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New hafnocene triarylstannyl complexes were prepared and were shown to undergo clean thermal decompositions via alpha-aryl-elimination to produce the corresponding stannylene and a hafnocene aryl complex. The rate of the decomposition is highly dependent on the nature of the ancillary ligand, with the stabilities of the CpCp*Hf(SnPh(3))X compounds following the order X = NMe(2) > Np (alpha-agostic) > OMe > Cl > Me. Mechanistic information suggests that alpha-aryl-elimination may be viewed as a concerted process involving nucleophilic attack of the migrating aryl group onto the electrophilic metal center.
The Peer-to-Peer (P2P) architectures that are most prevalent in today's Internet are decentralized and unstructured. Search is blind in that it is independent of the query and is thus not more effective than probing randomly chosen peers. One technique to improve the effectiveness of blind search is to proactively replicate data. We evaluate and compare different replication strategies and reveal interesting structure: Two very common but very different replication strategies - uniform and proportional - yield the same average performance on successful queries, and are in fact worse than any replication strategy which lies between them. The optimal strategy lies between the two and can be achieved by simple distributed algorithms. These fundamental results o.er a new understanding of replication and show that currently deployed replication strategies are far from optimal and that optimal replication is attainable by protocols that resemble existing ones in simplicity and operation.
The electron irradiation induced TiCl4 deposition on a gold polycrystalline foil and on a Au (100) single crystal in ultra-high vacuum conditions is reported. Titanium chloride ultrathin films are prepared at 250−300 K by irradiation of the substrate with 1 keV electrons in a background pressure of TiCl4 of 1 × 10-8 to 5 × 10-7 Torr. The deposited films are characterized by AES, XPS, and temperature-programmed desorption (TPD). We can grow titanium chloride films of the maximum thickness of about 25 Å under our experimental conditions. The film consists of 3−4 layers of TiCl2 with 1 monolayer of TiCl4 chemisorbed on its surface. A comparison is made with the titanium chloride film grown on MgCl2 ultrathin films by electron irradiation induced TiCl4 deposition as previously reported. This film is very similar to the titanium chloride film deposited on Au and can be described as few layers of TiCl2 deposited on a defective MgCl2-x film. One monolayer of TiCl4 is chemisorbed on the TiCl2 surface.
Abstract In recent years, supramolecular micellar assemblies formed from amphiphilic block copolymers have been receiving attention as potential drug carriers. The size of the carriers is ideal for avoiding rapid renal exclusion and reticuloendothelial uptake, and enables them to be targeted to certain tissues such as tumors. One important issue determining the effectiveness of a micellar drug carrier is the ability to control the time over which drug release takes place, or to possibly trigger drug release at a specific location or time. The mildly acidic pH encountered in tumor and inflammatory tissues as well as in the endosomal and lysosomal compartments of cells has inspired the development of micellar carriers capable of releasing their drug load in response to small changes in pH. One approach to the development of these systems has been to incorporate “titratable” groups such as amines and carboxylic acids into the copolymer backbone, thus altering the solubility of the polymer upon protonation and disrupting micelle formation. Another approach has been to incorporate acid-degradable linkages into the copolymer, either for direct attachment of the drug, or to cause a structural change of such magnitude that micellar integrity is lost and the drug is released.
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ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTStructure sensitivity of catalytic reactionsGabor A. Somorjai and Jose CarrazzaCite this: Ind. Eng. Chem. Fundamen. 1986, 25, 1, 63–69Publication Date (Print):February 1, 1986Publication History Published online1 May 2002Published inissue 1 February 1986https://pubs.acs.org/doi/10.1021/i100021a009https://doi.org/10.1021/i100021a009research-articleACS PublicationsRequest reuse permissionsArticle Views2747Altmetric-Citations143LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access options Get e-Alerts
This thesis presents a novel dataset of 12,000 segmentations of 1,000 natural images by 30 human subjects. The subjects marked the locations of objects in the images, providing ground truth data for learning grouping cues and benchmarking grouping algorithms. We feel that the data-driven approach is critical for two reasons: (1) the data reflects "ecological statistics" that the human visual system has evolved to exploit, and (2) innovations in computational vision should be evaluated quantitatively. <p>We develop a battery of segmentation comparison measures that we use both to validate the consistency of the human data and to provide approaches for evaluating grouping algorithms. In conjunction with the segmentation dataset, the various measures provide "micro-benchmarks" for boundary detection algorithms and pixel affinity functions, as well a benchmark for complete segmentation algorithms. Using these performance measures, we can systematically improve grouping algorithms with the human ground truth as our goal. <p>Starting at the lowest level, we present local boundary models based on brightness, color, and texture cues, where the cues are individually optimized with respect to the dataset and then combined in a statistically optimal manner with classifiers. The resulting detector is shown to significantly outperform prior state-of-the-art algorithms. Next, we learn from data how to combine the boundary model with patch-based features in a pixel affinity model to settle long-standing debates in computer vision with empirical results: (1) brightness boundaries are more informative than patches, and vice versa for color; (2) texture boundaries and patches are the two most powerful cues; (3) proximity is not a useful cue for grouping, it is simply a result of the process; and (4) both boundary-based and region-based approaches provide significant independent information for grouping
Active corrosion of carbon steel in reinforced concrete occurs when the chloride ion concentration exceeds the chloride threshold (CT). CT is affected by many physical and chemical parameters including primary variables (pH, corrosion potential, breakdown potential, and temperature) and secondary variables (cemenet composition, concreete porosity, and water/cement ratio). A Kohonen-self organized map (KSOM) and regression artificial neural network (ANN) coupled methodology was developed to find the missing values of independent variables in the sparse database and for quantitatively evaluating the effects of these variables on CT values that are expressed in %TotalCl/cem (or %FreeCl/cem), and [Cl<sup>-</sup>]/[OH<sup>-</sup>].
Luminescence extraction has played a tremendous role in improving the efficiency of solar photovoltaics. This has been assisted by the development of a highly reflective rear mirror. At the same time, thermophotovoltaic efficiency has shown to benefit from a rear mirror. The low-energy, unabsorbed photons in the thermophotovoltaic cells can be reflected by the mirror, thereby assisting in photon regeneration. In both cases, it has been shown that device efficiency has an increasing return with improvement rear mirror reflectivity. However, the realization of broadband mirrors with reflectivity >98% has remained elusive. Here, we demonstrate a mirror that can achieve broadband 99.3% reflectivity, for thermophotovoltaic cells. The design concept can be equally extended to photovoltaic cells as well, thereby enhancing the efficiencies closer to the thermodynamic limits.
Force feedback coupled with a real-time physically realistic graphic display provides a human operator with an artificial sense of presence in a virtual environment. Furthermore, it allows a human operator to interact with the virtual environment through "touch". We describe a haptic simulation system that allows a human operator to perform real-time interaction with soft 3D objects that go through large global deformations. We model and simulate such a global deformation using geometrically nonlinear finite element methods (FEM). We also introduce an efficient method that computes the force feedback, in real-time, by simulating the collision between the virtual "proxy" and the deformable object. To perceptually satisfy a human operator, haptics requires a much higher update frequency (at least 1000 Hz) than graphics. We update the graphics using full simulation and interpolate the fully simulated states at a higher frequency to render haptics. The interpolation is made possible by intentionally delaying the display (both graphics and haptics) by one full simulation cycle.
Surface growth lithography is an attractive technique that eliminates the need for resist transparency. Critical to the success of this method is a smooth and homogeneous film capable of immobilizing a high concentration of initiator on the surface. This report outlines the design, synthesis, and preliminary testing of a polymeric photoactive acid generator (PAG), which is suitable for use with cationic surface growth lithography.
