The disclosure provides for metal organic frameworks (MOFs) which comprise a plurality of SBUs comprising different metals or metal ions and/or a plurality of organic linking moieties comprising different functional groups.
We demonstrate that shape contexts can be used to quickly prune a search for similar shapes. We present two algorithms for rapid shape retrieval: representative shape contexts, performing comparisons based on a small number of shape contexts, and shapemes, using vector quantization in the space of shape contexts to obtain prototypical shape pieces.
The photophysical properties of a series of laser−dye-labeled poly(aryl ether) dendrimers, generations 1−4, have been determined. The dendrimers act as extremely efficient light-harvesting antennae capable of transferring light energy through space from their periphery to their core. The light-harvesting ability of these molecules increases with generation due to an increase in the number of peripheral chromophores. The energy-transfer efficiency was found to be quantitative for generations 1−3, with only a slight decrease observed for the fourth generation (∼93%). Due to the high extinction coefficients and fluorescence quantum yields of the chromophores and the efficient intramolecular energy transfer of the dendritic assemblies, these macromolecules have the potential to become integral components of molecular photonic devices.
Electrochemical and mechanical experiments were conducted to analyze the environmentally influenced cracking behavior of a bulk amorphous metal, Zr41.2Ti13.8Cu12.5Ni10Be22.5. This study was motivated by a scientific interest in mechanisms of fatigue–crack propagation in an amorphous metal, and by a practical interest in the use of this amorphous metal in applications that take advantage of its unique properties, including high specific strength, large elastic strains, and low damping. The objective of the work was to determine the rate and mechanisms of subcritical crack growth in this metallic glass in an aggressive environment. Specifically, fatigue–crack propagation behavior was investigated at a range of stress intensities in air and aqueous salt solutions by examining the effects of loading cycle, stress-intensity range, solution concentration, anion identity, solution deaeration, and bulk electrochemical potential. Results indicate that crack growth in aqueous solution in this alloy is driven by a stress-assisted anodic reaction at the crack tip. Rate-determining steps for such behavior are reasoned to be an electrochemical, stress-dependent reaction at near-threshold levels, and mass transport at higher (steady-state) growth rates.
Linking molecular building units by covalent bonds to make crystalline extended structures has given rise to metal-organic frameworks (MOFs) and covalent organic frameworks (COFs), thus bringing the precision and versatility of covalent chemistry beyond discrete molecules to extended structures. The key advance in this regard has been the development of strategies to overcome the "crystallization problem", which is usually encountered when attempting to link molecular building units into covalent solids. Currently, numerous MOFs and COFs are made as crystalline materials in which the large size of the constituent units provides for open frameworks. The molecular units thus reticulated become part of a new environment where they have (a) lower degrees of freedom because they are fixed into position within the framework; (b) well-defined spatial arrangements where their properties are influenced by the intricacies of the pores; and (c) ordered patterns onto which functional groups can be covalently attached to produce chemical complexity. The notion of covalent chemistry beyond molecules is further strengthened by the fact that covalent reactions can be carried out on such frameworks, with full retention of their crystallinity and porosity. MOFs are exemplars of how this chemistry has led to porosity with designed metrics and functionality, chemically-rich sequences of information within their frameworks, and well-defined mesoscopic constructs in which nanoMOFs enclose inorganic nanocrystals and give them new levels of spatial definition, stability, and functionality.
Significance Neural oscillations have been shown to support a range of cognitive abilities. Here we demonstrate that delta activity (2–4 Hz) in the prefrontal cortex tracked the current task context and modulated sensory processing in a top-down manner. We show that frontal delta and parietooccipital alpha (8–12 Hz) oscillations are functionally coupled and jointly guide visual perception to integrate sensory evidence with current task demands. We observed strong moment-to-moment behavioral fluctuations, which cycled at the rate of the endogenous prefrontal oscillatory brain activity. Our findings suggest that neuronal oscillations provide the functional basis for context-dependent visual perception.
Generative adversarial nets (GANs) have generated a lot of excitement. Despite their popularity, they exhibit a number of well-documented issues in practice, which apparently contradict theoretical guarantees. A number of enlightening papers have pointed out that these issues arise from unjustified assumptions that are commonly made, but the message seems to have been lost amid the optimism of recent years. We believe the identified problems deserve more attention, and highlight the implications on both the properties of GANs and the trajectory of research on probabilistic models. We recently proposed an alternative method that sidesteps these problems.
Work over the past decade has shown that the critical voltage and induction time for the breakdown of passive films in aqueous systems containing aggressive anions follow statistical frequency distributions. Recently, we have demonstrated that the point defect model (PDM) can be used to explain the frequency distributions in and as a function of voltage ( only), chloride concentration, and pH. Furthermore, we developed the solute/vacancy interaction model (SVIM) to account for the effects of minor alloying elements (e.g., Mo) on the breakdown parameters for a single site on a film. This model assumes that highly charged solutes, when substitutionally present in the film, electrostatically interact with mobile cation vacancies resulting in a shift in the breakdown voltage to more positive values and in the induction times to longer times. In this paper, we combine the models to account for the effects of minor alloying elements on the distributions in the breakdown voltage and induction time for the nucleation of pits on heterogeneous metal surfaces. This is done by estimating solute/vacancy equilibrium constants using ion‐pairing theory with an appropriate Debye‐Huckel correction for screening. The model is shown to account for the shift in for ferritic stainless steels containing molybdenum (Fe‐17Cr, Fe‐18Cr) in sodium chloride solutions, assuming that the molybdenum exist in the +6 state. The model also predicts that solute/vacancy complexing will shift the distribution in to longer times, thereby further enhancing the resistance of the film to environmentally induced breakdown.
