Extending the Colloidal Transition Metal Dichalcogenide Library to ReS2 Nanosheets for Application in Gas Sensing and Electrocatalysis

Among the large family of transition metal dichalcogenides, recently ReS₂ has stood out due to its nearly layer‐independent optoelectronic and physicochemical properties related to its 1T distorted octahedral structure. This structure leads to strong in‐plane anisotropy, and the presence of active sites at its surface makes ReS₂ interesting for gas sensing and catalysts applications. However, current fabrication methods use chemical or physical vapor deposition (CVD or PVD) processes that are costly, time‐consuming and complex, therefore limiting its large‐scale production and exploitation. To address this issue, a colloidal synthesis approach is developed, which allows the production of ReS₂ at temperatures below 360 °C and with reaction times shorter than 2h. By combining the solution‐based synthesis with surface functionalization strategies, the feasibility of colloidal ReS₂ nanosheet films for sensing different gases is demonstrated with highly competitive performance in comparison with devices built with CVD‐grown ReS₂ and MoS₂. In addition, the integration of the ReS₂ nanosheet films in assemblies together with carbon nanotubes allows to fabricate electrodes for electrocatalysis for H₂ production in both acid and alkaline conditions. Results from proof‐of‐principle devices show an electrocatalytic overpotential competitive with devices based on ReS₂ produced by CVD, and even with MoS₂, WS₂, and MoSe₂ electrocatalysts.     

Designer Shape Anisotropy on Transition‐Metal‐Dichalcogenide Nanosheets

MoS₂ and generally speaking, the wide family of transition‐metal dichalcogenides represents a solid nanotechnology platform on which to engineer a wealth of new and outperforming applications involving 2D materials. An even richer flexibility can be gained by extrinsically inducing an in‐plane shape anisotropy of the nanosheets. Here, the synthesis of anisotropic MoS₂ nanosheets is proposed as a prototypical example in this respect starting from a highly conformal chemical vapor deposition on prepatterend substrates and aiming at the more general purpose of tailoring anisotropy of 2D nanosheets by design. This is envisioned to be a suitable configuration for strain engineering as far as strain can be spatially redistributed in morphologically different regions. With a similar approach, both the optical and electronic properties of the 2D transition‐metal dichalcogenides can be tailored over macroscopic sample areas in a self‐organized fashion, thus paving the way for new applications in the field of optical metasurfaces, light harvesting, and catalysis.     

Functionalized Graphdiyne Nanowires: On‐Surface Synthesis and Assessment of Band Structure,Flexibility, and Information Storage Potential

Carbon nanomaterials exhibit extraordinary mechanical and electronic properties desirable for future technologies. Beyond the popular sp²‐scaffolds, there is growing interest in their graphdiyne‐related counterparts incorporating both sp² and sp bonding in a regular scheme. Herein, we introduce carbonitrile‐functionalized graphdiyne nanowires, as a novel conjugated, one‐dimensional (1D) carbon nanomaterial systematically combining the virtues of covalent coupling and supramolecular concepts that are fabricated by on‐surface synthesis. Specifically, a terphenylene backbone is extended with reactive terminal alkyne and polar carbonitrile (CN) moieties providing the required functionalities. It is demonstrated that the CN functionalization enables highly selective alkyne homocoupling forming polymer strands and gives rise to mutual lateral attraction entailing room‐temperature stable double‐stranded assemblies. By exploiting the templating effect of the vicinal Ag(455) surface, 40 nm long semiconducting nanowires are obtained and the first experimental assessment of their electronic band structure is achieved by angle‐resolved photoemission spectroscopy indicating an effective mass below 0.1m₀ for the top of the highest occupied band. Via molecular manipulation it is showcased that the novel oligomer exhibits extreme mechanical flexibility and opens unexplored ways of information encoding in clearly distinguishable CN‐phenyl trans–cis species. Thus, conformational data storage with density of 0.36 bit nm^?2 and temperature stability beyond 150 K comes in reach.     

A pattern classification proposal for object‐oriented audio coding in MPEG‐4

The future MPEG4 standard will adopt an objectoriented encoding strategy whereby an audio source is encoded at a very low bitrate by adapting a suitable coding scheme to the local characteristics of the signal. One of the most delicate issues in this approach is that the overall performance of the audio encoder greatly depends on the accuracy with which the input signal is classified. This paper shows that the difficult problem of audio classification for objectoriented coding can be effectively solved by selecting a salient set of acoustic parameters and adopting a fuzzy model for each audio object, obtained by a soft computinghybrid learning tool. The audio classifier proposed operates at two levels: recognition of the class to which the input signal belongs (talkspurt, music, noise, signaling tones) and then recognition of the subclass to which it belongs. The results obtained show that fuzzy logic is a valid alternative to the matching techniques of a traditional pattern recognition approach.     

Does antisymmetry matter in b.c.c. 3He crystals?

By comparing the results of both variational and exact Diffusion Monte Carlo (DMC) results for states of different symmetries we conclude that antisymmetry plays a fundamental role in stabilizing the b.c.c. ³ He crystal. We performed calculations for a system of 54 particles of mass 3 at density = 0.02557 Å, just above the experimental freezing point. Symmetric (Jastrow and Shadow wave functions) and unsymmetrized wave functions (of the Nosanow-Jastrow type), fail to describe the system. In particular, a shadow wave function predicts a fluid as lowest energy state at the density considered, and this is confirmed by the computation of the exact symmetric ground state with DMC, which predicts an energy well below the experimental energy of the crystal. On the other hand, DMC calculations projecting the ground state in the space of the Nosanow–Jastrow functions, give an energy which is much above the experimental energy. The use of antisymmetric functions, and in particular of the recently introduced Fermionic Shadow Wave Function (FSWF), leads to the prediction that the b.c.c. crystal is the stable ground state. Antisymmetry plays therefore a fundamental role in this system. FSWF calculations also demonstrate the peculiar characteristics of this crystal (very low order parameter, a non Gaussian density profile around the lattice sites, and very wide vibrations of the atoms around the lattice sites, small dependence of the energy with respect to the magnetic order), which cannot be seen in the Nosanow framework.     

State space reduction by non-standard semantics for deadlock analysis

In recent years many techniques have been developed for automatically verifying concurrent systems and most of them are based on the representation of the concurrent system by means of a transition system. State explosion is one of the most serious problems of this approach: often the prohibitive number of states renders the verification inefficient and, in some cases, impossible.

We propose a method for reducing the state space of the transition system corresponding to a CCS process that suites deadlock analysis. The reduced transition system is generated by means of a non-standard operational semantics containing a set of rules which are, in some sense, an abstraction, preserving deadlock freeness, of the inference rules of the standard semantics. Our method does not build the standard transition system, but directly generates an abstract system with a fewer number of states, so saving memory space. We characterize a class of processes whose abstract transition system is not exponential in the number of parallel components.     

A constraint-based querying system for exploratory pattern discovery

In this article we present ConQueSt, a constraint-based querying system able to support the intrinsically exploratory (i.e., human-guided, interactive and iterative) nature of pattern discovery. Following the inductive database vision, our framework provides users with an expressive constraint-based query language, which allows the discovery process to be effectively driven toward potentially interesting patterns. Such constraints are also exploited to reduce the cost of pattern mining computation. ConQueSt is a comprehensive mining system that can access real-world relational databases from which to extract data. Through the interaction with a friendly graphical user interface (GUI), the user can define complex mining queries by means of few clicks. After a pre-processing step, mining queries are answered by an efficient and robust pattern mining engine which entails the state-of-the-art of data and search space reduction techniques. Resulting patterns are then presented to the user in a pattern browsing window, and possibly stored back in the underlying database as relations.     

On the complexity of constrained Nash equilibria in graphical games

A widely accepted rational behavior for non-cooperative players is based on the notion of Nash equilibrium. Although the existence of a Nash equilibrium is guaranteed in the mixed framework (i.e., when players select their actions in a randomized manner) in many real-world applications the existence of “any” equilibrium is not enough. Rather, it is often desirable to single out equilibria satisfying some additional requirements (in order, for instance, to guarantee a minimum payoff to certain players), which we call constrained Nash equilibria.In this paper, a formal framework for specifying these kinds of requirement is introduced and investigated in the context of graphical games, where a player p may directly be interested in some of the other players only, called the neighbors of p. This setting is very useful for modeling large population games, where typically each player does not directly depend on all the players, and representing her utility function extensively is either inconvenient or infeasible.Based on this framework, the complexity of deciding the existence and of computing constrained equilibria is then investigated, in the light of evidencing how the intrinsic difficulty of these tasks is affected by the requirements prescribed at the equilibrium and by the structure of players’ interactions. The analysis is carried out for the setting of mixed strategies as well as for the setting of pure strategies, i.e., when players are forced to deterministically choose the action to perform. In particular, for this latter case, restrictions on players’ interactions and on constraints are identified, that make the computation of Nash equilibria an easy problem, for which polynomial and highly-parallelizable algorithms are presented.     

Closed-loop Live Marked Graphs under Generalized Mutual Exclusion Constraint Enforcement

Enforcing a supervisory control policy to avoid forbidden states on a discrete event system modeled by a Petri net may result in a non live system. This may happen even if the admissible states are specified by Generalized Mutual Exclusion Constraints (GMECs). This leads to the problem of synthesizing a maximally permissive control policy preserving liveness of the system under a GMEC. This problem is very interesting in practice, but difficult even for a restricted class of systems. In this paper, we focus on systems which can be modeled as live and safe Marked Graphs (MGs). On such systems, when some of the transitions are uncontrollable, a GMEC can be forced by a monitor place if a not maximally permissive policy is accepted, otherwise a more complex control has to be adopted. Anyway, liveness of the closed-loop system (plant plus control) is not guaranteed. Two sufficient conditions to verify the closed-loop liveness of a live and safe MG plant controlled by a monitor are derived. A sufficient condition for closed loop liveness of MGs where a GMEC has been enforced on is derived. In addition, a set of predicates is provided that enforces, in a maximally permissive way, a GMEC while preserving closed-loop liveness on live and safe MG systems under some restrictions.