featuring metallic surface states surrounding an insulating bulk. The associated unique electronic structure of the helical Dirac surface states results in many exotic physical properties, such as the topological magneto-electric effect, [6] Majorana fermions, [7] and the quantum anomalous Hall effect. [8] However, because of the low formation energy of intrinsic defects, [9] the resulting bulk conductivity often obscures or even suppresses the desired TI behavior. [10][11][12] The realization of these novel topological phases requires high-quality TI thin films with sufficiently low defect concentration, typically obtained by molecular beam epitaxy growth. [13] Chemical vapor deposition (CVD) and polyol methods, which offer facile and cost-effective synthetic routes promising for large-scale device applications, have also received interest with successful demonstrations of the ambipolar field effect, [14] Aharonov-Bohm, [15,16] and Shubnikov-de Hass [17] oscillations in (Bi x Sb 1−x ) 2 Te 3 nano plates, as well as in Bi 2 Se 3 and Be 2 Te 3 nanoribbons. Nevertheless, the quantum Hall effect as a hallmark of Dirac surface states [18] has not yet been realized in these TI nanostructures. One possible reason might be the appreciable bulk conduction associated with Topological insulators (TIs) are quantum materials with topologically protected surface states surrounding an insulating bulk. However, defectinduced bulk conduction often dominates transport properties in most TI materials, obscuring the Dirac surface states. In order to realize intrinsic topological insulating properties, it is thus of great significance to identify the spatial distribution of defects, understand their formation mechanism, and finally control or eliminate their influence. Here, the electronic heterogeneity in polyol-synthesized Bi 2 Se 3 and chemical vapor deposition-grown Sb 2 Te 3 nanocrystals is systematically investigated by multimodal atomicto-mesoscale resolution imaging. In particular, by combining the Drude response sensitivity of infrared scattering-type scanning near-field optical microscopy with the work-function specificity of mirror electron microscopy, characteristic mesoscopic patterns are identified, which are related to carrier concentration modulation originating from the formation of defects during the crystal growth process. This correlative imaging and modeling approach thus provides the desired guidance for optimization of growth parameters, crucial for preparing TI nanomaterials to display their intrinsic exotic Dirac properties.Topological Insulators

We use Chu spaces and an algebra of them to give a denotational semantics of a subset of BPEL. The emphasis is on the scope-based fault handling mechanism. We propose BPEL-F as an abstraction of the subset of BPEL including typical control flow and fault handling. Chu spaces form the main semantic domain. We study the influence of fault handling to the algebraic operators of Chu spaces. and present modified versions of the sequence and concurrence operators. The trigger operator is designed to model the scope-based fault handling. We present valuation functions mapping BPEL-F constructs to Chu spaces.

We present a Chu spaces semantics of typical control flow of BPEL including fault handling and link semantics. BPEL cf is proposed as a simplification of this subset of BPEL. For the compositional modeling of BPEL, we present a Chu spaces process algebra consisting of seven operators. These operators allow faults to be thrown at any point of execution and take link-based synchronization into consideration. We present the abstract syntax of BPEL cf , the semantic algebra, and the valuation functions for computing the Chu spaces denotation of BPEL cf programs. The valuation functions are straightforward because of the power of the Chu spaces process algebra.

Finite Chu spaces are proposed for the modeling and verification of concurrent programs. In order to model not only typical concurrent behaviors but also modern exception handling and synchronization mechanisms, we design an enriched process algebra of Chu spaces from a practical point of view. To illustrate the power of finite Chu spaces and the process algebra while abstracting away from language-specific details, an imaginary concurrent programming language (ICL) is designed. A denotational semantics of ICL is presented using finite Chu spaces and the enriched process algebra. The valuation functions are fairly straightforward since the carefully designed operators have done much of the job. The enriched process algebra is also used as the specification language for Chu spaces, with which process-algebraic properties can be specified. Verification algorithms are presented with their time complexities discussed.

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This paper presents a Chu spaces semantics of typical control flow of WS-BPEL including fault handling and link semantics. BPEL-CF is proposed as a simplification of this subset of WS-BPEL. For the compositional modeling of BPEL, the authors present a Chu spaces process algebra. This algebra allows faults to be thrown at any point of execution and take link-based synchronization into consideration. The paper gives the abstract syntax of BPEL-CF, the semantic algebra, and the valuation functions for computing the Chu spaces denotations of BPEL-CF programs.

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