An Alloy Verification Model for Consensus-Based Auction Protocols

Max Consensus-based Auction (MCA) protocols are an elegant approach to establish conflict-free distributed allocations in a wide range of network utility maximization problems. A set of agents independently bid on a set of items, and exchange their bids with their first hop-neighbors for a distributed (max-consensus) winner determination. The use of MCA protocols was proposed, $e.g.$, to solve the task allocation problem for a fleet of unmanned aerial vehicles, in smart grids, or in distributed virtual network management applications. Misconfigured or malicious agents participating in a MCA, or an incorrect instantiation of policies can lead to oscillations of the protocol, causing, $e.g.$, Service Level Agreement (SLA) violations. In this paper, we propose a formal, machine-readable, Max-Consensus Auction model, encoded in the Alloy lightweight modeling language. The model consists of a network of agents applying the MCA mechanisms, instantiated with potentially different policies, and a set of predicates to analyze its convergence properties. We were able to verify that MCA is not resilient against rebidding attacks, and that the protocol fails (to achieve a conflict-free resource allocation) for some specific combinations of policies. Our model can be used to verify, with a "push-button" analysis, the convergence of the MCA mechanism to a conflict-free allocation of a wide range of policy instantiations

Shortest path and maximum flow problems in planar flow networks with additive gains and losses

In contrast to traditional flow networks, in additive flow networks, to every edge e is assigned a gain factor g(e) which represents the loss or gain of the flow while using edge e. Hence, if a flow f(e) enters the edge e and f(e) is less than the designated capacity of e, then f(e) + g(e) = 0 units of flow reach the end point of e, provided e is used, i.e., provided f(e) != 0. In this report we study the maximum flow problem in additive flow networks, which we prove to be NP-hard even when the underlying graphs of additive flow networks are planar. We also investigate the shortest path problem, when to every edge e is assigned a cost value for every unit flow entering edge e, which we show to be NP-hard in the strong sense even when the additive flow networks are planar

Synthesis and Structural Analysis of Macrocyclic Arenes: Experimental and Computational Insights

Synthesis, properties and applications of macrocyclic molecules have been one ofthe interesting branches of organic chemistry during the past century. Several classes ofmacrocyclic molecules, based on their repeating unit and connectivity pattern, have beendiscovered. Macrocyclic arenes, cyclo[n]veratrylenes, calix[n]arenes and pillar[n]arenes,were among the most interesting and studied molecules. The major difference betweenthese molecules is the methylene-bridged connectivity pattern. In the present thesis, Iattempted to synthesize these molecules using novel approach which has been developedin our group and performing some structural analysis using experimental andcomputational techniques.The first synthesized and investigated molecule is the cyclotetraveratrylene(CTTV) which has the ortho (1,2) methylene-bridged connectivity pattern. This moleculeshowed conformational flexibility at the room temperature. This phenomenon intrigued usto investigate its conformational changes upon the one-electron oxidation. The results ofboth experimental and computational studies revealed that the most stable conformer ofthis molecule is different in the neutral (sofa) and cation-radical (boat) states. However,due to instability of the cation-radical structure we have not been able to isolate the crystalstructure of this system.The second synthesized molecules possessing the meta (1,3) methylene-bridgedconnectivity pattern, calix[4]arenes. Herein, I synthesized a series of calix[4]arenes withdifferent substituents to show how the solvent environment and crystal packing forces cantotally change the most stable conformation of these molecules. The results revealed thatin the solution the 1,3-alternate is the most stable conformer, however, in the solid state,the boat is more stable. This phenomenon can be attributed to the intermolecular interactionof calix[4]arenes in the solution with the solvent molecules and in the solid states as theinter-calix[4]arene-calix[4]arene interactions.Pillar[n]arenes are the third class of macrocyclic arenes that were investigated inthis study which have para (1,4) methylene-bridged connectivity pattern. Since the fortuitusdiscovery of pillar[5]arne in 2008, selective synthesis of higher sizes (n \u3e 5) has remainedas an intriguing challenge for organic chemists around the world. Herein, I developed anovel synthetic method which can help us to synthesize pillar[n]arenes (n = 5, 6) selectivelywith high yield. The experimental and computational results indicated that the solvent hassignificant role in the size of the synthesized product. While the dichloromethane cangenerate more pillar[5]arene, using chloroform as the solvent can lead to pillar[6]arene asthe dominant product. This effect can be attributed to the templating effect of the solvent

A theory of flow network typings and its optimization problems

Many large-scale and safety critical systems can be modeled as flow networks. Traditional approaches for the analysis of flow networks are whole-system approaches in that they require prior knowledge of the entire network before an analysis is undertaken, which can quickly become intractable as the size of network increases. In this thesis we study an alternative approach to the analysis of flow networks, which is modular, incremental and order-oblivious. The formal mechanism for realizing this compositional approach is an appropriately defined theory of network typings. Typings are formalized differently depending on how networks are specified and which of their properties is being verified. We illustrate this approach by considering a particular family of flow networks, called additive flow networks. In additive flow networks, every edge is assigned a constant gain/loss factor which is activated provided a non-zero amount of flow enters that edge. We show that the analysis of additive flow networks, more specifically the max-flow problem, is NP-hard, even when the underlying graph is planar. The theory of network typings gives rise to different forms of graph decomposition problems. We focus on one problem, which we call the graph reassembling problem. Given an abstraction of a flow network as a graph G = (V,E), one possible definition of this problem is specified in two steps: (1) We cut every edge of G into two halves to obtain a collection of |V| one-vertex components, and (2) we splice the two halves of all the edges, one edge at a time, in some order that minimizes the complexity of constructing a typing for G, starting from the typings of its one-vertex components. One optimization is minimizing “maximum” edge-boundary degree of components encountered during the reassembling of G (denoted as α measure). Another is to minimize the “sum” of all edge-boundary degrees encountered during this process (denoted by β measure). Finally, we study different variations of graph reassembling (with respect to minimizing α or β) and their relation with problems such as Linear Arrangement, Routing Tree Embedding, and Tree Layout

Using alloy to formally model and reason about an OpenFlow network switch

Openflow provides a standard interface for separating a network into a data plane and a programmatic control plane. This enables easy network reconfiguration, but introduces the potential for programming bugs to cause network effects. To study OpenFlow switch behavior, we used Alloy to create a software abstraction describing the internal state of a network and its OpenFlow switches. This work is an attempt to model the static and dynamic behaviour a network built using OpenFlow switches

Improving Performance of the SMD Solvation Model: Bondi Radii Improve Predicted Aqueous Solvation Free Energies of Ions and pK\u3csub\u3ea\u3c/sub\u3e Values of Thiols

Calculation of the solvation free energy of ionic molecules is the principal source of errors in the quantum chemical evaluation of pKa values using implicit polarizable continuum solvent models. One of the important parameters affecting the performance of these models is the choice of atomic radii. Here, we assess the performance of the solvation model based on density (SMD) implicit solvation model employing SMD default radii (SMD) and Bondi radii (SMD-B), a set of empirical atomic radii developed based on the crystallographic data. For a set of 112 ions (60 anions and 52 cations), the SMD-B model showed lower mean unsigned error (MUE) for predicted aqueous solvation free energies (4.0 kcal/mol for anions and 2.4 kcal/mol for cations) compared to the standard SMD model (MUE of 5.0 kcal/mol for anions and 2.9 kcal/mol for cations). In particular, usage of Bondi radii improves the aqueous solvation energies of sulfur-containing ions by \u3e5 kcal/mol compared to the SMD default radii. Indeed, for a set of 45 thiols, the SMD-B model was found to dramatically improve the predicted pKa values, with ∼1 pKa unit mean deviation from the experimental values, compared to ∼7 pKa units mean deviation for the SMD model with the default radii. These findings highlight the importance of the choice of atomic radii on the performance of the implicit solvation models

An Electron‐Rich Calix[4]arene‐Based Receptor with Unprecedented Binding Affinity for Nitric Oxide

Calixarenes have found widespread application as building blocks for the design and synthesis of functional materials in host–guest chemistry. The ongoing desire to develop a detailed understanding of the nature of NO bonding to multichromophoric π‐stacked assemblies led us to develop an electron‐rich methoxy derivative of calix[4]arene (3), which we show exists as a single conformer in solution at ambient temperature. Here, we examine the redox properties of this derivative, generate its cation radical (3+.) using robust chemical oxidants, and determine the relative efficacy of its NO binding in comparison with model calixarenes. We find that 3/3+. is a remarkable receptor for NO+/NO, with unprecedented binding efficacy. The availability of precise experimental structures of this calixarene derivative and its NO complex, obtained by X‐ray crystallography, is critically important both for developing novel functional NO biosensors, and understanding the role of stacked aromatic donors in efficient NO binding, which may have relevance to biological NO transport

Molecular Actuators in Action: Electron-Transfer-Induced Conformation Transformation in Cofacially Arrayed Polyfluorenes

There is much current interest in the design of molecular actuators, which undergo reversible, controlled motion in response to an external stimulus (light, heat, oxidation, etc.). Here we describe the design and synthesis of a series of cofacially arrayed polyfluorenes (MeFnHm) with varied end-capping groups, which undergo redox-controlled electromechanical actuation. Such cofacially arrayed polyfluorenes are a model molecular scaffold to investigate fundamental processes of charge and energy transfer across a π-stacked assembly, and we show with the aid of NMR and optical spectroscopies, X-ray crystallography and DFT calculations that in the neutral state the conformation of MeFnH1 and MeFnH2 is open rather than cofacial, with a conformational dependence that is highly influenced by the local environment. Upon (electro)chemical oxidation, these systems undergo a reversible transformation into a closed fully π-stacked conformation, driven by charge-resonance stabilization of the cationic charge. These findings are expected to aid the design of novel wire-like cofacially arrayed systems capable of undergo redox-controlled actuation

Multiobjective and Simultaneous Two-Problem Allocation of a Hybrid Solar-Wind Energy System Joint with Battery Storage Incorporating Losses and Power Quality Indices

In this paper, a multiobjective and simultaneous two-problem allocation of a hybrid distributed generation (HDG) system comprises of solar panels, wind turbines, and battery storage is proposed in a 33-bus unbalanced distribution network which can decrease total losses and improve power quality (PQ). The PQ indices are defined as voltage swell, total harmonic distortion, voltage sag, and voltage unbalance. In this study, the two problems of hybrid system design and its allocation in the distribution network are solved simultaneously. In the allocation problem, the HDG is placed ideally in the network to reduce energy losses and enhance PQ indices. The HDG is measured to minimize the cost of energy generation, including the initial investment, maintenance, and operation costs. The decision variable including the size of HDG components and its location is optimally determined via escaping bird search (EBS) algorithm which is inspired by the maneuvers of the swift bird to avoid predation. The results cleared that the proposed methodology using the wind and solar resources integrated with battery storage reduced the losses, voltage swell, total harmonic distortion, voltage sag, and voltage unbalance by 34.31%, 49.60%, 0.25%, 40.19%, and 2.18%, respectively, than the base network via the EBS and the results demonstrated the better network performance using all renewable resources against wind or solar application only. The outcomes demonstrated the superiority of the EBS in achieving the highest improvement of the different objectives compared with particle swarm optimization (PSO) and manta ray foraging optimization (MRFO). Moreover, the superior capability of the EBS-based methodology is proved in comparison with previous studies