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Epitaxial liftoff is an alternative to lattice-mismatched heteroepitaxial growth. Multilayer AlxGa1−xAs epitaxial films are separated from their growth substrates by undercutting an AlAs release layer in HF acid (selectivity ≳108 for x≤0.4). The resulting AlxGa1−xAs films tend to bond by natural intermolecular surface forces to any smooth substrate (Van der Waals bonding). We have demonstrated GaAs thin-film bonding by surface tension forces onto Si, glass, sapphire, LiNbO3, InP, and diamond substrates, as well as self-bonding onto GaAs substrates. In transmission electron microscopy the substrate and thin-film atomic lattices can be simultaneously imaged, showing only a thin (20–100 Å) amorphous layer in between.
A pH sensor has been developed for precise pH measurements of high temperature aqueous solutions based on a yttria‐stabilized zirconia (9% ) membrane electrode with a solid‐state internal element. In these investigations, the use of calculated pH values in evaluating the performance of the sensor has been eliminated. The excellent one‐to‐one correlation obtained between the potential of the sensor and a hydrogen reference electrode measured against a , reference electrode confirms that the pH sensor behaves in a Nernstian manner. The sensor is capable of withstanding high temperatures and pressures and is unaffected by hydrogen and oxygen gases and chloride ion concentration. The electrode remains stable over long periods of time, thus showing its potential use in monitoring the pH of waters in nuclear reactors, geothermal brines, and other high temperature aqueous systems.
A method for the synthesis of biaryls and heterobiaryls from arenes and haloarenes without the intermediacy of unstable boronic acids is described. Pinacol boronate esters that are analogous to unstable boronic acids are formed in high yield by iridium-catalyzed C-H borylation of heteroarenes and fluoroarenes. These boronates are stable in the solid state or in solution and can be generated and used in situ. They couple with aryl halides in the presence of simple palladium catalysts, providing a convenient route to biaryl and heteroaryl products that have been challenging to prepare via boronic acids.
The reforming reaction is one of the most important catalytic processes in the petroleum industry. The object of this process is to increase the octane number of the naphtha fraction of the crude oil distillate by converting paraffins into aromatic compounds. The presence of Re in the Pt-Re bimetallic system significantly enhanced the stability and reactivity of the catalyst. The Pt-Re bimetallic catalyst shows its unique property of naphtha reforming when it is sulfided to suppress the high hydrogenolysis activity of Re. All experiments were performed in a stainless steel ultrahigh vacuum system equipped with an Auger electron spectrometer, low-energy electron diffraction optics, a quadrupole mass spectrometer, and an internal isolation cell for catalytic reactions. Initial sulfiding changed the selectivity of the catalysts. The most significant change was a decrease in hydrogenolysis activity and an increase in cyclization activity.
This brief shows how lessons from European Union’s (EU) fiscal rules could help the People’s Republic of China (PRC) bolster local government debt sustainability through flexible, transparent frameworks that support stable economic growth. It looks at how the PRC and EU both use multi-year fiscal planning, details the EU’s Stability and Growth Pact, and notes its “escape clause” for crises. It explains how PRC revenue collection is centralized although more than two-thirds of public spending is at local level, and shows how adopting adaptable and politically feasible fiscal rules can tackle local government indebtedness and improve public resource allocation.
This paper is a sequel to an earlier paper under the same title. Here we use a more realistic model of the Josephson-junction and present a rigorous analysis of its nonlinear dynamics under various ranges of model parameters. In particular, we prove that the qualitative properties of our model and of the simplified one are similar. This rigorous proof thereby justifies the choice of a simpler Josephson-junction model, which was chosen in the past mainly for tractability. The peculiar constant voltage-step (devil's staircase) phenomenon widely reported in the literature is carefully analyzed further in this paper. For the first time, we can give a fairly complete explanation of the mechanism leading to this exotic phenomenon. In particular, the variations in the length of the constant voltage steps which have baffled many researchers in the past can now be given a rational explanation. An analysis of the mechanisms which give rise to chaotic dynamics in the Josephson-junction circuit is also presented.
We present a framework for learning single-view shape and pose prediction without using direct supervision for either. Our approach allows leveraging multi-view observations from unknown poses as supervisory signal during training. Our proposed training setup enforces geometric consistency between the independently predicted shape and pose from two views of the same instance. We consequently learn to predict shape in an emergent canonical (view-agnostic) frame along with a corresponding pose predictor. We show empirical and qualitative results using the ShapeNet dataset and observe encouragingly competitive performance to previous techniques which rely on stronger forms of supervision. We also demonstrate the applicability of our framework in a realistic setting which is beyond the scope of existing techniques: using a training dataset comprised of online product images where the underlying shape and pose are unknown.
Broad Hα emission lines have been detected in the nuclei of many bright galaxies such as M81 and M87. These lines are similar to, but much weaker than, those seen in type 1 Seyfert nuclei and QSOs. If massive black holes are responsible for the broad lines and the immense luminosities of classical AGNs, continuity arguments suggest that they also produce the features observed at lower levels in the relatively ‘‘normal’’ galaxies studied here, especially since the intensity ratios of the narrow emission lines are like those expected from gas photoionized by dilute nonstellar (e.g., power‐law) radiation. The possible presence of massive black holes in nearby galaxies is consistent with the conclusion that the nucleus of our own Milky Way may harbor such an object.
No abstract is provided for this article.
pH-Sensitive linkages designed to undergo hydrolysis at mildly acidic pH can trigger the release of therapeutics selectively at targets such as tumor and inflammatory tissues and in the endosomes and lysosomes of cells. Acetals have the potential to be used as linkages for a range of alcohol functionalities, and, by altering their chemical structure, it is possible to tune their hydrolysis rate. The syntheses of four conjugates of model drug molecules with PEO using acetals of varying chemical structure are described herein. Primary and secondary alcohols, as well as syn-1,2-diols, were incorporated in the conjugates. The hydrolysis kinetics were investigated by HPLC, and the conjugates had half-lives ranging from less than 1 min to several days at pH 5.0, with slower hydrolysis at pH 7.4 in all cases. These acetal linkages are therefore promising for use in a variety of drug delivery applications ranging from polymer-drug conjugates to pH-sensitive micelles and nanoparticulate systems.
