Oscillator phase noise: a tutorial

Linear time-invariant (LTI) phase noise theories provide important qualitative design insights but are limited in their quantitative predictive power. Part of the difficulty is that device noise undergoes multiple frequency translations to become oscillator phase noise. A quantitative understanding of this process requires abandoning the principle of time invariance assumed in most older theories of phase noise. Fortunately, the noise-to-phase transfer function of oscillators is still linear, despite the existence of the nonlinearities necessary for amplitude stabilization. In addition to providing a quantitative reconciliation between theory and measurement, the time-varying phase noise model presented in this tutorial identifies the importance of symmetry in suppressing the upconversion of 1/f noise into close-in phase noise, and provides an explicit appreciation of cyclostationary effects and AM-PM conversion. These insights allow a reinterpretation of why the Colpitts oscillator exhibits good performance, and suggest new oscillator topologies. Tuned LC and ring oscillator circuit examples are presented to reinforce the theoretical considerations developed. Simulation issues and the accommodation of amplitude noise are considered in appendixes

Land use patterns and access in Mexico City

The problem of distribution of land uses in urban space in Latin American cities has been examined under different perspectives. Most authors tend to model patterns of population and land use as a consequence of social and economic processes alone, failing to address urban space as an intrinsic variable. Instead, the theory of cities as movement economies argues that land use patterns are influenced by movement flows, which are in turn strongly affected by the urban grid. As a result, land uses such as retail would seek highly accessible locations to take advantage of such flows while residential uses would avoid them. However, space syntax techniques traditionally used to point out this relationship do not seem to reveal it so easily in non-organic cities like Mexico. This paper addresses the relationship between patterns of accessibility and land use in the first ring of Mexico City as a spatial strategy. A new functional description of the city where plots are nodes connected to flows that represent the street network is adopted. This model enables us to measure accessibility at the level of plots. Following this, we focus on the occurrence of land use types in highly or low accessible locations using cumulative distribution functions. If the distribution of land uses was random, the proportion of land use types would be more or less uniform throughout the area. It is shown that the relationship between accessibility and land use is not linear and is guided by movement economy forces. It is suggested that the understanding of these relationship is key to plan for sustainable growth objectively

Changing boundaries and meanings of middle class houses in Sri Lanka

Houses are distinctively organised spatial networks that embody social norms and meaning of a given culture. Normally it is accepted that visually identifiable house ‘types’ which also closely fit the culture of a group are adopted by society. In Sri Lanka, there was popular house ‘types’ among the middle class until about 1980. Today, house forms of the middle class are diverse with apparent new trends in recent years. If contemporary middle class house forms are not visually characterized by type/s, how does ‘culture’ influence house form? This paper explores whether there are ‘types’ with distinctive spatial networks among the diverse house forms and the nature of embodied social norms. In the context of apparent change, such exploration advances the understanding of the association of house form and culture for the contemporary society of Sri Lanka. By using space syntax analysis, this paper argues that although eclectic in visual appearance, middle class houses share a cultural ‘gene’ in their spatial configuration as a ‘genotype’ that operate beneath the visual. Analysis of forty houses revealed that an older genotype named as the O model is diminishing and that a new genotype named as the M model had stabilised after 1980. The contemporary ‘genotype’ classifies space to accommodate meanings of a new everyday home life. The older genotype which classified space to accommodate meaning of a by-gone lifestyle is no longer popular. The negotiation between the new genotype and heterogeneous phenotypes allow for the affirming of class solidarities in new ways in contemporary Sri Lank

Performance modelling of the Cambridge Fast Ring protocol

The Cambridge Fast Ring is high-speed slotted ring. The features that make it suitable for use at very large transmission rates are the synchronous transmission, the simplicity of the medium-access-control protocol, and the possibility of immediate retransmission of erroneous packets. A novel analytical model of the Cambridge Fast Ring with normal slots is presented. The model is shown to be accurate and usable over wide range of parameters. A performance analysis based on this model is presented

Integrating Horizontal Gene Transfer and Common Descent to Depict Evolution and Contrast It with ‘‘Common Design

Horizontal gene transfer (HGT) and common descent interact in space and time. Because events of HGT co-occur with phylogenetic evolution, it is difficult to depict evolutionary patterns graphically. Tree-like representations of life’s diversification are useful, but they ignore the significance of HGT in evolutionary history, particularly of unicellular organisms, ancestors of multicellular life. Here we integrate the reticulated-tree model, ring of life, symbiogenesis whole-organism model, and eliminative pattern pluralism to represent evolution. Using Entamoeba histolytica alcohol dehydrogenase 2 (EhADH2), a bifunctional enzyme in the glycolytic pathway of amoeba, we illustrate how EhADH2 could be the product of both horizontally acquired features from ancestral prokaryotes (i.e. aldehyde dehydrogenase [ALDH] and alcohol dehydrogenase [ADH]), and subsequent functional integration of these enzymes into EhADH2, which is now inherited by amoeba via common descent. Natural selection has driven the evolution of EhADH2 active sites, which require specific amino acids (cysteine 252 in the ALDH domain; histidine 754 in the ADH domain), iron- and NAD1 as cofactors, and the substrates acetyl-CoA for ALDH and acetaldehyde for ADH. Alternative views invoking ‘‘common design’’ (i.e. the non-naturalistic emergence of major taxa independent from ancestry) to explain the interaction between horizontal and vertical evolution are unfounded

Evanescent-wave coupled right angled buried waveguide: Applications in carbon nanotube mode-locking

In this paper we present a simple but powerful subgraph sampling primitive that is applicable in a variety of computational models including dynamic graph streams (where the input graph is defined by a sequence of edge/hyperedge insertions and deletions) and distributed systems such as MapReduce. In the case of dynamic graph streams, we use this primitive to prove the following results: -- Matching: First, there exists an $\tilde{O}(k^2)$ space algorithm that returns an exact maximum matching on the assumption the cardinality is at most $k$. The best previous algorithm used $\tilde{O}(kn)$ space where $n$ is the number of vertices in the graph and we prove our result is optimal up to logarithmic factors. Our algorithm has $\tilde{O}(1)$ update time. Second, there exists an $\tilde{O}(n^2/\alpha^3)$ space algorithm that returns an $\alpha$-approximation for matchings of arbitrary size. (Assadi et al. (2015) showed that this was optimal and independently and concurrently established the same upper bound.) We generalize both results for weighted matching. Third, there exists an $\tilde{O}(n^{4/5})$ space algorithm that returns a constant approximation in graphs with bounded arboricity. -- Vertex Cover and Hitting Set: There exists an $\tilde{O}(k^d)$ space algorithm that solves the minimum hitting set problem where $d$ is the cardinality of the input sets and $k$ is an upper bound on the size of the minimum hitting set. We prove this is optimal up to logarithmic factors. Our algorithm has $\tilde{O}(1)$ update time. The case $d=2$ corresponds to minimum vertex cover. Finally, we consider a larger family of parameterized problems (including $b$-matching, disjoint paths, vertex coloring among others) for which our subgraph sampling primitive yields fast, small-space dynamic graph stream algorithms. We then show lower bounds for natural problems outside this family

Multiple centrality assessment in Parma : a network analysis of paths and open spaces

One of the largest of Europe, the recently realized university campus 'Area of the Sciences' in Parma, northern Italy, has been planned for a comprehensive programme of renovation and revitalization with a special focus on vehicular accessibility and the quality of open spaces. As part of the problem setting phase, the authors, with Rivi Engineering, applied Multiple Centrality Assessment (MCA) - a process of network analysis based on primal graphs, a set of different centrality indices and the metric computation of distances - in order to understand why the existent system of open spaces and pedestrian paths is so scarcely experienced by students as well as faculty and staff members and why it appears so poorly supportive of social life and human exchange. In the problem-solving phase MCA was also applied, turning out to offer a relevant contribution to the comparative evaluation of two alternative proposed scenarios, leading to the identification of one final solution of urban design. In the present paper, the first professional application of MCA, an innovative approach to the network analysis of geographic complex systems, is presented and its relevance in the context of a problem of urban design illustrated