Source Of Perturbations Research Articles

Probabilistic Design Space Mapping: Application to Airfoil Design for HAWT

This work presents an airfoil probabilistic design methodology for wind energy applications, using an analytical approach to estimate the angle-of-attack fluctuations produced by non-uniformities in the incoming wind field. The contemplated wind speed perturbations include wind shear, yaw misalignment and atmospheric turbulence, and several combinations of the perturbation sources are considered. A probabilistic design space mapping is carried out to evaluate which wind conditions occur more often in practice and how likely each specific combination of perturbation sources is to occur, for both an onshore and offshore scenario. The proposed probabilistic method and specifically the level of angle-of-attack fluctuations is verified by employing the aero-elastic simulation tool FAST for each case. Finally, the probabilistic approach is used to design airfoils sections employing the genetic multi-objective airfoil optimization tool Optiflow, where the probability of angle of attack fluctuations for a given scenario is used to prescribe the operational angle of attack range over which the airfoil performance is relevant. Results of the airfoil optimization for a 24% thick section are presented, illustrating the trends in foil geometry and aerodynamic performance for three different possible optimization objective functions.

Expandir, repetir, conservar: a sexualidade sob o Eros freudiano

O presente artigo deseja evidenciar que, ainda que a libido e a sexualidade tenham sido incluídas no conceito de Eros a partir de Além do princípio do prazer, a sexualidade no interior no pensamento freudiana não perdeu seu caráter disruptivo e não deixou de ser considerada como causa de profundas perturbações para a vida psíquica humana. Para tal, serão reconstruídos os argumentos sobre a natureza conservadora das pulsões e se procurará propor a ideia de que os conceitos de expansão, repetição e conservação, intimamente associados à dinâmica pulsional, não podem ser vistos como elementos que teriam retirado à sexualidade sua natureza disruptiva e conflitiva no interior da obra freudiana.

Converter-Based Electrochemical Impedance Spectroscopy for High-Power Fuel Cell Stacks With Resonant Controllers

Impedance spectrum is a key signature of a fuel cell stack (FCS). The variations of the impedance spectrum reflect the internal status of an FCS. Enabling electrochemical impedance spectroscopy (EIS) with the onboard power conditioning converter (PCC) provides an attractive approach for in situ diagnostics and condition monitoring of an FCS in end applications, such as heavy-duty vehicles. Although a few previous attempts were made with the PCC being controlled as the source of ac perturbations, the issue of how to properly produce a wide frequency range of perturbations to a high-power FCS has not been well recognized and addressed. In particular, the high-frequency portion is limited by the converter switching frequency and controller bandwidth. Different from existing approaches that fall short of being practical solutions for a high-power FCS, this article proposes the use of PI plus resonant controllers for the PCC to generate quality high-frequency perturbations without any additional hardware. Enabled by the proposed EIS method, an example application showing the effective detection of the impedance changes of an emulated FCS is also presented. The design and implementation of the scheme and the considerations of response measurement and impedance calculation are given in detail. Experimental verifications on a scaled-down laboratory setup demonstrate the validity and possibility of the proposed methods.

Large-eddy simulations of turbulent flow in a channel with streamwise periodic constrictions

Abstract

Experimental study and analysis of shock train self-excited oscillation in an isolator with background waves

A study of shock train self-excited oscillation in an isolator with background waves was implemented through a wind tunnel experiment. Dynamic pressure data were captured by high-frequency pressure measurements and the flow field was recorded by the high-speed Schlieren technique. The shock train structure was mostly asymmetrical during self-excited oscillation, regardless of its oscillation mode. We found that the pressure discontinuity caused by background waves was responsible for the asymmetry. On the wall where the pressure at the leading edge of the shock train was lower, a large separation region formed and the shock train deflected toward to the other wall. The oscillation mode of the shock train was related to the change of wall pressure in the oscillation range of its leading edge. The oscillation range and oscillation intensity of the shock train leading edge were affected by the wall pressure gradient induced by background waves. When located in a negative pressure gradient region, the oscillation of the leading edge strengthened; when located in a positive pressure gradient region, the oscillation weakened. To find out the cause of self-excited oscillation, correlation and phase analyses were performed. The results indicated that the instability of the separation region induced by the leading shock was the source of perturbation that caused self-excited oscillation, regardless of the oscillation mode of the shock train.

Cross-code comparison of the impact of the fill tube on high yield implosions on the National Ignition Facility

Fill tubes are used to inject deuterium and tritium fuel into inertial confinement fusion capsules fielded on the National Ignition Facility. These fill tubes have been shown to have a detrimental effect on capsule performance, primarily by introducing a low-density pathway into the central fuel region that enables the jetting of ablation material into the hot spot. Due to the complexity of the highly nonlinear flow associated with the fill tube and the challenge of diagnosing the evolution of the fill tube jet late in the implosion experiments, the uncertainty in how this perturbation source evolves is great. Here, we report on the results of a detailed code comparison performed to understand uncertainties in computational modeling of the impact of fill tubes on implosion performance. The study employed two radiation-hydrodynamics codes, HYDRA and xRAGE, which employ very different meshing strategies and hydrodynamics solvers, as well as two radiation transport methodologies, discrete ordinates and multi-group diffusion. Our results demonstrate generally good agreement between codes through most of the implosion although they indicate sensitivity to opacity averaging methods. Late in the implosion, differences arise in the distribution and amount of contaminant although these differences have a remarkably small impact on the amount of yield reduction due to the fill tube. While these results demonstrate sensitivity in fill tube modeling to algorithmic choices, the observed differences between codes are small relative to known sensitivities due to expected variations in the fill tube geometry. Finally, we have developed a methodology for performing multi-group diffusion simulations that show good agreement with the more accurate discrete ordinates method.

On the observation of magnetic events on broad-band seismometers

The objective of this contribution is to get new insights into the effects of magnetic field variations of natural and anthropogenic origin on broad-band seismic stations. Regarding natural sources of magnetic perturbations, we have investigated if the Sudden Storm Commencements (SSC) cataloged during the 24th solar cycle (2008–2019) can be systematically identified in broad-band seismic stations distributed worldwide. The results show that the 23 SSC events with a mean amplitude above 30 nT and most of those with lower energy but still clearly identified in the magnetometer detection network can be observed at broad-band stations’ network using a simple low-pass filter. Although the preliminary impulse of those signals is usually stronger at stations located at high latitudes, major SSC are observed at seismic stations distributed worldwide. Regarding anthropogenic sources, we focus on the short period seismic signals recorded in urban environments which are correlated with the activity of the railway transportation system. We have analyzed collocated measurements of electric field and seismic signals within Barcelona, evidencing that significant changes in the electric field following the activity of the transportation systems can be attributed to leakage currents transmitted to the soil by trains. During space weather events, electric currents in the magnetosphere and ionosphere experience large variations inducing telluric currents near the Earth surface, which in turn generate a secondary magnetic field. In the case of underground trains, leakage currents are transmitted to the soil, which in turn can result in local variations in the magnetic field. The observed signals in modern seismometers can be related to the reaction of the suspension springs to these magnetic field variations or to the effect of the magnetic field variations on the force transducers used to keep the mass fixed.

Shift-symmetric orbital inflation: Single field or multifield?

We present a new class of two-field inflationary attractor models, known as `shift-symmetric orbital inflation', whose behaviour is strongly multi-field but whose predictions are remarkably close to those of single-field inflation. In these models, the field space metric and potential are such that the inflaton trajectory is along an `angular' isometry direction whose `radius' is constant but arbitrary. As a result, the radial (isocurvature) perturbations away from the trajectory are exactly massless and they freeze on superhorizon scales. These models are the first exact realization of the `ultra-light isocurvature' scenario, previously described in the literature, where a combined shift symmetry emerges between the curvature and isocurvature perturbations and results in primordial perturbation spectra that are entirely consistent with current observations. Due to the turning trajectory, the radial perturbation sources the tangential (curvature) perturbation and makes it grow linearly in time. As a result, only one degree of freedom (i.e. the one from isocurvature modes) is responsible for the primordial observables at the end of inflation, which yields the same phenomenology as in single-field inflation. In particular, isocurvature perturbations and local non-Gaussianity are highly suppressed here, even if the inflationary dynamics is truly multi-field. We comment on the generalization to models with more than two fields.

Meta-Analysis of the Alzheimer’s Disease Human Brain Transcriptome and Functional Dissection in Mouse Models

SUMMARYWe present a consensus atlas of the human brain transcriptome in Alzheimer’s disease (AD), based on meta-analysis of differential gene expression in 2,114 postmortem samples. We discover 30 brain coexpression modules from seven regions as the major source of AD transcriptional perturbations. We next examine overlap with 251 brain differentially expressed gene sets from mouse models of AD and other neurodegenerative disorders. Human-mouse overlaps highlight responses to amyloid versus tau pathology and reveal age- and sex-dependent expression signatures for disease progression. Human coexpression modules enriched for neuronal and/or microglial genes broadly overlap with mouse models of AD, Huntington’s disease, amyotrophic lateral sclerosis, and aging. Other human coexpression modules, including those implicated in proteostasis, are not activated in AD models but rather following other, unexpected genetic manipulations. Our results comprise a cross-species resource, highlighting transcriptional networks altered by human brain pathophysiology and identifying correspondences with mouse models for AD preclinical studies.

Determination of the Parameters of a Submerged Source by Perturbations of the Liquid Surface Based on Machine Learning Methods

The inverse problem of generating surface waves in a liquid is to determine the parameters of the source of perturbations from the waves it creates on the liquid surface. A new approach to solving this problem based on machine learning methods and the theory of neural networks is proposed. On the basis of the data from a laboratory experiment on water surface perturbations, the parameters of the model moving in the water column are restored.

Three-dimensional CFD simulation of pattern formation in a shallow packed-bed reactor for oxidative coupling of methane

Stationary or spatio-temporal patterns of catalytic reactions can cause operating challenges in shallow packed-bed reactors with large diameter to depth aspect ratios. Partial ignition patterns were observed in a pilot scale oxidative coupling of methane (OCM) reactor operating on the ignited branch near the extinction point. A three-dimensional (3D) computational fluid dynamics (CFD) model was developed for the down-flow shallow packed-bed reactor using porous media approach, with user-defined functions for heterogeneous heat transfer and Langmuir-Hinshelwood form reaction kinetics. The CFD simulation results show that, once the operating condition is nearing or beyond the extinction point (at lower feed temperature or shorter space time), 3D temperature patterns form due to either thermo-flow or thermo-kinetic steady-state multiplicity. The simulations provide insights into the pattern locking mechanism that stems from the non-linear hydrodynamic-kinetic-thermal coupling in the bed. Specific pattern observed in the CFD solution depends on perturbation sources such as unstructured space discretization, local heat loss through refractory walls, variations in catalyst activity or porosity of the packed-bed, as well as non-uniform initial conditions such as preheating, among others. The results indicate that the non-uniformity of bed physical and chemical properties (such as packing porosity, catalyst activity, or thermal properties) can dominate the pattern in practical reactor operation. Based on parametric studies, methods to mitigate pattern formation are recommended, such as more uniform incoming flow, uniform catalyst bed, uniformly preheated bed, higher catalyst activity (operating farther from extinction point), and/or higher bed thermal conductivity.

Spatiotemporal trajectory characteristic analysis for traffic state transition prediction near expressway merge bottleneck

The theoretical analysis of traffic flow with empirical vehicle trajectory data contained within this study allows for the explanation, reconstruction, and prediction of spatiotemporal transition characteristics of traffic conditions. Using an unmanned aerial vehicle (UAV) during a morning rush hour on a working day, observations of congestion evolution near an on-ramp bottleneck of an expressway was captured. The empirical high-fidelity trajectory data of 621 vehicles were extracted. The major findings include:(1) Macroscopic perspective: Three traffic states (free flow, metastable traffic flow, and jam) were observed with different spatiotemporal physical structures and their critical characteristics in a continuous first-order phase transition. The spontaneous spatiotemporal traffic breakdown and capacity drop were also captured, the critical points of which were also recorded. The features of widening synchronized flow pattern, general pattern, and the nature of nucleation described in the three-phase traffic theory were identified, which provides a new observational cognition for congestion formation and development.(2) Microscopic perspective: The impact of lane changes on immediate vehicles were modeled and quantified with the fluctuation magnitude of speed and the theoretical lag distance, which provides a method to identify the source of perturbation and determine the microscopic critical threshold of vehicle between macroscopic phase transitions. The research shows a lane changer could cause a forced deceleration of an immediate vehicle on a target lane after inserting itself with critical spacing headway below approximately 15–20 m. The average deceleration duration of vehicles in different traffic states can be captured as crucial driving features from downstream to help predict traffic state transition in a real bottleneck.

Limits on primordial magnetic fields from primordial black hole abundance

Primordial magnetic field (PMF) is one of the feasible candidates to explain observed large-scale magnetic fields, for example, intergalactic magnetic fields. We present a new mechanism that brings us information about PMFs on small scales based on the abundance of primordial black holes (PBHs). The anisotropic stress of the PMFs can act as a source of the super-horizon curvature perturbation in the early universe. If the amplitude of PMFs is sufficiently large, the resultant density perturbation also has a large amplitude, and thereby, the PBH abundance is enhanced. Since the anisotropic stress of the PMFs is consist of the square of the magnetic fields, the statistics of the density perturbation follows the non-Gaussian distribution. {Assuming Gaussian distributions and delta-function type power spectrum for PMFs, based on a Monte-Carlo method, we obtain an approximate probability density function of the density perturbation, and it is an important piece to relate the amplitude of PMFs with the abundance of PBHs.} Finally, we place the strongest constraint on the amplitude of PMFs as a few hundred nano-Gauss on 102 Mpc-1 ⩽ k ⩽ 1018 Mpc-1 where the typical cosmological observations never reach.

Tracing water perturbation using NO3−, doc, particles size determination, and bacteria: A method development for karst aquifer water quality hazard assessment

Karst systems, as well as springs, are vulnerable to water perturbation brought by infiltration. In this research, sources of water perturbations were examined. The first objective is to provide a method that can determine the origin of the water flowing in the karst outlet. The second objective is to identify the associated water quality hazards caused by the infiltration source. The method relies on these parameters: turbidity, DOC, NO3−, particle size, and bacteria (E. coli, enterococcus and total coliforms). As the method was applied during flood events, measurement of the water flow is also needed to have a basic knowledge on the hydrodynamic of the water resource.The proposed method is based on a high resolution monitoring of physico chemical parameters of the water flowing during flood events. Using this proposed method, (1) the origin of the water can be identified, (2) the type and nature of water perturbation can be described, and (3) the type of water perturbation that accompanies contaminants such as the one with anthropogenic source (e.g. NO3−) and bacterial nature can be determined. In identifying the water origin, this proposed method employed NO3− and DOC data normalization. Values are projected in the NO3−_norm = f(DOC_norm) reference frame. These are aligned to the slope. Depending on the obtained slope (α), water origin can be disclosed. If α > 1, the increase of concentration of DOC weighs more, characterizing water from surface runoff. Whereas, if α < 1, the consideration is more on the increase of NO3− concentration, characterizing water from unsaturated zone. However if α cannot be calculated because there is no evident slope, this characterizes the water already present in the system.Water originating from the surface runoff is prone to inorganic and bacterial contamination adsorbed by the particles. Identifying the type of water perturbation needing water treatment is important in managing the water resource. Hence, the evolution through time of NO3− and DOC with the particle size distribution, anthropogenic nature type of contaminant (i.e. in this study NO3−), and presence or absence of bacteria were examined.This method was applied in the springs of the Toulon, an important drinking water source of the city of Périgueux in France. This site was chosen considering the following factors: (1) its karst nature being vulnerable to infiltrations, having fractures and sinkholes; (2) its land use being influenced by the anthropogenic activities such as agriculture; and (3) its observed pronounced turbidity incidence. The first flood events of two hydrological cycles were assessed.Three water origins of the spring water and the respective water quality hazards were identified: (i) water from saturated zone with minerals, (ii) water from unsaturated zone with nitrate, and (iii) water from surface runoff with the presence of bacteria. The second and third types of water perturbation gave evidence that the Toulon springs can be contaminated. Hence, in terms of resource management, the information obtained can be used as a basis in forecasting and planning the management actions or water quality treatments needed.

Modification of Mode Parameters of Main Oil Pipelines under the Condition of Depressurizing

The characteristics of Ukrainian oil transportation system are presented; the emergency risks of Ukrainian oil pipelines are established. The analysis of the accident rate of oil pipeline transportation in Ukraine, Russia and the USA was carried out. The processes of initiation and progression of man-made emergencies in Ukraine during the oil pipelines operation are considered. The article presents the technique of specifying the incidental pressure in a pipeline, depending on the amount of oil loss at the site of oil leaks. It gives an opportunity to calculate the amount of oil loss and to evaluate the environmental hazards caused by oil pipeline transportation emergencies. It is based on the equations of motion and continuity of fluid flow. This technique makes it possible to calculate the pressure at each point of a pipeline in transient mode caused by changes in pressure at the beginning and at the end of the section and the emergence of concentrated oil offtake. It also gives an opportunity to monitor the change in mode parameters along the pipeline under conditions of pipeline depressurization. Maximum discrepancy in calculation results becomes typical when the range of fluctuations is maximal. It has been established that discrepancy increases when the distance from the source of perturbation becomes bigger. The discrepancy in calculation results is practically non-existent for the pressure fluctuations at the point of perturbation start (). Based on the results of calculations, the author constructs a graph of pressure change of the oscillatory process in the oil pipeline caused by the jump in the pressure at the beginning and at the end of the section, and the presence of probable leaks at the certain point of the pipeline route. The line section of the main oil pipelines is the most dangerous part since all emergencies are associated with emergency processes of different intensity in the form of outflow of oil into the environment, and are dangerous because of system breakdowns can take place. Both the process of the generation of the oil pollution zone and its time period depend on the amount of oil leakage, its intensity and depth of the oil pipeline.

Entropy production in affine inflation

Multiple scalar fields nonminimally interacting through pure affine gravity are considered to generate primordial perturbations during an inflationary phase. The couplings considered give rise to two distinct sources of entropy perturbations that may not be suppressed in the long wavelength limit. The first is merely induced by the presence of more than one scalar and arises even in the minimal coupling limit. The second source however is restricted to nonminimal interaction. Unlike the case of metric gravity, and due to the absence of anisotropic stresses, the second source disappears for single scalar, showing that nonminimal couplings become relevant to non-adiabatic perturbations only when more than one scalar field are considered. Hence the notion of adiabaticity is not affected by the transition to minimal coupling contrary to the metric gravity case where it is confused by changing the frames. Precise data that might be able to neatly track different sources of isocurvature modes, if any, must not only distinguish between different models of inflation but also determine the most viable approach to gravity which underlies the inflationary dynamics itself.

Single-Molecule Toroic Design through Magnetic Exchange Coupling

Summary Toroidal molecular magnets represent promising candidates for next-generation ultra-dense information storage. These wheel-like molecules are able to store one bit per molecule because of their insensitivity to homogeneous magnetic fields—one of the main sources of magnetic perturbations. However, synthesis of molecules possessing a well-defined and stable vortex arrangement of the on-site magnetic moments in the ground state represents a challenge. Here, we show that 16 magnetic metal ions can be alternately arranged into a macrocycle named {Fe8Dy8}. The net toroidal moment can be experimentally determined at 0.23 Tesla. Moreover, ab initio calculations were performed to reveal that ferromagnetic exchange interactions between the FeIII and DyIII metal centers are the key to generate this toroidal moment. This feature is significantly distinguished from the previously described dipole-dipole interaction-based single-molecule toroics (SMTs), showing the importance of exchange-coupling interactions in the design of next-generation SMTs.

GREEN TENSOR OF MOTION EQUATIONS OF TWO COMPONENTS BIOT’S MEDIUM BY STATIONARY VIBRATIONS

Here processes of wave propagation in a two-component Biot’s medium are considered which are generated by periodic forces actions. By use Fourier transformation of generalized functions, the Green tensor - a fundamental solutions of oscillation equations of this medium has been constructed. This tensor describes the process of propagation of harmonic waves of a fixed frequency in spaces of dimension N = 1,2,3 under the action of power sources concentrated at the coordinates origin, described by a singular delta -function. Based on it, generalized solutions of these equations are constructed under the action of various sources of periodic perturbations, which are described by both regular and singular generalized functions. For regular acting forces, integral representations of solutions are given that can be used to calculate the stress-strain state of a porous water-saturated medium.

Thermal history of the early Universe and primordial gravitational waves from induced scalar perturbations

We study the induced primordial gravitational waves (GW) coming from the effect of scalar perturbation on the tensor perturbation at the second order of cosmological perturbation theory. We use the evolution of the standard model degrees of freedom with respect to temperature in the early Universe to compute the induced gravitational waves bakcground. Our result shows that the spectrum of the induced GW is affected differently by the standard model degrees of freedom than the GW coming from first order tensor perturbation. This phenomenon is due to the presence of scalar perturbations as a source for tensor perturbations and it is effective around the quark gluon deconfinement and electroweak transition. In case of considering a scalar spectral index larger than one at small scales or a non-Gaussian curvature power spectrum this effect can be observed by gravitational wave observatories.

A cosmological Higgs collider

The quantum fluctuations of the Higgs field during inflation could be a source of primordial density perturbations through Higgs-dependent inflaton decay. By measuring primordial non-Gaussianities, this so-called Higgs-modulated reheating scenario provides us a unique chance to probe Higgs interactions at extremely high energy scale, which we call the Cosmological Higgs Collider (CHC). We realize CHC in a simple scenario where the inflaton decays into Higgs-portal scalars, taking account of the decay of the Higgs fluctuation amplitude after inflation. We also calculate the CHC signals of Standard Model particles, namely their imprints in the squeezed bispectrum, which can be naturally large. The concept of CHC can be straightforwardly generalized to cosmological isocurvature colliders with other types of isocurvature perturbations.