Domain Viewpoint Research Articles

The Camp Nou Stadium as a Testbed for City Physiology: A Modular Framework for Urban Digital Twins

In this paper, the Camp Nou stadium is used as a testbed for City Physiology, a theoretical framework for urban digital twins. With this case study, the modularity and adaptability of the framework, originally intended for city-scale simulations, are tested on a large facility venue. As a proof of concept, several statistical techniques and an agent-based simulation platform are coupled to simulate a crowd in the stadium, and a process of four steps is followed to build the case study. Both the conceptual (interdomain) and technical (domain specific) layers of the digital twin are defined and connected in a nonlinear process so that they represent the complexity of the object to be simulated. The result obtained is a strategy to build a digital twin from the domain point of view, paving the way for more complex, more ambitious simulators.

Channel Estimation and Transmission Strategy for Hybrid mmWave NOMA Systems

This paper presents a novel channel estimation and transmission strategy for millimeter wave (mmWave) non-orthogonal multiple access communication system with hybrid architecture. We first propose a general iterative index detection-based channel estimation algorithm that can obtain both direction of arrival and channel gain of each channel path. We then design an enhanced hybrid precoding scheme from the angle domain viewpoint to reduce the inter-beam interferences. Next, we investigate the multi-user scheduling and power allocation with the objective of maximizing the overall achievable rate. The problem turns to be non-convex and then we decompose it into two sub-problems, which separately consider user scheduling and power allocation. The former is solved by a novel algorithm based on the many-to-one two sided matching theory while the latter is solved by an iterative optimization algorithm. Simulation results show that the proposed channel estimation and user scheduling can be better than traditional methods. Finally, numerical examples are provided to corroborate the proposed studies.

Model Based Self‐Learning System Engineering Approach

AbstractSystem requirements engineering is relatively matured discipline with many trusted and dependable methods and techniques that fairly helps in identifying, analyzing, specifying, managing, verifying, and validating the system requirements. Yet the major challenge perceived in system engineering and development of software that is persisting over many years and pervasive across all domains is the requirements development, analysis, management, and validation. Still there are projects attributing to the defects in system requirements as the prime cause of its failure. Is a radical change to the current approach and techniques is essential or is it that we are not able to put the best practices designed into good use or both? Is there something else amiss that is not proportioned into these methods or tools and needs to be accounted into it? Several approaches attempt to increase the standardized portion by making it more objective and diminish the subjective substance. Towards this objective numerous tools and models were evolved over past several years aiming to standardize the requirements acquisition practice through various instruments like a questionnaire, design of use‐cases or models that consumes inputs from every stakeholder and use a standard template that brings in objectivity eliminating the ambiguity. These models are as intelligent as per the capabilities of the templates or the outlines created and matures per their exposure levels to the scenarios. They concentrates more on the methodology, patterns or blueprint to capture different characteristics and properties associated to the product in the requirements and the domain perspective is less deliberated. Domain viewpoint is of utmost importance to ensure the functioning of the product in the required environment and ambiance with required performance criteria that is suitable to the product. The “Domain Driven Design” is yet another approach to capture the requirements, develop and maintain it. A study of these three different approaches from the existing literature is done in this paper bringing out their prominent features, advantages and shortcomings. The proposed model delves deep into augment the domain facets of the products to ensure the definition of requirements are comprehensive and all‐inclusive to facilitate the flawless development and complete testing by reducing the ambiguity and enhancing the clarity. It also targets to produce all relevant artifacts like use cases, test scenarios, documentation etcetera. Collation and embedding of the precious and adept data from the experienced system engineers is one of the best features of the suggested model.

Frequency domain regularization of d-dimensional structure tensor-based directional fields

The present work is intended to address two of the major difficulties that can be found when tackling the estimation of the local orientation of the data in a scene, a task which is usually accomplished by means of the computation of the structure tensor-based directional field. On one hand, the orientation information only exists in the non-homogeneous regions of the dataset, while it is zero in the areas where the gradient (i.e. the first-order intensity variation) remains constant. Due to this lack of information, there are many cases in which the overall shape of the represented objects cannot be precisely inferred from the directional field. On the other hand, the orientation estimation is highly dependent on the particular choice of the averaging window used for its computation (since a collection of neighboring gradient vectors is needed to obtain a dominant orientation), typically resulting in vector fields which vary from very irregular (thus yielding a noisy estimation) to very uniform (but at the expense of a loss of angular resolution). The proposed solution to both drawbacks is the regularization of the directional field; this process extends smoothly the previously computed vectors to the whole dataset while preserving the angular information of relevant structures. With this purpose, the paper introduces a suitable mathematical framework and deals with the d-dimensional variational formulation which is derived from it. The proposed formulation is finally translated into the frequency domain in order to obtain an increase of insight on the regularization problem, which can be understood as a low-pass filtering of the directional field. The frequency domain point of view also allows for an efficient implementation of the resulting iterative algorithm. Simulation experiments involving datasets of different dimensionality prove the validity of the theoretical approach.

Identity and divergence of protein domain architectures after the yeast whole-genome duplication event

Gene duplication is a key mechanism in evolution for generating new functionality, and it is known to have produced a large proportion of genes. Duplication mechanisms include small-scale, or "local", events such as unequal crossing over and retroposition, together with global events, such as chromosomal or whole genome duplication (WGD). In particular, different studies confirmed that the yeast S. cerevisiae arose from a 100-150 million-year old whole-genome duplication. Detection and study of duplications are usually based on sequence alignment, synteny and phylogenetic techniques, but protein domains are also useful in assessing protein homology. We develop a simple and computationally efficient protein domain architecture comparison method based on the domain assignments available from public databases. We test the accuracy and the reliability of this method in detecting instances of gene duplication in the yeast S. cerevisiae. In particular, we analyze the evolution of WGD and non-WGD paralogs from the domain viewpoint, in comparison with a more standard functional analysis of the genes. A large number of domains is shared by genes that underwent local and global duplications, indicating the existence of a common set of "duplicable" domains. On the other hand, WGD and non-WGD paralogs tend to have different functions. We find evidence that this comes from functional migration within similar domain superfamilies, but also from the existence of small sets of WGD and non-WGD specific domain superfamilies with largely different functions. This observation gives a novel perspective on the finding that WGD paralogs tend to be functionally different from small-scale paralogs. WGD and non-WGD superfamilies carry distinct functions. Finally, the Gene Ontology similarity of paralogs tends to decrease with duplication age, while this tendency is weaker or not observable by the comparison of the domain architectures of paralogs. This suggests that the set of domains composing a protein tends to be maintained, while its function, cellular process or localization diversifies. Overall, the gathered evidence gives a different viewpoint on the biological specificity of the WGD and at the same time points out the validity of domain architecture comparison as a tool for detecting homology.

On Efficient AR Spectral Estimation for Long-Range Predictions

ABSTRACT This article discusses the concept of asymptotic efficiency from the frequency domain point of view making use of the direct method for multiple prediction. In particular, it is shown that with the use of a new autoregressive model selection at each prediction time h, the asymptotic lower bound of the integrated relative squared error of an AR spectral estimate is attained by the order selected for multistep prediction by the AIC selection procedure Akaike (1973) and its alike when the underlying process is a non zero mean infinite order not necessarily Gaussian AR process.

Spectral diffusion induced by sudden jump processes

A concise analytical method is given to describe the spectral diffusion in the system with several sudden jump modulators from the frequency domain viewpoint. Spectral diffusion of chromophores in low temperature glasses is investigated by this method with the standard two-level system model. Under the standard approximation, the spectral diffusion has exactly the same form as the stimulated photon echo result. The time-dependent heterogeneous line width increases as the logarithm of waiting time.

Macrodomain structure related to the electric field-induced phase transition in Pb(Mg1/3Nb2/3)O3

Abstract The first-order electric field-induced phase transition in Pb(Mg1/3Nb2/3)O3, [PMN] single crystals, from the average cubic phase to a macroscopically polar 3m phase, was studied more specifically by the optical domain examinations with polarized light microscopy. Different aspects of induced macrodomain structure and phase boundary related to the establishment, decay and reversal of the induced polarization were presented. The mechanism of the induced phase transition was described, from the domain point of view, as a transformation from polar nanodomains to polar macrodomain states resulting in a trigonal distortion with symmetry breaking.

Identification for Adaptive Control - Algorithm Design from a Frequency Domain Perspective

Popular recursive parameter estimation algorithms are reexamined from a frequency domain viewpoint, using an approach by Gunnarsson and Ljung. In particular, we take another look at a number of algorithm modifications, introduced in the area of adaptive control. These modifications can be shown to have natural interpretations in the frequency domain, and this fact suggests that other useful modifications may be motivated from frequency domain considerations.

Experimental frequency response analysis of flexible mechanisms

This paper presents some experimental results of the frequency analysis of flexible mechanisms. The objective is to help understand the general trend of vibration characteristics of the flexible mechanisms, and to clarify some debatable phenomena in the kineto-elasto-dynamics (KED) area from the frequency domain view point. Both single link and assembled linkage analyses have been conducted to compare the single link natural frequency with the system natural frequency. Some of the experimental results are quite different from the predictions of the current analytical models.

Linear periodic control: A frequency domain viewpoint

Periodic control is a well studied design strategy in which the coefficients of the control law are varied periodically in time. The technique has been extensively studied in the timedomain and has been shown to lead to a range of perceived benefits including high gain and phase margins. However, in view of the periodic nature of the feedback, we argue that it is more natural to adopt an alternative viewpoint in the frequency domain. We show that, within this framework, the action of the periodic controller can be viewed as a form of amplitude modulation (as in communication systems). This gives new theoretical insights into the method, including a clearer understanding of the action of the controller and a complete characterisation of the frequency content of the input and output signals.

Correlation of power variables—frequency domain

This publication is a third paper in a series considering the concept of power correlation. Power correlation is treated herein from a frequency domain viewpoint with major emphasis being placed on the power frequency response function, PFRF. A PFRF relates power at a driving point to power at another point in a vibratory system. A theoretical formula for power frequency response function is derived, and experimentally determined PFRF's are presented. A PFRF is complex valued, the real part relating the transfer of real power from one point in a system to another. This function provides further insight into power flow in a vibratory system.

Transient response characteristics in identification and imaging

Three different solutions to problems in identification and inverse scattering using restricted far-zone scattering data are reviewed and illustrated. The data are restricted in the sense that the frequencies, aspects, and polarizations are limited. All three solutions are based in part on a fundamental time domain viewpoint whereby the far-zone scattering characteristics of any finite object are uniquely summarized by its impulse response waveforms. Insight provided by these waveforms is exploited via geometrical characteristics extracted from steady-state, forced, and free responses of the object. For the present purposes the fundamental importance of signaling waveforms whose wavelengths are within an order of magnitude of the object dimension is demonstrated. The basic methods discussed have been previously identified in the literature as natural resonance estimation, radar imaging from ramp response signatures, and low frequency classification. Related common features, additional insight, and some new results are given. Applications of all three methods to objects ranging from simple to complex geometries are described.

Improvements of the Procedures Used to Study the Fluctuations of Oscillators

Considering that procedures currently used to study the fluctuations in oscillators do not give directly useful results, we have tried to define a procedure more suitable for experimentalists. We have tempted to obtain a function ?(T) which would be a kind of variance of the frequency fluctuations observed in a duration T. Taking a frequency domain point of view, we find a procedure which can yield also an estimation of the spectral density of the frequency.

Spectral Measurements of Sliding Tones

The response of a spectrum analyzer to sliding tones is considered. A sliding tone is defined as a frequency which changes linearly with time. It is assumed that the spectrum analyzer is the equivalent of a bank of filters whose outputs are measured at. a single point in time. The problem of obtaining spectral measurements is treated in the frequency domain. Results are first developed for the spectral density of a finite fixed duration sinusoid of linearly time varying frequency, from an interpretation of the Cornu spiral. This is referred to as the input spectrum. The response of a filter to a sliding tone is then determined by convolution of the input spectrum with the selectivity characteristics of the filter. The filter selectivity characteristic is obtained by Fourier transforming a periodic representation of the filter impulsive response. This approach to computation of the filter response to sliding tones provides a convenient interpretation of the effects of the characteristics of the filter and the input and facilitates computation of the filtering action. In addition it helps suggest filter characteristics that are desirable from a spectral measurement point of view. Results are presented which indicate the response of a variety of filters to a sliding tone input. The contribution of the approach presented to the evaluation of the response of filters to sliding tones has the two major advantages of: 1. Its usefulness for approximate analysis and the interpretation of the effects of filter and signal parameters. 2. The ease and economy of computation of accurate results. For completeness, filter responses to a very rapidly sliding tone are discussed from the time domain point of view.