Perturbation Level Research Articles

Scalar Field Evolution at Background and Perturbation Levels for a Broad Class of Potentials

AbstractIn this paper, a non‐interacting scalar field cosmology with an arbitrary potential using the f‐deviser method that relies on the differentiability properties of the potential is investigated. Using this alternative mathematical approach, a unified dynamical system analysis at a scalar field's background and perturbation levels with arbitrary potentials is presented. For illustration, a monomial and double exponential potential is considered. These two classes of potentials comprise the asymptotic behavior of several classes of scalar field potentials, and, therefore, they provide the skeleton for the typical behavior of arbitrary potentials. Moreover, the linear cosmological perturbations in the matterless case by considering three scalar perturbations: the evolution of the Bardeen potentials, the comoving curvature perturbation, the so‐called Sasaki‐Mukhanov variable, or the scalar field perturbation in uniform curvature gauge is analyzed. Finally, an exhaustive dynamical system analysis for each scalar perturbation is presented, including the evolution of Bardeen potentials in the presence of matter.

Growth of matter perturbations in some parametrization of dark energy models

In this work, we investigate the growth of matter perturbations in some known parameterizations of dark energy (DE) models i.e, CPL, JBP, BA, and a new parameterization of DE introduced in this study. We examine the growth of perturbations in the linear region by assuming the possibility of perturbations in DE. Then, we follow an overall likelihood analysis to put the same constraints on models using background and growth rate data, and we conclude that the reviewed DE parameterizations are compatible with the observational data at both background and perturbation levels. Furthermore, we find that DE parameterizations are comparable with each other, and with the Lambda CDM model. In particular, we obtain the following significant results: (i) the growth rate of matter perturbations in the homogeneous DE case is smaller than its value in the clustered case for CPL and BA models, while it is the opposite for JBP and the new model. (ii) The growth rate of matter perturbations related to the CPL and BA models have very similar behavior for both homogeneous and clustered DE cases at all redshift z. This is also true for JBP and the new model. (iii) We show that the growth rate of matter perturbations relevant to the models is lower than its value in the Lambda CDM model at low redshifts, and at high redshifts, the difference between them is insignificant. Finally, using AIC and BIC analysis, we conclude that the selection of a model that has better compatible with the observational data depends on the background and perturbation data.

The role of B2B digital platforms for managing future worldwide crisis. A strategic sensitivity framework for exploiting the breakthrough technological innovations

The recent years have been dominated by the urgency of mitigating the effects of dramatic emergencies. In the first step the sudden outbreak of Covid19 and next the Ukraine conflict raising have put under stress the stability of worldwide B2B digital platforms sectors. In response to the unpredictable catastrophes the worldwide organizations started to adopt several breakthrough technologies by means of confused response strategies. The literature did not sufficiently address the issue of which could be the most effective ways to relief a crisis picking solutions from the new breakthrough innovations in B2B digital platform systems. The analysis of B2B digital platforms during a crisis is not trivial because of the system complexity. To fill the literature, gap this paper exploits the line of study of crisis theory. Through the lens of analysis of the adaptive management model, the paper aims at creating a theoretical model based on the most impactful breakthrough innovations on B2B digital platforms mechanisms. Related to dual adaptive management approaches, the study creates four different scenarios to simulate through a system dynamic method. The results of the simulation come up with four main mitigation strategy patterns associated with the different levels of crisis perturbation and adaptive approach style. The paper aims at expanding the study on B2B digital platform technological evolution and provides some interesting insights on how to configure an effective crisis mitigation strategy.

Challenges and cooperation in emergency and disaster risk management: The way forward through COVID-19 and beyond.

Diseases can be viewed as minor or major perturbations to the normal functioning of the human body. Depending on the level of perturbations and the total number of cases, some outbreaks of infectious diseases can become disasters.

Using Cosmological Perturbation Theory to Distinguish between GR and Unimodular Gravity

Unimodular gravity is one of the oldest geometric gravity theories and alternatives to general relativity. Essentially, it is based on the Einstein–Hilbert Lagrangian with an additional constraint on the determinant of the metric. It can be explicitly shown that unimodular gravity can be recast as general relativity in the presence of a cosmological constant. This fact has led to many discussions on the equivalence of both theories at the classical and quantum levels. Here, we present an analysis focused on the classical scalar perturbations around a cosmological background. We focus on the unusual situation in which the typical conservation laws are not adopted. The discussion is extended to the case where a non-minimal coupled scalar field is introduced. We also present a gauge-invariant analysis showing that perturbations in unimodular gravity display instabilities. Our results reinforce that the equivalence is not verified completely at a cosmological perturbative level.

A Deep-Learning-Based Graph Neural Network-Long-Short-Term Memory Model for Reservoir Simulation and Optimization With Varying Well Controls

Summary A new deep-learning-based surrogate model is developed and applied for predicting dynamic oil rate and water rate with different well controls. The surrogate model is based on the graph neural networks (GNNs) and long-short-term memory (LSTM) techniques. The GNN models are used to characterize the connections of injector-producer pairs and producer-producer pairs, while an LSTM structure is developed to simulate the evolution of the constructed GNN models over time. In this way, we use geological attributes at wells and well controls with different times as input data. The oil rates and water rates at different times are generated. In this study, the GNN-LSTM surrogate model is applied to a high dimensional oil-gas-water field case with flow driven by 189 wells (i.e., 96 producers and 93 injectors) operating under time-varying control specifications. A total of 500 high-fidelity training simulations are performed in the offline stage, out of which 450 simulations are used for training the GNN-LSTM surrogate model, which takes about 150 minutes on an RTX2060 GPU. The trained model is then used to provide production forecasts under various well control scenarios, which are shown to be consistent with those obtained from the high-fidelity simulations (e.g., around 4.8% and 4.3% average relative errors for water production rates and oil production rates, respectively). The online computations from our GNN-LSTM model take about 0.3 seconds per run, achieving a speedup of over a factor of 1,000 relative to the high-fidelity simulations, which takes about 363 seconds per run. Overall, this model is shown to provide reliable and fast predictions of oil rates and water rates with a large level of perturbations in the well controls. Finally, the proposed GNN-LSTM model, in conjunction with the particle swarm optimization (PSO) technique, is applied to optimize the field oil production by varying the well control schedule of all injectors. Due to the significant speedup and high accuracy of the proposed surrogate model, the improved well-control strategies can be efficiently obtained.

Stepping strategies of young adults undergoing sudden external perturbation from different directions

Stepping strategies following external perturbations from different directions is investigated in this work. We analysed the effect of the perturbation angle as well as the level of awareness of individuals and characterised steps out of the sagittal plane between Loaded Side Steps (LSS), Unloaded Medial Steps (UMS) and Unloaded Crossover Steps (UCS). A novel experimental paradigm involving perturbations in different directions was performed on a group of 21 young adults (10 females, 11 males, 20–38 years). Participants underwent 30 randomised perturbations along 5 different angles with different levels of awareness of the upcoming perturbations (with and without wearing a sensory impairment device) for a total of 1260 recorded trials. Results showed that logistic models based on the minimal values of the Margin of Stability (MoS) or on the minimal values of the Time to boundary (Ttb) performed the best in the sagittal plane. However, their accuracy stayed above 79% regardless of the perturbation angle or level of awareness. Regarding the effect of the experimental condition, evidences of different balance recovery behaviours due to the variation of perturbation angles were exposed, but no significant effect of the level of awareness was observed. Finally, we proposed the Distance to Foot boundary (DtFb) as a relevant quantity to characterise the stepping strategies in response to perturbations out of the sagittal plane.

Union label smoothing adversarial training: Recognize small perturbation attacks and reject larger perturbation attacks balanced

Recently, several adversarial training methods have been proposed for rejecting perturbation-based adversarial examples, which enhance the robustness of deep neural networks to larger perturbations. However, they often perform unsatisfactorily when dealing with examples with lower level perturbations. To address these issues, we introduce a novel adversarial training approach called the union label smoothing adversarial training (ULSAT), which employs a new label smoothing curve and a union strategy for adversarial training. The label smoothing curve assigns soft labels to perturbed examples, allowing for a more reasonable adjustment of calibration. The union strategy adds interpolation examples and combines adversarial examples generated under different perturbation tolerances into the training stage, which improves the rejection ability of the model and balances it with the classification ability. Through theoretical analysis and ablation study, we demonstrate the effectiveness of our proposed approach. Numerical experiments show that ULSAT can accurately classifies less disturbed examples while maintaining a good rejection ability for adversarial examples with higher levels of perturbation. Moreover, we introduce an evaluation index that comprehensively considers the classification ability and rejection ability of the model. Under this index, ULSAT achieves state-of-the-art results.

Self-excited oscillations in variable density counter-current round jets

The paper investigates the global instability phenomenon in variable-density counter-current round jets. The analysis is performed using a large eddy simulation and the computations are carried out employing a high-order numerical code. The configuration of two co-axial nozzles, where suction applied in an annular nozzle is a driving force for the counterflow, is investigated. In order to simulate conditions conducive to the emergence of global instability a wide range of velocity and density ratios is considered. Depending on these parameters two different types of modes are observed, i.e., Mode I — shear layer mode, and Mode II — jet column mode. The former is recognized by a high level of perturbations in the shear layer which vanish away from the shear layer reaching a low level at the jet centerline. The latter is characterized by strong disturbances throughout the entire jet region. The results obtained are in remarkable agreement with the theoretical basis reported in the literature. They reveal that the critical velocity ratio for which global instability emerges decreases along with the density ratio. Additionally, the transition from Mode II to Mode I is found for sufficiently strong suction. In general, the lower the density ratio, the weaker suction is required to induce Mode I. Consistently to the literature, Mode II is characterized by a lower frequency of oscillations compared to Mode I for which an increase in density ratio and/or velocity ratio shifts the peaks of the velocity spectra toward higher frequencies.

Abstract B073: Inhibiting prostate cancer by targeting the metabolic mevalonate pathway

Abstract Background: A major challenge in the clinical management of prostate cancer (PCa) is inhibiting progression to lethal castrate-resistant PC (CRPC). Deregulated activity of mevalonate (MVA), cholesterol biosynthetic pathway is a recognized hallmark of PCa cells. Statins are potent inhibitors of this metabolic pathway that have been used for decades in the control of hypercholesterolemia. Statins have recently been shown to have anti-PCa activity, however statin treatment triggers a feedback response that restores the MVA pathway, which reduces statin efficacy and contributes to resistance. This restorative feedback loop is controlled by the transcriptional activity of sterol regulatory-element binding protein (SREBP), which primarily induces fatty acid biosynthesis and MVA pathway genes. We have recently identified the anti-platelet agent dipyridamole (DP) as an inhibitor of the statin-induced SREBP-mediated feedback response. However, DP is not SREBP-specific and given its anti-platelet activity, may not be suitable for every cancer patient. Thus, our goal was to identify additional drugs that potentiate the pro-apoptotic activity of statins, which can be used to treat PCa patients. Methods: Two independent, yet complimentary strategies were used. The first focused on performing an in silico analysis to identify drugs that had similar properties to DP at the level of drug structure, molecular perturbations and cell line sensitivity. The second strategy involved a high-content imaging analysis of 1508 FDA approved drugs, which was performed in LNCaP (relatively statin insensitive and feedback competent) and PC3 cells (statin sensitive and feedback incompetent). Cells were treated with a sub-lethal dose of fluvastatin, the drugs or the fluvastatin-drug combination, then treated with apoptotic stains (TMRE, Annexin, Draq 5). Captured images were analyzed using a machine learning approach. Results: Validation of hits from the in silico MVA-DNF approach and high-content screening has identified several drugs that fulfill our criteria of potentiating statin-induced cell death in a feedback-dependent or feedback-independent manner. Interestingly, many show higher Z-scores compared to DP indicating their superior statin potentiation activity to drive PCa cell death. Moreover, a sub-set of these drug significantly inhibit statin-triggered expression of MVA pathway genes HMGCS1 and INSIG1 (p < 0.001) more potently than DP. Conclusions: We have detailed two successful strategies to identify drugs that inhibit SREBP activation in response to statin treatment. These statin-drug combinations represent an effective ‘one-two punch’ to inhibit CRPC progression. These novel inhibitors of SREBP activation potentiate statin at clinically relevant concentrations more potently than DP and have no effect on the platelet activity. Excitingly, many of these agents are FDA-approved and can be immediately used in combination with statins for the treatment of PCa. Overall, our research will lead to novel therapies to improve patient outcome. Citation Format: Diandra Zipinotti dos Santos, Mohamad Elbaz, Emily Branchard, Wiebke Schormann, David W. Andrews, Linda Z. Penn. Inhibiting prostate cancer by targeting the metabolic mevalonate pathway [abstract]. In: Proceedings of the AACR Special Conference: Advances in Prostate Cancer Research; 2023 Mar 15-18; Denver, Colorado. Philadelphia (PA): AACR; Cancer Res 2023;83(11 Suppl):Abstract nr B073.

Testing the growth rate in homogeneous and inhomogeneous interacting vacuum models

In this work we consider a class of interacting vacuum corresponding to a generalised Chaplygin gas (gCg) cosmology. In particular we analyse two different scenarios at perturbation level for the same background interaction characterised by the parameter α: (i) matter that follows geodesics, corresponding to homogeneous vacuum, and (ii) a covariant ansatz for vacuum density perturbations. In the latter case, we show that the vacuum perturbations are very tiny as compared to matter perturbations on sub-horizon scales. In spite of that, depending on the value of the Chaplygin gas parameter α, vacuum perturbations suppress or enhance the matter growth rate as compared to the case (i). We use Cosmic Microwave Background (CMB), type Ia supernovae (SNe) and Redshift Space Distortion (RSD) measurements to test the observational viability of the model. We found that the mean value of our joint analysis clearly favours a positive interaction, i.e., an energy flux from dark matter to dark energy, with α ≈ 0.143 in both cases, while the cosmological standard model, recovered for α = 0, is ruled out by 3σ confidence level. Noteworthy, the positive value of interaction can alleviate both the H 0 and S 8 tension for the dataset considered here.

Analysis and design of single-cell experiments to harvest fluctuation information while rejecting measurement noise.

Introduction: Despite continued technological improvements, measurement errors always reduce or distort the information that any real experiment can provide to quantify cellular dynamics. This problem is particularly serious for cell signaling studies to quantify heterogeneity in single-cell gene regulation, where important RNA and protein copy numbers are themselves subject to the inherently random fluctuations of biochemical reactions. Until now, it has not been clear how measurement noise should be managed in addition to other experiment design variables (e.g., sampling size, measurement times, or perturbation levels) to ensure that collected data will provide useful insights on signaling or gene expression mechanisms of interest. Methods: We propose a computational framework that takes explicit consideration of measurement errors to analyze single-cell observations, and we derive Fisher Information Matrix (FIM)-based criteria to quantify the information value of distorted experiments. Results and Discussion: We apply this framework to analyze multiple models in the context of simulated and experimental single-cell data for a reporter gene controlled by an HIV promoter. We show that the proposed approach quantitatively predicts how different types of measurement distortions affect the accuracy and precision of model identification, and we demonstrate that the effects of these distortions can be mitigated through explicit consideration during model inference. We conclude that this reformulation of the FIM could be used effectively to design single-cell experiments to optimally harvest fluctuation information while mitigating the effects of image distortion.

ILS-based algorithms for the profit maximizing uncapacitated hub network design problem with multiple allocation

This study addresses a hub network design problem to maximize net profit. This problem considers an incomplete hub network with multiple allocation that does not impose capacity constraints, does not allow direct connections between non-hub nodes, and accepts the demand to be partially met, being satisfied only when profitable. To tackle this problem, which is NP-hard, we propose two heuristic algorithms based on the Iterated Local Search (ILS) metaheuristic, a standard ILS algorithm, and an Enhanced ILS algorithm, which increases the perturbation level only after a few unsuccessful attempts at improvement. Both algorithms use Random Variable Neighborhood Descent in the local search. Computational experiments were performed using benchmark instances for hub location problems, and statistical analyzes of the algorithms were presented. Numerical results confirm that both algorithms yield good-quality solutions with an acceptable runtime. In particular, the proposed algorithms obtain the optimal solution for most instances with up to 150 nodes, which have known optimal solutions. Furthermore, the proposed algorithms were able to handle instances with up to 500 nodes.

Dynamical system analysis of interacting dark energy-matter scenarios at the linearized inhomogeneous level

We carry out the dynamical system analysis of interacting dark energy-matter scenarios by examining the critical points and stability for not just the background level cosmological evolution, but at the level of the linear density perturbations as well. While an analysis at the background level can lead to a stable phase space trajectory implying that the universe eventually transpires to a dark energy dominated (de-Sitter) era, a two-fold degeneracy in the spectrum of the critical points is found to arise in the inhomogeneous picture, due to the possible growth and decay of matter density perturbations. Analysing the phase space dynamics of the growth factor, we show that it turns out to be greater than unity initially, for one of the critical points, and leads to a stable configuration as the fluctuations in the matter density die out asymptotically. As to the growth index, we show that the only trajectory which is physically plausible is the one that evolves mildly at high redshifts and gets steeper as time progresses. However, such a trajectory amounts to the average value of the growth index, throughout the expansion history of the universe, not much deviated from the value 6/11, corresponding to the background ΛCDM cosmology.

Testing gravity with gravitational wave friction and gravitational slip

Gravitational waves (GWs) emitted by binary sources are interesting signals for testing gravity on cosmological scales since they allow measurements of the luminosity distance. When followed by electromagnetic counterparts, in particular, they enable a reconstruction of the GW-distance-redshift relation. In the context of several modified gravity (MG) theories, even when requiring that the speed of propagation is equal to that of light, this GW distance differs from the standard electromagnetic luminosity distance due to the presence of a modified friction in the GW propagation. The very same source of this friction, which is the running of an effective Planck mass, also affects the scalar sector generating gravitational slip, i.e. a difference between the scalar potentials, an observable that can be inferred from large-scale structure (LSS) probes. In this work, we use a model within effective field theories for dark energy to exemplify precisely the fact that, at the linear perturbation level, parametrizing a single function is already enough to generate simultaneous deviations in the GW distance and the slip. By simulating multimessenger GW events that might be detected by the Einstein Telescope in the future, we compare the constraining power of the two observables on this single degree of freedom. We then combine forecasts of an Euclid-like survey with GW simulations, coming to the conclusion that, when using Planck data to better constrain the cosmological parameters, those future data on the scalar and tensor sectors are competitive to probe such deviations from General Relativity, with LSS giving stronger (but more model-dependent) results than GWs.

High redshift constraints on extended logotropic models

A single logotropic fluid, responsible for the existence of the whole dark sector, is here extensively revised at intermediate redshifts. In particular, by investigating possible generalizations that conceptually overcome previous issues of standard logotropic scenarios, we fix bound over classes of logotropic models that exhibit additional terms in the equation of state. Employing σ8 measurements combined with low redshift data sets of Supernovae and Hubble observational data, we show the statistical significance of those extensions and their departure from the standard cosmological model. Evidences against generalized versions of logotropic models are, in particular, prompted. Our outcomes definitively show that any departure from the original logotropic model, including the Anton–Schmidt dark energy, are clearly disfavored at the level of perturbations and/or background cosmology. This indicates that, in order to have a logotropic fluid, plausible generalized versions of it would point out to reduce the complexity of the fluid itself, instead of adding extra terms.

Nonsmooth Dynamic Tracking Control for Nonlinear Systems With Mismatched Disturbances: Algorithm and Practice

This article addresses a dynamic tracking control issue for a class of nonlinear systems subject to mismatched disturbances. As an alternative control design algorithm for practitioners, a simple nonsmooth tracking scheme with a self-tuning scaling gain is proposed under a nonrecursive synthesis framework. In reference to the existing related works, a main distinguishable feature is that the scaling gain of the proposed regulation law can be adaptively adjusted subject to different perturbation levels; therefore, the control system is able to achieve an improved transient-time control performance while an accurate tracking objective is guaranteed. In addition, the proposed nonrecursive design philosophy is able to obtain the simplest state-feedback expression of the controller through essentially detaching the stability analysis with controller design procedure, i.e., without going through recursive determination steps of classical virtual controllers. The efficacy of the proposed method is validated by an illustrative numerical example and a real-life application to a dc–dc boost converter system.

Stability studies of first-order spin-hydrodynamic frameworks

We study the stability of first-order dissipative spin-hydrodynamic frameworks. We considered two different first-order dissipative spin-hydrodynamic frameworks. The first one considers the spin-chemical potential (${\ensuremath{\omega}}^{\ensuremath{\alpha}\ensuremath{\beta}}$) to be first order [$\mathcal{O}(\ensuremath{\partial})$] in the hydrodynamic gradient expansion. The hydrodynamic gradient ordering of the spin-chemical potential is a debatable issue within the frameworks of spin hydrodynamics. Therefore, as a second choice, we also consider the spin-hydrodynamic equations with ${\ensuremath{\omega}}^{\ensuremath{\alpha}\ensuremath{\beta}}\ensuremath{\sim}\mathcal{O}(1)$. We find that, for both frameworks, at the level of linear perturbations some spin modes can be unstable. To remove these generic instabilities, we consider the Frenkel condition. We argue that the Frenkel condition helps get rid of the unstable solutions in both cases but with a physical drawback for the case where ${\ensuremath{\omega}}^{\ensuremath{\mu}\ensuremath{\nu}}\ensuremath{\sim}\mathcal{O}(\ensuremath{\partial})$.

VLF and Ionospheric D‐Region Perturbations Associated With WWLLN‐Detected Lightning in the South Pacific Region

AbstractThe subionospheric early very low frequency (VLF) perturbations observed on NWC (19.8 kHz) navigational transmitter signal monitored at a low‐latitude station, Suva (18.1°S, 178.5°E), Fiji, during campaign periods of November 2011, 2012, and 2014 and December 2014, are presented. Early VLF events are associated with D‐region conductivity changes mainly produced by lightning‐generated transient luminous events (TLEs). Early VLF events occurred both during daytime and nighttime, with a considerably higher occurrence at nighttime. VLF perturbations caused by lightning strokes located up to 100 km off the transmitter‐receiver great circle path (TRGCP) are attributed to narrow‐angle scattering, while lightning strokes 100–500 km off the TRGCP are considered to cause early VLF events by wide‐angle scattering. Using the World Wide Lightning Location Network data, for the first time, we have studied the relationship between the energy of lightning strokes and the level of VLF perturbations. Greater is the energy of lightning, greater would be the strength of the VLF perturbation. However, the low‐energy lightning stroke can also produce a comparable level of perturbation to that of strong lightning. The modeling results of scattered amplitude (M) and echo phase (ϕE) of the unusually long recovery early/fast VLF event showed a better exponential fit (r ∼ 0.9) than the logarithmic fit. Long‐wavelength propagation capability (LWPC) code modeling of nighttime early VLF events considering causative TLE width of 50 km column indicated a decrease in the D‐region reference height (Hʹ) by up to 30 km and an increase in the sharpness factor (β) by 0.25 km−1.

Young adults use whole-body feedback and ankle proprioception to perceive small locomotor disturbances

To prevent a fall when a disturbance to walking is encountered requires sensory information about the disturbance to be sensed, integrated, and then used to generate an appropriate corrective motor response. Prior research has shown that feedback of whole-body motion (e.g., center-of-mass kinematics) drives this corrective response. Here, we hypothesized that young adults also use whole-body motion to perceive locomotor disturbances. 15 subjects performed a locomotor discrimination task in which the supporting leg was slowed during stance every 8–12 steps to emulate subtle slips. The perception threshold of these disturbances was determined using a psychometrics approach and found to be 0.08 ± 0.03 m/s. Whole-body feedback was examined through center-of-mass (CoM) kinematics and whole-body angular momentum (WBAM). Perturbation-induced deviations of CoM and WBAM were calculated in response to the two perturbation levels nearest each subject's perception threshold. Consistent with our hypothesis, we identified significantly higher perturbation induced deviations for perceived perturbations in sagittal-plane WBAM, anteroposterior CoM velocity, and vertical CoM velocity and acceleration. Because whole body motion is not sensed directly but instead arises from the integration of various sensory feedback signals, we also explored local sensory feedback contributions to the perception of locomotor disturbances. Local sensory feedback was estimated through kinematic analogues of vision (head angle), vestibular (head angular velocity), proprioception (i.e., sagittal hip, knee, and ankle angles), and somatosensation (i.e., anterior-posterior & mediolateral center-of-pressure, COP). We identified significantly higher perturbation induced deviations for perceived perturbations in sagittal-plane ankle angle. These results provide evidence for both whole-body feedback and ankle proprioception as important for the perception of subtle slip-like locomotor disturbances in young adults. Our interpretation is ankle proprioception is a dominant contributor to estimates of whole-body motion to perceive locomotor disturbances.