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[Image: see text] MOFs on the move: A copper coordinated [2]pseudorotaxanate which reacts with zinc nitrate to form an extended structure, consisting of three-fold interpenetrated networks, retains most of its solution-state chemistry including its ability to undergo electronic switching of some of the copper(I) ions under redox control.
In the first billion years after the Big Bang, sources of ultraviolet (UV) photons are believed to have ionized intergalactic hydrogen, rendering the Universe transparent to UV radiation. Galaxies brighter than the characteristic luminosity $L^{*}$ do not provide enough ionizing photons to drive this cosmic reionization. Fainter galaxies are thought to dominate the photon budget; however they are surrounded by neutral gas that prevents the escape of the Lyman-$α$ photons, which has been the dominant way to identify them so far. JD1 was previously identified as a triply-imaged galaxy with a magnification factor of 13 provided by the foreground cluster Abell 2744, and a photometric redshift of $z\sim10$. Here we report the spectroscopic confirmation of this very low luminosity ($\sim0.05 L^{*}$) galaxy at $z=9.79$, observed 480 Myr after the Big Bang, by means of the identification of the Lyman break and redward continuum, as well as multiple $\gtrsim4σ$ emission lines, with the Near-InfraRed Spectrograph (NIRSpec) and Near-InfraRed Camera (NIRCam) instruments. The combination of the James Webb Space Telescope (JWST) and gravitational lensing shows that this ultra-faint galaxy ($M_{\rm UV}=-17.35$) -- with a luminosity typical of the sources responsible for cosmic reionization -- has a compact ($\sim$150 pc) and complex morphology, low stellar mass (10$^{7.19}$ M$_\odot$), and subsolar ($\sim$0.6 $Z_{\odot}$) gas-phase metallicity.
Abstract Natural Killer (NK) cells play several important roles in hematopoietic cell transplantation. Host NK cells can reject allogeneic transplants that lack major histocompatibility complex (MHC) molecules of the host (so-called “missing self” reactivity), whereas donor NK cells in the marrow can promote engraftment, inhibit graft versus host disease, and mediate rejection of host leukemic cells (graft versus tumor (GVT) response). Like T cells, NK cells can distinguish allogeneic cells from self-cells, and “learn” self vs. non-self so as to establish self-tolerance. This presentation will summarize current understanding of some of these processes based primarily on studies in mice, and present new data that may be relevant for the success of human bone marrow transplantation. The self-tolerance of T cells and B cells is established in large part by developmental processes that either remove or suppress self-reactive clones as the cells differentiate from hematopoietic stem cells. Studies will be presented that show that NK cell self-tolerance is regulated quite differently, by an adaptation process that occurs quite rapidly and acts on mature NK cells. NK cell reactivity against susceptible untransformed cells (e.g., cells from animals lacking MHC of the NK cell donor) is rapidly lost after transfer of such NK cells to susceptible hosts, indicating that self-tolerance is an adaptation that occurs rapidly under non-inflammatory conditions. Irradiation chimeras were employed to identify the cell types that induce tolerance of NK cells to cells from MHC-deficient mice, as one model of missing self-recognition. Stable tolerance of wild type NK cells to MHC-deficient cells was established when NK cells were exposed in chimeras to either MHC-deficient hematopoietic cells or MHC-deficient non-hematopoietic cells. Interestingly, however, tolerance induced by exposure solely to MHC-deficient hematopoietic cells was unstable in the face of inflammatory conditions arising from infections or exposures to inflammatory cytokines in vivo. Specifically, mixed chimeras consisting of WT and MHC-deficient hematopoietic cells in WT hosts were stably chimeric until the mice were exposed to viral or bacterial infections, at which time the MHC-deficient cells were rapidly eliminated. In contrast, tolerance induced by non-hematopoietic cells was much more stable. Specifically, mixed chimeras consisting of WT and MHC-deficient hematopoietic cells in MHC-deficient hosts were stably chimeric whether or not they underwent infections. These findings suggest that tolerance may be imposed by multiple mechanisms depending on the cell types that induce tolerance, with distinct properties as a result. Most importantly from a clinical perspective, the results suggest that depending on the host/donor combination, intense infections may jeopardize the stability of bone marrow transplants. Previous studies have shown that tolerance of NK cells to MHC-deficient cells is accompanied by a state of hyporesponsiveness of the NK cells, characterized by low functional responses to stimulation via crosslinking of activating receptors ex vivo. Accordingly, it has been widely accepted that hyporesponsiveness to stimulation is the mechanism of NK cell self-tolerance when NK cells lack inhibitory receptors specific for host MHC molecules. However, our recent analysis of chimeric NK cells showed that this cannot be the sole explanation. When NK cells developed in MHC+ hosts in the presence of MHC-deficient hematopoietic cells, the cells became responsive to activating receptor stimulation despite being tolerant of MHC-deficient cells. Hence, tolerance can occur even when NK cells are responsive to stimulation. In contrast, when NK cells developed in MHC-deficient hosts, they became hyporesponsive. These data suggest that non-hematopoietic cells in the host impart hyporesponsiveness. Furthermore, exposure to MHC-deficient hematopoietic cells induces tolerance by a mechanism distinct from hyporesponsiveness. The latter mechanism is relatively unstable as it can be broken as a result of infections. Disclosures Raulet: Innate Pharma: Membership on an entity's Board of Directors or advisory committees; Novo Nordisk: Consultancy.
Pristine monocrystalline graphene is claimed to be the strongest material known with remarkable mechanical and electrical properties. However, graphene made with scalable fabrication techniques is polycrystalline and contains inherent nanoscale line and point defects—grain boundaries and grain-boundary triple junctions—that lead to significant statistical fluctuations in toughness and strength. These fluctuations become particularly pronounced for nanocrystalline graphene where the density of defects is high. Here we use large-scale simulation and continuum modelling to show that the statistical variation in toughness and strength can be understood with ‘weakest-link’ statistics. We develop the first statistical theory of toughness in polycrystalline graphene, and elucidate the nanoscale origins of the grain-size dependence of its strength and toughness. Our results should lead to more reliable graphene device design, and provide a framework to interpret experimental results in a broad class of two-dimensional materials.
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Abstract An impasse point of the implicit differential‐algebraic system equation image . Has been characterized in Part I of this paper as a limit point of an induced solution curve equation image In this paper we use the Liapunov‐Schmidt procedure to derive an analytical test for identifying impasse points. We also invoke the transversality theory from differential topology to show that almost all singular points (X o , y o ) of S, which occur when the Jacobian matrix equation image is singular, are in fact impasse points.
Recent advances in the understanding of prokaryotic gene expression have led scientists to look beyond traditional promoter control for new methods of regulating gene expression. A promising, new technique centers on controlling the stability of messenger RNA. To exploit the potential of mRNA stability for gene expression control, it is important to understand the mechanisms of prokaryotic mRNA decay as well as the cellular factors that can be used to enhance bacterial gene expression through mRNA stabilization. Factors involved in controlling prokaryotic mRNA stability such as nucleases, secondary structures, translation influences, and transcription effects are discussed and analyzed within the context of three prevailing mRNA decay theories. Several strategies for manipulating mRNA stability in genetically-engineered cells are developed from these discussions and presented as a future direction in gene expression control. In the near future, it should be possible to use these strategies to control mRNA stability in such applications as pharmaceutical protein production and metabolic pathway design.
A cluster expansion is used to determine the energy of substitutionally disordered alloys as a function of configuration. The expansion is exact in the sense that the basis functions are complete and orthonormal. The coefficients, effective cluster interactions (ECI's), are computed directly from their definition by means of the method of direct configurational averaging, which is described in detail in the context of a tight-binding linear muffin-tin orbital (TB-LMTO) Hamiltonian. The alloy Hamiltonian is constructed from a combination of the pure-element TB-LMTO Hamiltonians, the hopping integrals between unlike pairs of atoms (simply given by the geometric mean of the pure-element integrals), and the potentials of the alloy, which are computed consistent with the condition that each configurationally averaged atom of the alloy be neutral. This scheme of self-consistency is tested against the results of fully self-consistent LMTO calculations on ordered compounds. The ECI's are computed on the fcc lattice for six alloy systems: Rh-Ti, Rh-V, Pd-Ti, Pd-V, Pt-Ti, and Pt-V. It is shown how the ECI's may be used in conjunction with properties of the energy expansion to exactly solve for the ground-state superstructures of fcc. This ground-state search is contingent upon minimizing the configurational energy subject to a number of geometric constraints. A large number of these constraints are formulated using group-theoretic means on the (13--14)-point clusters of the fcc lattice. The use of this large number of constraints makes possible the inclusion of fourth-nearest-neighbor pair ECI's as well as multiplet ECI's in the ground-state search. Both these types of interactions are shown to be essential towards obtaining a convergent energy expansion. In all six alloy systems, agreement between the theoretically predicted ground states and the experimental evidence of fcc superstructures is excellent: in no case is an unambiguously experimentally determined fcc-based phase missing from the results of the ground-state search.
We present a discriminative Hough transform based object detector where each local part casts a weighted vote for the possible locations of the object center. We show that the weights can be learned in a max-margin framework which directly optimizes the classification performance. The discriminative training takes into account both the codebook appearance and the spatial distribution of its position with respect to the object center to derive its importance. On various datasets we show that the discriminative training improves the Hough detector. Combined with a verification step using a SVM based classifier, our approach achieves a detection rate of 91.9% at 0.3 false positives per image on the ETHZ shape dataset, a significant improvement over the state of the art, while running the verification step on at least an order of magnitude fewer windows than in a sliding window approach.