How to Play Optimally for Regular Objectives?

This paper studies two-player zero-sum games played on graphs and makes contributions toward the following question: given an objective, how much memory is required to play optimally for that objective? We study regular objectives, where the goal of one of the two players is that eventually the sequence of colors along the play belongs to some regular language of finite words. We obtain different characterizations of the chromatic memory requirements for such objectives for both players, from which we derive complexity-theoretic statements: deciding whether there exist small memory structures sufficient to play optimally is NP-complete for both players. Some of our characterization results apply to a more general class of objectives: topologically closed and topologically open sets.Comment: Full version of ICALP 2023 conference paper. 28 pages, 8 figure

SYNTHESIS AND EVALUATION OF METAL-SILICA CORE-SHELL NANOMATERIALS FOR CATALYSIS

Nanocatalysts have drawn considerable interest because of their high selectivity and reactivity compared with conventional catalysts. However, the catalyst deactivation due to the sintering under moderate/high temperature operation and coke formation in hydrocarbon participating systems poses a challenge for their usage. Our work focuses on solving the above issues by designing and developing a series of metal core silica shell materials. The fundamental understanding of core shell materials is facilitated by systematic investigation via synthesis, characterization (XRD, TEM, BET, EDX) and catalytic tests (CO oxidation, ethylene hydrogenation, CO methanation and catalytic partial oxidation of methane). The synthesis and post-treatment methods for this newly developed core shell material are optimized and standardized. We demonstrate fine control over the key structural elements of nickel core silica shell material. Two different nickel core silica shell structures are obtained with the distinction of a pronounced cavity in the core. The synthesis route is not limited to nickel particles, but also applied for a range of other metals (e.g. Cu, Co, Pd). The pore size of silica shell is around ~1nm independent of the shell thickness and structure difference. The thermal stability of nickel particles as a function of particle size as well as silica support is thoroughly studied. The nickel particles in core shell materials are stabilized under 5nm up to 1000C with the comparison of strong sintering of unprotected nickel particles beyond 10nm as low as 500C. The stable core shell material not only shows its advantage for stable operation under high temperature reactive condition (>800C), but also possesses the highly coking resistant property in fuel participating reactions. Even though the presence of silica shell is beneficial for improving stability of nickel particles, it brings up significant mass transfer limitation when shell thickness is beyond 10nm. We not only demonstrate the capability to synthesize the well controlled nanocatalysts with high temperature stability and minimal mass transfer limitation, but also understand the structure correlated reactivity in several reaction systems. Additionally, we highlight the correlation between sintering, mass transfer and coking properties of the catalysts

Aspects of the constructive omega rule within automated deduction

In general, cut elimination holds for arithmetical systems with the w -rule, but not for systems with ordinary induction. Hence in the latter, there is the problem of generalisation, since arbitrary formulae can be cut in. This makes automatic theorem -proving very difficult. An important technique for investigating derivability in formal systems of arithmetic has been to embed such systems into semi- formal systems with the w -rule. This thesis describes the implementation of such a system. Moreover, an important application is presented in the form of a new method of generalisation by means of "guiding proofs" in the stronger system, which sometimes succeeds in producing proofs in the original system when other methods fail

Aberration corrected (S)TEM of Nanoparticle and Atomically Dispersed Catalysts

The field of catalysis is of paramount importance. Catalysts allow chemical reactions to be carried out with lower energy than otherwise possible. They play an important role in the reduction of harmful emissions from todays vehicles and are crucial for designing alternative energy sources for tomorrows vehicles. Many catalysts take the form of nano-sized particles which brings about challenges for their design and characterisation. In this thesis, aberration corrected electron microscopy is utilised for atomically resolved investigations of the structure of catalytically active nanoparticles as freshly produced and to provide insights of deactivation in treated and used catalysts. Platinum and palladium nanoparticles are used for the reduction of harmful emissions from diesel car exhausts. Here, fresh insights are provided into the loss of activity in genuine road aged diesel oxidation catalysts. They include the segregation of alloys in the bimetallic variant in which the less active palladium moves to the surface where it can more easily form an oxide. Nano-beam diffraction was used in this study as well as for a model platinum system. The seldom used nano-beam diffraction technique was employed to provide additional structural information on very small nanoparticles, including those that contained defects. Using nano-beam diffraction, no oxides were found in the platinum model catalyst and loss of activity was due to sintering. Ex-situ studies can only provide before and after information. Here, results from the latest developments in environmental scanning transmission electron microscopy are presented with model catalysts, namely atomically dispersed platinum and palladium. Single atoms of the metals were observed at temperatures as high as 500 degree-celsius and in O2 which represents the current state of the art in this field. The limitations of the Z contrast technique is also investigated for heavy atoms located on heavy supports, such as atomically dispersed gold on ceria. Intricacies in the reduction of Co3O4 to CoO are provided using in-situ transmission electron microscopy in H2 at elevated temperatures. A new fuse wire like transformation is seen in large crystals in addition to dislocations to accomodate strain into the crystal structure