Electron energy-loss spectroscopy of anomalous plutonium behavior in nuclear waste materials

Plutonium-enriched layer has been observed in corroded spent uranium oxide fuel (CSNF). These Pu-enriched regions were examined with analytical transmission electron microscopy combined with electron energy-loss spectroscopy (EELS). The enriched region also contained U, Am, Ru, Zr, but only minor enrichment of rare earth elements. The Pu, possibly as Pu(V) according to EELS measurements, was dispersed within re-precipitated uranium oxide (identified as U3O8) nano-crystals between U(VI) secondary phases and the CSNF surface. The U, Pu, and Am enrichment was observed in the corrosion products with tests on different nuclear fuels. This may have implications for the long-term behavior of CSNF under storage in a geologic waste repository. Furthermore, there may be an increased potential for the generation of Pu-bearing colloids from this type of weathered CSNF.     

Degradable conjugates from oxanorbornadiene reagents

Oxanorbornadienedicarboxylate (OND) reagents were explored for purposes of binding and releasing drugs from serum albumins as representative macromolecular carriers. Being highly reactive Michael acceptors, ONDs form adducts with thiols and amines, which then undergo retro-Diels-Alder fragmentation. A study of more than 30 model adducts revealed a number of modifications that can be used to influence adduct stability. For the most reactive OND linkers, the labeling of the single available bovine serum albumin (BSA) cysteine residue was complete within minutes at a mid-micromolar concentration of reactants. While a selectivity of greater than 1000-fold for thiol over amine was observed with model amino acids, the labeling of protein amines with ONDs is fast enough to be practical, as demonstrated by the reaction with thiol-depleted BSA. The OND-amine adducts were found to be up to 15 times more stable than OND-thiol adducts, and to be sensitive to acid by virtue of a stereochemically dependent acceleration of cycloreversion. The release rate of fluorescent cargo from serum albumins was tuned by selecting the coupling partners: the available half-lives ranged from 40 min to 7 days at 37 °C. Such versatility of release profiles from protein carriers, controlled by the nature of the OND linkage, is a useful addition to the drug delivery toolbox.     

Glycomimetic ligands for the human asialoglycoprotein receptor

The asialoglycoprotein receptor (ASGPR) is a high-capacity galactose-binding receptor expressed on hepatocytes that binds its native substrates with low affinity. More potent ligands are of interest for hepatic delivery of therapeutic agents. We report several classes of galactosyl analogues with varied substitution at the anomeric, C2-, C5-, and C6-positions. Significant increases in binding affinity were noted for several trifluoromethylacetamide derivatives without covalent attachment to the protein. A variety of new ligands were obtained with affinity for ASGPR as good as or better than that of the parent N-acetylgalactosamine, showing that modification on either side of the key C3,C4-diol moiety is well tolerated, consistent with previous models of a shallow binding pocket. The galactosyl pyranose motif therefore offers many opportunities for the attachment of other functional units or payloads while retaining low-micromolar or better affinity for the ASGPR.     

Reversible light switch for macrocycle mobility in a DNA rotaxane

A recent trend in DNA nanotechnology consists of the assembly of architectures with dynamic properties that can be regulated by employing external stimuli. Reversible processes are important for implementing molecular motion into DNA architectures as they allow for the regeneration of the original state. Here we describe two different approaches for the reversible switching of a double-stranded DNA rotaxane architecture from a stationary pseudorotaxane mode into a state with movable components. Both states only marginally differ in their respective topologies but their mechanical properties are fundamentally different. In the two approaches, the switching operation is based on strand-displacement reactions. One of them employs toehold-extended oligodeoxynucleotides whereas in the other one the switching is achieved by light-irradiation. In both cases, multiple back and forth switching between the stationary and the mobile states was achieved in nearly quantitative fashion. The ability to reversibly operate mechanical motion in an interlocked DNA nanostructure opens exciting new avenues in DNA nanotechnology.     

An acousto-optic beamformer

There is a great variety of beamforming techniques that can be used for localization of sound sources. The differences among them usually lie in the array layout or in the specific signal processing algorithm used to compute the beamforming output. Any beamforming system consists of a finite number of transducers, which makes beamforming methods vulnerable to spatial aliasing above a certain frequency. The present work uses the acousto-optic effect, i.e., the interaction between sound and light, to localize sound sources in a plane. The use of a beam of light as the sensing element is equivalent to a continuous line aperture with an infinite number of microphones. This makes the proposed acousto-optic beamformer immune to spatial aliasing. This unique feature is illustrated by means of simulations and experimental results within the entire audible frequency range. For ease of comparison, the study is supplemented with measurements carried out with a line array of microphones.     

On the Equations of Capillarity

Some conceptual ambiguities in the derivation of the equations of capillarity on the basis of the principle of virtual work are addressed, and hypotheses are proposed toward obtaining a physically correct characterization in general circumstances. It is shown that under the hypotheses, the classical equations of capillarity for an interface of an incompressible fluid with a fluid of negligible density can be obtained on the basis of global phenomenological reasoning, without recourse to consideration of intermolecular attractions. More generally, the procedure is applied to derive the specific equations arising from a compressible fluid configuration with idealized pressure-density relationship in a capillary tube, and a general necessary condition for existence of a solution is established. It is shown that for symmetric domains, the condition is also sufficient for existence of a unique symmetric solution.     

Plausible inferences and plausible reasoning

The paper focuses on the central aspect of any intelligentlike system: formal models of reasoning (plausible reasoning and plausible inference) and methods of mechanized implementation of these models in computer systems. A classification of inference types is presented and the historical development of the relevant theories is briefly reviewed. The so-called JSM method (for John Stuart Mill) of mechanized hypothesis generation is described in detail. This method is used in the plausible inference + reliable inference solver in logical information-computing systems.Translated from Itogi Nauki i Tekhniki, Seriya Teoriya Veroyatnostei, Matematicheskaya Statistika, Teoreticheskaya Kibernetika, Vol. 28, pp. 3–84, 1988.     

Non uniqueness and uniqueness of capillary surfaces

It is shown that for any gravity fieldg and contact angle, a containerC can be found which can be partially filled with liquid in a continuum of distinct ways, so as to obtain a one parameter familyF of capillary surface interfaces, no two of which are mutually congruent, and all of which bound the same liquid volume and yield the same mechanical energy. This answers affirmatively a question raised by Gulliver and Hildebrandt, who obtained such a container in the caseg=0,=/2. For a particular configuration inF, the second variation of energy is calculated and it is shown that-at least for small g- it can be made negative. As a consequence, a rotationally symmetric container deviating arbitrarily little from a circular cylinder is characterized, so that an energy minimizing configuration filling half the container exists but cannot be symmetric. Finally, a condition on rotationally symmetric container shapes is given, for the existence of a unique disk-type symmetric stationary surface. In the particular case of a spherical container in zero gravity, this surface is unique and minimizing among all disk-type surfaces with the given contact angle and enclosed volume.The major part of this work was completed while the author was visiting at the Max-Planck-Institut in Bonn. The work was also supported in part by grants from the Fulbright Commission, from the National Science Foundation, and from the National Aeronautics and Space AdministrationI wish to thank K. -S. Chua, P. Concus, M. Grüter, and R. Gulliver for helpful comments and discussions.