lack of current research.
Petroleum coke and biomass/coal co-gasification is a promising approach for efficiently integrating the individual advantages of different gasification feedstocks with syngas production. Therefore, research on syngas production, reactivity characteristics, and synergy behavior of co-gasification is critical. In this review, the main reaction processes during co-gasification were described and the influencing factors for syngas production and reactivity characteristics of co-gasification were summarized. Moreover, the non-catalytic/catalytic synergy mechanisms in co-gasification were also discussed in detail. H2-rich syngas derived from co-gasification could be acquired in case of (i) feedstock with high H/C ratio or alkali and alkaline earth metals (AAEMs) concentrations, (ii) high coal/biomass proportion in blends, (iii) relatively low gasification temperature, and (iv) low O2 concentration or high steam concentration in gasification agent. Higher co-gasification reactivity could be acquired in case of (i) coal/biomass with more disordered carbon structures, more developed pore structures and higher AAEMs concentrations, (ii) higher coal/biomass proportion in blends, (iii) higher gasification temperature, and (iv) higher O2 or steam concentration in gasification agent. The synergy behavior on co-gasification reactivity varied as reaction proceeded. The synergy mechanism of co-gasification showed great relationships with the migration and transfer of free radical and inherent AAEMs. The limitations and challenges within this research field were also addressed. For instance, the transfer and migration mechanisms of free radicals and AAEMs during co-gasification, and kinetics models involving parameters related to synergy behavior.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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