On the 1/f frequency noise in ultra-stable quartz oscillators

The frequency flicker of an oscillator, which appears as a 1/f3 line in the phase noise spectral density, and as a floor on the Allan deviation plot, originates from two basic phenomena, namely, (1) the 1/f phase noise turned into 1/f frequency noise via the Leeson effect, and (2) the 1/f fluctuation of the resonator natural frequency. The discussion on which is the dominant effect, thus on how to improve the stability of the oscillator, has been going on for years without giving a clear answer. This article tackles the question by analyzing the phase noise spectrum of several commercial oscillators and laboratory prototypes, and demonstrates that the fluctuation of the resonator natural frequency is the dominant effect. The investigation method starts from reverse engineering the oscillator phase noise in order to show that if the Leeson effect was dominant, the resonator merit factor Q would be too low as compared to the available technology.     

Recent Developments in the Stereoselective Synthesis of Nitrogen‐Containing Heterocycles using N‐Acylimines as Reactive Substrates

This report focuses on the utilization of N‐acylimines in addition reactions aimed at the preparation of heterocyclic compounds. These can be directly obtained by reaction of N‐acylimines with suitable nucleophilic reagents or prepared by further elaboration of the initially formed adducts. The asymmetric synthesis of these hetero‐ and polyheterocyclic derivatives is mostly achieved using chiral catalyzed reactions, including the recently introduced enantioselective Biginelli reaction. Applications of isatin ketimines to the stereoselective preparation of biologically active spiroxindole compounds are also reported.

     

A Virtual Reality Experiment on Flashing Lights at Emergency Exit Portals for Road Tunnel Evacuation

A virtual reality (VR) experiment with 96 participants was carried out to provide recommendations on the design of flashing lights at emergency exit portals for road tunnel emergency evacuation. The experiment was carried out in a Cave Automatic Virtual Environment laboratory. A set of variables was investigated, namely (1) colour of flashing lights, (2) flashing rate, (3) type of light source, (4) number and layout of the lights on the portal. Participants were immersed in a VR road tunnel emergency evacuation scenario and they were then asked to rank different portal designs using a questionnaire based on the Theory of Affordances. Results show that green or white flashing lights perform better than blue lights. A flashing rate of 1 and 4 Hz performed better than a flashing rate of 0.25 Hz. A light emitting diode light source performed better than single and double strobe lights. The three layouts of the lights under consideration performed similarly.     

The combined use of resilience and loop diameter uniformity as a good indirect measure of network reliability

The aim of this paper is to show that the combined use of the resilience index (Todini, 2000) with a loop based diameter uniformity index (here formulated) yields a good indirect reliability measure, which can be conveniently used within the optimization processes of the water distribution system design. The methodology adopted to show the advantages of the combined use of the two indexes consists of (a) a three-objective optimization performed in order to simultaneously minimize costs (first objective function) and maximize both the resilience and the loop diameter uniformity indexes (second and third objective functions respectively); (b) a retrospective assessment of performance indicators relative to critical operational scenarios on the solutions of the Pareto surface obtained at the end of the optimization process. Applications were performed considering a simple case study, which made it possible to easily compare the new approach, based on a three-objective optimization, with the two-objective optimization process based on the use of the resilience index alone and also with the two-objective optimization process based on the modified resilience index formulated by Prasad, Sung-Hoon, and Namsik (2003) (where the diameter uniformity is defined at nodal level and inserted as a weight in Todini's resilience index), being both indexes a surrogate to reliability. The comparison pointed out that using resilience and loop diameter uniformity as two separate objective functions in an optimization process leads to solutions which perform better during critical operational scenarios (particularly when dealing with segment isolation) than the equally expensive solutions obtained adopting the resilience index (independently of its formulation) alone as reliability related objective function. Since the proposed approach suggests that a three-objective optimization be utilized to perform an appropriate pipe-network optimal design, an improvement in the well-known NSGA-II algorithm (Deb, Pratap, Agarwal, & Meyarivan, 2002) is proposed as its original formulation proved to have some difficulties dealing with more than two objectives.     

Correlation-induced Suppression of Bilayer Splitting in High-T c Cuprates: A Variational Cluster Approach

We carry out a theoretical study of the bilayer single-band Hubbard model in the undoped and in the superconducting phases by means of the variational cluster approach. In particular, we focus on the splitting between the ??bonding?? and ??antibonding?? bands induced by the interlayer hopping, as well as its interplay with strong correlation effects. We find that the splitting is considerably suppressed in both the normal and superconducting phases, in qualitative agreement with experiments on Bi₂Sr₂CaCu₂O_8+?? . In addition, in the superconducting phase, the shape of the splitting in k space is modified by correlations.     

Schnyder Decompositions for Regular Plane Graphs and Application to Drawing

Schnyder woods are decompositions of simple triangulations into three edge-disjoint spanning trees crossing each other in a specific way. In this article, we generalize the definition of Schnyder woods to d-angulations (plane graphs with faces of degree d) for all d≥3. A Schnyder decomposition is a set of d spanning forests crossing each other in a specific way, and such that each internal edge is part of exactly d?2 of the spanning forests. We show that a Schnyder decomposition exists if and only if the girth of the d-angulation is d. As in the case of Schnyder woods (d=3), there are alternative formulations in terms of orientations (“fractional” orientations when d≥5) and in terms of corner-labellings. Moreover, the set of Schnyder decompositions of a fixed d-angulation of girth d has a natural structure of distributive lattice. We also study the dual of Schnyder decompositions which are defined on d-regular plane graphs of mincut d with a distinguished vertex v ^?: these are sets of d spanning trees rooted at v ^? crossing each other in a specific way and such that each edge not incident to v ^? is used by two trees in opposite directions. Additionally, for even values of d, we show that a subclass of Schnyder decompositions, which are called even, enjoy additional properties that yield a reduced formulation; in the case d=4, these correspond to well-studied structures on simple quadrangulations (2-orientations and partitions into 2 spanning trees). In the case d=4, we obtain straight-line and orthogonal planar drawing algorithms by using the dual of even Schnyder decompositions. For a 4-regular plane graph G of mincut 4 with a distinguished vertex v ^? and n?1 other vertices, our algorithms places the vertices of Gv ^? on a (n?2)×(n?2) grid according to a permutation pattern, and in the orthogonal drawing each of the 2n?4 edges of Gv ^? has exactly one bend. The vertex v ^? can be embedded at the cost of 3 additional rows and columns, and 8 additional bends. We also describe a further compaction step for the drawing algorithms and show that the obtained grid-size is strongly concentrated around 25n/32×25n/32 for a uniformly random instance with n vertices.     

A cost-effective cloud computing framework for accelerating multimedia communication simulations

Multimedia communication research and development often requires computationally intensive simulations in order to develop and investigate the performance of new optimization algorithms. Depending on the simulations, they may require even a few days to test an adequate set of conditions due to the complexity of the algorithms. The traditional approach to speed up this type of relatively small simulations, which require several develop–simulate–reconfigure cycles, is indeed to run them in parallel on a few computers and leaving them idle when developing the technique for the next simulation cycle. This work proposes a new cost-effective framework based on cloud computing for accelerating the development process, in which resources are obtained on demand and paid only for their actual usage. Issues are addressed both analytically and practically running actual test cases, i.e., simulations of video communications on a packet lossy network, using a commercial cloud computing service. A software framework has also been developed to simplify the management of the virtual machines in the cloud. Results show that it is economically convenient to use the considered cloud computing service, especially in terms of reduced development time and costs, with respect to a solution using dedicated computers, when the development time is longer than one hour. If more development time is needed between simulations, the economic advantage progressively reduces as the computational complexity of the simulation increases.     

A history of AI and Law in 50 papers: 25?years of the international conference on AI and Law

We provide a retrospective of 25?years of the International Conference on AI and Law, which was first held in 1987. Fifty papers have been selected from the thirteen conferences and each of them is described in a short subsection individually written by one of the 24 authors. These subsections attempt to place the paper discussed in the context of the development of AI and Law, while often offering some personal reactions and reflections. As a whole, the subsections build into a history of the last quarter century of the field, and provide some insights into where it has come from, where it is now, and where it might go.     

Organocatalytic Enantioselective Decarboxylative Addition of Malonic Half Thioesters to Imines

We describe a biomimetic organocatalytic enantioselective decarboxylative addition of malonic acid half thioesters to imines. This simple protocol makes use of readily available Cinchona‐derived organocatalysts and nucleophiles at the carboxylate oxidation state. The resulting β‐amino thioesters, being attractive precursors for the preparation of optically active β‐amino acids, are formed in good yields and in up to 79 % ee. As suggested by several mechanistic insights the desired products are formed via initial formation of a thioester acetate enolate via decarboxylation of the malonic acid half thioester, followed by addition to the imine.