Search Results (14)

Advanced Persistent Threat (APT) refers to a highly targeted, sophisticated, and prolonged form of cyberattack, typically directed at specific organizations or individuals. The primary objective of such attacks is the theft of sensitive information or the disruption of critical operations. APT attacks are characterized by their stealth and complexity, often resulting in significant economic losses. Furthermore, these attacks may lead to intelligence breaches, operational interruptions, and even jeopardize national security and political stability. Given the covert nature and extended durations of APT attacks, current detection solutions encounter challenges such as high detection difficulty and insufficient accuracy. To address these limitations, this paper proposes an innovative high-accuracy APT attack detection model, CNN-KOA-BiGRU, which integrates Convolutional Neural Networks (CNN), Bidirectional Gated Recurrent Units (BiGRU), and the Kepler optimization algorithm (KOA). The model first utilizes CNN to extract spatial features from network traffic data, followed by the application of BiGRU to capture temporal dependencies and long-term memory, thereby forming comprehensive temporal features. Simultaneously, the Kepler optimization algorithm is employed to optimize the BiGRU network structure, achieving globally optimal feature weights and enhancing detection accuracy. Additionally, this study employs a combination of sampling techniques, including Synthetic Minority Over-sampling Technique (SMOTE) and Tomek links, to mitigate classification bias caused by dataset imbalance. Evaluation results on the CSE-CIC-IDS2018 experimental dataset demonstrate that the CNN-KOA-BiGRU model achieves superior performance in detecting APT attacks, with an average accuracy of 98.68%. This surpasses existing methods, including CNN (93.01%), CNN-BiGRU (97.77%), and Graph Convolutional Network (GCN) (95.96%) on the same dataset. Specifically, the proposed model demonstrates an accuracy improvement of 5.67% over CNN, 0.91% over CNN-BiGRU, and 2.72% over GCN. Overall, the proposed model achieves an average improvement of 3.1% compared to existing methods. Full article

The Kepler optimization algorithm (KOA) is a metaheuristic algorithm based on Kepler’s laws of planetary motion and has demonstrated outstanding performance in multiple test sets and for various optimization issues. However, the KOA is hampered by the limitations of insufficient convergence accuracy, weak global search ability, and slow convergence speed. To address these deficiencies, this paper presents a multi-strategy fusion Kepler optimization algorithm (MKOA). Firstly, the algorithm initializes the population using Good Point Set, enhancing population diversity. Secondly, Dynamic Opposition-Based Learning is applied for population individuals to further improve its global exploration effectiveness. Furthermore, we introduce the Normal Cloud Model to perturb the best solution, improving its convergence rate and accuracy. Finally, a new position-update strategy is introduced to balance local and global search, helping KOA escape local optima. To test the performance of the MKOA, we uses the CEC2017 and CEC2019 test suites for testing. The data indicate that the MKOA has more advantages than other algorithms in terms of practicality and effectiveness. Aiming at the engineering issue, this study selected three classic engineering cases. The results reveal that the MKOA demonstrates strong applicability in engineering practice. Full article

Multi-Dimensional Optimal Power Flow (MDOPF) is a fundamental task in power systems engineering aimed at optimizing the operation of electrical networks while considering various constraints such as power generation, transmission, and distribution. The mathematical model of MDOPF involves formulating it as a non-linear, non-convex optimization problem aimed at minimizing specific objective functions while adhering to equality and inequality constraints. The objective function typically includes terms representing the Fuel Cost (FC), Entire Network Losses (ENL), and Entire Emissions (EE), while the constraints encompass power balance equations, generator operating limits, and network constraints, such as line flow limits and voltage limits. This paper presents an innovative Improved Kepler Optimization Technique (IKOT) for solving MDOPF problems. The IKOT builds upon the traditional KOT and incorporates enhanced local escaping mechanisms to overcome local optima traps and improve convergence speed. The mathematical model of the IKOT algorithm involves defining a population of candidate solutions (individuals) represented as vectors in a high-dimensional search space. Each individual corresponds to a potential solution to the MDOPF problem, and the algorithm iteratively refines these solutions to converge towards the optimal solution. The key innovation of the IKOT lies in its enhanced local escaping mechanisms, which enable it to explore the search space more effectively and avoid premature convergence to suboptimal solutions. Experimental results on standard IEEE test systems demonstrate the effectiveness of the proposed IKOT in solving MDOPF problems. The proposed IKOT obtained the FC, EE, and ENL of USD 41,666.963/h, 1.039 Ton/h, and 9.087 MW, respectively, in comparison with the KOT, which achieved USD 41,677.349/h, 1.048 Ton/h, 11.277 MW, respectively. In comparison to the base scenario, the IKOT achieved a reduction percentage of 18.85%, 58.89%, and 64.13%, respectively, for the three scenarios. The IKOT consistently outperformed the original KOT and other state-of-the-art metaheuristic optimization algorithms in terms of solution quality, convergence speed, and robustness. Full article

The Kepler space telescope has detected a large number of variable stars. We summarize 2261 $\delta$ Scuti and hybrid variables in the literature, and perform time-frequency analysis on these variable stars. Two non-eclipsing binary systems, KIC 5080290 and KIC 5480114, are newly discovered. They both pass more detailed aperture photometry and bright star contamination checks. The results of the time-frequency analysis demonstrate that the companions are stellar objects with orbital periods of approximately 265 days and 445 days, respectively. The orbital parameters of the two systems and the lower mass limits of the companions are obtained. The primary stars of both systems are slightly evolved intermediate-mass stars. The detection of intermediate-mass binary stars is helpful to understand the formation and evolution mechanism of binary stars in this mass region. Full article

Many stars show activity cycles like the Sun. Kepler has gathered ∼200,000 light curves. Most of the Kepler stars only have long-cadence light curves, which limits their applicable methods. Some metrics, for example $S_{ph}$, are effective for long-cadence light curves but require rotation periods. In order to improve the utilization of Kepler light curves, we introduce and use the smoothness metric. The smoothness metric is able to analyze stars without a measured rotation period and is applicable for long-cadence light curves. We test and validate our metric, resulting in the detection of the 11 years solar cycle and a 457 days cycle for our prototype star KIC 9017220. We analyze 92,084 Kepler long-cadence light curves, and as our main results, we detect 4455 magnetic activity cycle candidates, but about 20 percent are false cycles and 50 percent are lower limits of the real cycles, and we analyze their causes in detail. As an investigation into the performance of our method, we simulate disturbance factors and prove that the p-value test is invalid under certain circumstances. Full article

It is generally accepted that the limit on the stable rotation of neutron stars is set by gravitational-radiation reaction (GRR) driven instabilities, which cause the stars to emit gravitational waves that carry angular momentum away from them. The instability modes are moderated by the shear viscosity and the bulk viscosity of neutron star matter. Among the GRR instabilities, the f-mode instability plays a historically predominant role. In this work, we determine the instability periods of this mode for three different relativistic models for the nuclear equation of state (EoS) named DD2, ACB4, and GM1L. The ACB4 model for the EoS accounts for a strong first-order phase transition that predicts a new branch of compact objects known as mass-twin stars. DD2 and GM1L are relativistic mean field (RMF) models that describe the meson-baryon coupling constants to be dependent on the local baryon number density. Our results show that the f-mode instability associated with $m=2$ sets the limit of stable rotation for cold neutron stars ($T\lesssim {10}^{10}$ K) with masses between $1M_{\odot }$ and $2M_{\odot }$. This mode is excited at rotation periods between 1 and 1.4 ms (∼20% to ∼40% higher than the Kepler periods of these stars). For cold hypothetical mass-twin compact stars with masses between $1.96M_{\odot }$ and $2.10M_{\odot }$, the $m=2$ instability sets in at rotational stellar periods between 0.8 and 1 millisecond (i.e., ∼25% to ∼30% above the Kepler period). Full article

In this article, a variable step size strategy is adopted in formulating a new variable step hybrid block method (VSHBM) for the solution of the Kepler problem, which is known to be a rigid and stiff differential equation. To derive the VSHBM, the step size ratio r is left the same, halved, or doubled in order to optimize the total number of steps, minimize the number of formulae stored in the code, and ensure that the method is zero-stable. The method is formulated by integrating the Lagrange polynomial with limits of integration selected at special points. The article further analyzed the stability, order, consistency, and convergence properties of the VSHBM. The stability regions of the VSHBM at different values of the step size ratios were also plotted and plots showed that the method is fit for solving the Kepler problem. The results generated were then compared with some existing methods, including the MATLAB inbuilt stiff solver (ode 15 s), with respect to total number of failure steps, total number of steps, total function calls, maximum error, and computation time. Full article

Let ${\left(F_n\right)}_{n=1}^{\infty }$ be the classical Fibonacci sequence. It is well known that the $lim{F}_{n+1}/F_n$ exists and equals the Golden Mean. If, more generally, ${\left(F_n\right)}_{n=1}^{\infty }$ is an order-k linear recurrence with real constant coefficients, i.e., $F_n={\sum }_{j=1}^k{\lambda }_{k+1-j}{F}_{n-j}$ with $n>k$, ${\lambda }_j\in \mathbb{R}$, $j=1,\dots ,k$, then the existence of the limit of ratios of consecutive terms may fail. In this paper, we show that the limit exists if the first k elements $F_1,F_2,\dots ,F_k$ of ${\left(F_n\right)}_{n=1}^{\infty }$ are positive, ${\lambda }_1,\dots ,{\lambda }_{k-1}$ are all nonnegative, at least one being positive, and $max({\lambda }_1,\dots ,{\lambda }_k)={\lambda }_k\ge k$. The limit is characterized as fixed point, bounded below by ${\lambda }_k$ and bounded above by ${\lambda }_1+{\lambda }_2+\cdots +{\lambda }_k$. Full article

Among the few exactly solvable problems in theoretical physics, the 2D (two-dimensional) Newtonian free fall problem in Euclidean space is perhaps the least known as compared to the harmonic oscillator or the Kepler–Coulomb problems. The aim of this article is to revisit this problem at the classical level as well as the quantum level, with a focus on its dynamical symmetries. We show how these dynamical symmetries arise as a special limit of the dynamical symmetries of the Kepler–Coulomb problem, and how a connection to the quartic anharmonic oscillator problem, a long-standing unsolved problem in quantum mechanics, can be established. To this end, we construct the Hilbert space of states with free boundary conditions as a space of square integrable functions that have a special functional integral representation. In this functional space, the free fall dynamical symmetry algebra is shown to be isomorphic to the so-called Klink’s algebra of the quantum quartic anharmonic oscillator problem. Furthermore, this connection entails a remarkable integral identity for the quantum quartic anharmonic oscillator eigenfunctions, which implies that these eigenfunctions are in fact zonal functions of an underlying symmetry group representation. Thus, an appropriate representation theory for the 2D Newtonian free fall quantum symmetry group may potentially open the way to exactly solving the difficult quantization problem of the quartic anharmonic oscillator. Finally, the initial value problem of the acoustic Klein–Gordon equation for wave propagation in a sound duct with a varying circular section is solved as an illustration of the techniques developed here. Full article

Neutron stars are the densest known objects in the universe and an ideal laboratory for the strange physics of super-condensed matter. Theoretical studies in connection with recent observational data of isolated neutron stars, as well as binary neutron stars systems, offer an excellent opportunity to provide robust solutions on the dense nuclear problem. In the present work, we review recent studies concerning the applications of various theoretical nuclear models on a few recent observations of binary neutron stars or neutron-star–black-hole systems. In particular, using a simple and well-established model, we parametrize the stiffness of the equation of state with the help of the speed of sound. Moreover, in comparison to the recent observations of two events by LIGO/VIRGO collaboration, GW170817 and GW190425, we suggest possible robust constraints. We also concentrate our theoretical study on the resent observation of a compact object with mass ∼$2.{59}_{-0.09}^{+0.08}{M}_{\odot }$ (GW190814 event), as a component of a system where the main companion was a black hole with mass ∼$23M_{\odot }$. There is scientific debate concerning the identification of the low mass component, as it falls into the neutron-star–black-hole mass gap. This is an important issue since understanding the nature of GW190814 event will offer rich information concerning the upper limit of the speed of sound in dense matter and the possible phase transition into other degrees of freedom. We systematically study the tidal deformability of a possible high-mass candidate existing as an individual star or as a component in a binary neutron star system. Finally, we provide some applications of equations of state of hot, dense nuclear matter in hot neutron stars (nonrotating and rapidly rotating with the Kepler frequency neutron stars), protoneutron stars, and binary neutron star merger remnants. Full article

The flattening of spiral-galaxy rotation curves is unnatural in view of the expectations from Kepler’s third law and a central mass. It is interesting, however, that the radius-independence velocity is what one expects in one less dimension. In our three-dimensional space, the rotation curve is natural if, outside the galaxy’s center, the gravitational potential corresponds to that of a very prolate ellipsoid, filament, string, or otherwise cylindrical structure perpendicular to the galactic plane. While there is observational evidence (and numerical simulations) for filamentary structure at large scales, this has not been discussed at scales commensurable with galactic sizes. If, nevertheless, the hypothesis is tentatively adopted, the scaling exponent of the baryonic Tully–Fisher relation due to accretion of visible matter by the halo comes out to reasonably be 4. At a minimum, this analytical limit would suggest that simulations yielding prolate haloes would provide a better overall fit to small-scale galaxy data. Full article

Obtaining the inverse of a nonlinear monotonic function $f\left(x\right)$ over a given interval is a common problem in pure and applied mathematics, the most famous example being Kepler’s description of orbital motion in the two-body approximation. In traditional numerical approaches, this problem is reduced to solving the nonlinear equation $f\left(x\right)-y=0$ in each point y of the co-domain. However, modern applications of orbital mechanics for Kepler’s equation, especially in many-body problems, require highly optimized numerical performance. Ongoing efforts continually attempt to improve such performance. Recently, we introduced a novel method for computing the inverse of a one-dimensional function, called the fast switch and spline inversion (FSSI) algorithm. It works by obtaining an accurate interpolation of the inverse function $f^{-1}\left(y\right)$ over an entire interval with a very small generation time. Here, we describe two significant improvements with respect to the performance of the original algorithm. First, the indices of the intervals for building the spline are obtained by k-vector search combined with bisection, thereby making the generation time even smaller. Second, in the case of Kepler’s equation, a multistep method for the optimized calculation of the breakpoints of the spline polynomial was designed and implemented in Cython. We demonstrate results that accurately solve Kepler’s equation for any value of the eccentricity $\mathrm{e}\in [0,1-ϵ]$, with $ϵ=2.22\times {10}^{-16}$, which is the limiting error in double precision. Even with modest current hardware, the CPU generation time for obtaining the solution with high accuracy in a large number of points of the co-domain can be kept to around a few nanoseconds per point. Full article

A one-dimensional wave function is assumed whose logarithm is a quadratic form in the configuration variable with time-dependent coefficients. This trial function allows for general time-dependent solutions both of the harmonic oscillator (HO) and the reversed harmonic oscillator (RO). For the HO, apart from the standard coherent states, a further class of solutions is derived with a time-dependent width parameter. The width of the corresponding probability density fluctuates, or "breathes" periodically with the oscillator frequency. In the case of the RO, one also obtains normalized wave packets which, however, show diffusion through exponential broadening with time. At the initial time, the integration constants give rise to complete sets of coherent states in the three cases considered. The results are applicable to the quantum mechanics of the Kepler-Coulomb problem when transformed to the model of a four-dimensional harmonic oscillator with a constraint. In the classical limit, as was shown recently, the wave packets of the RO basis generate the hyperbolic Kepler orbits, and, by means of analytic continuation, the elliptic orbits are also obtained quantum mechanically. Full article

A series of eight new materials based on the ionic association between 1-methyl-3-alkylimidazolium cations and the nanometric anionic Keplerate [Mo₁₃₂O₃₇₂(CH₃COO)₃₀(H₂O)₇₂]⁴²⁻ has been prepared and characterized in the solid state. The liquid crystal properties of these materials were investigated by the combination of Polarized Optical Microscopy, Differential Scanning Calorimetry and Small-angle X-Ray Diffraction showing a self-organization in lamellar (L) mesophases for the major part of them. From the interlamellar spacing h and the intercluster distance a_hex, we demonstrated that the cations are not randomly organized around the anionic cluster and that the alkyl chains of the cations are certainly folded, which limits the van der Waals interactions between the cations within the liquid crystal phase and therefore harms the quality of the mesophases. Full article