Turbulent Scenario Research Articles

Dynamics of homogeneous shear turbulence: A key role of the nonlinear transverse cascade in the bypass concept.

To understand the mechanism of the self-sustenance of subcritical turbulence in spectrally stable (constant) shear flows, we performed direct numerical simulations of homogeneous shear turbulence for different aspect ratios of the flow domain with subsequent analysis of the dynamical processes in spectral or Fourier space. There are no exponentially growing modes in such flows and the turbulence is energetically supported only by the linear growth of Fourier harmonics of perturbations due to the shear flow non-normality. This non-normality-induced growth, also known as nonmodal growth, is anisotropic in spectral space, which, in turn, leads to anisotropy of nonlinear processes in this space. As a result, a transverse (angular) redistribution of harmonics in Fourier space is the main nonlinear process in these flows, rather than direct or inverse cascades. We refer to this type of nonlinear redistribution as the nonlinear transverse cascade. It is demonstrated that the turbulence is sustained by a subtle interplay between the linear nonmodal growth and the nonlinear transverse cascade. This course of events reliably exemplifies a well-known bypass scenario of subcritical turbulence in spectrally stable shear flows. These two basic processes mainly operate at large length scales, comparable to the domain size. Therefore, this central, small wave number area of Fourier space is crucial in the self-sustenance; we defined its size and labeled it as the vital area of turbulence. Outside the vital area, the nonmodal growth and the transverse cascade are of secondary importance: Fourier harmonics are transferred to dissipative scales by the nonlinear direct cascade. Although the cascades and the self-sustaining process of turbulence are qualitatively the same at different aspect ratios, the number of harmonics actively participating in this process (i.e., the harmonics whose energies grow more than 10% of the maximum spectral energy at least once during evolution) varies, but always remains quite large (equal to 36, 86, and 209) in the considered here three aspect ratios. This implies that the self-sustenance of subcritical turbulence cannot be described by low-order models.

AN ALMA SEARCH FOR SUBSTRUCTURE, FRAGMENTATION, AND HIDDEN PROTOSTARS IN STARLESS CORES IN CHAMAELEON I

ABSTRACT We present an Atacama Large Millimeter/submillimeter Array (ALMA) 106 GHz (Band 3) continuum survey of the complete population of dense cores in the Chamaeleon I molecular cloud. We detect a total of 24 continuum sources in 19 different target fields. All previously known Class 0 and Class I protostars in Chamaeleon I are detected, whereas all of the 56 starless cores in our sample are undetected. We show that the Spitzer+Herschel census of protostars in Chamaeleon I is complete, with the rate at which protostellar cores have been misclassified as starless cores calculated as <1/56, or <2%. We use synthetic observations to show that starless cores collapsing following the turbulent fragmentation scenario are detectable by our ALMA observations when their central densities exceed ∼108 cm−3, with the exact density dependent on the viewing geometry. Bonnor–Ebert spheres, on the other hand, remain undetected to central densities at least as high as 1010 cm−3. Our starless core non-detections are used to infer that either the star-formation rate is declining in Chamaeleon I and most of the starless cores are not collapsing, matching the findings of previous studies, or that the evolution of starless cores are more accurately described by models that develop less substructure than predicted by the turbulent fragmentation scenario, such as Bonnor–Ebert spheres. We outline future work necessary to distinguish between these two possibilities.

Homogeneous shear turbulence – bypass concept via interplay of linear transient growth and nonlinear transverse cascade

We performed direct numerical simulations of homogeneous shear turbulence to study the mechanism of the self-sustenance of subcritical turbulence in spectrally stable (constant) shear flows. For this purpose, we analyzed the turbulence dynamics in Fourier/wavenumber/spectral space based on the simulation data for the domain aspect ratio 1 : 1 : 1. Specifically, we examined the interplay of linear transient growth of Fourier harmonics and nonlinear processes. The transient growth of harmonics is strongly anisotropic in spectral space. This, in turn, leads to anisotropy of nonlinear processes in spectral space and, as a result, the main nonlinear process appears to be not a direct/inverse, but rather a transverse/angular redistribution of harmonics in Fourier space referred to as the nonlinear transverse cascade. It is demonstrated that the turbulence is sustained by the interplay of the linear transient, or nonmodal growth and the transverse cascade. This course of events reliably exemplifies the wellknown bypass scenario of subcritical turbulence in spectrally stable shear flows. These processes mainly operate at large length scales, comparable to the box size. Consequently, the central, small wavenumber area of Fourier space (the size of which is determined below) is crucial in the self-sustenance and is labeled the vital area. Outside the vital area, the transient growth and the transverse cascade are of secondary importance - Fourier harmonics are transferred to dissipative scales by the nonlinear direct cascade. The number of harmonics actively participating in the self-sustaining process (i.e., the harmonics whose energies grow more than 10% of the maximum spectral energy at least once during evolution) is quite large - it is equal to 36 for the considered box aspect ratio - and obviously cannot be described by low-order models.

El método etnográfico y su relación con el análisis de dominio

Analiza la relación teórico-conceptual del método etnográfico con el análisis de dominio. Se realizó un análisis documental explorando las categorías Análisis de Dominio y Método Etnográfico. Se obtuvo como resultado el análisis de los puntos de contacto entre el Análisis de Dominio y el Método Etnográfico desde un punto de vista epistemológico, metodológico y procedimental. Se concluye que el método etnográfico constituye una herramienta de investigación importante para escudriñar los convulsos escenarios socio-culturales que suceden a lo interior de las comunidades discursivas que componen a los dominios de conocimientos.

Wind Turbine Fault Detection through Principal Component Analysis and Statistical Hypothesis Testing

This paper addresses the problem of online fault detection of an advanced wind turbine benchmark under actuators (pitch and torque) and sensors (pitch angle measurement) faults of different type: fixed value, gain factor, offset and changed dynamics. The fault detection scheme starts by computing the baseline principal component analysis (PCA) model from the healthy or undamaged wind turbine. Subsequently, when the structure is inspected or supervised, new measurements are obtained are projected into the baseline PCA model. When both sets of data—the baseline and the data from the current wind turbine—are compared, a statistical hypothesis testing is used to make a decision on whether or not the wind turbine presents some damage, fault or misbehavior. The effectiveness of the proposed fault-detection scheme is illustrated by numerical simulations on a well-known large offshore wind turbine in the presence of wind turbulence and realistic fault scenarios. The obtained results demonstrate that the proposed strategy provides and early fault identification, thereby giving the operators sufficient time to make more informed decisions regarding the maintenance of their machines.

A Fast and Robust Scan-Line Search Algorithm for Object-to-Image Projection of AirbornePushbroom Images

AbstractThe projection of a 3D object point onto a 2D image plane (i.e., the object-to-image projection) is one of the fundamental operations in photogrammetric data processing. Unlike that for a frame image, the object-to-image projection for a pushbroom image is not a straightforward process because each scan line is exposed at a distinct instant of time, and a preliminary step is therefore required to determine the corresponding scan-line coordinate of the ground point to be projected. This paper presents a new scan-line search algorithm for the object-to-image projection of airborne pushbroom images, which employs a coarse-to-fine strategy following four consecutive steps: affine transformation, iterative search, sequential search, and sub-pixel inter-polation. The experimental results with 255 pushbroom images captured in various flight conditions show that the proposed algorithm is robust and can save at least 15 percent of the computational time when compared to the previous methods, while the latter often cannot yield correct results in strong turbulence scenarios.

Managing knowledge and going global at FragraAroma

Purpose – The purpose of this paper is to help students understand how companies combine and leverage their existing knowledge capabilities in order to build strategic advantage for the company. The case also throws some light on the opportunities and challenges faced by SME's of emerging markets in going international in turbulent macroeconomic scenarios. Design/methodology/approach – The case has been written for the purpose of teaching and class discussion. Interviews with protagonist provided the primary data and published reports and archives of the company provided the secondary data for the case. Findings – After the class discussion, students will be able to figure out how SME's can best leverage their existing knowledge base, efficiently manage that knowledge base and accurately assess the impact of these knowledge management activities for international expansion. Originality/value – This is among the first few cases in the area of knowledge management from the perspective of SME's in emerging markets in the fragrance and other allied industries.

MULTI-SPACECRAFT OBSERVATIONS OF LINEAR MODES AND SIDEBAND WAVES IN ION-SCALE SOLAR WIND TURBULENCE

In the scenario of weak turbulence, energy is believed to be cascaded from smaller to larger wave numbers and frequencies due to weak wave-wave interactions. Based on its perturbative treatment one may regard plasma turbulence as a superposition of linear modes (or normal modes) and sideband waves (or nonlinear modes). In this study, we use magnetic field and plasma measurements of nine solar wind events obtained by the Cluster spacecraft and make extensive use of a high-resolution wave vector analysis method, the Multi-point Signal Resonator technique, to find frequencies and wave vectors of discrete modes on ion kinetic scales in the plasma rest frame. The primarily unstructured wave observations in the frequency-wave number diagram are classified into three distinct linear modes (proton Bernstein modes, helium-alpha Bernstein modes, and kinetic Alfven waves) and the sideband waves by comparing with the dispersion relations derived theoretically from linear Vlasov theory using observational values of the plasma parameter beta and the propagation angle from the mean magnetic field. About 60% of the observed discrete modes can be explained by the linear modes, primarily as the proton Bernstein and the kinetic Alfven waves, within the frequency uncertainties, while the rest of the population (about 40%) cannot be classified as linear modes due to the large deviation from dispersion relations. We conclude that both the linear modes and sideband wave components are needed to construct the wave picture of solar wind turbulence on ion-kinetic scales.

Employing circle polarization shift keying in free space optical communication with gamma–gamma atmospheric turbulence channel

A novel theoretical model of a circular polarization shift keying (CPolSK) system for free space optical links through an atmospheric turbulence channel, is proposed. Intensity scintillation and phase fluctuation induced in atmospheric turbulence, from weak to strong levels, are specifically researched with respect to circular polarization control error caused by the system design. We derive closed form expressions of the bit error rate (BER) and outage probability for evaluating the BER performance and communication interruption in the Gamma–Gamma distributed channel model. Simulation results show that atmospheric turbulence and circular polarization control error have significant effects on the BER performance and interruption of communication in the CPolSK system. The deterioration in BER performance, caused by intensity scintillation and phase fluctuation, is augmented by the power penalty conditioned by the circular polarization control error. This consequently adds to the demand for emissive power from the CPolSK system. Furthermore, we demonstrate that controlling the circular polarization control error below 8° as well as the normalized threshold within 8dB, 9dB and 10dB in turbulent scenarios from weak to strong levels can significantly reduce the probability of communication interruption occurring. This study provides reference material for further design of the CPolSK system.

Extended high-angular-frequency analysis of turbulence effects on short-exposure imaging

An improved analysis of optical turbulence effects on short-exposure passive (SE) imaging is described, resulting in a new analytic expression for the SE modulation transfer function (MTF). This analysis expands on a 2011 study that examined characteristics of a tilt-phase component discovered in the standard theory of SE turbulence effects characterization. The analysis introduces an improved integration technique and a reformulated phase structure function, facilitating computation of a 38,007 element database of MTF results at low- to high-angular frequencies covering a wide range of diffraction and turbulence conditions. Analysis of this database is described, yielding a new analytic SE MTF, accurate to a root-mean-square error of 0.000218 versus the database. Comparisons show that the new expression is well correlated to an alternative computationally intensive method, and it is a factor 29 to 64 improvement over prior analytic expressions. Limits of applicability of the approach for incoherent imaging are also discussed. The low-computational cost of the new method is suit- able for systems performance modeling of turbulence impacts, including path-varying turbulence scenarios.©The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part

AN AHP-BASED APPROACH TO CREDIT RISK EVALUATION OF MORTGAGE LOANS

Mortgage loans for home purchase require careful analysis by all parties involved in the transaction, and credit-scoring is usually adopted to assist the decision process. From a credit institution standpoint, credit-scoring for mortgage loan risk evaluation becomes even more important in scenarios of economic turbulence and recession, primarily because of the severe restrictions imposed on credit availability that result from reduced access to both money and debt markets and subsequent decreasing liquidity. Employing an AHP – Analytic Hierarchy Process – based approach in the creditscoring system used by one of the major banks in Portugal, this study proposes a methodological framework conceived to adjust trade-offs among evaluation criteria and provide decision makers with a more transparent mortgage risk evaluation system. Practical implications of our framework are also discussed.

Multiwavelength observations of the γ-ray-emitting narrow-line Seyfert 1 PMN J0948+0022 in 2011

We report on radio-to-gamma-ray observations during 2011 May-September of PMN J0948+0022, the first narrow-line Seyfert 1 (NLSy1) galaxy detected in gamma-rays by Fermi-LAT. Strong variability was observed in gamma-rays, with two flaring periods peaking on 2011 June 20 and July 28. The variability observed in optical and near-infrared seems to have no counterpart in gamma-rays. This different behaviour could be related to a bending and inhomogeneous jet or a turbulent extreme multi-cell scenario. The radio spectra showed a variability pattern typical of relativistic jets. The XMM spectrum shows that the emission from the jet dominates above 2 keV, while a soft X-ray excess is evident in the low-energy part of the X-ray spectrum. Models where the soft emission is partly produced by blurred reflection or Comptonisation of the thermal disc emission provide good fits to the data. The X-ray spectral slope is similar to that found in radio-quiet NLSy1, suggesting that a standard accretion disc is present, as expected from the high accretion rate. Except for the soft X-ray excess, unusual in jet-dominated AGNs, PMN J0948+0022 shows all characteristics of the blazar class.

Health Sector Reform and Social Determinants of Health: building up theoretical and methodological interconnections to approach complex global challenges.

Health Sector Reform and Social Determinants of Health are central issues for the current international policy debate, considering the turbulent scenario and the threat of economic recession in a global scale. Although these themes have been discussed for a long time, three major issues still calls the attention of the scientific community and health policymakers. The first one is the matter of how to approach scientifically the intricate connections between them in order to understand the consequences of policies for healthcare services, once this debate will become much more tensioned in the coming years. The second one is the lack of explanatory frameworks to investigate the policies of reform strategies, simultaneously observed in a variety of countries within distinct health services, which aim to achieve multiple and contradictory goals vis-à-vis the so-called social determinants of health. The third one is the challenge that governments face in developing and sustaining equitable health services, bearing in mind the intense political dispute behind the health sector reform processes. This article discusses an all-embracing theoretical and methodological scheme to address these questions. The aim is to connect macro- and middle-range theories to examine Social Determinants and Health Sector Reform interdependent issues, with view to developing new knowledge and attaining scientific understanding upon the role of universal and equitable healthcare systems, in order to avoid deepening economic crises.

THE DYNAMICAL STATE OF THE SERPENS SOUTH FILAMENTARY INFRARED DARK CLOUD

We present the results of N$_2$H$^+$ ($J=1-0$) observations toward Serpens South, the nearest cluster-forming, infrared dark cloud. The physical quantities are derived by fitting the hyperfine structure of N$_2$H$^+$. The Herschel and 1.1-mm continuum maps show that a pc-scale filament fragments into three clumps with radii of $0.1-0.2$ pc and masses of $40-230M_\odot$. We find that the clumps contain smaller-scale ($\sim 0.04$ pc) structures, i.e., dense cores. We identify 70 cores by applying CLUMPFIND to the N$_2$H$^+$ data cube. In the central cluster-forming clump, the excitation temperature and line-width tend to be large, presumably due to protostellar outflow feedback and stellar radiation. However, for all the clumps, the virial ratios are evaluated to be $0.1-0.3$, indicating that the internal motions play only a minor role in the clump support. The clumps exhibit no free-fall, but low-velocity infall, and thus the clumps should be supported by additional forces. The most promising force is the globally-ordered magnetic field observed toward this region. We propose that the Serpens South filament was close to magnetically-critical and ambipolar diffusion triggered the cluster formation. We find that the northern clump, which shows no active star formation, has a mass and radius comparable to the central cluster-forming clump, and therefore, it is a likely candidate of a {\it pre-protocluster clump}. The initial condition for cluster formation is likely to be a magnetically-supported clump of cold, quiescent gas. This appears to contradict the accretion-driven turbulence scenario, for which the turbulence in the clumps is maintained by the accretion flow.

Route diversity analyses for free-space optical wireless links within turbulent scenarios

Free-Space Optical (FSO) communications link performance is highly affected when propagating through the time-spatially variable turbulent environment. In order to improve signal reception, several mitigation techniques have been proposed and analytically investigated. This paper presents experimental results for the route diversity technique evaluations for a specific case when several diversity links intersects a common turbulent area and concurrently each passing regions with different turbulence flows.

Impact of Flight Disturbances on Airborne Radar Tracking

This correspondence is devoted to the study of the impact of flight disturbances due to the atmospheric turbulence on airborne radar tracking. The performance of a turbulence-ignorant tracking filter is assessed in a turbulent simulated scenario. The turbulence is modelled according to the Dryden model, a correlated, zero-mean, Gaussian random process. A quasi-ellipsoidal racetrack course is chosen for the air platform that carries the radar. The performance of the turbulence-ignorant tracking algorithm is analyzed in terms of mean value and standard deviation of the estimation errors for each component of the position and velocity vectors and compared with the posterior Cramer-Rao lower bound (PCRLB), evaluated for the ideal case of absence of platform vibrations.

A numerical model for wind-borne compact debris trajectory estimation: Part 2 – Simulated vertical gust effects on trajectory and mass momentum

In a companion paper [1], the trajectory of compact debris was estimated by accounting for the many uncertainties associated with debris flight. Compact debris are objects possessing non-negligible mass but negligible moment of inertia (e.g., a particle-type object); the wind-driven motion of the debris is predominantly controlled by aerodynamic drag with a limited influence of aerodynamic lift or moment. A numerical algorithm for investigating the probability of wind-borne compact debris impacting on the vertical façade of tall buildings was discussed.In this study, the effect of a “sudden” vertical gust on the trajectory of compact objects was analyzed. Since at initial stages of the flight the effect of turbulence may have an influence on the trajectory, a “Küssner-like” Gust model was proposed, incorporated in the loading model and used in conjunction with the equations of the motion. The numerical simulations, accounting for this simulated vertical gust, indicate that the effect of a simplified vertical turbulence scenario may often be neglected for estimating the trajectory of a compact object. Nevertheless, some effect of this simulated gust on “Iso-probability Impact Contours” and “Universal Probability Curve”, described in [1], was observed and quantified.

GRB PROMPT EMISSION: TURBULENCE, MAGNETIC FIELD AND JITTER RADIATION

The jitter radiation, which is the emission of relativistic electrons in the random and small-scale magnetic field, is utilized to investigate the high-energy emission of gamma-ray bursts. We produce the random and small-scale magnetic field using turbulent scenario. The electrons can be accelerated by stochastic acceleration. We also estimate the acceleration and cooling timescales, aiming to identify the validation of jitter regime under the GRB fireball framework. The possible maximum energy of electrons in our case is estimated as well.

Curing and Preventing Euroarea’s Sovereign Debt Crises: Some Issues and a Recipe

The sovereign debt crisis that has now been troubling the euro area for nearly three years originated as part of the scenario of the global financial turbulence that started in the summer of 2007, but it is characterised by specific causes and peculiar problems. The efforts to diagnose its causes, as well as to cure it and to prevent future difficulties of the same kind and severity, require careful consideration of the features of the institutions of the European Union, of the organisation of the financial sector of the euro area and of the economic policies of the member countries.

Change Management through Productive Social Networking

The study identifies the forces of changes in todays turbulent industrial scenario dominated by technology and diverse workforce. It explores the concept of change management with the insights on Productive Social Networking within the organizations. The study proposes the model of agile organisation based on constructive social networking and e-learning. Also, Sustainability requirements is identified as the major driving force for strategic agility in response to changes. The model explains the role of productive social networking in fostering creativity and innovation among employees and employee groups. It also focuses on the requirement of agility in human resources or talent to have creative solutions in the direction of sustainable development. The study proposes concept of agile change management with appropriate use of technology. st Century, Organisations are surrounded by information technology that affects how they are designed and managed. In todays workplace, many employees work on computers only and many work on virtual teams also. Employees and employee groups are electronically connected to colleagues, partners around the world. It requires leaders to be not only tech-savvy but also be responsible for managing web of relationships that reaches far beyond the boundaries of the physical organization. The opportunity and challenge of building a flexible link between a company , its employees, vendors, customers. Further, growing workforce diversity has brought variety of challenges in front of the organizations. The challenges include maintaining a corporate culture, balancing work and quality of life, coping with cultural conflicts, etc. Uncertainty in the macro-environment is the matter of challenge for any organization. The two important aspects of this uncertainty are -i) Information about the environment and ii) Resources available in the environment . The dynamic market conditions of complexity and the continuous change demands a greater need to collect the information and orgaisational response based on that information. In the new business ecosystems, managers have learnt to work in more horizontal process rather than vertical hierarchical structures. Important initiatives are not top down, rather they are formed in the every corner of the organization and also cut across the boundaries of the organization. Leaders must learn to utilize the technology for scanning the environment, opportunities and build up strong and sustainable relationships with multiple stakeholders.