Perturbation Level Research Articles

Gedanken experiments at high-order approximations: Kerr-Newman black hole cannot be overcharged and overspun

The weak cosmic censorship conjecture (WCCC) of black holes is a fundamental hypothesis in general relativity. The proof of this hypothesis has become a frontier issue in the study of gravity. Recently, Sorce and Wald proposed a new version of the gedanken experiment and examined that the WCCC of Kerr-Newman (KN) black holes is valid under the second-order approximation of the matter fields perturbation. But it is not enough to study the WCCC under the second-order approximation because there is an additional condition that makes the validity of the hypothesis impossible to judge in this case. Therefore, the higher-order approximation of the perturbation process should be further considered to examine the conjecture strictly. Based on the new version of the gedanken experiment, from the two assumptions that the spacetime geometry satisfies the stability condition and that the matter fields should obey the null energy condition, we deduce the $n$th-order perturbation inequality and demonstrate that the event horizon of KN black holes always exists under the $n$th-order approximation of the matter fields perturbation. It indicates that the hypothesis is always satisfied under the arbitrary high-order approximation and also shows that the WCCC of KN black holes has been examined rigorously at the perturbation level.

Plasma mannose as a novel marker of myocardial infarction across different glycaemic states: a case control study

BackgroundPlasma mannose, an emerging novel biomarker of insulin resistance, is associated with both diabetes mellitus and coronary atherosclerosis, but the relationship between mannose concentrations and myocardial infarction (MI) across different glycaemic states remains to be elucidated. The aim of this study was to investigate the independent association between mannose and a first MI in a group of subjects characterized according to their glycaemic state.MethodsFasting plasma mannose concentrations were analysed in 777 patients 6–10 weeks after a first myocardial infarction and in 770 matched controls by means of high-performance liquid chromatography coupled to tandem mass spectrometry. Participants without known diabetes mellitus were categorized by an oral glucose tolerance test (OGTT) as having normal glucose tolerance (NGT, n = 1045), impaired glucose tolerance (IGT, n = 246) or newly detected type 2 diabetes (T2DM, n = 112). The association between mannose and MI was investigated across these glycaemic states by logistic regression.ResultsMannose levels increased across the glycaemic states (p < 0.0001) and were significantly associated with a first MI in the whole study population (odds ratio, OR: 2.2; 95% CI 1.4 to − 3.5). Considering the different subgroups separately, the association persisted only in subjects with NGT (adjusted OR: 2.0; 95% CI 1.2–3.6), but not in subgroups with glucose perturbations (adjusted OR: 1.8, 95% CI 0.8–3.7).ConclusionsMannose concentrations increased across worsening levels of glucose perturbations but were independently associated with a first MI only in NGT individuals. Thus, mannose might be a novel, independent risk marker for MI, possibly targeted for the early management of previously unidentified patients at high cardiovascular risk.

Virtual Laser Scanning Approach to Assessing Impact of Geometric Inaccuracy on 3D Plant Traits

In recent years, 3D imaging became an increasingly popular screening modality for high-throughput plant phenotyping. The 3D scans provide a rich source of information about architectural plant organization which cannot always be derived from multi-view projection 2D images. On the other hand, 3D scanning is associated with a principle inaccuracy by assessment of geometrically complex plant structures, for example, due the loss of geometrical information on reflective, shadowed, inclined and/or curved leaf surfaces. Here, we aim to quantitatively assess the impact of geometrical inaccuracies in 3D plant data on phenotypic descriptors of four different shoot architectures, including tomato, maize, cucumber, and arabidopsis. For this purpose, virtual laser scanning of synthetic models of these four plant species was used. This approach was applied to simulate different scenarios of 3D model perturbation, as well as the principle loss of geometrical information in shadowed plant regions. Our experimental results show that different plant traits exhibit different and, in general, plant type specific dependency on the level of geometrical perturbations. However, some phenotypic traits are tendentially more or less correlated with the degree of geometrical inaccuracies in assessing 3D plant architecture. In particular, integrative traits, such as plant area, volume, and physiologically important light absorption show stronger correlation with the effectively visible plant area than linear shoot traits, such as total plant height and width crossover different scenarios of geometrical perturbation. Our study addresses an important question of reliability and accuracy of 3D plant measurements and provides solution suggestions for consistent quantitative analysis and interpretation of imperfect data by combining measurement results with computational simulation of synthetic plant models.

Experimental study of effect of a pair of weak shock waves on laminar-turbulent transition in the boundary layer of flat plate at Mach number 2

An experimental study of the effect of longitudinal vortices generated by weak shock waves on the laminar-turbulent transition in the boundary layer of a flat plate at a Mach number 2 is conducted. To amplify the effect of the longitudinal vortices generation, a model with leading edge blunting radius of 0,5 mm was used. The disturbance intensity was measured with a constant temperature hotwire anemometer and a single-wire sensor. To change the Reynolds numbers in the flow, the method of varying the pressure in the pretest section of a supersonic wind tunnel was used. According to the experimental conditions, the level of mass flow perturbations in the test section T325 of ITAM SB RAS did not exceed 0,1 % of the mean flow in the frequency range from 0,2 to 50 kHz. In this work, it is obtained for the first time that stationary streamwise vortices that arise in the boundary layer of a flat plate because of the action of a pair of weak shock waves on its leading edge lead to an early laminar-turbulent transition at different Reynolds numbers. In the case of a homogeneous boundary layer, the transition is achieved at Rex≈ 3,1 × 106, and in measurements in the region of vortices from shock waves at Rex≈ 1,5 × 106and Rex≈ 2 × 106.

DFTMicroagg: a dual-level anonymization algorithm for smart grid data

The introduction of advanced metering infrastructure (AMI) smart meters has given rise to fine-grained electricity usage data at different levels of time granularity. AMI collects high-frequency daily energy consumption data that enables utility companies and data aggregators to perform a rich set of grid operations such as demand response, grid monitoring, load forecasting and many more. However, the privacy concerns associated with daily energy consumption data has been raised. Existing studies on data anonymization for smart grid data focused on the direct application of perturbation algorithms, such as microaggregation, to protect the privacy of consumers. In this paper, we empirically show that reliance on microaggregation alone is not sufficient to protect smart grid data. Therefore, we propose DFTMicroagg algorithm that provides a dual level of perturbation to improve privacy. The algorithm leverages the benefits of discrete Fourier transform (DFT) and microaggregation to provide additional layer of protection. We evaluated our algorithm on two publicly available smart grid datasets with millions of smart meters readings. Experimental results based on clustering analysis using k-Means, classification via k-nearest neighbor (kNN) algorithm and mean hourly energy consumption forecast using Seasonal Auto-Regressive Integrated Moving Average with eXogenous (SARIMAX) factors model further proved the applicability of the proposed method. Our approach provides utility companies with more flexibility to control the level of protection for their published energy data.

Nonlinear analysis of the delayed tyre model with control-based continuation

In this study, the numerical bifurcation analysis of a shimmying wheel is performed with a non-smooth, time-delayed model of the tyre-ground contact. This model is capable of reproducing the bistable behaviour often observed in experiments: a stable equilibrium and a stable periodic orbit coexisting for the same set of system parameters, that the simpler quasi-steady tyre models fail to capture. In the bistable parameter domain, there also exists an unstable periodic orbit within the separatrix between the domains of attractions of the two stable steady-state solutions. Although this solution never appears in a real-life system, one may still gain valuable information from tracing it as it gives an indication about the level of perturbation that would drive the system from one stable solution to the other. However, the complexity of the laws governing partial sticking and sliding in the tyre-ground contact makes the numerical bifurcation analysis with the traditional, collocation-based techniques infeasible. Instead, this study is based on numerical simulations and the technique of control-based continuation (CBC) to track the stable and unstable periodic solutions of the system allowing for the assessment of the accuracy of the non-smooth, delayed tyre model in replicating the dynamics observed in experiments. In the meantime, the physics-based model provides an insight into the relationship between the sticking and sliding regions appearing in the tyre-ground contact and the global dynamics of the system.

A novel pathway mutation perturbation score predicts the clinical outcomes of immunotherapy.

The link between tumor genetic variations and immunotherapy benefits has been widely recognized. Recent studies suggested that the key biological pathways activated by accumulated genetic mutations may act as an effective biomarker for predicting the efficacy of immune checkpoint inhibitor (ICI) therapy. Here, we developed a novel individual Pathway Mutation Perturbation (iPMP) method that measures the pathway mutation perturbation level by combining evidence of the cumulative effect of mutated genes with the position of mutated genes in the pathways. In iPMP, somatic mutations on a single sample were first mapped to genes in a single pathway to infer the pathway mutation perturbation score (PMPscore), and then, an integrated PMPscore profile was produced, which can be used in place of the original mutation dataset to identify associations with clinical outcomes. To illustrate the effect of iPMP, we applied it to a melanoma cohort treated with ICIs and identified seven significant perturbation pathways, which jointly constructed a pathway-based signature. With the signature, patients were classified into two subgroups with significant distinctive overall survival and objective response rate to immunotherapy. Moreover, the pathway-based signature was consistently validated in two independent melanoma cohorts. We further applied iPMP to two non-small cell lung cancer cohorts and also obtained good performance. Altogether, the iPMP method could be used to identify the significant mutation perturbation pathways for constructing the pathway-based biomarker to predict the clinical outcomes of immunotherapy. The iPMP method has been implemented as a freely available R-based package (https://CRAN.R-project.org/package=PMAPscore).

Generalized covariant entropy bound in Lanczos-Lovelock gravity

In this paper, we investigate the generalized covariant entropy bound in the theory where the Einstein gravity is perturbed by the higher-order Lovelock terms. After choosing the light sheet that is smooth under the perturbation limit, replacing the Bekenstein-Hawking entropy with the Jacobson-Myers entropy, and introducing two reasonable physical assumptions, we show that the corresponding generalized covariant entropy bound is satisfied under a higher-order approximation of the perturbation from the higher-order Lovelock terms. Our result implies that the Jacobson-Myers entropy strictly obeys the entropy bound under the perturbation level, and the generalized second law of Lanczos-Lovelock gravity is also satisfied when the Einstein gravity is perturbed by the higher-order Lovelock terms.

Structure formation in dark matter particle production cosmology

We investigate a cosmological scenario in which the dark matter particles can be created during the evolution of the Universe. By regarding the Universe as an open thermodynamic system and using non-equilibrium thermodynamics, we examine the mechanism of gravitational particle production. In this setup, we study the large-scale structure (LSS) formation of the Universe in the Newtonian regime of perturbations and derive the equations governing the evolution of the dark matter overdensities. Then, we implement the cosmological data from Planck 2018 CMB measurements, SNe Ia and BAO observations, as well as the Riess et al. (2019) local measurement for H0 to provide some cosmological constraints for the parameters of our model. We see that the best case of our scenario (χtot2=3834.40) fits the observational data better than the baseline ΛCDM model (χtot2=3838.00) at the background level. We moreover estimate the growth factor of linear perturbations and show that the best case of our model (χfσ82=39.85) fits the LSS data significantly better than the ΛCDM model (χfσ82=45.29). Consequently, our model also makes a better performance at the level of the linear perturbations compared to the standard cosmological model. Although the improvement in χtot for Model 2 compared to ΛCDM at the background level may arise somewhat from the additional degree of freedom, the better consistency of this model at the level of linear perturbations results mainly from the impact of particle production on the sound speed at low redshifts.

Kinetic axion F(R) gravity inflation

In this work we investigate the quantitative effects of the misalignment kinetic axion on ${R}^{2}$ inflation. Due to the fact that the kinetic axion possesses a large kinetic energy that dominates its potential energy, during inflation its energy density redshifts as stiff matter fluid and evolves in a constant-roll way, making the second slow-roll index to be nontrivial. At the equations of motion level, the ${R}^{2}$ term dominates the evolution; thus the next possible effect of the axion could be found at the cosmological perturbations level, via the second slow-roll index which is nontrivial. As we show, the latter elegantly cancels from the observational indices; however, the kinetic axion extends the duration of the inflationary era to an extent that it may cause a 15% decrease in the tensor-to-scalar ratio of the vacuum ${R}^{2}$ model. This occurs because as the ${R}^{2}$ model approaches its unstable quasi--de Sitter attractor in the phase space of $F(R)$ gravity due to the $⟨{R}^{2}⟩$ fluctuations, the kinetic axion dominates over the ${R}^{2}$ inflation and in effect the background equation of state is described by a stiff era, or equivalently a kination era, different from the ordinary radiation domination era. This in turn affects the duration of the inflationary era, increasing the $e$-foldings number up to $5e$-foldings in some cases, depending on the reheating temperature, which in turn has a significant quantitative effect on the observational indices of inflation and especially on the tensor-to-scalar ratio.

Gravitational particle production and the validity of effective descriptions in loop quantum cosmology

The effective approach in loop quantum cosmology (LQC) has provided means to obtain predictions for observable quantities in LQC models. While an effective dynamics in LQC has been extensively considered in different scenarios, a robust demonstration of the validity of effective descriptions for the perturbative level still requires further attention. The consistency of the description adopted in most approaches requires the assumption of a test field approximation, which is limited to the cases in which the backreaction of the particles gravitationally produced can be safely neglected. Within the framework of LQC, some of the main approaches to quantize the linear perturbations are the dressed metric, the hybrid approaches and the closed or deformed algebra approach. Here, we analyze the consistency of the test field assumption in these frameworks by computing the energy density stored in the particles gravitationally produced compared to the background energy density. This analysis ultimately provides us with a consistency test of the effective descriptions of LQC.

Generating Black-Box Adversarial Examples in Sparse Domain

Applications of machine learning (ML) models and convolutional neural networks (CNNs) have been rapidly increased. Although state-of-the-art CNNs provide high accuracy in many applications, recent investigations show that such networks are highly vulnerable to adversarial attacks. The black-box adversarial attack is one type of attack that the attacker does not have any knowledge about the model or the training dataset, but it has some input data set and their labels. In this paper, we propose a novel approach to generate a black-box attack in sparse domain whereas the most important information of an image can be observed. Our investigation shows that large sparse (LaS) components play a critical role in the performance of image classifiers. Under this presumption, to generate adversarial example, we transfer an image into a sparse domain and put a threshold to choose only <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$k$</tex-math></inline-formula> LaS components. In contrast to the very recent works that randomly perturb <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$k$</tex-math></inline-formula> low frequency (LoF) components, we perturb <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$k$</tex-math></inline-formula> LaS components either randomly (query-based) or in the direction of the most correlated sparse signal from a different class. We show that LaS components contain some middle or higher frequency components information which leads fooling image classifiers with a fewer number of queries. We demonstrate the effectiveness of this approach by fooling six state-of-the-art image classifiers, the TensorFlow Lite (TFLite) model of Google Cloud Vision platform, and YOLOv5 model as an object detection algorithm. Mean squared error (MSE) and peak signal to noise ratio (PSNR) are used as quality metrics. We also present a theoretical proof to connect these metrics to the level of perturbation in the sparse domain.

Unified dark sectors in scalar-torsion theories of gravity

We present a unified description of the matter and dark energy epochs using a class of scalar-torsion theories. We provide a Hamiltonian description, and by applying Noether's theorem and requiring the field equations to admit linear-in-momentum conservation laws, we obtain two specific classes of scalar-field potentials. First, we extract analytic solutions and perform a detailed dynamical analysis. We show that the system possesses critical points that correspond to scaling solutions in which the effective, total equation-of-state parameter is close to zero and points in which it is equal to the value $\ensuremath{-}1$; the equation of state of the cosmological constant. Therefore, during evolution, the Universe remains for sufficiently long at the epoch corresponding to dust-matter domination, while at later times it enters the accelerated epoch and eventually results in the de Sitter phase. Finally, in contrast to other unified scenarios, such as Chaplygin gas-based models and Horndeski-based constructions, the present scenario is free from instabilities and pathologies at the perturbative level.

Observational constraints on the massive neutrinos induced late-time cosmic acceleration

We investigate a late-time cosmological scenario at the both cosmological background and linear perturbative level which is based on a mass-less λ ϕ 4 theory in which the scalar field is inextricably coupled to massive neutrino matter with Z 2 symmetry by a well defined conformal coupling. The chosen coupling generically leads to the spontaneous symmetry breaking at late times, as the coupling builds up dynamically, such that the field acquires a non-zero mass proportional to the neutrino mass and rolls down slowly around the true ground state which emerges after spontaneous symmetry breaking. From our parametric estimations, we find the given scenario is well supported by the background level cosmological observations and is also in a good agreement with the evolution of growth of matter perturbations.

Perturbation-Induced Protective Arm Responses: Effect of Age, Perturbation-Intensity, and Relationship with Stepping Stability: A Pilot Study.

During balance recovery from slip perturbations, forward flexion (elevation) of the arms serves to counterbalance the posteriorly displaced center of mass (CoM). We aimed to investigate whether aging affects modulation of arm responses to various intensities of unpredictable slip perturbations and whether arm responses are related to compensatory stepping stability. Ten healthy young adults and ten healthy older adults participated. Participants were asked to react naturally to three randomly administered levels of slip-like surface perturbations (intensity 1 (7.75 m/s2), intensity 2 (12.00 m/s2) and intensity 3 (16.75 m/s2), which occurred by means of forward acceleration of the treadmill belt while standing. Kinematic data were collected using a motion capture system. Outcomes included arm elevation displacement, velocity, and margin of stability (MoS) of compensatory stepping. The results reveal no modulation of arm elevation velocity in older adults from perturbation intensity 1 to 2, whereas younger adults demonstrated progressive increases from intensity 1 to 2 to 3. At intensity 3, older adults demonstrated reduced maximal arm elevation velocity compared to younger adults (p = 0.02). The results in both groups combined reveal a positive correlation between maximal arm elevation velocity and first compensatory step MoS at intensity 3 (p = 0.01). Together, these findings indicate age-related decreases in arm response modulation and the association of arm elevation response with protective stepping stability, suggesting that fall prevention interventions may benefit from an emphasis on arm elevation velocity control in response to greater perturbation intensities.

Strategies to Overcome Foreign Language Reading Anxiety among Globalized EFL Learners

Perhaps, one of the most well-articulated hurdles daunting globalized EFL learners’ academic literacy dynamics can be attributed to foreign language reading anxiety. Under the massive expansion of foreign language reading anxiety, EFL learners commonly experience a higher level of perturbation while attempting to comprehend the contents forming in their specific reading texts due to the inevitable complexities presented during this process. This current small-scale library study aimed to exhaustively investigate particular effective strategies to overcome foreign language reading anxiety among globalized EFL learners to provide some illuminations for ELT experts, practitioners, and educators to devise more sophisticated reading strategies that can potentially alleviate foreign language reading anxiety. There were three main themes inferred in this present small-scale qualitative study namely: (1) The internalization of more comprehensible reading materials, (2) the promotion of more enjoyable reading circumstances, and (3) the inducement of more relevant reading strategies. For the future betterment of worldwide L2 reading enterprises, second language teachers are strongly commissioned to identify particular situations provoking excessive foreign language reading anxiety among EFL teachers in order to progressively design more authentic and meaningful reading activities.

Quantum Inelastic Scattering of ArHAr+, HeHHe+, and NeHNe+ with He on New Potential Energy Surfaces

The recent interstellar detections of ArH+ and HeH+ have increased the interest in noble molecules. In this work, we develop potential energy surfaces (PESs) at a high level of theory for the HeHHe+ + He, ArHAr+ + He, and NeHNe+ + He complexes and study the collision dynamics. A large number of ab initio energies are computed at the coupled-cluster with single, double, and perturbative triple excitations level of theory for the systems. A grid of energies at the complete basis set limit is fitted to an analytical function for each complex. These PESs are then employed in close-coupling calculations at low collision energies. The rotational state-to-state rate coefficients of HeHHe+ by collision He are compared with previous studies, and an excellent agreement is found. Furthermore, the available quenching rate coefficients for ArH+, HeH+, and NeH+, by He, are compared with those computed in this work, and the rotational de-excitations of the diatoms are more efficient than with the triatomic systems. Finally, a set of rate coefficients for ArHAr+ + He, HeHHe+ + He, and NeHNe+ + He at low temperatures is reported.

Stability measure of multicriteria integer linear programming problem with a parametric optimality principle

In this paper, we consider a multicriteria integer linear programming problem with a parametric principle of optimality. Parameterization is realized by dividing the set of criteria into several disjoint groups (subsets) of criteria ordered by importance, with Pareto dominance within each group. The introduced parametric principle of optimality made it possible to connect such classical principles of optimality as lexicographic and Pareto ones. For the stability radius, which is the limiting level of perturbations of the parameters of the problem, not causing the appearance of new optimal solutions, the upper and lower estimations are obtained in the case of arbitrary Hölder’s norms in the criterion space and solution space. Some previously known results on the stability of the Boolean linear programming problem are formulated as corollaries.

Stabilising all Kähler moduli in perturbative LVS

In this work we investigate the moduli stabilisation problem and the requirements for de Sitter vacua within the framework of type IIB string theory. Using perturbative effects arising from the various sources such as α′ corrections, logarithmic as well as KK and winding-type string-loop corrections along with the higher derivative F4-contributions, we present a moduli stabilisation scheme in which the overall volume is realised at exponentially large values such that leftlangle mathcal{V}rightrangle simeq {e}^{a/{g}_s^2} in the weak coupling regime, where a is a parameter given as a=frac{zeta left[3right]}{2zeta left[2right]}simeq 0.365381 . We also present a concrete global construction using a K3-fibred CY threefold with h1,1 = 3 which shares many of its properties with those of the standard toroidal case, and subsequently generates the appropriate corrections needed to fix all the three Kähler moduli at the perturbative level. We further discuss whether de Sitter vacua can be ensured through appropriate contributions of uplifting terms in the effective potential.

Structure and dynamics of a laminar separation bubble near a wing root: towards reconstructing the complete LSB topology on a finite wing

The influence of the wing root junction on the laminar separation bubble forming on the suction surface of a semispan NACA 0018 wing cantilevered from the wind tunnel test section wall is studied using surface flow visualisations, particle image velocimetry and surface pressure measurements at a chord Reynolds number of 125 000 and an angle of attack of 6 $^\circ$ . The test section wall boundary layer upstream of the wing is turbulent, and the spanwise influence of the junction on the separation bubble extends well beyond the test section wall boundary layer thickness. Substantial three-dimensionality is seen in the separation bubble flowfield near the wing root, where earlier transition and a reduction in separation bubble thickness is observed. In contrast with the wing tip, earlier transition and a reduction in separation bubble length occurs near the wing root. Outside of the junction affected region, the separation bubble is similar to separation bubbles forming on two-dimensional geometries, and displays mild spanwise waviness. The transition process away from the end affected regions is characterised by the formation of spanwise roll-up vortices that are shed in a nearly two-dimensional manner across the span. The analysis of the results shows that, near the wing root, the increased level of perturbations leads to earlier vortex roll-up and spanwise flow contributes to more rapid vortex breakdown. The results in the wing root region are complemented by the analysis of data from Toppings and Yarusevych (J. Fluid Mech., vol. 929, 2021, A39) in the wing tip region to provide a more holistic outlook on the laminar separation bubble topology and dynamics on the entire finite wing.